# The movement of electrons around the nucleus and the energy levels

## The movement of electrons

The electrons are negatively ( – ve ) charged particles , They revolve around the nucleus with very high speed , The electron has a negligible mass relative to that of the proton or the neutron , so the mass of the atom is concentrated in the nucleus .

The number of the 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 .

The atomic number = the number of the protons = the number of the electrons .

The mass number = the number of the protons ( the atomic number ) + the number of neutrons .

### What are the energy levels ?

The electrons revolve around the nucleus in a number of orbits called the energy levels , and during their movement , they seem to be as a cloud around the nucleus , The energy levels are the imaginary regions around the nucleus in which the electrons move according to their energies .

The nucleus contains the protons and the neutrons , the first energy level can hold a maximum 2 electrons in one orbital , the second level can hold a maximum of 8 electrons that total distributed over 4 different orbitals , and the third energy level can hold a maximum of 18 electrons distributed over 9 different orbitals .

The arrangement of electrons in an atom .

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

Each level has a certain amount of energy increases by the increase of the distance from the nucleus , The first energy level ( K ) has the least energy followed by the second level ( L ) and so on .

The seventh energy level ( Q ) has the highest energy , and the energy of level ( L ) is greater than that of level ( K ) , The energy of the electron depends on the energy of the level which it revolves in , where the energy of the electron = the energy of the level .

The electron is not transferred from one level to a higher one unless it gains some energy called the quantum which equals the difference between the energies of two levels and the atom will be excited atom .

The electrons loses this energy , it returns to its original level and the state of the atom is the ground state .

The excited atom

The excited atom is the atom that gains a quantum of energy , and the quantum is the amount of energy lost or gained by an electron when it transfers from one energy level to another .

Theories explaining the covalent bond , Octet rule & Overlapped orbitals concept

The quantum numbers and principles of distributing electrons

Chemical combination , Types of bonds ( Chemical bonds & Physical bonds )