Chapter 3: Atomic Structure

Which number determines the position of an element in the Periodic Table?

• nucleon number

• proton number

• neutron number

• electron number

Answer explanation

Each element has a UNIQUE proton number, hence it will determine the position of the element in the Periodic Table i.e. hydrogen has a proton number 1, hence it is the 1st element in the Periodic Table.

Why is an atom electrically neutral?

• The charges of the protons and the neutrons balanced out each other.

• The charges of the protons and the electrons balanced out each other.

• The charges of the electrons and the neutrons balanced out each other.

• Proton, neutron and electron are all neutral.

Answer explanation

In an atom, the proton has a +1 charge, electron has a -1 charge. Neutron has no charge. Since number of electrons and protons in an atom is the same, the charges will balance out.

What is another name given for atomic number?

• neutron number

• electron number

• proton number

• nucleon number

The nuclide notation of element X is as shown.

What does the nucleus contains?

• 32 protons and 32 electrons

• 32 neutrons and 41 protons

• 32 protons and 73 neutrons

• 32 protons and 41 neutrons

Answer explanation

The NUCLEUS contains protons and neutrons only. Since the nucleon number (proton number + neutron number) of X is 73, then X has 32 protons and 41 neutrons.

The electronic configuration of the atoms of four elements are given below

Which is an atom of aluminium?

• 2, 1

• 2, 5

• 2, 8, 3

• 2, 8, 8, 1

Answer explanation

Aluminum has 13 electrons, hence the electronic configuration 2,8,3.

Note:

First electron shell - maximum 2 electrons

Second electron shell - maximum 8 electrons

Third electron shell - maximum 8 electrons

An element has an electronic configuration of 2,8,2. Determine the Group Number this atom can be found under, without referring to the Periodic Table.

• Group 1

• Group 2

• Group 12

• Group 16

Answer explanation

Elements are grouped according to the number of valence electrons (electrons in the outermost shell) they have. If the atom has an electronic configuration of 2,8,2, it has 2 valence electrons, and hence placed under Group 2.

An element has an electronic configuration of 2,8,6. Determine the Group Number this atom can be found under, without referring to the Periodic Table.

• Group 1

• Group 2

• Group 12

• Group 16

Answer explanation

Elements are grouped according to the number of valence electrons (electrons in the outermost shell) they have. If the atom has an electronic configuration of 2,8,6, it has 6 valence electrons, and hence placed under Group 16 (Deduct the ten from 16, 16-10 = 6 valence electrons) .

Element Z has two isotopes.

The electronic configuration of the first isotope is 2,8,4 and has a mass number of 37.

 

Which option represents the number of sub-atomic particles in an atom of the second isotope?

• A

• B

• C

• D

Answer explanation

Isotopes are atoms of the same element with the SAME number of protons but DIFFERENT number of neutrons.

For this atom with electronic configuration of 2,8,4, it has 14 electrons, hence 14 protons and 23 neutrons (37-14=23).

For the second isotope, it must have a different neutron number different from the first isotope.

Particle Z has the respective numbers of sub-atomic particles as shown.

Which of the following chemical symbols is correct for Z?

• Z

• Z^2-

• Z²⁺

• Z^3-

Answer explanation

Particle Z has different number of protons and electrons. It has gained 3 electrons and is now an ION and not a neutral atom. Since each electron carries a negative charge, Z will have a overall charge of 3-.

Which electronic configuration belongs to an atom that is chemically UNREACTIVE?

There may be more than 1 answer.

• 2,8,1

• 2,8

• 2,8,6

• 2,8,8

• 2,2

Answer explanation

Group 18 elements are known to be unreactive because they all have fully-filled valence shell [their outermost shell is already filled with the maximum number of electrons].