Atoms and Molecules
NCERT CH.3
Law of conservation of mass = mass can neither be created nor be destroyed in a chemical reaction
By - Antoine Lavoisier [here, scientists name is important]
Law of constant proportion = In a chemical reaction elements are present in definite proportion by mass
By - Joseph L. Proust
Daltons atomic theory: (All six postulates)
- All matter is made up of very tiny particles called atoms
- Atoms are indivisible particles, which cannot be created or destroyed in a chemical reaction
- Atoms of given element are identical in mass and chemical properties
- Atoms of different elements have different masses and chemical properties
- Atoms combine in the ratio of small whole numbers to form compounds
- The relative number and kinds of atoms are constant in a given compound
Very important points about Daltons postulate :
(Important for exam questions)
- 2nd postulate of dalton is for “Law of conservation of mass” which states atoms are indivisible particles , which cannot be created not be destroyed in a chemical reaction and is the result of law of conservation of mass
- 5th postulate of dalton is for “Law of definite proportion” which states that All atoms combine in the ration of small whole number to form compound.
Flow points -
- 1nm(nanometer) = 1/10^9 m( 10 to the power of 9)
- 1m = 10^9 nm
- Full form of IUPAC - International union of Pure and Applied Chemistry
Atomic mass unit - An atomic unit of mass is defined as accurately 1/12th the mass of a carbon (C-12) isotope. The C-12 atoms has six neutrons and six protons in its nucleus. The atomic unit mass is symbolised as ‘amu’ or ‘AMU’.
1 amu = average of the protons and neutron.
1amu=1.66 x 10 to the power of -24 Kg
Polyatomic Ion - A group of atoms carrying a charge is known as polyatomic ion. It is covalently bonded set of two or more atoms. Examples for polyatomic ions are : Dichromate ion Cr2O7-2 ( here -2 charge is there and dichromate Is a group of atoms)
More examples: NO-3.
ALL NCERT GIVEN ELEMENTS
- Hydrogen chloride - HCL
- Hydrogen Sulphide - H2S
- Carbon tetra chloride - CCL4
- Magnesium Chloride - MgCl2
- Aluminium oxide - Al3O3
- Calcium oxide - Al2O3
- Sodium Nitrite - NaNO3
- Calcium Hydroxide - Ca(OH)2
- Sodium Carbonate - Na2CO3
- Ammonium sulphate - (NH4)2SO4
- Aluminium Sulfate - Al2(SO4)3
- Calcium Chloride - CaCl2
- Potassium Sulfate - K2SO4
- Potassium Nitrate - KNO3
- Calcium Carbonate - CaCO3
- Nitric Acid - HNO3
Mole concept
- Avogadro number - (Amedeo Avogadro) - 6.022x10-23
1 dozen - 12 nos.
1 gross - 144 nos.
1 mole of carbon - 12g of carbon atoms - 6.022x10-23 atoms of C
1 mole of molecules - molecular mass in grams (g) - 6.022x10-23 numbers of molecules
- Mass of 1 mole of substance is called its molar mass
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