CHEMISTRY: ATOMIC STRUCTURE

STRUCTURE OF AN ATOMIC

Atom.

Is the smallest indivisible particle at an element which can exist on its own.

OR

Atom is the smallest indivisible particle that take place during chemical reaction.

Atomic theory.

There are two theories describing an atom, they are

(i)                  Dalton’s atomic theory

(ii)                New / modern atomic theory.

(I)                 DALTON’S ATOMIC THEORY.

He described an atom on the followings.

(i)                  All matter are made up of atiny indivisible particle called Atoms

(ii)                Atom can neither be created nor destroyed.

(iii)               Atoms of the same element are identical and have the same mass and same chemical properties.

(iv)              Atoms of different elements are non- identical and have no the same mass and having different chemical properties.

(v)                Atoms of different elements may combine to form a molecule or a compound.

(II)               MODERN ATOMIC THEORY.

(i)                  Atoms can be destroyed and new atoms be formed by means of nuclear reaction./ nuclear fission.

Eg  ²²² Ra  +  ⁴He                      208 Rn

                                                          ^{86           2}                               84

Radium                                           Radon

(ii)                Atom is made upot even smaller sub- atomic particles called protons, Nuutrons and electrons.

(iii)               Atoms of the same element may have different atomic mass i.e Isotipes.

Eg. ¹²C , ¹³C  and ¹⁴C

               6              6

(iv)              Atoms of different element may combine and form a complex compound

SUB – ATOMIC PARTICLES.

-          Ana atom is further composed of three particle (sub – atomic particles) called:-

(i)                  Protons (p)

(ii)                Neutrons. (N)

(iii)               Electrons. (e).

-          On an atom they are show as following diagram indicates.

P      N

 

Ø  Protons and neutrons are found are in the nucleons of an atom, collectively they are called Nucleans.

Ø  Electrons they are found on the shells of an atom.

Properties of sub- atomic particles

(I)                 PROTONS.

-These are the particles that carry positive charge

-They are denoted by the symbol 1P

                                                             1

-Has approximately the same mass like that of hydrogen

-It is found in side the nucleus.

       (II)           ELECTRONS (e-)

                         -Are the particle which carry negative charge( –ve)

                          -thy have very small mass of about 1/100 of that protons have (Relative mass is 1/1840)

                           -they are denoted by a symbol “e-“

                             -they are found inside of atom’s shells.

(III)             NUTRONS(n)

These are particles which carry no charge.

They are found in side the nucleus of an atom.

They are denoted by “n”

ARRANGEMENT OF ELECTRONS IN ANATOM.

Ø  In arranging the electron in the atom, in 1913 Neil Bohr suggested that.

-          Electrons are arranged in certain number of electrons obeying the formula e= 2(n)2 . where nis the number of shells from the nearest to the shells.

-          The shells may be represented by the letters K, L, M and N respectively from the nucleus.

NB:

Shells – are the places where electrons revolve around the nucleus.

Orbit – Is the path where electrons revolve around the nucleus.