Atoms And Moleculers

IUPAC stands for International Union of Pure and Applied Chemistry. It is a scientific organization which develops nomenclature for chemical compounds.

(a) Law of conservation of mass was given by Antoine Lavoisier in 1744. According to this law, “Matter can neither be created nor destroyed in a chemical reaction”.

(b) Law of constant proportions was given by Joseph Proust in 1799. According to this law, “a chemical compound always contains same elements in definite proportion by mass and it does not depend on the source of compound.”

(a) Law of conservation of mass was given by Antoine Lavoisier in 1744. According to this law, “Matter can neither be created nor destroyed in a chemical reaction”.

(b) Law of constant proportions was given by Joseph Proust in 1799. According to this law, “a chemical compound always contains same elements in definite proportion by mass and it does not depend on the source of compound.”

Atomic theory of matter was given by John Dalton. It was the first complete attempt to describe all the matter in the form of atoms and their properties.

According to law of conservation of mass describes that, “Matter can neither be created nor destroyed in a chemical reaction”. This law gives result to the postulate of Dalton’s atomic theory which states that, “Atoms can neither be created and nor destroyed by physical and chemical changes.”

According to law of constant proportions describes that, “a chemical compound always contains same elements in definite proportion by mass and it does not depend on the source of compound.”

This law gives result to the postulate of Dalton’s atomic theory which states that, “When two elements combine to form two or more than two different compounds then the different masses of one element B which combine with fixed mass of the other element bear a simple ratio to one another.”

Maharshi Kanada was ancient Indian scientist and sage who suggested that all matter is composed of very small particles. He named the smallest particles as “Parmanu”.

Law of conservation of mass was given by Antoine Lavoisier in 1744. According to this law, “Matter can neither be created nor destroyed in a chemical reaction”.

Law of constant proportions was given by Joseph Proust in 1799. According to this law, “a chemical compound always contains same elements in definite proportion by mass and it does not depend on the source of compound.”

The above statement justifies the Law of constant proportions which was given by Joseph Proust in 1799. According to this law, “a chemical compound always contains same elements in definite proportion by mass and it does not depend on the source of compound.” This suggests that whatever be the source of water, it will always contain 1:8 ratio of Hydrogen and oxygen respectively.

The above statement justifies the Law of constant proportions which was given by Joseph Proust in 1799. According to this law, “a chemical compound always contains same elements in definite proportion by mass and it does not depend on the source of compound.” This suggests that whatever be the source of water, it will always contain 1:8 ratio of Hydrogen and oxygen respectively.

Matter is made up of indivisible particles known as Atoms. Atoms are the building blocks of matter.

The size of an atom is indicated by its radius which is called atomic radius (radius of an atom). Atomic radius is measured in nanometre (nm) (1 metre = 109 nanometres or 1nm = 10_9m).

Atomic radius is measured in nanometre (nm) (1 metre = 109 nanometres or 1nm = 10_9m).

A nanometer is one billionth part of metre. 1 metre = 1/109 nanometres or 1nm = 10_9m).

The symbol ‘nm’ represents Nanometre. A nanometer is one billionth part of metre. 1 metre = 1/109 nanometres or 1nm = 10_9m).

Atoms are the building blocks of the matter. They are very small in size. Hence Why is it not possible to see an atom even with the most powerful microscope.

False, the symbol of element cobalt is Co.

The molecular mass of a substance (an element or a compound) can be defined as the average relative mass of a molecule of the substance as compared with mass of an atom of carbon (C-12 isotope) taken as 12 atomic mass unit. The molecular mass of a substance can be determined by adding atomic masses of all the atoms present in the molecule of the substance.

The symbol of oxygen is O₂ which means it contains two atoms of oxygen. The molecular mass of one atom of oxygen is 16.

Hence the molecular mass of O₂ is 32.

(a) 8:1, whatever be the source of water, it will always contain 1:8 ratio of Hydrogen and oxygen respectively.

(b) Law of conservation of mass.

(a) Let the valency of element A be y, then 2y + 5(-2) = 0

So, y = valency of element A = 5

(b) As valency of element A is 5 and valency of chlorine is -1,

So, the formula of chloride of A is ACl₅.

Valency of X -

(i) In H₂X: -2

(ii) In CX₂: -2

(iii) In XO₂: +4

(iv) In XO₃: +6

Let the valency of X be y, then 2 x (+3) + 3 x y = 0

So, valency of X = y = -2

As valency of Mg is +2 and that of X is -2 so the formula of Magnesium salt of X will be MgX.

According to formula M₂CO₃, the metal M is univalent having valency of +1 and valency of carbonate is -2 i.e. bivalent.

(a) Iodine is univalent as valency of iodine is -1, hence formula of iodide = MI

(b) Nitrogen is trivalent as valency of nitrogen is -3, hence formula of nitride = M₃N

(c) Phosphorus is trivalent as valency of phosphorus is -3, hence formula of phosphate = M₃PO₄

(a). Anion will be formed by element X; Symbol: X-

(b) (i). No. of protons in X = 17

(ii) No. of electrons in X = 18

(iii) No. of neutrons in X = 18

(c) Cation will be formed by element Y; Symbol: Y+

(d) (i). No. of protons in Y = 11

(ii) No. of electrons in Y = 10

(iii) No. of neutrons in Y = 12

(e) Atomic mass of X = No. of protons (17) + No. of neutrons (18) = 35 u

Atomic mass of Y = No. of protons (11) + No. of neutrons (12) = 23 u

(f) Element X is Chlorine (Cl).

Element Y is Sodium (Na).

The group of 6.022 × 10²³ particles is known as One mole of a substance.

A group of 6.022 × 10²³ particles (atom, molecules or ions) of a substance is called a mole of that substance.

The numerical value of Avogadro number is 6.022 × 10²³.

One gram atomic mass = 6.022 × 10²³ atoms.

