Why Does The Ionization Energy Change When Moving Down A Group Of Elements?

Learning Objective

Recognize the general periodic trends in ionization energy.

Key Points

The ionization energy is the energy required to remove an electron from its orbital around an atom to a point where it is no longer associated with that atom.
The ionization energy of an element increases equally one moves beyond a period in the periodic table because the electrons are held tighter past the college constructive nuclear accuse.
The ionization energy of the elements increases as one moves up a given group considering the electrons are held in lower-energy orbitals, closer to the nucleus and therefore are more tightly spring (harder to remove).

Term

ionization energyThe energy needed to remove an electron from an cantlet or molecule to infinity.

Periodic Trends in the Ionization Energy

The ionization energy of a chemic species (i.east., an atom or molecule) is the free energy required to remove electrons from gaseous atoms or ions. This property is also referred to every bit the ionization potentia and is measured in volts. In chemistry, it frequently refers to 1 mole of a substance (molar ionization free energy or enthalpy) and is reported in kJ/mol. In atomic physics, the ionization energy is typically measured in the unit of measurement electron volt (eV). Large atoms or molecules take low ionization free energy, while pocket-size molecules tend to accept higher ionization energies.

The ionization free energy is different for electrons of different atomic or molecular orbitals. More than generally, the nth ionization energy is the free energy required to strip off the nth electron later on the get-go due north-1 electrons have been removed. It is considered a measure of the trend of an atom or ion to give up an electron or the strength of the electron binding. The greater the ionization free energy, the more hard it is to remove an electron. The ionization energy may be an indicator of the reactivity of an chemical element. Elements with a low ionization energy tend to exist reducing agents and class cations, which in plough combine with anions to form salts.

**Ionization free energy**This graph shows the start ionization energy of the elements in electron volts.

Moving left to right within a period or upwardly within a group, the beginning ionization energy generally increases. Every bit the atomic radius decreases, it becomes harder to remove an electron that is closer to a more positively charged nucleus. Conversely, as one progresses downwards a grouping on the periodic table, the ionization free energy volition likely subtract since the valence electrons are farther abroad from the nucleus and experience greater shielding. They feel a weaker attraction to the positive charge of the nucleus. Ionization free energy increases from left to correct in a period and decreases from meridian to bottom in a group.

Rationale for the Periodic Trends in Ionization Free energy

The ionization free energy of an element increases as 1 moves across a period in the periodic table considering the electrons are held tighter by the higher effective nuclear charge. This is because additional electrons in the same shell practice not substantially contribute to shielding each other from the nucleus, notwithstanding an increase in atomic number corresponds to an increment in the number of protons in the nucleus.

The ionization energy of the elements increases as one moves up a given grouping considering the electrons are held in lower-energy orbitals, closer to the nucleus and thus more tightly leap (harder to remove).

Based on these two principles, the easiest element to ionize is francium and the hardest to ionize is helium.

Periodic trends in ionization energy – YouTubeThis video explains the periodic trends in ionization free energy….periodicity. The periodic table is bundled in a manner to show trends in the characteristics of the elements.