Atomic Structure

In Basic Chemistry such as GCE-O Levels, we have learned that Atom is the smallest unit of an element.

We also learned that Atom itself are made up of 3 Sub-Atomic Particles know as

• Protons
• Electrons
• Neutrons

The Protons and Neutrons (collectively known as Nucleons) are located together in the Nucleus of the Atom, while the electrons are found in region of space surrounding the nucleus (we call them the electron shells).

It is important to know the relative mass and charges of the 3 Sub-Atomic Particles.

	Proton	Neutron	Electron
Relative Charges	+1	o	-1
Relative Masses	1	1	1 / 1840

As you can see, Protons and Neutrons have much larger mass than electrons, and almost all the mass of an atom is concentrated in the nucleus.

The sum of the Protons in an atom is known as Proton Number. It is also commonly known as Atomic Number.

The sum of the Protons and Neutrons in an atom is known as Nucleon Number. Since Proton and Neutron contribute most of the mass of an atom, it is also know as Mass Number.

Few things to note:

• In a Neutral Atom, the number of electrons is equal to the number of protons.
• In a Negative Ion (Anion), the number of electrons is greater than the number of protons since a negative ion is obtained by adding electron (s) to a neutral atom.
• In a Positive Ion (Cation), the number of electrons is lesser than the number of protons  since a positive ion is obtained by removing electron (s) from a neutral atom.

Let’s check out a few questions that are being asked in GCE A-Level H2 Chemistry syllabus in Junior Colleges (JC) in Singapore.

Question 1:

Which particle has the largest mass?

A) ¹H₂

B) ⁴He

C) ²H^–

D) ⁴He²⁺

and

Question 2:

Which of the following pairs of atoms or ions contains the same number of neutrons?

A) ¹⁴C and ¹²C

B) ¹⁹F- and ²⁰Ne

C) ²³Na⁺ and ²⁴Mg²⁺

D) ³²S and ²⁷Al

Try it out!

PS: You can leave your suggested answer in the comment section below. I would love to hear from you.