One gram molecular mass = 6.022 × 10²³ molecules.

Avagadro’s Number is the name given number 6.022 × 10²³

Given Mass of oxygen gas(O2) = 12g

Molar mass of oxygen gas(O2) = 32g

As we know that, Number of moles = mass of an element/molar mass of an element

Hence, Number of moles = 12g /32g = 0.375.

Given Mass of water(H2O) = 3.6g

Molar mass of water(H2O) = 18g

As we know that, Number of moles = mass of an element/molar mass of an element

Hence, Number of moles = 3.6g / 18g = 0.2 mole.

Molar mass of oxygen atom(O) = 16g

Number of moles present = 0.2 mole

As we know that, Number of moles = G mass of an element/molar mass of an element

Hence mass of an element = No. of moles X molar mass of an element.

Mass of oxygen atoms = 0.2×16 = 3.2g

Molar mass of oxygen atom(O) = 16g

Number of moles present = 2 mole

As we know that, Number of moles = G mass of an element/molar mass of an element

Hence mass of an element = No. of moles X molar mass of an element.

Mass of oxygen atoms = 2×16 = 32g

(a) 6.022 × 10²³

(b) Avogadro

(c) 5

(d) 20 g

(e) 4

The number of atoms present in 12g of carbon-12 element = 6.022 × 10²³ atoms

Avogadro number

Mole

One mole of O₂ = 32 gm

6.022 × 10²³ molecules of O₂ have mass = 32 gm

So, 12.044 × 10²⁵ molecules of O₂ will have mass = 6400 gm = 6.4 Kg

1 mole of ammonia contains 6.022 × 10²³ molecules.

Therefore, 1.5 mole of ammonia contains = 6.022 × 10²³ × 1.5 = 9.03 × 1023 molecules of ammonia

Molar mass of calcium carbonate (CaCO₃) = 40+12+48 = 100g

Mass of the substance = 10g

As we know that, Number of moles = mass of an element/molar mass of an element

Hence Number of moles = 10/100 = 0.1 mole.

Since One mole of O₂ contains = 6.022 × 10²³ molecules of oxygen

So, 1 molecule of O₂ has = 1/6.022 × 10²³ moles of O₂

Therefore, 1.2 × 10²² molecules of O2 will have = 1.2 × 10²² / 6.022 × 10²³ moles of O₂

= 0.0199 moles of O₂

Since 1 mol of nitrogen contains 6.02 × 10²³ molecules.

So according to given information, 6.022 × 10²³ molecules of N₂ weigh = 28 gm

So, 1 molecule of N₂ will weigh = 28 / 6.022 × 10²³ grams of N₂

= 4.648 × 10^-23 grams of N₂

Molar mass of sodium(Na) = 23g

Given Mass of the sodium = 34.5g

As we know that, Number of moles= mass of an element/molar mass of an element

Hence Number of moles = 34.5/23 = 1.5 moles.

Mole concept provides a relationship between number of particles(atoms) and their mass. Thus it is possible to calculate the number of particles in a given mass.

Molar mass of Zinc(Zn) = 65g

Given Mass of the Zinc = 10g

As we know that, Number of moles = mass of an element/molar mass of an element

Hence Number of moles= 10g/65g = 0.15 moles.

Since 1 mol of zinc contains 6.02 × 10²³ atoms

Therefore, 0.15 mol of zinc contains = 6.02 × 10²³ × 0.15 mol = 9.03 × 10²² atoms of zinc

Mass of 6.022 × 10²³ atoms of Carbon = 12 g

So, Mass of 1 Carbon atom = 12/6.022 × 10²³ g

Hence, mass of 3.011 × 10²⁴ atoms of Carbon = 3.011 × 10²⁴ × 12 / 6.022 × 10²³ = 60 g

6.022 × 10²³ atoms of Oxygen weigh = 16g

So, mass of 1 atom of Oxygen = 16/6.022 × 10²³ = 2.656 × 10^-23 g.

1 mole of hydrogen contains = 6.022 × 10²³ atoms of hydrogen

So, 0.25 moles of hydrogen will have = 6.022 × 10²³ × 0.25 = 1.50 × 10²³ atoms of hydrogen.

6.022 × 10²³ atoms of phosphorus contains = 1 mole of phosphorus

So, 12.044 × 10²⁵ atoms of phosphorus will have = 12.044 × 10²⁵/6.022 × 10²³ = 200 moles

Molar mass of chloroform (CHCl₃) = (12+1+3x35.5) = 119.5g

Given Mass of the chloroform (CHCl₃) = 0.0239g

As we know that, Number of moles = mass of an element/molar mass of an element

Hence Number of moles of chloroform (CHCl₃) = 0.0239g/119.5g = 0.0002 moles.

Molar mass of sodium carbonate (Na₂CO₃) = 2×23+12+3×16 = 106 g

Mass of one mole of sodium carbonate (Na₂CO₃) = 106g

Mass of five moles of sodium carbonate (Na₂CO₃) = 5×106g = 530g.

Mole concept provides a relationship between number of particles and their mass. Thus it is possible to calculate the number of particles in a given mass.

Molar mass of oxygen(O₂) = 32g

As we know that, Number of moles = Given mass of an element/molar mass of an element

Hence, Number of moles of oxygen = 4g/32g = 0.12 moles

Since 1 mole of oxygen contains 6.022 × 10²³ molecules.

Therefore, 0.12 mole of oxygen contains =

Molar mass of glucose, C₆H₁₂O₆ = 6×12+12×1+16×6 = 180g

Given Mass of the glucose, C₆H₁₂O₆ = 100g

As we know that, Number of moles = mass of an element/molar mass of an element

Hence Number of moles glucose, C₆H₁₂O₆ = 100g/180g = 0.55 moles.

For converting mole into mass in grams and vice-versa, we always need a relationship between mass and mole.

