Helium and element ‘X’ have outer electronic configuration of \(ns^2\). Identify the element ‘X’.

Be

The outermost electron configuration of an atom is the arrangement of its valence electrons, which are the electrons in the highest energy level of the atom. The valence electrons are responsible for the chemical behavior of the atom.

In the case of beryllium (Be), the outermost electron configuration is \(ns^2\), where n is the principal quantum number. The principal quantum number tells us the energy level of the electron. For beryllium, the principal quantum number is 2, so the outermost electrons are in the 2s orbital.

The 2s orbital is a spherical orbital that can hold up to two electrons. When beryllium has a full 2s orbital, it is considered to be stable. This is because the 2s orbital is the closest orbital to the nucleus, so the electrons are more tightly held to the nucleus and are less likely to interact with other atoms.

Helium (He) and neon (Ne) are also considered to be stable because they have full valence electron configurations. Helium has an outer electron configuration of \(1s^2\), which means that it has two electrons in the 1s orbital. Neon has an outer electron configuration of \(2s^2\) \(2p^6\), which means that it has eight electrons in the 2s and 2p orbitals.

Sodium (Na) has an outer electron configuration of \(3s^1\), which means that it has one electron in the 3s orbital. This electron is not paired, so it is more likely to interact with other atoms. This is why sodium is more reactive than beryllium.

Here is a table summarizing the electron configurations of these elements:

As you can see, the only element with an outer electron configuration of \(ns^2\) is beryllium (Be). Therefore, the element ‘X’ is beryllium (Be).