Learn Class 9 Science - Atoms and Molecules

The atom refers to the building block of matter. These are the smallest units of matter of subatomic particles, such as neutrons, protons, and electrons.

The electrons are negatively charged atoms. And their mass is considered negligible, or we can say that it is 1, i.e., Negative. When we see the electron symbol, it is negative.

Molecule

The molecule refers to the smallest part of an element that consists of the independent charge.
The elements of the molecule are the constituents that are made of similar atoms.
The molecule can be monatomic, polyatomic, or di-atomic.
The molecule can join together to get the definite proportion of the different atoms.

Valency

The valency is the combining capacity of the atoms that will do their reaction to get the molecules with the same or different elements.
The elements consist of the outermost shell that is full of chemical activities.
And when we see their combined capacity, it is equal to zero.

Ions

The ions are known as small particles.
They can be negative or positive.
The positive charge ion is known as Cation,i.e., Na.
The negative charge of the ion is known as Anion,i.e., C1.

Molecular mass

The term molecular mass refers to the total atomic mass of the substance.

Learning Videos for 9th Grade Science - Atoms and Molecules

Atoms and Molecules Sample Questions for Class 9

Question 1

Select the correct statement concerning atoms and molecules.

A. Atoms and molecules are the same.

B. Atoms are similar to molecules, just smaller.

C. A atom is the smallest unit of an element and a molecule is the smallest unit of a compound.

D. A molecule is the smallest unit of an element and a atom is the smallest unit of a compound.

Question 2

Which cannot take place during a chemical reaction?

A. Formation of new atoms

B. Bonds breaking between atoms

C. Formation of new molecules

D. Bonds forming between atoms

Question 3

Molecules and atoms tend to always move around.

A. True

B. False

Question 4

Chemical reaction in which two or more atoms or molecules combine to form larger molecules is called a .

A. decomposition reaction

B. synthesis reaction

C. displacement reaction

D. catabolic reaction

Question 5

What is the atomic mass of nitrogen?

A. 7 u

B. 14.0067 u

C. 8 u

D. 2 u