Molar mass of hydrogen sulphide, H₂S = 1×2+32 g /mol = 34g/mol

Therefore, number of grams of hydrogen sulphide, H₂S in 0.17 mol of it = 0.17 mol of oxygen × 34 g /mol = 5.78 g of hydrogen sulphide, H₂S.

One mole of CO₂ weighs (12+2×16)g = 44g

5 moles of CO₂ weighs 5×44g = 220g

One mole of H₂O weighs (1×2+16)g = 18g

5 moles of H₂O weighs 5×18g = 90g

Hence from above calculation, it can be concluded that there is a difference of 130 g between 5 moles of CO₂ and 5 moles of H₂O.

Molar mass of calcium, Ca = 40g

Given Mass of the calcium = 240g

As we know that, Number of moles = mass of an element/molar mass of an element

Hence Number of moles of Calcium = 240g/40g = 6 moles.

Molar mass of magnesium, Mg = 24g

Given Mass of the magnesium, Mg = 240g

As we know that, Number of moles = mass of an element/molar mass of an element

Hence Number of moles of magnesium = 240g/24g = 10 moles.

From above calculation, the molar ratio can be inferred - 6:10 = 3:5

Mole is defined as the amount of substance that contains as many specified elementary particles (such as atoms, molecules) as the number of atoms in 12g of carbon-12 isotope. One mole is also defined as the amount of substance which contains Avogadro number (6.023 x 10²³) of particles.

1.5 moles of Na₂SO₃ has 1.5×2 = 3 moles of Na

1.5 moles of Na₂SO₃ has 1.5×1 = 1.5 mole of S

1.5 moles of Na₂SO₃ has 1.5×3 = 4.5 moles of O.

As we know that Mass of an element= number of moles x atomic mass

Thus, mass of sodium = 3 × 23 g = 69g

Mass of sulphur = 1.5 × 32 = 48g

Mass of oxygen = 4.5 × 16 g = 72g

A mole of carbon atoms means a carbon sample measuring 12 g and containing 6.022 x 10²³ carbon atoms.

Atomic mass of Al = 27u

1 mole of aluminium weighing 27g contains N = 6.022 x 10²³ atoms of Al

So, 50g of Al contains = 50 × N(6.022 × 1023)/27 atoms of Al = 11 × 10²³ atoms of Al

Atomic mass of Fe = 56 u

1 mole of iron weighing 56g contains N = 6.022 × 10²³ atoms of Fe

So, 50g of Fe contains = 50 × N(6.022 × 10²³)/56 atoms of Fe = 5 × 10²³ atoms of Fe

Thus, 50g of Al has more no. of atoms as compared to 50g of Fe. This is because Aluminium has a smaller atomic mass and is lighter.

The atomic mass of an element expressed in grams is called gram atomic mass. It is determined by taking the atomic weight for an element on the periodic table and expressing it in gram. Weight in grams is numerically equal to the atomic weight of the element.

The gram atomic mass of oxygen is equal to 16.

Moles of oxygen atom are -

(i). Al₂O₃ : 3 moles

(ii). CO₂ : 2 mole

(iii). Cl₂O₇ : 7 mole

(iv). H₂SO₄ : 4 mole

(v). Al₂(SO₄)₃ : 12 mole

Gram molecular mass of a substance is known as the quantity of the substance whose mass expressed in grams is numerically equal to its molecular mass. For example: The molecular mass of CO₂ is 44 u, its gram molecular mass is 44g.

The gram molecular mass of oxygen(O₂) = 2×16g = 32g

Given mass of sulphur, S₈ = 100g

Atomic mass of sulphur, S₈ = 32 × 8 g = 256g

Number of moles = Given mass of the element / Atomic mass of the element

Number of moles = 100/ 256 = 0.39 moles.

Molar mass can be defined as the mass of one mole of a substance (may be an element or a compound). For example, One mole of oxygen(O₂) weighs 32.0 g. Thus, Molar mass of one mole molecules of oxygen = 32 g /mol

Molar mass of ozone (O₃) = 3 × gram atomic mass of O = 3 × 16 g = 48 g/ mole

(ii) Molar mass of Ethanoic acid (CH₃COOH) = 2×C + 4×H + 2×O = (24 + 4 + 32)u = 60 g/ mole

Molar mass of magnesium = 24g

Given mass of magnesium = 12g

Number of moles = given mass of the element/ atomic weight of element

Number of moles of magnesium = 12/24 = 0.5 moles

Molar mass of carbon = 12g

Given mass of carbon = 6g

Number of moles = given mass of the element/ atomic weight of element

Number of moles of carbon = 6/12 = 0.5 moles

Hence, 12 g of magnesium and 6 g of carbon represents a mole ratio of 1 : 1

One mole of water = 18 g

20 moles of water = 360g; it supports option (ii)

Atomic weight of sulphur = 32g

One atom of sulphur weighs 32g

Atomic weight of oxygen is 16g

Hence, 2 atoms of oxygen weighs 32g

6.022 × 10²³ atoms of magnesium = one mole of magnesium

3.011 × 10²³ atoms of magnesium = 0.5 moles of magnesium

Mass of magnesium = atomic weight x number of moles

Mass of magnesium = 24 × 0.5 = 12g

Similarly 6.022 × 10²³ atoms of carbon = one mole of carbon

3.011 × 10²³ atoms of carbon = 0.5 moles of carbon

Mass of carbon = atomic weight × number of moles

Mass of carbon = 12 × 0.5 = 6g

Molar mass of magnesium = 24g

Given mass of magnesium = 12g

Number of moles = given mass of the element/ atomic weight of element

Number of moles of magnesium = 12/24 = 0.5 moles

Molar mass of sulphur = 32g

Given mass of sulphur = 16g

Number of moles = given mass of the element/ atomic weight of element

Number of moles of sulphur = 16/32 = 0.5 moles

Hence, 12 g of magnesium and 16 g of sulphur represents a mole ratio of 1 : 1

Atomic weight of carbon = 12g

One atom of carbon weighs 12g

Atomic weight of magnesium is 24 g

Hence, 1/2 atom of magnesium weighs 12g

18 g of CH₄ has the maximum number of atoms.

