# Difference Between Ground State and Excited State

## Main Difference – Ground State vs Excited State

Atoms are composed of an atomic nucleus and electrons that are in the movement around that nucleus. Electrons have no specific location in an atom; they only have a “probability” of being somewhere around the nucleus. According to these probabilities, scientists have found discrete energy levels that have the highest probability of containing electrons. These energy levels contain electrons having a certain amount of energy. The energy levels that are near to the atomic nucleus have a lower energy compared to the farther energy levels. When an atom is given a certain amount of energy, it moves to an excited state from the ground state due to the movement of an electron from a lower energy level to a higher energy level. The main difference between ground state and excited state is that ground state is a state where electrons in a system are in the lowest possible energy levels whereas excited state is any state of the system that has a higher energy than the ground state.

### Key Areas Covered

1. What is Ground State
– Definition, Explanation
2. What is Excited State
– Definition, Explanation
3. What is the Difference Between Ground State and Excited State
– Comparison of Key Differences

Key Terms: Atom, Atomic Nucleus, Electron, Energy Level, Excited State, Ground State, Vacuum State

## What is Ground State

Ground state refers to the state in which all electrons in a system (an atom, molecule or ion) are in the lowest possible energy levels. Therefore, the ground state is known to have no energy when compared to an excited state because the electrons are in a “zero” energy level. The ground state is also called the vacuum state.

When energy is provided to an atom in the ground state, it can move to an excited state by absorbing energy. But the lifetime of the excited state is less, Thus, the atom returns to the ground state, emitting the absorbed energy as shown in the following image.

Figure 1: Emission of Absorbed Energy

Therefore, ground state is highly stable when compared to the excited state and has a longer lifetime. In ground state atoms, the distance between electrons and the atomic nucleus has the least possible distance. The electrons reside closer to the atomic nucleus.

## What is Excited State

Excited state of an atom refers to the state which has a higher energy than the ground state of that atom. Here, one or more electrons are not at their lowest possible energy level. Electrons have moved to a higher energy level by absorbing energy provided from outside. But, in order to move to an excited state, the provided amount of energy should be equal to the energy difference between the two energy levels. Otherwise, no excitation would take place.

However, excited state is not stable since higher energy levels are not stable and atoms tend to return to the ground state by emitting the absorbed energy. This emission leads to the formation of an electromagnetic spectrum that has emission lines.

Figure 2: Emission of Absorbed Energy from an Excited State

The lifetime of an excited state is very short since the excited state is unstable due to its high energy. Here, the distance between the atomic nucleus and the electrons are not the least possible distances.

## Difference Between Ground State and Excited State

### Definition

Ground State: Ground state refers to the state in which, all electrons in a system (an atom, molecule or ion) are in the lowest possible energy levels.

Excited State:  Excited state is any state of the system that has a higher energy than the ground state.

### Energy

Ground State:  Ground state of a system is known to be having a “zero” energy.

Excited State:  Excited state of a system has a high energy.

### Stability

Ground State:  Ground state is highly stable.

Excited State:  Excited state is highly unstable.

Ground State: Ground state has a long lifetime.

Excited State:  Excited state has a short lifetime.

### Distance from Atomic Nucleus

Ground State: The distance between the ground state electron and the atomic nucleus is the least possible distance.

Excited State:  The distance between the excited state electron and the atomic nucleus is higher compared to that of the ground state.

### Location of Electrons

Ground State: In ground state, electrons are located in the lowest possible energy levels.

Excited State: In excited state, electrons are located in higher energy levels.

### Conclusion

Ground state and excited state of a system are related to the electron movement between two energy levels. The main difference between ground state and excited state is that ground state is a state whereas electrons in a system are in the lowest possible energy levels whereas excited state is any state of the system that has a higher energy than the ground state.

##### Reference:

1. “Ground state.” OChemPal, Available here.
2. “Ground State Vs. Excited State of an Atom: A Definitive Analysis.” ScienceStruck, Available here.

##### Image Courtesy:

1. “Spontaneousemission” By Ilmari Karonen – http://en.wikipedia.org/wiki/Image:Spontaneousemission.png (CC BY-SA 3.0) via Commons Wikimedia
2. “Bohr-atom-PAR” By JabberWok at the English language Wikipedia (CC BY-SA 3.0) via Commons Wikimedia