ELEMENTS IN A PERIOD
ELEMENT IN PERIOD THREE
PROPERTIES IN PERIOD 3
Trends of changes across Period 3
1. The atomic radius decreases across the period.
a) all the elements in the Period 3 have three filled
electron shells but the proton number increases by
one unit across the period.
b) the increases in the number of proton increases the
electrostatic forces between the nucleus and the
valence electrons.
c) the valence electrons are pulled closer to the nucleus,
causing the atomic radius to decrease.
2. The number of valence electrons increases across the period.
a) proton number increases, the number of
electrons increases.
b) the number of valence electrons increases by 1 from one element to the next across the period.
3. The electronegativity increases across the period. Electronegativity is a measurement of the tendency of an element to attract electrons.
a) The atomic radius decreases across the period.
b) The proton number increases across the period.
c) It will causes an increases in the force of attraction of the nucleus.
4. Melting points and boiling points increase from the left of the period to the middle of the period and then decrease again.
a) Sodium, magnesium and aluminium are metals with strong metallic bonds between the metal atoms. Hence they have high melting and boiling points.
b) Silicon has very high melting and boiling point. It has strong covalent bonds between atoms.
5. Oxide of the elements
a)Elements on the left of the period, which are metals, form metal oxides. The metal oxides are usually basic oxides.
b)Basic oxides react with acids to form salts and water. Example :
c)Elements on the right of the period are non-metals. Non-metallic oxides are acidic oxides.