1 mole of SO₂ = Mass of S + 2 × Mass of O = 64 grams

64 g of SO₂ = 1 mole

So, 1 g of SO₂ = 1/64 mole

Now since equal moles of all the substances contain equal number of molecules so, 1/64 mole of O₂ will also contain x molecules like SO₂.

32 g of oxygen = 1 mole

So, 1 g of oxygen = 1/32 mole

Now, 1/64 mole of oxygen contains = x molecules

So, 1/32 mole of oxygen will contain = x × 64/32 = 2x molecules

Mass of one molecule of substance = 4.65 × 10^-23 u

So, mass of 1 mole of substance = Mass of 6.022 × 10²³ molecules of the substance

= 4.65 × 10^-23 × 6.022 × 10²³ u = 28 u

The substance is Nitrogen with molecular mass 28 u.

Molar mass of SO₂ = (32 + 2×16) g = 64g

Given mass of SO₂ = 10g

1 mole of substance = 6.023 × 10²³ particles of the substance

No. of moles of SO₂ = 10g/64g = 0.15

Total no. of molecules of SO₂ = 0.15 × 6.022 × 10²³ = 0.90 × 10²³ molecules of SO₂

Molar mass of oxygen (O₂) = 32g

Given mass of oxygen (O₂) = 10g

1 mole of substance = 6.023 × 10²³ particles of the substance

No. of moles of O₂ = 10g/32g = 0.31

Total no. of molecules of O₂ = 0.31 × 6.022 × 10²³ = 1.88 × 10²³ molecules of O₂

Thus, 10g of O₂ contains more no. of molecules.

Given mass of nitrogen = 56g

Molar mass of nitrogen = 14g

No. of moles of nitrogen = given mass of the element/ molar mass of the element = 56g/14g = 4 moles

Equal number of moles of all the susbtances contain equal number of molecules.

So, 4 moles of nitrogen and 4 moles of oxygen contains same no. of molecules.

Hence, mass of 4 mole of oxygen = 4 × 16g = 64 g

Given mass of water = 1.8g

Molar mass of water = 18g

No. of moles of water = given mass of the element/ molar mass of the element = 1.8g/18g = 0.1 moles

Equal number of moles of all the substances contain equal number of molecules.

So, 0.1 moles of water and 0.1 moles of nitrogen contains same no. of molecules.

Hence, mass of 0.1 mole of nitrogen = 0.1 × 28 g = 2.8 g.

32 g of S = 1 mole

So, 1 g of S = 1/32 mole

Now since equal moles of all the substances contain equal number of atoms so, 1/32 mole of oxygen will also contain x atoms like S.

16 g of oxygen = 1 mole

So, 1 g of oxygen = 1/16 mole

Now, 1/32 mole of oxygen contains = x atoms

So, 1/16 mole of oxygen will contain = x × 32/16 = 2x atoms.

Given mass of carbon = 6g

Molar mass of carbon = 12g

No. of moles of carbon = Given mass of element/ Molar mass of element = 6g/12g = 0.5 moles

Equal number of moles of all the substances contain equal number of molecules.

So, 0.5 moles of carbon and 0.5 moles of magnesium contains same no. of molecules.

Hence, mass of 0.5 mole of magnesium = 0.5 × 24g = 12g

(i) Mass of one atom of element X = 2 × 10^-23 g

Mass of 1 mole of atom of element X = 2 × 10^-23 × 6.022 × 10²³ = 12.044 g

So, atomic mass of the element X = mass of 1 mole of element = 12 u

(ii) Element X is CARBON.

Carbon is the element used as a standard for atomic mass scale.

C-12 atom is used for this purpose.

12 atomic mass unit (amu) is the mass of this reference atom.

According to one of the main postulate of Dalton's atomic theory, atoms were being considered as indivisible. But according to the modern theory, it is now known that that atoms can be further divided into still smaller/subatomic particles called electrons, protons and neutrons.

According to one of the main postulate of Dalton's atomic theory, atoms were being considered as indivisible. But according to the modern theory, it is now known that that atoms can be further divided into still smaller/subatomic particles called electrons, protons and neutrons.

To see atoms of different elements a special type of microscope called Scanning Tunnelling microscope [STM] is used. It is an electron microscope for imaging surfaces at the atomic level. It produces 3D images of the sample.

Symbol may be defined as the abbreviation/Sign used for the name of an element. The symbol of an element is generally either the first letter or the first two letters or the first and the third letters of the name of the element.

For examples- Oxygen has symbol O, Aluminum has symbol Al.

(a) Aluminum- Al and Barium- Ba

Iron(ferrum)- Fe and Copper(cuprum)- Cu.

Hydrogen- H, Helium-He, Lithium- Li , Beryllium-Be, Boron-B

Sodium- Na; Potassium- K; Iron- Fe; copper- Cu; Mercury- Hg; Silver- Ag.

Hg- Mercury; Pb- Lead; Au- Gold; Ag- Silver; Sn-Tin

The number of atoms which constitutes a molecule of an element or a compound is known as atomicity of the element. For example -The atomicity of the noble gases is 1, that of hydrogen, nitrogen, oxygen etc. is 2 each and of ozone is 3. Thus, noble gases, hydrogen and ozone are respectively monoatomic, diatomic and triatomic molecules.

(a) Oxygen -2

(b) Ozone-3

(c) Neon-1

(d) Sulphur-8

(e) Phosphorus-4

(f) Sodium-1

The chemical formula of a compound describes the composition of the molecules of the compound in terms of the symbols of elements and the number of atoms of each element present in one molecule of the compound. In the chemical formula of a compound, the elements present are denoted by their symbols and the number of atoms of each element are shown by writing their number as subscripts to the symbols of the respective elements.

