SS1 First Term Chemistry Lesson Note – Chemical Combination

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WEEK 8

 TOPIC: CHEMICAL COMBINATION

 CONTENTS:

1. Periodic table (First 20 elements)
2. Types of chemical bonds
3. IUPAC system of naming inorganic compounds.

PERIOD 1: PERIODIC TABLE (FIRST 20 ELEMENTS)

Chemical combination: The atoms of noble gases e.g. Helium He, Neon Ne are very stable; because their outermost shells are completely filled with electrons. The tendency of the other elements is to attain this stable structure possessed by the noble gases. This is achieved during chemical combination. Thus, chemical bonding is the coming together of atoms of the same or different elements, in order to form a stable structure.

The Periodic Table

Periodic table is the arrangement of chemical elements in order of their atomic numbers. Atomic number, Z, of an element is the number of protons in one atom of that element while, Mass number, A, of an element is the sum of the protons and neutrons in it.

Many scientists have attempted to classify chemical elements based on their properties. They include Newland, Lothar Meyer, Dobereiner and Mendeleev. The modern periodic table is based on Mendeleev’s original idea in 1869. The basic assumption behind the modern periodic table known as Periodic Law which states that “the properties of the elements are a periodic function of their atomic number”

The modern periodic Table

The modern periodic table is divided into vertical columns of elements called Groups and horizontal rows of elements called Periods. There are seven (7) periods and eight (8) groups. The first twenty (20) elements are:

1. 1. Hydrogen – 11. Sodium
   2. Helium – 12. Magnesium
   3. Lithium – 13. Aluminum
   4. Beryllium – 14. Silicon
   5. Boron – 15. Phosphorus
   6. Carbon – 16. Sulphur
   7. Nitrogen – 17. Chlorine
   8. Oxygen – 18. Argon
   9. Fluorine – 19. Potassium
   10. Neon – 20. Calcium

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