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Ionization Energy

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Ionization energy is the energy required to remove an electron from a gaseous atom or ion. Where the atom or ion is assumed to be in its ground state. The ionization energy for a particular electron in an atom is a source of information about the energy of the orbital it occupies in the atom.

The ionization energy is the energy required to remove the most loosely held electron from a gaseous atom or ion. The higher the value of the ionization energy, the herder it is to remove that electron. In general, the ionization energy of atom decreases within a group from top to bottom.

Ionization Energy Definition

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Define Ionization Energy

"Ionization energy is defined as the energy required to remove an electron from an atom." Energy is always required to remove electrons.

Most of the elements in the periodic table are metals. When they react with other elements to form compounds, they generally do so by losing one or more electrons to form positive ions. An input of energy is required to remove one or more electrons from an atom, and the energy involved is known as ionization energy.

Ionization Energy Trend

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The trends in ionization energy suggest that elements on the left side of the periodic table especially the lower left form cations (lose electrons) more readily than the elements on the right. The elements with lower ionization energies are the metals and the elements with higher ionization energies are the nonmetals.

The trends in ionization energy is shown below.

Ionization Energy Trend

As atomic number increases within a period, the general trend in ionization energy is an increase. The general trend among elements in the same group in the periodic table is a decrease.

First Ionization Energy

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The minimum amount of energy required to ionize an atom which is in its ground state that is to remove its loosely bound electron is called the first ionization energy of the atom.

The first ionization energy is often referred to simply as the ionization energy. This particularly so in the case of hydrogen which has only one electron and therefore no higher ionization energies than the first.

Second Ionization Energy

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The second ionization energy of an atom is the energy required to remove an electron from an isolated singly charged positive ion of that atom. The second ionization energy of a lithium atom for example is the energy required for the following process.

Li+(g) $\rightarrow$ Li2+(g) + e-

Ionization energy is the energy required to remove an electron from an atom. It thus depends on how strongly the electron is bound in the atom. The stronger the binding the higher will be the ionization energy.

Third Ionization Energy

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The third ionization energy of an atom is the energy required to remove an electron from an isolated doubly charged positive ion of that atom. So the energy required to remove the third electron is called third ionization energy.

The third ionization energy corresponds to removing an electron from the core of the atom that is from a noble gas configuration. The equation for third ionization energy is represented by

X2+ $\rightarrow$ X3+ + e-

Ionization Energy Chart

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ionization energy determines the ease with which an atom forms a positive ion. The first ionization energy of an atom is the energy required to remove the least tightly held electron from an isolated atom in the vapor state to form a positive ion.

With the first electron gone the removal of succeeding electrons becomes more difficult because of the imbalance between the positive nuclear charge and the remaining electrons. The ionization energy of elements are given below.

S.No
Elements
Ionization energies (kcal/mol of atoms)
1
Ionization energy of hydrogen
313
2
Ionization energy of sodium 119
3
Ionization energy of lithium
125
4
Ionization energy of helium
567
5
Ionization energy of oxygen
314
6
Ionization energy of potassium
100
7
Ionization energy of magnesium
176
8
Ionization energy of calcium
141
9
Ionization energy of aluminum 138
10
Ionization energy of nitrogen
336
11
Ionization energy of carbon260
12
Ionization energy of fluorine
402
13
Ionization energy of chlorine 300
14
Ionization energy of silicon 188
15
Ionization energy of boron 191
16
Ionization energy of cesium
90
17
Ionization energy of argon
363
18
Ionization energy of phosphorus
242
19
Ionization energy of gold890
20
Ionization energy of zinc
906
21
Ionization energy of water 456
22
Ionization energy of barium 120
23
Ionization energy of nickel
737
24
Ionization energy of tin
169
25
Ionization energy of mercury
1007
26
Ionization energy of germanium
182

Ionization Energy of Elements

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Ionization energies are lower as the atomic number increases within the group. The energy required to remove a second electron from the 1+ ion of an element is its second ionization energy and removing a third electron requires the third ionization energy.

Highest Ionization Energy

Helium placed in the upper right corner of the periodic table has the highest ionization energy. We may also conclude that the ionization energy decreases from top to the bottom of any group in the periodic table and it increases from left to right across a period in the periodic table

Lowest Ionization Energy

Group I elements have low ionization energies because the loss of an electron forms a stable octet. The lowest ionization energy is found with the least electronegative atom.

Ionization Energy on Periodic Table

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Ionization energies of atoms exhibit periodic behavior. In any given row in periodic table the ionization energies generally increase with increasing atomic number being smallest for the lithium family and largest for the helium family.

Ionization Energy Formula

The ionization energy is important because it is a measure of the binding energy of the atoms outermost valence electron. Of course it is this valence electron and orbital that is most likely to be involved in chemical reactions.

Eionization energy = E+ - E

where E+ is the energy of the cation and E is the energy of the neutral ion.

The Ionization Energy Units is kcal/mol of atoms.

Ionization Energy Graph

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The first ionization energy is the minimum energy required to remove one electron from an isolated atom in the gas phase. In other words it is the energy for the process.

E(g) $\rightarrow$ E+(g) + e-(g)

Where E represents an element. All ionization energies are positive because it always requires energy to remove the electron. A plot of ionization energy against atomic number provides compelling evidence for the existence of shells and sub shells.

A plot of ionization energy against atomic number provides compelling evidence for the existence of shells and sub shells.

Ionization Energy Graph