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Science
Atoms and Molecules
LAWS OF CHEMICAL COMBINATIONS : -
There are two types of chemical combinations
1. Law of conservation of mass
2. Law of constant proportion (It is also called law of definite composition)LAW OF CONSERVATION OF MASS : -
The scientist Lavoisier in 1774. It is not possible to create or destroy the mass of a substance by chemical reactions.
Mass of substance before reaction (reactant) = Mass of substance after reaction (product).LAW OF CONSTANT PROPORTION : -
The scientist Proust in 1779. In a chemical substance its constituent elements are present in definite proportion by mass. A pure compound has a definite composition by mass of its constituent elements.
MAIN POSTULATES OF DALTON'S ATOMIC THEORY OF MATTER.
1. Matter is made of very small particles called atoms.
2. Atoms cannot be created or destroyed in a chemical reaction.
3. All the atoms of a given element are same mass, same size and same chemical properties.
4. The atoms of different elements have different masses and different chemical properties.
5. Atoms of different elements combine in the ratio of small whole numbers to form the compounds.
6. The type and relative numbers of atoms in a given compounds are fixed.
7. When a compound is decomposed the same type of atoms are obtained which constituted the compound.
A. Which postulate of Dalton's atomic theory is the result of the law of conservation of mass?
ANS : -
The postulate of Dalton's atomic theory that atoms are the ultimate particles of matter which cannot be created or destroyed in a chemical reaction is the result of the law of conservation of mass.
CONCEPT OF ATOM : -
According to Dalton's atomic theory the atom is smallest constituent particles of matter. Atom is different for different type of element with reference to number of protons, neutrons and electrons.
SIZE OF THE ATOM : -
An atom is very small. Its radius is of the order of nanometer (nm).
ATOMIC MASS : -
The mass of an atom of an element is called its atomic mass.
RELATIVE ATOMIC MASS : -
It is the mass of an atom of a substance relative to 1/12 (one-twelfth) of the mass of a carbon atom.
Relative atomic mass = mass of one atom of a substance
1/12 mass of one atom of C-12ATOMIC MASS UNIT : -
One-twelfth the mass of one C-12 atoms is called atomic mass unit.
1u = mass of one atom of C-12 = 1.6603 X 10-24
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Submitted By Mr. Ajay Kumar
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