Atoms And Molecules

Question 1

What were the laws of chemical combination? Who established them?

Answer 1

The laws of chemical combination was establushed by Antoine Lavoisier and Joseph L Proust respectively.

1. Law of conservation of mass - mass can neither be created nor destroyed in a chemical reaction.
   eg- x= copper sulphate (1.25g), Y - Sodium Carbonate (1.43g), x+y = CuSo4 + NaCo3 = Na2So4 + Co2 + CuO5
2. Law of constant proptions -> In a chemical substance, the elements are always present in definite proportions by mass.

Question 2

What were the postulates in Dalton’s Atomic theory?

Answer 2

1. All matter is made of very tiny particles called atoms, which participate in chemical reactions.
2. Atoms are indivisible particles, which can neither be created nor destroyed in a chemical rwaction.
3. Atoms of a given element are identical in mass and chemical peoperties.
4. Atoms of different elements have different masses and chemical properties.
5. Atoms combine in the ratio of small whole numbers to form compounds.
6. The relative number and kinds of atoms are constant in a given compiund. -> fixed ratio.

Question 3

What’s the IUPAC?

Answer 3

International Union Of Pure and Applied Chemistry is an international scientific organization which approves names of elements, symbols and units.

Question 4

What’s one atomic mass?

Answer 4

One atomic mass is a mass unit equal to 1/12th of the mass of one atoms of carbon-12.

The relative atomic masses of all elements have been found with respct to carbon-12.

Question 5

What is a molecule? Difference between the molecule of an element and molecule of a compound.

Answer 5

A molecule is in general a group of two or more atoms that are chemically bonded together.
It is the smallest particle of an element or a compound that is capable of an independent existence and shows all the properties of that substance.

Molecule of an element - It is formed by the combination of 2
or more atoms of the same element. Eg-> H2 , O2 , P4 , S8,

Molecule of a compound -> It is formed when 2 or more atoms of
different elements combine together in a definite proportion by mass

Question 6

What is atomicity?

Answer 6

The number of atoms constituting a molecule is known as its atomicity

Question 7

What is Valency?

Answer 7

The combining power (or capacity) of an element is known as its valency.

Question 8

What is molecular mass?

Answer 8

The molecular mass of a susbstance is the sum of the atomic masses of all the atoms in a molecule of the susbtance.

Question 9

What is formula unit mass?

Answer 9

Sum of atomic masses of all atoms in a fomula unit of a compound.