Difference between Atom and Ion: Overview, Questions, Preparation

An atom is defined as the smallest unit of matter which forms an element. Earlier thought to be indivisible, later experiments proved that atoms can in fact be broken down further into subatomic particles - the proton, neutron, and electrons. 

All atoms have the same number of electrons and protons and are therefore electrically neutral.

When an atom loses or gains electrons, they become charged. Such charged particles are called ions. They can be positively charged if electrons are lost and these are called cations, or negatively charged if electrons are gained, called anions. 

For eg.

Here the electron in the outer valence shell of sodium is lost to give a positively charged Sodium cation.

Chlorine gains an electron to form chloride anion.

The two ions form an ionic bond to give a stable Sodium Chloride molecule.

Such ionic compounds are aggregates of ions. They are held by strong electrostatic forces of attraction. 

The first atomic theory was provided by John Dalton and proposed that the atom was indivisible. Later experiments proved that atoms were in fact made up of protons, neutrons and electrons. 

Many models of the atom were proposed, until settled upon by the quantum mechanical model of the atom. According to this, the electrons in the atom are said to be arranged in shells which are further divided into subshells and orbitals. The electrons in the completely filled shells are known as core electrons, and the electrons that are added to the electronic shell with the highest principal quantum number are called valence electrons.

Here is how the configuration of the sodium ion will look like when it loses its outer electron.

1. Show the formation of magnesium chloride with the help of electron dot structures. What are the ions present in it?

Answer:

The ions are: cation:  Mg⁺²  

                       anion: Cl⁻

2. Which of the following are isoelectronic species, i.e., those having the same number

of electrons?

Na+, K+, Mg2+, Ca2+, S2–, Ar.

Answer: Na+, Mg2+, Ca2+

                Ar, S2– and K+

3. Write the electronic configurations of the following ions: (a) H– (b) Na+ (c) O2–

(d) F–

Answer: (a) 1s2 (b) 1s2 2s2 2p6; (c) 1s22s22p6 (d) 1s22s22p6

Q: Can all atoms be ions?

Q: What determines the charge of a monoatomic ion?

Q: Is an ion different than their parent atom?

Q: Is there a difference between covalent compounds and ionic compounds?

Q: Can a polyatomic ion have different kinds of bonds?