Formula of a compound- Water-H20

Formula of an element-Sodium- Na.

(a) Water- H2O; As conveyed by the formula, elements present are hydrogen and oxygen.

(b) Ammonia-NH3; As conveyed by the formula, elements present are nitrogen and hydrogen.

(c) Methane-Ch4; As conveyed by the formula, elements present are carbon and hydrogen.

(d) Sulphur dioxide-SO2; As conveyed by the formula, elements present are sulphur and oxygen.

(e) Ethanol-C2H5OH; As conveyed by the formula, elements present are carbon, hydrogen and oxygen.

Both 2N and N2 are the forms of nitrogen. 2N denotes two separate atoms of nitrogen whereas N2 denotes one molecule of nitrogen gas.

(a) O - one atom of oxygen

(b) 2O - two separate atoms of oxygen

(c) O₂ - one molecule of oxygen gas

(d) 3O₂ - three molecules of oxygen

The above compound is Sulphuric acid (H₂SO₄). According to chemical formula of H₂SO₄, H₂ denotes two atoms of hydrogen, S denotes one atom of sulphur and O₄ denotes four atoms of oxygen.

Atoms of the majority of elements (except noble gases) are chemically very reactive and does not exist in the free state (as a single atom). Oxygen gas is diatomic and hence its molecular formula is O₂.

The atoms of only a few elements are chemically unreactive which are called noble gases (such as helium, neon, argon etc.). They exist in the free state (as single atom).

Both 2H and H₂ are the forms of hydrogen. 2H denotes two separate atoms of hydrogen whereas H₂ denotes one molecule of hydrogen gas.

All of the above options are the forms of nitrogen.

(i) N denotes one atom of nitrogen.

(ii) 2N denotes two separate atoms of nitrogen

(iii) N₂ denotes one molecule of nitrogen gas.

(iv) 2N₂ denotes two molecules of nitrogen gas.

With the help of molecular formula of a compound, we can calculate its percentage composition by mass. First, we calculate the molecular mass of the compound. From this we can find out mass of one mole of the compound, which is equal to its gram molecular mass.

Molecular formula of glucose is C6H12O6

Molecular mass of glucose = (6xC) + (12xH) + (6xO) = 72 + 12 + 96 = 180u.

(a) Molecular mass of Hydrogen (H₂) = 2 x H = 2 x 1 u = 2 u

(b) Molecular mass of oxygen (O₂) = 2 x O = 2 x 16 u = 32 u

(c) Molecular mass of chlorine (Cl2) = 2 x Cl = 2 x 35.5 = 71 u

(d) Molecular mass of Ammonia (NH₃) = 1 x N + 3 x H = 14 + 3 = 17 u

(e) Molecular mass of carbon dioxide (CO₂) = 1 x C + 2 x O = 12 + 32 = 44 u

(a). Molecular mass of methane (CH₄) = 12 + 4 = 16 u

(b). Molecular mass of ethane (C₂H₆) = 2 x 12 + 6 x 1 = 30 u

(c). Molecular mass of ethane (C₂H₄) = 2 x 12 + 4 x 1 = 28 u

(d). Molecular mass of ethyne (C₂H₂) = 2 x 12 + 2 x 1 = 26 u

(a) Molecular mass of Methanol (CH₃OH) = 1 x C + 3xH + 1xO +1xH = (12+3+16+1)u = 32u

(b) Molecular mass of Ethanol (C₂H₅OH) = 2xC + 5xH + 1xO + 1xH = (24 + 5 + 16 + 1) = 46u

Molecular mass of ethanoic acid (CH₃COOH) = 1xC + 3xH + 1xC + 2xO + 1xH = 12+3+12+32+1 = 60u

Molecular mass of Nitric acid (HNO₃) = 1xH + 1xN + 3xO = (1 + 14 + 48) u = 63 u

Molecular mass of chloroform (CHCl₃) = 1 x C + 1 x H + 3 x Cl = (12 + 1 + 106.5)u = 119.5 u

Molecular mass of hydrogen bromide (HBr) = 1 x H + 1 x Br = (1 + 80) u = 81u

(a) Molecular mass of hydrogen sulphide (H₂S) = 2xH + 1xS = (2+32)u = 34u

(b) Molecular mass of Carbon disulphide (CS₂) = 1xC + 2xS = (12+2 x 32)u = 76 u

Law of conservation of mass was given by Antoine Lavoisier in 1744. According to this law, “Matter can neither be created nor destroyed in a chemical reaction”. This law states that mass of an isolated system will remain constant over time. It means that when mass is enclosed in a system and nothing is allowed in or out, its quantity will never change. That is mass will be conserved, and hence this is called Law of Conservation of Mass. This means total mass of products is always equal to the total mass of reactants.

In a chemical reaction, the substances that combine or react are known as reactants and the new substance/substances formed are called product or products. A chemical reaction can be represented in general as follows:

Reactant + Reactant → Product

Example: When calcium oxide is dissolved in water, then calcium hydroxide is formed. The reaction involved in this can be written as:

Calcium oxide + Water → Calcium hydroxide

In this reaction calcium oxide and water are reactants while calcium hydroxide is product.

In this reaction 74 g of calcium hydroxide is obtained when 56 g of calcium oxide reacts with 18 g of water, which is proved by experiment.

Calcium oxide (56 g) + Water (18 g) → Calcium hydroxide (74 g)

{CaO = Ca(40) + O(16) = 56g; H2O = H2(2)+O(16) = 18g; Ca(OH)2 = Ca(40)+O(32)+H(2) = 74g}

Here the total mass of reactants, i.e. calcium oxide and water is equal to 74 g. And the mass of product, i.e. calcium hydroxide is also equal to 74g. This proves that the total mass of reactants is always equal to the total mass of product, which proves the Law of Conservation of Mass.

