ATOMS AND MOLECULES

contents

•Laws of Chemical Combination•Law of Conservation of Mass•Law of Constent Proportion

•Atom•Molecule

IntroductionWhat 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

Law of chemical combination

• atoms exist in the combined formI. Law of conservation of massII. Law of constent proportion

Law of conservation of mass

• A Lavoisier-father of chemistry• mass can be neither created nor be destroyed

Law of constent proportion

• Joseph Proust: pure chemical compound contain element in definite proportion by mass

ATOM• Atomic symbols:short hand reperesentation for the name

of elementEg:H - hydrogen,Ne – neon

• Atomic mass:mass of an atom of an elementEg:H - 1,Ca - 16

• Atomic mass unit:mass of one twelth of mass of 1 carbon 12 atom

• Average atomic mass:atomic mass of isotopesEg:H-1.008 and it is taken as 1 unit

• Gram atomic mass: atomic mass expressed in gramsEg: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 atomsII. Heteroatomic: 2 or more types of atoms

• Ions:atom having +ve or –ve chargeI. Cation: +ve charged ionII. Anion: -ve charged ion

MOLECULE• Molecular mass: mass of the molecules of a chemical compound. Expressed in amu Determined by adding the individual atomic massEg: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

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

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