Table of contents |
|
Laws of Chemical Combination |
|
Dalton's Atomic Theory |
|
Molecule |
|
Writing Chemical Formulae |
|
Mole ConceptDefinition of Mole |
|
Molar Mass |
|
Given by Lavoisier and Joseph L. Proust as follows:
Mass can neither be created nor destroyed in a chemical reaction.
Example:
A + B → C + D
Reactants → Products
Mass of reactants = Mass of products
Mass of Reactants = Mass of Products
In a chemical substance, the elements are always present in definite proportions by mass.
Example: In water, the ratio of the mass of hydrogen to the mass of oxygen is always 1:8 respectively.
These laws lacked explanation. Hence, John Dalton gave his theory about the nature of matter. He said that the smallest particles of matter are called ‘atom’.
An illustration describing the mass ratio of elements in a few compounds.
Atomic radius is measured in nanometres.
Atomic radii of hydrogen atom = 1 × 10–10 m.
(a) Symbols for some elements as proposed by Dalton:
Symbols for Elements as Proposed by Dalton(b) Symbols of some common elements:
The number of atoms constituting a molecule is known as its atomicity.
The chemical formula of a compound is a symbolic representation of its composition.
It is the sum of the atomic masses of all the atoms in a molecule of the substance. It is expressed in the atomic mass unit (u).
It is the sum of the atomic masses of all atoms in a formula unit of a compound. The constituent particles are ions.
It is defined as one mole of any species (atoms, molecules, ions or particles) is that quantity in number having a mass equal to its atomic or molecular mass in grams. 1 mole = 6.022 × 1023 in number
mass of 1 mole → is always expressed in grams and is also known as gram atomic mass.
1u of hydrogen has → 1 atom of hydrogen
1g of hydrogen has → 1 mole of hydrogen
= 6.022 × 1023 atoms of hydrogen
66 videos|352 docs|97 tests
|
1. What are the laws of chemical combination? | ![]() |
2. What is Dalton's Atomic Theory? | ![]() |
3. What is atomic mass? | ![]() |
4. What is a molecule? | ![]() |
5. What is the mole concept? | ![]() |
66 videos|352 docs|97 tests
|
![]() |
Explore Courses for Class 9 exam
|
|