Law of constant proportions was given by Joseph Proust in 1799. According to this law, “a chemical compound always contains same elements in definite proportion by mass and it does not depend on the source of compound.” Compounds are formed by the combination of two or more elements. In a compound the ratio of the atoms or element by mass remains always same irrespective of the source of compound. This means a certain compound always formed by the combination of atoms in same ratio by mass. If the ratio of mass of constituent atoms will be altered the new compound is formed.

Example: Water is formed by the combination of hydrogen and oxygen. The ratio of masses of hydrogen and oxygen is always in 1:8 in water irrespective of source of water. Whether you collect the water from a well, river, pond or from anywhere the ratio of their constituent atoms by mass will always same.

Main postulates of Dalton's atomic theory

1). Elements are made of extremely small/ indivisible particles called atoms.

2). Atoms of a given element are identical in size, mass, and other properties.

3). Atoms of different elements differ in size, mass, and other properties.

4). Atoms cannot be subdivided, created, or destroyed.

5). Atoms of different elements combine in simple ratios to form chemical compounds.

6). In chemical reactions, atoms are combined, separated, or rearranged.

According to law of conservation of mass which describes that, “Matter can neither be created nor destroyed in a chemical reaction”. This law gives result to the postulate of Dalton’s atomic theory which states that, “Atoms can neither be created and nor destroyed by physical and chemical changes.”

According to law of constant proportions which describes that, “a chemical compound always contains same elements in definite proportion by mass and it does not depend on the source of compound.”

This law gives result to the postulate of Dalton’s atomic theory which states that, “When two elements combine to form two or more than two different compounds then the different masses of one element B which combine with fixed mass of the other element bear a simple ratio to one another.”

Symbol may be defined as the abbreviation used for the name of an element. The symbol of an element are generally either the first letter or the first two letters of the name of element or the first and the third letters of the name of the element.

For example, the symbol of some elements are the first letter of the name of that element such as Hydrogen- H, Oxygen- O.

Some symbols are derived from the first two letters of the names of the element such as Calcium- Ca, Aluminum- Al.

Some symbol derived from the first and the third letter of the names of the elements such as Arsenic-As

Symbol of many elements are taken from their English name, while symbol of many elements are taken from their Greek or Latin names such as the latin name of sodium is Natrium, hence the symbol is Na.

Significance of symbol H

● The symbol H refers to the element hydrogen.

● The symbol H refers to one atom of hydrogen.

● The symbol H refers to one mole of hydrogen i.e., 6.022 × 10²³ atoms.

● The symbol H refers to 1 gram atomic mass of hydrogen.

The building blocks of all types of matter is called atoms. An atom is the smallest and indivisible part of an element that can take participate in a chemical reaction. Atoms of majority of the elements are very reactive and do not exist in the free state (as single atom). They exist in combination with the atoms of the same elements or another element.

A molecule is the smallest part of an element or compound that has independent existence. A molecule contain one or more than one atoms. The molecules of elements contain atoms of only one kind. For example Oxygen gas; it contains two atoms of oxygen. Hence it is a molecule.

Molecules of elements: The molecules of an element contain two or more similar atom chemically bonded together, for example oxygen gas has 2 oxygen atoms combined together whereas ozone gas has 3 oxygen atoms combined together, so ozone exists in the form of O3. In contrast to it, molecules of compounds contain two or more different types of atoms chemically bonded together. For example: the molecule sulphur dioxide (SO2) contain one atom of sulphur chemically bonded with two atom of oxygen.

‘amu’ is the symbol of Atomic mass unit, but nowadays it is denoted 1 by ‘u’.

Atomic mass of an element may be defined as the average relative mass of an atom of the element as compared with mass of an atom of carbon (C-12 isotope) taken as 12 amu

Carbon-12 is considered as unit to calculate atomic mass. Carbon-12 is an isotope of carbon. The relative mass of all atoms are found with respect to C-12.

One atomic mass = 1/12 of the mass of one atom of C-12.

This means atomic mass unit = 1/12th of carbon-12.

The atomic mass of oxygen is 16u, this means one atom of oxygen is 16 times heavier than 1/12^th of carbon atom.

Natrium is the latin name of Sodium.

The atomicity of ozone(O3) is 3, sulphur(S)- 8, phosphorus(P)- 4, Argon(noble gas, Ar)- 1.

Mercury is used in the making of thermometers. Its symbol is Hg.

John Dalton gave atomic theory of matter.

The atomicity of helium is 1. It is a noble gas.

the latin name of potassium is kalium.

The law of conservation of mass was given by Lavoisier.

The atomicity of phosphorus is 4.

CaCO3 gets decomposed into calcium oxide(CaO) and carbondioxide(CO2). According to law of conservation of mass

The law of constant proportions was given by proust.

Krypton has the lowest atomicity and Sulphur has highest atomicity i.e. 8.

1nm = 10^-9 m, whereas 1m = 100cm, hence 1nm = 10^-7 cm.

Berzelius proposed the first letter (or first letter and another letter) of the Latin or English name of an element as its symbol.

helium and neon are noble gases.

Neon has the same molecular mass as its atomic mass.

The proportion of oxygen and hydrogen by mass in water can be calculated as-

(H₂O) = 1xO(16): 2xH(1) = 16:2 = 8:1.

(b); The proportion of hydrogen and oxygen by mass in hydrogen peroxide can be calculated as-

(H₂O₂) = 2xH(1): 2xO(16) = 2:32 = 1:16.

It is the correct symbol of Helium; the correct symbols of cobalt, aluminium, and sodium are Co, Al and Na respectively.

