Anomalous Periodic Properties of Second Period Elements

All elements are special in their own way even if there are certain trends that have been observed by scientists over the years. The elements belonging to the second period display periodic properties that are especially anomalous. Let’s take a look at the elements that belong to the second period first:

periodic properties

It has been observed that Lithium, Beryllium, Boron, Carbon, Nitrogen, Oxygen, and Fluorine have slightly different periodic properties than the rest of the elements belonging to Groups 1, 2, 13-17 respectively. For example, Lithium and Beryllium form covalent compounds, whereas the rest of the members of Groups 1 and 2 form ionic compounds. Also, the oxide that is formed by Beryllium when it reacts with Oxygen is amphoteric in nature, unlike other Group 2 elements that form basic oxides. Yet another example is that of Carbon which can form stable multiple bonds, whereas Si=Si double bonds are not very common.

So, it has clearly been established that the second-period elements are different. In fact, they display periodic properties that are similar to the second element of the next group (i.e. Lithium is similar to Magnesium and Beryllium to Aluminium) or in other words, they have a diagonal relationship.

The reasons for differences in periodic properties and hence in chemical behavior are:

  • Small size of these atoms
  • High electronegativity
  • Large charge/radius ratio
  • These elements also have only 4 valence orbitals available (2s and 2p) for bonding as compared to the 9 available (3s, 3p, and 3d) to the other members of the respective groups, so their maximum covalency is 4. (This is why Boron can only form [BF4]whereas Aluminium can form [AlF6]3-).

These are the reasons for anomalous periodic properties of second-period elements, but there are several other normal trends in the periodic table as well. To know more about these periodic properties, visit or download Byju’s- The Learning App.

Practise This Question

Barring Helium, the melting and boiling points of every noble gas lie within a range of 10 degrees Celsius – True or false?