Question

which of the following elements will form anions and which will form cation 1. Na, 2. Al,3. Cl, 4.O

Answer 1

Na cation
Al cation
Cl anion
O anion

Answer 2

Na and Al will form cations whereas Cl and O will form an anion.

Anions and cations

• The decision of whether an element will form a positive ion or negative ion depends on whether it chooses to receive or donate an e-.
• Defined electronic configuration of Na= 1$s_{2}$,2$s_{2}$,2$p_{6}$,3$s_{1}$, we can tell that Na will lose one e- and become positively charged( cation).
• For Al, the electronic configuration = 1$s_2$,2$s_{2}$,2$p_{6}$,3$s_{2} 3p_{1}$.

        It will also donate an e- and become a positive ion.

• Cl configuration =  1$s_2$,2$s_{2}$,2$s_{6}$,3$s_{2} 3p_{5}$.

        Thus it prefers forming an anion by gaining one e-.

• Oxygen possesses a configuration =  1$s_2$,2$s_{2}$,2$s_{4}$

        Thus, it chooses to gain two e- and gett a negative charge (anion).