Which is the first element in the periodic table to have an electron configuration in the 4th energy level?

To determine the first element in the periodic table to have an electron configuration in the 4th energy level, we need to understand the electron configuration pattern.

The electron configuration of an element is a representation of how the electrons are distributed in its atomic orbitals. The energy levels, also known as shells, are labeled with numbers starting from 1. Each energy level can hold a specific number of electrons.

In general, the maximum number of electrons that can be accommodated in a particular energy level can be calculated using the formula 2n^2, where n is the energy level number.

For the 4th energy level, the maximum number of electrons it can hold is 2 * (4^2) = 32.

Now, we need to find the element in the periodic table that has an electron configuration reaching the 4th energy level.

Starting from the first element, hydrogen (H), we can determine the electron configuration by following the Aufbau principle, which states that electrons fill the lowest energy levels first.

As we move across the periodic table, we fill the 1s, 2s, 2p, 3s, 3p, 4s, and 3d orbitals in that order.

To find the element with an electron configuration in the 4th energy level, we need to look for an element that has electrons in the 4s or 3d orbitals.

The first element that meets this criterion is potassium (K), which has an electron configuration of 1s^2 2s^2 2p^6 3s^2 3p^6 4s^1. Here, we can see that the 4s orbital is partially filled.

Therefore, potassium (K) is the first element in the periodic table to have an electron configuration in the 4th energy level.