# NCERT Class-9 Science Solutions: Chapter 3-Atoms And Molecules Part 10

Question 40:

What are ionic and molecular compounds? Give examples.

Atoms of different elements join together in definite proportions to form molecules of compounds.

Examples - water, ammonia, carbon dioxide. Compounds composed of metals and non-metals contain charged species.

The charged species are known as ions. An ion is a charged particle and can be negatively or positively charged. A negatively charged ion is called an anion and the positively charged ion is called cation.

Examples - sodium chloride, calcium oxide.

Question 41:

Compute the difference in masses of one mole each of aluminium atoms and one mole of its ions. (Mass of an electron is). Which one is heavier?

Mass of 1 mole of aluminum atom = the molar mass of aluminum

An aluminum atom needs to lose three electrons to become an ion,

For one mole of ion, three moles of electrons are to be lost.

The mass of three moles of electrons

Molar mass of

Question 42:

A silver ornament of mass ‘m’ gram is polished with gold equivalent to of the mass of silver. Compute the ratio of the number of atoms of gold and silver in the ornament.