Electron affinity, Ionization energy and electronegativity.
in-organic
chemistry
Questions:
- What is electron affinity?
- Why ionization energy increases across the period and
decreases down the group
- Why do electronegativity increases across the period and
decrease down the group
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Electron affinity, Ionization energy and electronegativity.
Electron affinity, Ionization energy and electronegativity.
Question One
Electron affinity: electron affinity of an atom or molecule is defined as the amount
of energy released or spent when an electron is added to a neutral atom or molecule in
the gaseous state to form a negative ion. The first electron affinity is the energy released
when 1 mole of gaseous atoms each acquire an electron to form 1 mole of gaseous 1-
ions. This is more easily seen in symbol terms. It is the energy released (per mole of X)
when this change happens. First electron affinities have negative values.
Trends for electron affinity
This is an exothermic process for all non-noble gas elements. There are general
trends in electron affinity across and down the periodic table of elements. Electron
affinity generally increases across a period in the periodic table and sometimes
decreases down a group.
Question Two
Ionization energy: Here. moving left to right within a period or upward within a
group, the first ionization energy generally increases. As the atomic radius decreases, it
becomes harder to remove an electron that is closer to a more positively charged
nucleus.
How do we find ionization energy?
The first of two main methods which scientists used to calculate the ionization
energy is the Subtraction Method. This method entails some experimentation. You must
first find the energy value of the ion you are looking for. Then subtract the energy value
of the neutral atom
It is a well-known fact that the electrons in an atom are attracted by the positively
charged nucleus. In order to remove electron from an atom, energy has to be supplied
to it to overcome the attractive force. This energy is referred to as ionization energy.
Electron affinity, Ionization energy and electronegativity.
Electron affinity, Ionization energy and electronegativity.
Thus, Ionization energy may be defined as the amount of energy required to remove the
most loosely bound electron from the isolated gaseous atom in its ground state.
A (g) + Energy (I.E.) A+ (g) + e-
Ionization energy is a very important property which gives an idea about the
tendency of an atom to form a gaseous positive ion.
Ionization energy is expressed in terms of kilo Joules per mole of atoms (kJ moz-1)
Ionization energies decrease DOWN a Group, but increase across a PERIOD (from left to right).
Explanation:
Two properties are important in determining ionization energies: (i) nuclear charge; and
(ii) shielding by other electrons.
In partially filled shells, electrons shield each other very imperfectly, so across the
Period (from left to right) as the nuclear charge, Z, increases, ionization energies
markedly increase.
On the other hand, down a Group, the increased nuclear charge is effectively shielded
by the filled electronic shells. Nucleus/valence electron attraction becomes attenuated,
and ionization energies decrease.
As a chemist, as a physical scientist, you should look at some tables of ionization
energies, and see if what I have said is reasonable.
FACTORS ON WHICH ION IZATION ENERGY DEPENDS
The ionization energy depends upon the following factors:
1. Size of the atom;
2. Magnitude of nuclear charge;
3. Screening effect of the inner electron;
4. Penetration effect of the electrons; and
5. Electronic configuration.
Electron affinity, Ionization energy and electronegativity.
Electron affinity, Ionization energy and electronegativity.
Question Three
Electronegativity: This is a measure of the tendency of an atom to attract a bonding
pair of electrons. The Pauling scale is the most commonly used. Fluorine (the most
electronegative element) is assigned a value of 4.0, and values range down to caesium
and francium which are the least electronegative at 0.7.
So, as you move down a group on the periodic table, the electronegativity of an
element decreases because the increased number of energy levels puts the outer
electrons very far away from the pull of the nucleus. Electronegativity increases as you
move from left to right across a period on the periodic table.
What happens if two atoms of equal electronegativity bond together?
Consider a bond between two atoms, A and B. Each atom may be forming other bonds
as well as the one shown - but these are irrelevant to the argument.
If the atoms are equally electronegative, both have the same tendency to attract
the bonding pair of electrons, and so it will be found on average half way between the two
atoms. To get a bond like this, A and B would usually have to be the same atom. You will
find this sort of bond in, for example, H2 or Cl2molecules,
HABIBU Abdullahi
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Electron affinity, Ionization energy and electronegativity.
