What is first ionization energy?

Answer 1

Ionization energy is the energy required to REMOVE an electron from an atom. The trend is upwards and towards the right of the periodic table.

Think about the noble gases, they are so happy and stable. They have all the electrons they need. They do not want to remove any of them. If you try to, it will be very hard, (like taking a toy from a 2 year old). SO they would have the most ionization energy. It would take the most energy to remove an electron from them.

BUT the first column, alkali metals, are SO close to being a noble gases, all they need is to remove an electron. It would take very little energy to remove one because it is highly favored by them. That's why it would take the least amount of ionization energy.

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Answer 2

Ionization energy is the energy required to REMOVE one electron. The trend is upward and towards the right of the periodic table.

Think about the noble gases. They are the most stable, and they are so happy because they have their full octet, enough electrons. They do not want to add or remove any. So they REALLY don't want to remove electrons because they are so happy. So it would take the most ionization energy from the noble gases, because they really do not want to remove electrons.

BUT the first column are so close to being noble gases. All you have to do is remove one electron and then they become noble gases, so they really do not want that electron. It would take very little energy to remove an electron, therefore, they have the smallest ionization energy.