STATES OF MATTER

SOME BASIC CONCEPTS OF CHEMISTRY Learning Objectives:

1. Matter 2. Classification of matter 3. Law of chemical combination 4. Dalton’s Atomic theory 5. Mole concept 6. Stoichiometry Matter:

Anything which occupies space and has mass, is called a matter. Ex: Air, water, rock etc..

Laws of chemical combination: ● Law of conservation of mass: Matter can neither be created nor be destroyed. ● Law of definite proportion: A given compound always contains exactly the same proportion of elements by weight ● Law of multiple proportion: If two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of other element, are in the ratio of small whole numbers. ● Gay Lussac’s law of gaseous volume: When gases combine or are produced in a chemical reaction, they do so in a simple ratio by volume provided all gases are at same temperature and volume.

● Avogadro’s Law

Equal volume of gases at the same temperature

and pressure should contain the equal number

of molecules. Dalton’s atomic theory: Postulates: 1. Matter consists of indivisible atoms. 2. All the atoms of a given element have identical properties including identical mass. Atoms of different elements differ in mass. 3. Compounds are formed when atoms of different elements combine in a fixed ratio. 4. Chemical reactions involve reorganization of atoms. These are neither created nor destroyed in a chemical reaction. Limitations of Dalton’s atomic theory: ● It does not account for subatomic particles. ● It does not account for isotopes. ● It does not account for isobars. ● Elements need not combine in simple, whole-number ratios to form compounds. ● The theory does not account for allotropes. Atomic mass: ➤ Mass of one atom. Unit used: amu or ‘U’ 1 amu = (1/12)th of the mass of C-12 atom Therefore, 1 amu = 1.67 ✖ 10-27 kg Molecular mass ➤ Sum of the atomic masses of the elements present in a molecule.

Eg. Molecular mass of methane (CH4) = (1 ✖ 12 U + (4 ✖ 1 U) = 16 U Question: Dalton’s Atomic theory states that ______. a. An atom has predominantly empty space. b. Matter is composed of small indestructible particles. c. Energy is neither created nor destroyed in a chemical reaction. d. All elements have several isotopes. Question: Dalton’s Atomic theory states that ______. a. An atom has predominantly empty space. b. Matter is composed of small indestructible particles. c. Energy is neither created nor destroyed in a chemical reaction. d. All elements have several isotopes. Question: 1 Atomic mass unit is the number of times an atom of any element is equal to 1/2th of an atoms of a. C-12. b. C-13 c. Cl -35 d. Cl -37 Question: 1 Atomic mass unit is the number of times an atom of any element is equal to 1/2th of an atoms of a. C-12. b. C-13 c. Cl -35 d. Cl -37 Question:

What would be the molecular mass of a compound whose vapour density is 5 ? a. 5 b. 10 c. 15 d. 20 Question:

What would be the molecular mass of a compound whose vapour density is 5 ? a. 5 b. 10 c. 15 d. 20

Solution: Molecular mass = 2 × Vapour density Question:

What is the molecular weight of HNO3?

(Given: Atomic weight of N, H and O are 14, 1 and 16 respectively) a. 32 b. 63 c. 46 d. 23 Question:

What is the molecular weight of HNO3?

(Given: Atomic weight of N, H and O are 14, 1 and 16 respectively) a. 32 b. 63 c. 46 d. 23 Question:

Isotopes of any element have a. same atomic weight but different atomic number. b. same atomic weight and atomic number. c. different atomic weight but same atomic numbers. d. different atomic weight and atomic numbers. Question:

Isotopes of any element have a. same atomic weight but different atomic number. b. same atomic weight and atomic number. c. different atomic weight but same atomic numbers. d. different atomic weight and atomic numbers.

Join Vedantu JEE Telegram channel NOW!

Assignments Notes Daily Update https://vdnt.in/JEEVedantu