Here are the equations for copper sulphate solution reacting with sodium hydroxide solution:

copper sulfate + sodium hydroxide → copper hydroxide + sodium sulfate

CuSO4 + 2NaOH → Cu(OH)2 + Na2SO4

(15.95g + 8g → 9.75g + 14.2g)

23.95g = 23.95g

As all the reactants and products remain in the sealed reaction container then it is easy to show that the total mass is unchanged. This data shows the law of conservation of mass.

According to the above question-

According to the law of conservation of mass-

Mass of potassium chloride + mass of oxygen = Mass of potassium chlorate

Mass of oxygen(x) = Mass of potassium chlorate- mass of potassium chloride

X = 24.5g-14.9g

X = 9.6g

Hence mass of oxygen = 9.6 g

According to question-

Reaction 1-

So, 1 equivalent of Cu reacts with 0.25 equivalent of O2 to form 1.25 equivalent of copper oxide.

Reaction 2-

Here again, one can see that 1.25 equivalent of CuO decomposed to form 1 equivalent of Cu and 0.25 equivalent of oxygen.

Hence, law of constant proportion is verified.

According to question-

i.e. three equivalents of Mg reacts with 2 equivalents of O2 to form 1 equivalent of MgO.

When mass of Mg = 3x = 24 gm

So, x = 8 gm

Then, mass of oxygen required = 2x = 16 gm

When 5 gm of calcium is burnt in 2gm of oxygen, then 7 gm of calcium oxide is formed. So, calcium and oxygen combine in the fixed proportion of 5:2 by mass. Now, when 5 gm of calcium is burnt in 20 gm of oxygen, then also 7 gm of calcium oxide will be formed because chemical reactions follows law of constant proportion. As a result, 18 gm of oxygen will be left unreacted.

According to question-

(a) (i) Water (ii) Oxygen (iii) Hydrogen

(b) 1 : 8

(c) Law of Constant proportions

(d) Rivers and Wells

(e) Gas Y (oxygen) is necessary For breathing

According to question-

(a) Solid P - Calcium Carbonate (CaCO₃)

Gas Q - Carbon dioxide (CO₂)

Solid R - Calcium oxide (CaO)

(b) Total mass of Q and R = 22gm + 28gm = 50gm

(c) Total mass of Q and R (50gm) is equal to mass of reactant (50gm).

(d) The law of conservation of mass is followed, i.e. total mass of product is equal to mass of reactant.

(e) Law of conservation of mass is illustrated by the example.

Those particles which have more or less electrons than the normal atoms are called Ions.

(a) Those particles which have more electrons than the normal atoms are called Anions.

(b)Those particles which have less electrons than the normal atoms are called Cations.

Formula mass of an ionic compound is obtained by adding atomic masses of all the atoms in a formula unit of the compound. For example: Formula mass of sodium chloride (NaCl) = Atomic mass of sodium + atomic mass of chlorine = 39 + 35.5 = 74.5

(a) Anions are formed by the gain of electrons by atoms

(b) Cations are formed by the loss of electrons by atoms.

(a) A sodium ion has positive charge because it has more protons than a neutral atom

(b) A chloride ion has negative charge because it has more electrons than a neutral atom

(a) The formula of Calcium oxide is CaO

(b) The formula of Magnesium hydroxide is Mg(OH)2.

Valency of element Z = 3

Valency of oxygen = 2

So, formula of oxide of element = Z₂O₃

The valence electrons present in sodium atom are 11. In the above statement, there is loss of one electron shown which makes it Sodium ion(Cation) denoted by Na⁺.

The valence electrons present in chlorine atom are 17. In the above statement, there is gain of one electron shown which makes it chloride ion(anion) denoted by Cl^-.

(a) Anion is formed by the acceptance/gain of electrons by an atom.

(b) Cation is formed by donating/loss of electrons by an atom.

(c) ion

(d) electrons; protons

(e) protons; electrons

Water(H2O) is made up of two types of elements known as hydrogen and oxygen.

The valency of hydrogen is 1 as only one valence electron is present in its outermost shell and one is needed. The valency of oxygen is 2 as six valence electrons are present in its outermost shell and two are needed.

So according to the valencies of both the elements present in water, the formula becomes H2O.

The valency of hydrogen is 1 and that of nitrogen is 3. So according to the valencies of both the elements present in ammonia, The formula becomes NH3.

The valency of sulphur is 4 and that of oxygen is 2. So according to the valencies of both the elements present in sulphur dioxide, The formula becomes SO4.

The valency of carbon is 4 and that of sulphur is 2. So according to the valencies of both the elements present, the formula becomes CS2. The name of compound is carbon disulphide.

The valency of X is 4 and that of Y is 1. So according to the valencies of both the elements present, the formula becomes XY4. The name of compound is carbon disulphide.

When element B shows valency of 4 and oxygen has valency of 2. The formula becomes BO2.

When element B shows valency of 6 and oxygen has valency of 2. The formula becomes BO3.

The formula of the compound formed is X2Y3.

The valency of magnesium is 2 and that of hydrogen carbonate(HCO3) is 1. So according to the valencies of both the elements present in magnesium hydrogencarbonate, the formula becomes Mg(HCO₃)₂.

(a) The valency of element X is 2 and that of bromine is -1. So according to the valencies of both the elements, the formula becomes XBr₂.

(b) The valency of element X is 2 and that of oxide is -2. So according to the valencies of both the elements, the formula becomes XO.

(a) The valency of sodium is 1 and that of oxide is -2. So according to the valencies of both the elements, the formula becomes Na₂O.

(b) The valency of calcium is 2 and that of carbonate is -2. So according to the valencies of both the elements, the formula becomes CaCO₃.

