Atomic construction of matter

" Atomic structure of the matter " 

Previously, We learn that:

*Matter is composed of molecules.

*Molecules are composed of very smaller units called atoms.

The atom:

*it is the fundamental building unit of matter.
*it is the smallest individual unit of matter which can share in chemical reaction.

The atomic construction:

The scientists did many experiments to reach the final idea about the atomic construction, so they found that the atom consists of:
1-Nucleus:                                        
*it is the central core of the atom, where the mass of the atom is concentrated in it.
*it is positively charged because it contains:
-Protons: positively charged particles.
-Neutrons: electrically neutral particles ( uncharged ).
2-Electrons:
*they are negatively charged particles.
*They orbit around the nucleus in energy levels with very high speed, so they don't fall into the nucleus.

Notes:

1-The electron has a negligible mass relative to that of the proton or neutron, so the mass of the atom is concentrated in the nucleus.

2-The number of negative electrons which revolve around the nucleus is equal to the number of positive protons in the nucleus, so the atom is electrically neutral in its ordinary state.

                                                                                 

To express an atom of any element, we use two terms:

i. Atomic number: it is the number of protons in the nucleus of an atom. (it is the number of electrons revolve around the nucleus).

ii. Mass number: it is the sum of protons and neutrons in the nucleus of an atom. 

      

The energy levels:
They are imaginary regions (places) around the nucleus in which the electrons move according to their energies.

*The maximum number of energy levels is seven levels 
( in the heaviest atoms ) which are arranged from the nucleus according to their energies as follow:

Q	P	O	N	M	L	K	Level symbol
7	6	5	4	3	2	1	Level number

*Each level has a certain amount of energy increases by the increase of the level distance from nucleus, this means that:
-The first energy level (K) has the least energy followed by the second (L) and so on.
-The seventh energy level (Q) has the highest energy.

 

Electronic configuration ( distribution ):

*Each energy can take a definite number of electrons.

*The number of electrons which saturates the first four  energy levels can be calculated from the relation 2n², where (n) is the number of the energy level.

*This rule is applied only on the first four energy levels (K, L, M and N):

The no. of electrons which saturates the (K) level = 2 × 1² = 2e

The no. of electrons which saturates the (L) level = 2 × 2² = 8e

The no. of electrons which saturates the (M) level = 2 × 3² = 18e

The no. of electrons which saturates the (N) level = 2 × 4² = 32e

Examples:

1-Helium atomic structure:

2-Sodium atomic structure: