blacksacademy symbol
thumbnail


First Ionization energy


DOWNLOAD
FREE



thumbnail

First ionisation energies


Equations are omitted for technical reasons - download the original pdf

When an electron is removed from an atom in its gaseous state, the atom is said to have undergone ionisation. For example, the ionisation of hydrogen is [Equation goes here - download the original pdf to see it.] [Diagram goes here - download the original pdf to see it.] The symbol indicates the energy required in order to remove the electron from the outer shell of one mole of atoms of the element in their gaseous state. The first ionisation energy is given the subscript I1. We cannot remove a second electron from the hydrogen atom, but the removal of the second, third and subsequent electrons from an atom are given the obvious labels, I2, I3, In. For example, for Lithium, with proton number, 3. [Diagram goes here - download the original pdf to see it.] Ionisation is always an endothermic process. That means, in order to remove an electron from an atom it is always essential to add energy. This is because electrons are negatively charged and are attracted to the positive charge of the protons in the nucleus of the atom, so in order to remove an electron this electrostatic force of attraction must be overcome. If all electrons were in the same orbit in every atom, then ionisation energies would have to be the same for every element. It would make no difference, for example, removing an electron from an atom of iron than removing it from an atom of helium. Under this hypothesis, first ionisation energies for every element would be the same; so would second ionisation energies, and so forth. However, the quantum theory states that electrons in atoms are not all at the same energy level. According to the quantum theory the electrons in an atom are arranged in shells. An electron in the first shell will have a lower energy than an electron in the second shell. We can picture this by imagining that the electron in the first shell is closer to the nucleus than the electron in the second shell. Consequently, to remove the electron from the first shell we must add more energy than to remove an electron from the second shell. So the quantum theory basically predicts that there will be a trend in the ionisation energies, with the removal of electrons from an inner shell being more difficult than the removal of electrons from an outer shell.
Contents of
First Ionization energy

1 Evidence for the quantum theory
2 First ionisation energies
3 Effective nuclear charge
4 Table of first ionisation energies, trends in first ionisation energies
5 Groups in the periodic table
6 Exercise in Ionisation energies

Related articles: (1) Elementary quantum theory of the atom, (2) First Ionization energy