Chemistry (NTSE/Olympiad)  

3. Atoms & Molecules


An ion is a positively or negatively charged atom (or group of atoms). An ion is formed by the loss or gain of electrons by an atom, so it contains an unequal number of electrons and protons.
Example. Sodium ion Na+, magnesium ion Mg2+, chloride ion Cl, and oxide ion O2–.
There are two types of ions : cations and anions.
A positively charged ion is known as cation. A cation is formed by the loss of one or more electrons by an atom.
Example. Sodium atom loses 1 electron to form a sodium ion, Na+, which is cation:

The ions of all the metal elements are cations.


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