Chemical Properties Change Across a Period

  1. There is gradual chemical change across a period.
  2. The acidity (or basicity) of the oxide of element changes across a period.
  3. The metallic properties, the electronegativity of element also change across a period.

Acidic Oxide or Basic Oxide

From left to right across a period the oxides change from alkaline/basic (with metals e.g. Na2O) to acidic (with non-metals e.g. SO2).

Metal, Metalloid and Non-metal

  1. As we go across a period from left to right, the elements change from metals to non-metals.
  2. There are about 7 elements in the periodic table are classified as semi-metals.
  3. The metals in the periodic table are mainly found in the left hand columns (Groups 1 and 2) and in the central blocks of the transition elements.
  4. On the right hand side of the periodic table, there are 7 semi-metals form a staircase like pattern, act as a divider between metal and non-metal.
  5. The semi-metals are also called the metalloid.

Uses of Metalloids

  1. The most widely used semi-metals are silicon and germanium.
  2. It is used to make diodes and transistors in electronic industry.


  1. Electronegativity is a measure of the potential of atoms to attract electrons to form negative ions.
  2. Metals have low electronegativities.
  3. Non-metals have high electronegativities.
  4. Electronegativities of the elements increase across a period with increasing proton number. This is because
    1. as the proton number increases, the positive charge of the nucleus will increase accordingly.
    2. this will increase the ability of the atom to attract electrons from the surrounding and thus increase the electronegativity of the atom.


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