This document defines key concepts in chemistry including atoms, molecules, and laws of chemical combination. It states that atoms are the smallest particle of an element and may exist independently or combined with other atoms. Molecules are the smallest particle of a compound made of two or more atom types bonded together. The document also summarizes the laws of conservation of mass and constant proportion, and defines atomic and molecular mass, ions, and the mole concept in chemistry.

2. contents
•Laws of Chemical Combination
•Law of Conservation of Mass
•Law of Constent Proportion
•Atom
•Molecule

3. Introduction
What you mean by atom and molecule?
 Atom:
 Smallest particle of element
 May or may not exist independtly
 May or may not have properties of matter
 Molecule:
 Smallest particle of compound
 Always exist independtly
 Always posses the properties of matter

4. Law of chemical combination
• atoms exist in the combined form
I. Law of conservation of mass
II. Law of constent proportion

5. Law of conservation of mass
• A Lavoisier-father of chemistry
• mass can be neither created nor be destroyed

6. Law of constent proportion
• Joseph Proust: pure chemical compound
contain element in definite proportion by
mass

7. ATOM
• Atomic symbols:short hand reperesentation for the name of
element
Eg:H - hydrogen,Ne – neon
• Atomic mass:mass of an atom of an element
Eg:H - 1,Ca - 16
• Atomic mass unit:mass of one twelth of mass of 1 carbon 12
atom
• Average atomic mass:atomic mass of isotopes
Eg:H-1.008 and it is taken as 1 unit

8. • Gram atomic mass: atomic mass expressed in grams
Eg:C – 12g , N-14g
• Atomic combination: atoms are bonded together by strong
forces of attraction and the new species is called
molecules.Molecules are of 2 types
I. Homoatomic: same type of atoms
II. Heteroatomic: 2 or more types of atoms
• Ions:atom having +ve or –ve charge
I. Cation: +ve charged ion
II. Anion: -ve charged ion

9. MOLECULE
• Molecular mass: mass of the molecules of a chemical compound.
 Expressed in amu
 Determined by adding the individual atomic mass
Eg:molecular mass of NH3 =atomic mass of N + 3 * atomic mass of H
= 14+[3*1]
=17 amu
• Gram molecular mass: molecular mass expressed in grams
 Numericlly equal to molecular mass in amu
 Eg: I g molecule of H20 =18g

10. MOLE CONCEPT
• 1 Mole = 6.023 * 1023 number of particles
• 1 mole of any substance contain avagrado
number[6.023*1023] of particles which have weight
equvalent to atomic mass
• Number of moles = total mass
molecular mass
N= W
M

11. Conclusion
• All elemnts are made up of atom
• Atoms have differenr mass and organisation
• Electrons,protons,neutrons make atoms
• Molecule-2 or more atom combined to form
single species