Ionic Radius and Isoelectronic Species

This chemistry lecture covers the concept of isoelectronic species, which have the same number of electrons and electronic configuration. It explains the trend of ionic radii across Period 3, noting that ionic radii decrease from sodium to silicon ions but increase from silicon to phosphide ions. The lecture also compares ionic radii of isoelectronic species from Periods 2 and 3, highlighting that aluminum ion has the smallest size due to its high proton number and effective nuclear charge. The session concludes with an exercise for students to arrange species by size and explain their reasoning.

What does the term 'isoelectronic' refer to?

• Species with the same atomic mass

• Species with the same number of neutrons

• Species with the same number of protons

• Species with the same number of electrons and electronic configuration

Which of the following ions is isoelectronic with the oxide ion?

• Nitride ion

• Chloride ion

• Aluminum ion

• Sodium ion

What happens to the ionic radius as you move from sodium ion to silicon ion across period 3?

• It increases

• It decreases

• It fluctuates

• It remains constant

Why does the size of phosphide ion increase compared to silicon ion?

• Due to a smaller principal quantum number

• Due to a decrease in electron repulsion

• Due to an additional electron shell

• Due to a decrease in proton number

Which period do the cations in the comparison of isoelectronic species come from?

• Period 3

• Period 2

• Period 1

• Period 4

What is the main reason for the smallest size of aluminum ion among isoelectronic species?

• It has the largest proton number

• It has the smallest number of electrons

• It has the largest electron shell

• It has the smallest atomic mass

Which ion is the largest among the isoelectronic species discussed?

• Sodium ion

• Aluminum ion

• Oxide ion

• Nitride ion

What factor primarily affects the ionic radii of isoelectronic species?

• Electron affinity

• Atomic mass

• Effective nuclear charge

• Number of neutrons

Why are cations generally smaller than anions across a period?

• Anions have a smaller nuclear charge

• Cations have fewer protons

• Anions have a higher principal quantum number

• Cations have more electron shells

What exercise is suggested at the end of the lecture?

• Calculate the atomic mass of elements

• Arrange species in order of increasing size

• Determine the number of protons in ions

• Identify the period of each element