Periodic Properties: Ionization, Affinity, Electronegativity, and Oxidation, Slides of Chemistry

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Periodic

properties of

elements

• Topics
• Ionization energy
• Electron affinity
• Electronegativity
• Oxidation states with their variation in

periodic tables

Effective nuclear charge

▪ In a polyatomic atom, the internal electrons repel the outermost electrons. The results in decrease the nuclear attraction on the outermost electrons.

• Therefore, only a part of the nuclear charge is effective on the electrons of the outermost orbit. Thus, the inner electrons
• protect the nucleus and thereby decrease the effect of nuclear charges towards the electrons of the outermost orbits. ▪ Thus the part of the nuclear charge works against outer electrons, is knowns as effective nuclear charge. ▪ Z* = Z – s ▪ Z* = effective nuclear charge ▪ Z = atomic number ▪ S = screening constant

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Sizes of Ions

Ionic size depends upon:

Nuclear charge.

Number of electrons.

Orbitals in which electrons reside.

• Cations are smaller than their parent atoms.

➢ The outermost electron is removed and

repulsions are reduced.

• Anions are larger than their parent

atoms.

➢ Electrons are added and repulsions

are increased.

Ionization Energy

• Amount of energy required to remove an electron from the ground state of a gaseous atom or ion. - First ionization energy is that energy required to remove first electron. - Second ionization energy is that energy required to remove second electron, etc. El -------> El + + e - Na -------> Na + + e -

Ionization Energy

• It requires more energy to remove each successive electron.
• When all valence electrons have been removed, the ionization energy

takes a quantum leap.

(a) Radius (b) Z* (c)Orbital (d) E- configuration

Factors controlling ionization energy

In a group ionization energy is controlled by only radius. Ionization energy decreases in a group from top to bottom. Trend of I.E in a group Ex- Li>Na>K>Rb>Cs

Electron Affinity

Energy change accompanying addition of electron to gaseous atom: Cl + e−^ ⎯⎯→ Cl−

Trends in Electron Affinity

In general, electron affinity becomes more exothermic as you go from left to right across a row. There are also two discontinuities in this trend.

• The first occurs between Groups IA and IIA. ➢ Added electron must go in p - orbital, not s - orbital. ➢ Electron is farther from nucleus and feels repulsion from s - electrons.
• The second occurs between Groups IVA and VA. ➢ Group VA has no empty orbitals. ➢ Extra electron must go into occupied orbital, creating repulsion.

ELECTRONEGATIVITY Electronegativity is defined as the measure of the tendency of an atom to attract electrons towards itself. It describes how well an atom attracts an electron. Electronegativity is determined mainly by considering two important factors. The first is the nuclear charge where higher the number of protons in an atom stronger will be the force of attraction on electrons. The second is the location or the number of electrons in the atomic shells. The Importance Of Electronegativity Values Electronegativity is mainly used for two purposes;

• To predict if an atom will form an ionic or a covalent bond.
• To predict if the resulting molecule will be polar or nonpolar. There are also some electronegativity trends that can be observed On moving from left to right in the Periodic table, electronegativity increases whereas on moving from top to bottom, the electronegativity decreases. No. Element Symbol Electrone gativity 1 Hydrogen H 2. 2 Helium He no data 3 Lithium Li 0. 4 Beryllium Be 1. 5 Boron B 2. 6 Carbon C 2. 7 Nitrogen N 3. 8 Oxygen O 3. 9 Fluorine F 3. 10 Neon Ne no data

Oxidation states of p block elements Some p block elements have lot of oxidation numbers such as chlorine(-1, 0, +1, +3, +5, +7) and sulfur(-2, 0, +4, +6). And some have limited oxidation numbers like fluorine (-1). More than one oxidation numbers of a element Some elements can show more than one oxidation states. Specially d block elements show this behavior. Examples to more than one oxidation numbers of a element

• Chlorine : - 1 , 0 , +1 , +3 , +5 , +
• Manganese : 0 , +2 , +4 , +