Ionization

• When an atom absorbs energy from a heat source or from light, for example, the energies of the electrons are raised;
• The valence electrons possess more energy and are more loosely bound to the atom than inner electrons, so they can easily jump to higher energy shells when external energy is absorbed by the atom;
• If a valence electron acquires a sufficient amount of energy, called ionization energy, it can actually escape from the outer shell and the atom’s influence;
• The departure of a valence electron leaves a previously neutral atom with an excess of positive charge (more protons than electrons);
• The process of losing a valence electron is known as ionization, and the resulting positively charged atom is called a positive ion;
• For example, the chemical symbol for hydrogen is H;
• When a neutral hydrogen atom loses its valence electron and becomes a positive ion, it is designated H+;
• The escaped valence electron is called a free electron;
• The reverse process can occur in certain atoms when a free electron collides with the atom and is captured, releasing energy;
• The atom that has acquired the extra electron is called a negative ion;
• The ionisation process is not restricted to single atoms;
• In many chemical reactions, a group of atoms that are bonded together can lose or acquire one or more electrons;
• For some nonmetallic materials such as chlorine, a free electron can be captured by the neutral atom, forming a negative ion;
• In the case of chlorine, the ion is more stable than the neutral atom because it has a filled outer shell;