PARTICULATE NATURE OF MATTER - 1 (

 

ATOMIC MODELS:

The following scientists worked on Atomic Model.

1. J J THOMPSON: proposed a model of Atom consisting of positive and negative charge, present in equal amount so that an atom will be neutrally charged. He proposed that atom was a sphere but the negative and positive charge were embedded in it.

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2. ERNEST RUTHERFORD: Rutherford reversed the Thompson’s model which he showed with his experiment that atom has a small strong nucleus of positively charged. He stated that atom is composed of empty space mostly with electrons orbiting in a set, predictable paths around fixed positively charged nucleus.

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3. NEIL BOHR: His model was based on quantum principle. An atom has a positively charged nucleus, and electron travels in around the nucleus in a specified orbit

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DALTON’S ATOMIC THEORY

John Dalton, British Physicist and Chemist proposed the atomic theory thus: 

1.            All elements are made up of small indivisible particles called atoms.

2.            Atoms can neither be created nor destroyed in any chemical reaction.

3.            Atoms of the same elements are exactly alike in aspect and are different from atoms of all other elements.

4.            Atoms of different elements can combine in simple whole number ratios to form compounds.

5.            All chemical changes result from the combination or separation of atoms

 

MODIFICATIONS OF DALTON’S ATOMIC THEORY

Due to new discoveries in the twentieth century, Dalton’s atomic theory cannot hold in its entirety. There is need for its modification.

i.              The first statement has been proved wrong by Rutherford’s discovery of protons, electron and neutrons as constituents of the atom. An atom is not an indivisible solid piece.

ii.             The second statement still holds good for ordinary chemical reactions. During nuclear reactions, however, the nucleus can be broken into simpler atoms giving out large amount of heat (nuclear fission). This destroys the atoms involved.

iii.            The discovery of isotopes makes the third statement unacceptable. Chlorine for example has two atoms with different nucleus content and hence different relative atomic masses although the same proton numbers.

iv.            The fourth statement is true only for inorganic compounds which contain a few atoms per molecule. Carbon forms very large organic molecules such as proteins, starch and fats which contain thousands of Structure

 

ATOMS

Matter is made up of discrete particles. The three fundamental particles of an elements are; atoms, molecules, and ions.

 

 

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Structure Of An Atom.

 

The Nucleus contain PROTON and NUETRON, while the ELECTRON is in the shell.

 

Atomic Number – is the number of Proton

Mass Number – Is the Number of Proton and Nuetron in the nucleus.

 

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