Question

The atomic numbers of four elements P, Q, R, and S are 6, 10, 12, and 17 respectively. Which two elements can combine together to form a covalent bond?

• A. P and S
• B. Q and R
• C. Q and S
• D. P and R

Answer 1

The correct option is A P and S

Element	Atomic number	Electronic configuration
P	6	2, 4
Q	10	2, 8
R	12	2, 8, 2
S	17	2, 8, 7

• P has 4 valence electrons and can form covalent bonds by sharing its electrons.
• Q is a noble gas as its outer shell is completely filled and hence will not form any compound.
• R has 2 valence electrons and can form ionic bonds by losing 2 electrons.
• Q has 7 valence shell electrons and it needs only 1 valence electron to complete its octet.

So, P needs 4 electrons to complete its octet whereas S only needs one electron to complete its octet. Hence, 4 S atoms share electrons with 1 P atom to form a covalently bonded compound. The compound formed is $P{S}_4$.
The electron dot structure of ${\text{PS}}_4$ is as follows: