1. ATOMS AND MOLECULES
By,
Abhijith Rajeev,Shibin P shaji,Dollsy
Jeorge,Priya Jose

2. OUTLINE
•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