6th June 2020



DATE: 2nd June 2020


SUBJECT: Chemistry.

Topic: The periodic table.

Reference: Essential chemistry for sss.

Objectives: The pupils should be able to:

  1. State the periodic law.
  2. Define periodic table and atomic numbers.
  3. Name the property of the atom that the periodic table is based on and the use of atomic number.

Introduction (Brief explanation).

Periodic table represents a simple systematic way of classifying the elements. A Russian scientist by name Mendeleev (1869) was the first to formulate the periodic based on the relative atomic masses of the elements the modern version of the periodic table is based on their atomic numbers.

Below is a periodic table. Get your teacher to guide you on how to use it.

The law states that:

  1. The physical and chemical properties of elements are the periodic function of their atomic numbers.
  2. When elements are arranged in order of increasing atomic number, their chemical and physical properties recur periodically.

The following table show the criteria used for placing elements into the periodic table.

Elements are place based on their:

  1. Atomic number.
  2. Electronic configuration.
  3. Recurring chemical properties.

Atomic number

Atomic number or proton number is the number of protons in the nucleus of an atom.

The use of atomic number

  1. It is the change number of nucleus.
  2. It determines the identity of an element and many of its chemical properties.

What is electronic configuration?

Electronic configuration of an element describes how electrons are distributed in its atomic orbitals.


  1. What is atomic number?
  2. What is another name for atomic number?
  3. Name the criteria for placing elements on the periodic table.
  4. What is a periodic table?
  5. What is electronic configuration?