The Periodic Table of Elements

 

SCIENCE COMMUNITY
Chemistry Branch

THE PERIODIC TABLE

 Period 3 Elements

• Across the period, the proton number and electron number, each increase by one for each successive element.
• Across the period, the atomic radius decreases and the ions of the elements are isoelectronic [meaning that they lose different amounts of electrons, but electrons remaining are the same(Na^+ → Si^4+)].

The sketched graphs above give an idea of the general trends and behaviors of Period 3 elements.

THE METALS OF PERIOD 3

• Sodium (Na in group 1), Magnesium (Mg in group 2 also called the group of alkaline earth metals) & Aluminium (Al in group 13) are metals in period 3 and they have giant metallic structures. So from Na to Al, there is an increase in the number of delocalised electrons in their metallic bonds, therefore, there is also an increase in the electrostatic forces of attraction in the metallic bonds. Take note that the delocalised electrons are contributed by individual atoms. 
• Electrical conductivity increases from sodium to aluminium because of the increase in delocalised electrons in the respective metallic lattice, allowing more electric current to pass through aluminum than sodium.
• There is an increase in charge density (of the positively charged nucleus), which causes an increase of the electrostatic forces, hence, the increase in melting point. This is consistent with certain consecutive elements in Period 3.

THE METALLOID and NONMETALS IN PERIOD 3

• Silicon is also known as a metalloid.
• It is a metalloid because it is a semiconductor of electricity which does not have delocalised electrons in a solid state to allow the conduction to occur, but can conduct at a higher temperature in a molten state.
• It has a giant covalent structure or a macromolecular structure.
• Silicon (Si in group 14) has strong covalent bonds, therefore, a lot of energy is needed to overcome silicon’s strong covalent covalent bonds, until the silicon is molten or liquid.
• Phosphorus (P in group 15), Sulfur (S in group 16) and Chlorine (Cl in group 17 also known as the group of Halides) are nonmetals.
• The rapid drop from silicon to phosphorus (P) is evident because giant molecular structures have strong van der Waals' forces (in silicon), while for phosphorus, the simple molecular structures have weaker van der Waals’ forces and this goes on up to Chlorine.
• From phosphorus to argon, sulfur appears to have the highest melting point. Therefore, the arrangement according to the graph showing the melting points of period 3 elements: S>P>Cl>Ar, where sulfur is S8, phosphorus is P4, Chlorine is Cl2. Take note, the base number is the number of atoms per molecule. 

THE NOBLE GAS IN PERIOD 3

• Argon is a noble gas (Ar in group 18 also known as group 0 because group 18 elements have respective electronic configurations that show their ability to have full valence shells). 
• Argon has very weak van der Waals’ forces.