The positive and negative ion form when electrons are transferred between atoms. An ion with a positive charge is called a cation (most of them are metals). An ion with a negative charge is a anion (most of them are nonmetals).
What are the ions?
The energy required to remove an electron from an atom is called ionization energy. First ionization energy tends to decrease from top to bottom within a gorup and increase from left to right across a period.
What is ionization energy?
Recall that the atomic size increases as the atomic number increases within a group. As the size of atom increases, nuclear charge has a smaller effect on the electrons in the highest occupied energy level. So less energy is required to move an electron from this energy level and the first ionization energy is lower.
Why it tends decrease from top to bottom within the group?
The nuclear charge increases across the period, but the shielding effect remain constant. So there is an increase in the attraction of the nucleus for an electron. Thus it takes more energy to remove an electron from an atom.
Why it tends increase from left to right across the period?
Wow!!! That's so cooooool!!!
There are few exceptions in the periodic table, like Group 2A and Group 5A. The electrons of elements in Group 2A are full of the s block, so they are more stable. Ex: Mg > Al. The electrons of elements in Group 5A are half full of the p block, so they are more stable. Ex: P > S.
Why there are few elements are different than this trends?