3A+Daniel

= = =__ TRENDS IN THE PERIODIC TABLE __= =**__First Ionisation Energy__**=
 * __By Daniel Gunasekaran__**


 * Ionisation energy** is the energy required to remove electrons from gaseous atoms or ions. The energy needed to remove the first electron from the outer shell is called the ** First ionisation energy ** . The energy needed to remove the second electron is called the **Second ionisation energy**. When the electron that is to be removed from the atom is closer to the nucleus, more energy is needed to remove the electron. Once the valence electrons are removed from the outer shell in the atom, the atom will have a stable noble gas electron configuration. The ionisation energy needed to remove an electron will be very high, leading to a huge increase in ionisation energy.

**__Charge of the nucleus:__**
The higher the positive charge of the nucleus, the more the electrons will be attracted to the nucleus. Thus, requiring a lot of energy to remove.

__**The distance between the electron and the nucleus:**__
The further away the electron, the less attracted it is to the nucleus. Thus, electrons further away from the nucleus require a lot less energy to remove than those that are closer to the nucleus.

__**The number of electron shells between the valence electron and the nucleus:**__
The electron configuration of a Potassium atom is 2,8,8,1. The one valence electron is not attracted too strongly towards the nucleus because of the two full shells of electrons between it and the nucleus. The 19 protons in the Potassium's nucleus have their effect cut down by the 18 electrons in the first 2 shells. The valence electron therefore, only feels a net pull of +1 from the nucleus. This is known as the **shielding effect**. As you can see on the diagram, the ionisation energies decreases in general as we go down the periodic table.

Here's a video that shows how the first ionisation energies vary down the group and across groups:

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