Question:

An atom of an element has an atomic number of 20 and a mass number of 40. Determine the following:

a) The number of protons in the nucleus of the atom.

b) The number of neutrons in the nucleus of the atom.

c) The number of electrons in the atom.

d) The electronic configuration of the atom.

e) The group and period to which the element belongs in the periodic table.

Answer:

a) The atomic number of an element represents the number of protons in its nucleus. Therefore, an atomic number of 20 implies that the atom has 20 protons.

b) The mass number of an element represents the total number of protons and neutrons in its nucleus. To determine the number of neutrons, we subtract the atomic number from the mass number:

Number of neutrons = Mass number - Atomic number

Number of neutrons = 40 - 20 = 20

Therefore, the atom has 20 neutrons in its nucleus.

c) In a neutral atom, the number of electrons is equal to the number of protons. Hence, the atom has 20 electrons.

d) The electronic configuration of an atom refers to the arrangement of electrons in different energy levels or shells. Since the atomic number is 20, the electronic configuration can be determined as follows:

1s² 2s² 2p⁶ 3s² 3p⁶ 4s²

e) The group and period of an element in the periodic table are determined by its electronic configuration. From the electronic configuration obtained in part (d), we can conclude that the atom belongs to Group 2 (or Group IIA) and Period 4.