What is the melting point trend of Period 3 elements and how does it relate to bonding?

The melting point trend of Period 3 elements increases from sodium to silicon, then decreases.

The melting point trend of Period 3 elements can be explained by their bonding. Sodium and magnesium have metallic bonding, which is a strong attraction between positively charged metal ions and delocalized electrons. This results in a high melting point as a lot of energy is required to break the strong metallic bonds. Aluminium has a giant covalent structure, where each aluminium atom is covalently bonded to four other aluminium atoms. This results in a very high melting point as a lot of energy is required to break the strong covalent bonds.

Silicon also has a giant covalent structure, but with weaker covalent bonds than aluminium due to the larger atomic radius of silicon. This results in a slightly lower melting point than aluminium. Phosphorus, sulfur, chlorine and argon have simple molecular structures, where the molecules are held together by weak intermolecular forces. These forces are easily overcome, resulting in low melting points.

The trend in melting points can also be explained by the increasing size of the atoms across Period 3. As the atoms get larger, the distance between the nuclei and the outer electrons increases, resulting in weaker metallic and covalent bonds. This explains the decrease in melting point from silicon to argon.

In summary, the melting point trend of Period 3 elements can be explained by their bonding and the increasing size of the atoms across the period.