Show a diagram of how ions are formed when a sodium atom comes into close
contact with a chlorine atom.

When sodium atom comes close proximity to a chlorine atom it looses an electron to form Na^+ while chlorine atom gains an electron to form Cl^-.

An ionic compound is formed when electron(s) is/are transferred from a metal to a non metal. This leads to the formation of a cation (positively charged ion) and an anion (negatively charged ion). The both are kept together by electrostatic interaction between the ions involved to give an ion pair.

Sodium and chlorine form the ionic compound sodium chloride. The compound is formed when a sodium atom approaches a chlorine atom and looses its outermost electron to chlorine as shown in the image attached to this answer. When this occurs, sodium ions and chloride ions are formed as shown.

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The diagram is attached below.

Explanation:

when sodium and chlorine comes close together they form anion and cation. The compound formed is called sodium chloride.

Both atoms bonded together through ionic bond.

Ionic bond:

It is the bond which is formed by the transfer of electron from one atom to the atom of another element.  

Both bonded atoms have very large electronegativity difference. The atom with large electronegativity value accept the electron from other with smaller value of electronegativity.

For example:

Sodium chloride is ionic compound. The electronegativity of chlorine is 3.16 and for sodium is 0.93. There is large difference is present. That's why electron from sodium is transfer to the chlorine. Sodium becomes positive and chlorine becomes negative ion.