(a) Molecular mass of Na2O = (2 x Na) + (1 x O) = (2 x 23) + (1 x 16) = 62u

(b) Molecular Mass of Al₂O₃ = (2 x Al) + (3 x O) = (2 x 27) + (3 x 16) = 102u

(a) Copper sulphate; Cu²⁺ and

(b) Ammonium sulphate;

(c) Sodium oxide; Na⁺ and O^2-

(d) Sodium carbonate; Na⁺ and

(e) calcium chloride; Ca²⁺ and Cl^-

(a) Cation: Na⁺; Anion: CH₃COO^-

(b) Cation: Na⁺; Anion Cl^-

(c) H₂ is a covalent molecule. It has no cation and anion

(d) Cation: ; Anion:

(a) The valency of calcium is 2 and that of fluorine is -1. So according to the valencies of both the elements, the formula becomes CaF₂.

(b) The valency of hydrogen is 1 and that of sulphur is -2. So according to the valencies of both the elements, the formula becomes H₂S.

(c) The valency of nitrogen is -3 and that of hydrogen is 1. So according to the valencies of both the elements, the formula becomes NH₃.

(d) The valency of carbon is 4 and that of chlorine is -1. So according to the valencies of both the elements, the formula becomes CCl₄.

(e) The valency of sodium is 1 and that of oxygen is -2. So according to the valencies of both the elements, the formula becomes Na₂O.

(f) The valency of carbon is 4 and that of oxygen is -2. So according to the valencies of both the elements, the formula becomes CO₂.

(i) Ionic compounds- The compounds which are formed by the combination of metals and non-metals are called ionic compounds. For example- NaCl, CaCl₂.

(i) Molecular Compounds- These compounds are formed by the combination of two non-metal elements. For ex. HCl and H₂SO₄.

An ion is a charged particle and can be negatively or positively charged.

A negatively charged ion is called an „anion‟ and the positively charged ion, a „cation‟. For example, sodium chloride (NaCl). Its constituent particles are positively charged sodium ions (Na⁺) and negatively charged chloride ions (Cl^–). Ions may consist of a single charged atom or a group of atoms that have a net charge on them. A group of atoms carrying a charge is known as a polyatomic ion e.g. Calcium oxide (Ca+2 O-2)

i. Sodium phosphate - Na₃PO₄

ii. Ammonium sulphate - (NH₄)₂SO₄

iii. Calcium Hydroxide - Ca(OH)₂

iv. Lead bromide - PbBr₂

A positively charged ion is known as cation. For example : Sodium ion:Na , Magnesium ion: Mg2 A cation is formed by the loss of one or more electrons by an atom For example : sodium atom, loses one electron to form a sodium ion Na Sodium atom (A cation)

A negatively charged ion is known as anion. Cl- (chloride ion), O-2 (oxide ion) etc. An anions is formed by the gain of one or more electrons by an atom. For example a chlorine atom gains one electron to form a chloride ion Cl-. Chlorine atom Chloride ion (An anion).

(i). Na₂S

(ii). Cu (NO₃)₂

Formation of Sodium ion- The atomic number of sodium is 11. The arrangements of electrons in the shells of the sodium atom is in the combination of 2,8,1. The valence electron present in the outermost shell of sodium atom is 1. The sodium atom can lose one electron to form sodium ion(Na⁺). There will be reduction in number of electrons, E=10. Number of protons remain same as 11. Due to the decrease in one electron, there is positive charge on a sodium ion.

Formation of Chloride ion- The atomic number of chlorine is 17. The arrangements of electrons in the shells of the chlorine atom is in the combination of 2,8,7. The valence electron present in the outermost shell of chlorine atom is 1. The chlorine atom can lose one electron to form chlorine ion(Cl^-). There will be increase in number of electrons, E=18. Number of protons remain same as 17. Due to the increase in one electron, there is negative charge on a chloride ion.

Symbol of two simple ions⁻ Na⁺, Al³⁺

Symbol of two compound ions- NH4⁺, NO₃^2-

(i) The valency of chloride ion is -1. Hence the formula becomes YCl₄

(ii)The valency of oxide ion is -2. Hence the formula becomes YO₂

(iii) The valency of sulphate ion is -4. Hence the formula becomes Y(SO₄)₂

(iv) The valency of carbonate ion is -4. Hence the formula becomes Y(CO₃)₂

(v) The valency of nitrate ion is -1. Hence the formula becomes Y(NO₃)₄

Formula unit is defined as the empirical formula of a compound which gives the simplest whole number ratio of atoms of the various elements present in the molecule of the compound.

Formula Unit of Sodium Chloride- NaCl

Formula Unit of Magnesium Chloride- MgCl2.

(i) Formula Mass of Calcium chloride (CaCl₂) = 1xCa + 2xCl = (40+71) u = 111 u

(ii) Formula Mass of Sodium carbonate (Na₂CO₃) = 2xNa + 1xC + 3xO = (2x23 + 1x12 + 3x16) u = 106 u

X³⁺ indicates loss of three electrons. Hence the remaining no. of electrons present are 10.

according to the valencies of sodium(1) and nitrogen(3).

as the symbol suggests the gain of three electrons, the atomic number of Z is likely to be 7.

An anion is formed by the gain of electrons.

An anion is formed by the gain of electrons.

Sulphur has 2 valence electrons in its outermost shells. Hence it exhibits valencies of 2, 4 and 6.

as the symbol suggests the gain of two electrons, the atomic number is likely to be 18.

A cation is formed by the loss of electrons.

Nitrogen have 5 electrons in the outermost shell of its atom, hence its valencies are 5 and 3. Iron can lose 2 and 3 electrons from its outermost shell, so its valencies are 2 and 3.

as the symbol suggests the loss of two electrons, the atomic number is likely to be 12.

The loss of an electron in the above data proves that it is a cation.

An ionic compound will always formed by the combination of an anion and a cation.

Molecular compounds are usually formed by the combination between two different non-metals

As the formula suggests, the valencies of elements X and Y will be 1 and 3 respectively.

Nitrogen is trivalent as valency of nitrogen is -3, hence formula of nitride = XN