Ground State

In this article, you will learn what the ground state of atoms is, and more importantly how it is different from the excited state of atoms. Here you will find how different the ground state is applied to different atomic contexts of electronic configuration. You will learn how to draw electronic diagrams to represent the ground state of atoms, and how it exhibits periodicity. 

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Table of contents
    • In this article, you will be guided through the definition of the ground state of the atom.
    • You shall see how it can be applied to many different atomic contexts.
    • You will also learn the difference between the ground state and the excited state of atoms in the context of electronic configuration.

    Ground State Definition Chemistry

    So what is meant by the "ground state" of an atom?

    The simplest definition of the ground state of an atom refers to:

    Ground State (of an atom): the lowest possible energy level of the atom in question.

    To define this more broadly, we can say that the ground state is the state in which atoms are found if they are not charged or excited by external sources. These sources of excitation could be light (such as photons) or any other wavelength on the electromagnetic spectrum.

    When discrete amounts of energy, such as quanta, excite the atom, it triggers certain subatomic rearrangements and a shift in the electronic configuration. But in this case, the ground state refers to the state where this process does not occur and concentrates on the atom in its usual "uncharged" state.

    So what does the ground state mean in terms of the electrons within an atom? In fact, when speaking about the ground state of an atom, it is all about the electronic configuration and the energy states of the electrons present in the atom.

    Here, the energy state of the electrons refers to the energy levels of the electrons which can be either excited (if excitation occurs from an external source) or unexcited, which we call the ground state.

    This means that in the ground state, the atom is not excited and subsequently none of the electrons are excited. The electrons are in their lowest possible energy state. What happens in the ground state is that all the electrons line up in such a way as to be at the lowest possible energy of their individual positioning within the atom, and also of the overall system.

    There are a number of factors that determine the positioning of the electron within an atom, which we will cover in the next section. Yet it is crucial to remember that the electrons may occupy different states within an atom. The ground state will always refer to the state where the electrons are in their lowest possible energy configuration within the atom.

    Ground State Electronic Configuration

    So how can we visualize the ground state electronic configurations?

    We can use electron configuration diagrams, such as the arrow and box diagrams. Here, we will explore what they are and how they can be used to depict atoms in the ground state. As the definition of the ground state of atoms refers to their electronic energy levels, depicting them will help us understand the inner workings of the atom.

    Below, you will find a diagram of empty electron orbitals.

    Ground State, Orbitals, StudySmarterFig. 1 - Empty electron orbitals

    But how do electrons fill up these orbitals?

    There are three sets of rules which you need to think about when considering such problems: the Aufbau principle, Pauli's exclusion principle, and Hund's rule. Here you will find summaries of what they mean.

    1. Aufbau Principle: electrons will always tend to fill up the lowest possible energy state (orbital) before going onto subsequent higher energy orbitals.
    2. Pauli's Exclusion Principle: there can be a maximum of two electrons per orbital, each with an opposing spin state.
    3. Hund's Rule: electrons fill sublevels individually, which means that if there are other 'boxes' in the same energy orbital, then electrons will singly fill up all boxes before starting to pair up.

    So how does this relate to the notion of the ground state? You can take a look at how the electrons will preferentially line up in a ground state atom. Here, the way in which the atoms fill up naturally in an atom will be the ground state.

    This can be useful for determining the ground state electronic configurations of any atom, since if you apply the above-mentioned three rules, you will determine the ground state of the particular element. This is due to the fact that when atoms are in an excited state (which we will soon cover), the electronic arrangement changes and deviates from the canonical rules of Aufbau, Pauli, and Hund. On the other hand, we can see how applying the rules will give us the ground state configurations of the electrons in a given atom, as that will be suggestive of the way the electrons would arrange themselves if there would be no external source of energy applied or any type of deviation possible. This would result in the configuration of the lowest possible energy levels, hence the ground state configuration.

    Ground State of Atoms

    You can apply the aforementioned definition of the ground state as well as the theories on the electronic configuration to atomic models now. As stated above, you can construct electronic diagrams to match the ground state. At the bottom of this article, you will find examples of the ground state.

    A crucial distinction to be made regarding the ground state, especially when dealing with configuration diagrams, is the distinction between an electronic shell and an electronic orbital. When talking about these theoretical notions of the ground and excited state, there will be talk of electrons gaining energy (usually from an external energy source such as light or another wavelength from the electromagnetic spectrum). The gain of energy will be correlated with the electron moving into higher energy states, and in these contexts the two specified areas will be either a higher energy level (shell) or higher energy orbital.

