The process of ionising is when an electron is removed from the outer shell of an atom. This leads to the formation of a positive ion. Ionisation energy is the amount of energy required to remove the outer most valence electron from an atom leading to the formation of a positive ion and an unbound electron. In general the smaller the atom and the fewer shells of electrons the higher the ionisation energy will be. This leads to the general pattern in the periodic table that ionisation energy decreases down groups as there are more shells that reduce the nuclear charge and its effectiveness, this results in less energy needed to remove the outer electron.
Looking at the example of Group 1 the alkali metals require more energy to remove the one electron from its outer shell. Progress down the group results in a decrease in the ionisation energy as there are more shells reducing the nuclear charge.
Across a period however the ionisation energy increases. This is because there is the addition of a proton each time resulting in a higher nuclear charge due to the positive charge of the protons and there is no addition of more shells they have the same number of shells across a period. If we look at the example of lithium the ionisation energy is much lower than that of fluorine across period 2. This is because Lithium has fewer protons in the nucleus meaning it has a lower nuclear charge than fluorine. Lithium has 3 protons in its nucleus where as fluorine has 9 so it has a much larger nuclear charge and attraction to the outer electron. This means that more energy is needed to remove the outer electron.First and second ionisation energy The first ionisation energy of the atoms is the energy required to remove one mole of electrons from one mole of atoms to create one mole of positive ions. This is the energy required to remove the electrons to create a positive ion. In general the second ionisation energy is higher on all elements as removing one electron causes an atom to become a positive on meaning the nuclear charge increases drawing the electrons closer to them.
Outer electrons is the term given to the shell/energy level furthest from the nucleus containing the electron furthest from the nucleus
The electron is the smallest sub atomic particle that make up the atom. Has a negative charge and is located in shells that orbit the nucleus
A proton is a positive particle that makes up the atom in the nucleus with a positive charge
Nuclear charge is the attraction exerted by the nucleus on electrons due to the positive charge of the protons and negative charge of the electron
Ionisation energy is the amount of energy required to remove an electron from an atom creating a positvely charged ion
The valence electron is the outermost electron of an atom
Ionising is a term used to describe when an atom turns into an ion. Ionising radiation causes an atom to lose electrons
The nucleus is the term given to the centre of the atom comprising of the proton and neutron
The shell is the path that electrons follow outside the nucleus. Shells can be considered as energy levels and the further away from the nucleus the higher in energy.