Atoms and molecules

1.3. Dalton’s Atomic Theory

1. All matter is made of very tiny particles, called atoms. (tomia = divisible; atomia = indivisible)
2. Atoms are indivisible particles, which cannot be created or destroyed in a chemical reaction.
3. Atoms of a given element are identical in mass and chemical properties.
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 compound.

Demerit of Dalton’s atomic theory:

After the discovery of protons, neutrons and electrons, atom has been proved that it is divisible further.

Because of protons, neutrons and electrons are sub-atomic particles.

Antoine L. Lavoiser established two important laws of chemical combination.

Laws of chemical combinations

• Law of conservation of mass
• Law of constant proportion

1.1. Law of Conservation of mass

Mass can neither be created nor be destroyed in a chemical reaction.

Activity:
Materials required:
Conical flask
ignition tube
thread
copper sulphate 5% solution
sodium carbonate 5% solution
cork

Aim:

To prove the law of conservation of mass

Activity:
1) Ignition tube is filled with 5% copper sulphate solution.
2) Conical flask if filled with 5% soldium carbonate solution.
3) Ignition tube with its contents is suspended inside the conical flask with a thread
4) The conical flask is closed with a cork to prevent escape of any gas.
5) The conical flask along with its contents weighed as W1
6) The ignition tube is gently shaked to mix copper sulphate and sodium carbonate solution.
7) The conical flask is weighed as W2 after the reaction.
Observation:
W1 = W2
Report:
There is no change in mass before and after the chemical reaction. Thus law of conservation of mass is proved.

The same activity can be repeated with the following pairs of solutions
Barium chloride and sodium sulphate
Lead nitrate and sodium chloride

=============================================================

1.2. Law of constant proportions

In a chemical substance, the elements are always present in definite proportions by mass.

=======================================================

IUPAC Nomenclature of elments and molecules

IUPAC – International Union of Pure and Applied Chemistry

hydrogen – H

aluminium – Al ( not AL)

cobalt – Co (not CO)

sodium (natrium) – Na

potassium (kalium) – K

Element	Symbol	Atomic mass (u)
hydrogen carbon nitrogen oxygen sodium magnesium sulphur chlorine calcium	H C N O Na Mg S Cl Ca	1 12 14 16 23 24 32 35 40

Molecular Formula