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Properties Of Elements In Periods And Groups

Variance properties among elements of periods and groups Assignment / Homework Help
How do properties vary among elements of periods and groups?

In the earlier sessions we have seen how elements are classified into groups and periods. We also stated the importance of periodic table. Let us recall the importance of periodic table.

Importance of periodic table: it serves as an easy way to predict the behavior of the elements as we move through groups or periods.

Let us discuss how these various properties such as atomic radius, ionization energy, electron affinity and electronegativity vary across the elements of groups and periods.
  • Atomic radius: This is a measure of the radius of the atom from the center of the nucleus to the outer most orbital.

    Atomic radius reduces as we move from left to right in a period. This is mainly due to inclusion of excessive protons which draw the electrons very close to the nucleus.

    In case of groups, atomic radius increases from top to bottom. This is due to increase in the number of orbitals. With the increase in the number of orbitals, the valence electrons remain far away from the nucleus. Hence, nucleus cannot exert more attraction on the electrons, increasing the atomic radius.
  • Ionization Energy: ionization energy refers to the energy required to remove an electron from the valence shell. Ionization energy and the atomic radius are inversely related. Greater the atomic radius lesser will be ionization energy and lesser the atomic radius, greater will the ionization energy.

    With the increase in the atomic radius, the effect of nucleus on valence electrons decreases. Hence, they can be removed very easily. This trend is observed in case of groups i.e. ionization energy decreases as move down the group.

    In case of periods, atomic radius decreases as we towards right. Hence, protons exert more force on the electrons making it difficult to remove an electron. Thus, ionization increases from left to right in a period.
  • Electronegativity: it refers to the ability of an atom to attract electron so as to form an ionic bond.

    Electronegativity decreases as we move top to bottom in a group due to lesser effect of nucleus on the valence shells.

    Electronegativity increases as we move left to right in a period due to increased effect of nucleus on the valence electrons.
  • Electron affinity: electron affinity refers to the change in energy when an electron is added to an atom to form a negatively charged ion.

    Electron affinity increases as we move from left to right in a period. This is due to stronger attraction of the protons of the nucleus. Thus, metals are said to have less electron affinity compared to non-metals other than noble gases.

    Electron affinity decreases as move down the group. This is due to lesser effect of nucleus on the valence shell to attract the electrons.
As can be seen from the above discussion, it is very easy to describe the variation of properties among closely related elements with the help of periodic table.

Solved problems
  • Periodic table helps to predict which of the following properties of elements
    • atomic radius
    • ionization energy
    • a and b
    • atomic number
    Answer: c
  • Ionization energy __________ as we move down the group
    • increases
    • decreases
    • cannot be predicted
    • none
    Answer: b
  • Electron affinity __________ as move towards right of a period
    • Increases
    • Decreases
    • Cannot be predicted
    • None
    Answer: a
  • Energy required to remove an electron is termed as
    • Electron affinity
    • Ionization energy
    • Electronegativity
    • A or b
    Answer: b

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