Question

What causes an electron in an atom to move to a higher energy level?

Answer 1

To solve this question, we first need to know what energy levels are. An electron in an atom can only exist in certain values of energy known as energy levels. In an atomic orbital, the energy levels correspond to electronic shells which are governed by principal quantum numbers.

Complete answer:
Principal quantum number (n) corresponds to the shells of an atom in the increasing order of their energy. It has integer values n=1,2,3,4…
The shell closest to the nucleus, K, has principal quantum number 1 and has the least amount of energy.
A shell can have a maximum of $2{{n}^{2}}$ number of electrons.
Now, the filling of electrons in the shells of an atom is governed by the Aufbau Principle states that the electrons are filled in the increasing order of the energy of the orbitals.
An electron is said to be in the ground state when it is at the lowest possible energy level. If the electron has higher energy than the energy of that electron in the ground state, it is said to be excited.
Now, when energy is absorbed by an electron, it moves to a higher energy level, next to its present energy level. This energy absorbed can be provided by external forces like
- Increase in heat.
- Presence of electrical field,
- Collusion with other electrons, etc.

Additional information:
- The Hund's Rule states that if two or more orbitals of the same energy are present, all of them must be half-filled before pairing up.
- Pauli's exclusion principle states that two electrons in an atom cannot have the same values of all four quantum numbers. Hence there can only be two electrons in an orbital.

Note:
Electrons usually do not stay in their excited states for long. When the electrons in the excited state jump back to their ground state, they give off the energy of the same amount that was observed. This can result in giving off of a photon which results in the emission of light (flames, fireworks, etc.)