Question

The regulation of mineral ions in the cellular fluids of biological systems is performed by ion pumps that selectively transport ions of specific size and charge across cellular membranes. Which of the following isoelectronic species is the smallest ion?A.Na+[19%]B.F−[27%]C.Mg2+-correctD.O2−[13%]

Answer 1

Answer:

The smallest ion is : Mg 2+

Increasing Order of size :

Mg2+ < Na+ < F- < O2-

Explanation:

Isoelectronic Species : Species having same number of electrons .

$Z_{eff}$ = Effective attraction of the nucleus felt by the outer shell electrons.

The size of the atom is decided by :

• Its atomic number (number of proton)

• the effective nuclear charge.

As the positive charge increases the size of the ion decreases.

As the negative charge increases the size of ion also increases.

Negative charged ions :  F- , O2-

Negative charge are formed when electrons are added to the atoms.

When Negative ion is formed :

• Number of proton remain same

• Number of electron get increased

Hence it becomes difficult for the proton in the nucleus to attract the electrons.

Electron - electron Repulsion increases

$Z_{eff}$  = decreases

Size increase

Positive charged ions :  Na+ , Mg2+

Positive charge are formed when electrons are removed from the atoms.

When Positive ion is formed :

• Number of proton remain same

• Number of electron get reduced

Hence  more attraction of the nucleus is felt by the outer electron.

Electron - electron Repulsion Decreased

$Z_{eff}$  = increases

Size decreases