Question

How do positive and negative ions form?

Answer 1

As the name suggested that positive ions are those ions which bear a positive charge on itself and negative ions are those ions which bears a negative charge on itself, and it is formed due to exchange of electrons.

Complete answer:
As we know that in an atom the number of protons (carry positive charge) which are present inside the nucleus is always equal to the number of electrons (carry negative charge) present in the orbitals outside the nucleus.
-So due to presence of equal number of electrons and equal number of protons in an atom, positive and negative charges get cancelled and an atom is present in the neutral state.
-But every single atom wants to stay in the stable state where in the outermost shell of the atom eight or two electrons will present, and for obtaining this stable configuration an atom will accept electrons from outside or release electrons from inside.
-And due to this exchange of electrons an atom can form positive and negative ions.
-When an atom accepts an electron from outside then in this condition number of electrons are more than the number of protons present inside the nucleus and due to this one extra electron an atom will carry a negative charge and called negative ions.
${\text{A + }}{{\text{e}}^{\text{ - }}} \to {{\text{A}}^{\text{ - }}}$
-When an atom ejects an electron from its outermost shell then in this condition number of electrons are less than the number of protons present inside the nucleus and due to this one less electron an atom will carry a positive charge and called positive ions.
${\text{A}} \to {{\text{A}}^{\text{ + }}}{\text{ + }}{{\text{e}}^{\text{ - }}}$

Note:
Here some of you may think that due to addition of electrons an atom will carry positive charge or due to subtraction of electrons from the outermost shell an atom will carry negative charge, but this assumption is wrong.