Scribd
Upload
36 views1 page

Atoms and Molecules

The document discusses the laws of chemical combination, including the Law of Conservation of Mass and the Law of Constant Proportion, which outline fundamental principles of atomic theory. It defines molecules, differentiating between homoatomic and heteroatomic types, and explains molecular mass and the mole concept, highlighting Avogadro's number. Overall, it emphasizes the nature of atoms and their behavior in chemical reactions and compounds.

Uploaded by

atul kumar
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
36 views1 page

Atoms and Molecules

The document discusses the laws of chemical combination, including the Law of Conservation of Mass and the Law of Constant Proportion, which outline fundamental principles of atomic theory. It defines molecules, differentiating between homoatomic and heteroatomic types, and explains molecular mass and the mole concept, highlighting Avogadro's number. Overall, it emphasizes the nature of atoms and their behavior in chemical reactions and compounds.

Uploaded by

atul kumar
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
You are on page 1/ 1

Atoms and Molecules

Laws of Chemical Combination: Dalton's atomic theory:


Law of Conservation of Mass: Proposed by Antoine Lavoisier.
States that mass can neither be created nor destroyed in a chemical (i) All matter is made of very tiny particles called atoms.
(ii) Atoms are indivisible particles, which cannot be created or
reaction.
destroyed in a chemical reaction.
(iii) Atoms of a given element are identical in mass and chemical
The total mass of reactants equals to the total mass of products. properties. (Law of conservation of mass)
e.g., A + B → C + D Reactants → Products Mass of reactants = Mass (iv) Atoms of different elements have different masses and chemical
of products properties.
(v) Atoms combine in the ratio of small whole numbers to form
Law of Constant Proportion (Definite Proportions): Proposed by compounds. (Law of constant proportion)
Joseph Proust.

All pure sample of same compound contains same elements Atom existence
combined in same ratio. → Atoms of most of the elements are very reactive and does not
exist in free state
For example: (i) 18 gm of H2O = 2 gm of hydrogen + 16 gm of oxygen → Only the atoms of noble gases (such as He, Ne, Ar, Kr, Xe and Rn)
⇒ mass of hydrogen/mass of oxygen = 2/16 = 1/8 are chemically unreactive and can exist in the free state as single
(ii) 36 gm of H2O = 4 gm of hydrogen + 32 gm of oxygen atom.
⇒ mass of hydrogen/mass of oxygen = 4/32 = 1/8

Molecules
→ A molecule is in general a group of two or more atoms that are
chemically bonded together

(i) Homoatomic molecules (containing atom of same element)


Examples: H2, O2, O3, S8, P4 etc.
(ii) Heteroatomic molecules or compounds (containing atoms of
different elements)
Examples: H2O, CO2, NaCl, CaCO3etc.

Polyatomic – It has atomicity more than 4.

Molecular Mass: The sum of the atomic masses of all the atoms in a Mole Concept
molecule. → A group of 6.022×1023 particles (atoms, molecules or ions) of a
Calculated by adding the atomic masses of the constituent atoms in substance is called a mole of that substance.
the molecular formula. → 1 mole of atoms = 6.022×1023 atoms
For example, Molecular mass of H2O= 2 × Mass of one H-atom + → 1 mole of molecules = 6.022 × 1023 molecules
Mass of one O-atom = 2 ×1 + 16 = 18 u Example, 1 mole of oxygen = 6.022×1023 oxygen atoms
Note: 6.022×1023 is Avogadro Number (L).

You might also like