Science MCQs

This atom (like Magnesium) has 2 electrons in its outer shell. It will lose these 2 electrons to form a stable octet resulting in a valency of 2 and a positive charge (cation).

This is the configuration of a noble gas (like Argon). It has a full outer shell so its valency is 0.

A sodium atom (2 8 1) has 1 electron in its outer shell. It loses this one electron to achieve a stable octet forming Na⁺.

A sodium atom (Na) loses its single valence electron to form a sodium ion (Na⁺).

Nitrogen combines with three hydrogen atoms so its valency is 3.

To balance the charges you need two atoms of X (2 x 3+ = 6+) and three atoms of Y (3 x 2- = 6-). The formula is X₂Y₃.

An ion is an atom or group of atoms that has a net electrical charge due to the loss or gain of electrons.

When an atom loses electrons the number of protons exceeds the number of electrons resulting in a positive charge (cation).

When an atom gains electrons the number of electrons exceeds the number of protons resulting in a negative charge (anion).

The chloride ion has a single negative charge denoted by the superscript '-'.