    So what's the difference? In these contexts you have to imagine that the concepts of energy shell and orbital are interchangeable. This is just to signify the same definition: that an electron moves up to a higher energy state, hence creating an excited state.

    Take a look at the diagram to clarify how an electron moves up in energy. This distinction is what causes the difference between the ground state and the excited state of atoms.

    Ground State. Ground State. StudySmarterFig. 2 - An atom in the ground state being excited by a photon. This causes the electron to move to a higher energy shell

    Usually, the excited state of atoms is represented with an asterisk next to it. Below you will find an example:

    A (ground state)

    A* (excited state)

    A + energy = A*

    A* = A + energy

    Thus, you can assume that molecules or atoms are only in their excited state if there is an asterisk next to them. This will help you to identify the ground states of atoms in equations.

    Ground State vs Excited State Electron Configuration

    Take a look at the two electronic configurations below. In this example, the model element is carbon.

    Ground State, Carbon Ground State, StudySmarterFig. 3 - Ground state and excited state electronic configuration diagram of carbon

    Do you notice any differences between them? You can tell one of them clearly follows the three rules we set out earlier. As a reminder, these are the Aufbau principle, Pauli's exclusion principle, and Hund's rule.

    The above diagram depicting the ground state depicts the electrons arranging themselves according to these three key principles. So how does it differ in the excited state? Particularly, you can see how an electron from the 2s orbital moves to the 2p orbital. As you can see, there is a 'hole' in the 2s orbital, which means that electrons do not occupy the lowest energy states. We would call this the excited state, as one of the electrons has enough energy to move up an energy level, in this case into the 2p orbital.

    In the same way as it has gained energy to move up towards an excited state, the electron can reemit the energy and be lowered back down into the energy level it occupied before: the ground state.

    Ground State, Excited to ground state, StudySmarterFig. 4 - Shift from an excited state to the ground state of an atom

    As a reminder, below you will see how the electronic arrangement is depicted in the box and arrow diagrams according to ascending energy levels. You can use this to know the arrangement of subatomic particles and more importantly, to know if the element in question is in its ground state.

    Note that the below diagram shows only the electronic arrangement up to the 4p orbital, yet there are elements which go way beyond this, but there's no need to worry about those.

    Ground State, Aufbau principle of electron configuration, StudySmarterFig. 5 - Aufbau principle for electron configuration

    Examples of Ground State

    Here you will find a bunch of examples of the ground state electron configuration. Take a look at the figure below, which depicts the electronic configuration of the atoms from Boron to Oxygen.

    Ground State, Hund's rule, StudySmarterFig. 6 - Electronic configuration depicting ground state of the elements B, C, N, O

    What can you observe in the diagram above? You can tell how the elements given in the example increase in atomic number by 1, hence their number of electrons will increase by 1.

    Thinking about the gradual increase in electrons, take a look at what happens to the electronic configuration of the elements, and more importantly, how it changes from atom to atom. This way you will observe trends, and you'll see how Hund's rule plays a role in electronic configuration. All of this ultimately just shows the ground state of atoms being a process that is pattern-like and does not deviate from atom to atom. Using these examples, you can predict any electronic configuration of atoms in question, and determine whether they are in their ground state or excited state.

    Ground State - Key takeaways

    • The ground state of an atom refers to an unexcited state.
    • Excitation occurs when an electron moves up in energy states.
    • You can determine the state of an atom with its electronic configuration.
    • The electronic state of atoms can be determined by the:
      • Aufbau principle
      • Pauli's exclusion principle
      • Hund's Rule
    • Electronic configuration exhibits periodicity as seen by examples of atomic ground states.
    Frequently Asked Questions about Ground State

    What is the ground state?

    The ground state of an atom is the lowest energy state of the atom, where all electrons are in their lowest possible arrangement. 

    How do we write the ground state electron configuration?

    We do this using the box and arrow diagrams. Fill the boxes with arrows (representing electrons) according to the Aufbau principle, Pauli's exclusion principle, and Hund's rule to show electronic configuration of ground state electrons. 

    What is the ground state of an atom?

    The ground state of an atom is the state where all the electrons are in their lowest possible energy state. 

    What is the difference between ground state and excited state in chemistry?

    In the excited state, an atom has electrons which have been excited (moved) to higher energy orbitals, whilst in the ground state, an atom has electrons that occupy the lower energy orbitals.

    Test your knowledge with multiple choice flashcards

    Which of the following three states that electrons fill up an electron shell singly?

    Electrons in the same orbital can have the same spin state

    If an electronic configuration has gaps and inconsistencies, can the specified element be in its ground state?


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