Periodicity of properties
The properties both Chemical and physical which gradually changes both down the group and across the periods are called periodic properties and this phenomena is called periodicity. It depends on following factors and is as follow- Atomic size
- Ionization energy
- Electron affinity
- Shielding effects
- Electronegativity
Atomic Size
Half of the distance between the nuclei of two bonded atoms is called atomic size.
Factors effecting the atomic size
There are three main factors which effects the atomic size & is as follow
Energy level: Higher the energy level greater will be the atomic size
Nuclear charge: Higher the nuclear charge lesser will be the atomic size.
Shielding effects: Greater the shielding effects higher will be the atomic size.
Variation within a group
The atomic size of an atom is increases continuously down the group in periodic table due to the addition of electrons in the new shells and the force of attraction between the nucleus and outermost shell decreases. Such as Li < Na < K < Rb < Cs etc.
Variation across the periods
The atomic size of an atom decreases continuously across the periods in periodic table due to addition of electrons in the same shells. The force of attraction between the nucleus of an atom and outermost shell increases. Such as Li > Na > Be > B > C > N > O > F etc.
Ionization energy or Ionization potential energy
The amount of energy required to remove electron completely from its one atom to make it positive ion in gaseous state is called ionization energy.
If the energy required removing one electron from the outermost shell of an atom is called first ionization energy and so on. The energy required to remove electron is 496KJ/mole.
E (g) E + e– (where E is any element)
Na (g) Na+ + e– (ΔH = +496KJ/mole)
Factors effecting the Ionization energy
The following factors are
Energy level: Higher the energy level lesser will be the energy level.
Nuclear charge: Higher the nuclear charge greater will be the energy level.
Shielding effects: Greater the shielding effects lesser will be the energy level.
Variation within a group
Ionization energy decreases down the group due to increases atomic size and also decrease in the force of attraction between the nucleus and outermost shell electrons. Such as Li > Na > K > Rb > Cs etc.
Variation across the periods
Ionization energy increases along the period due to increase in the force of attraction between the nucleus and outermost shell of an atom and also decrease in the atomic size of an atom. Such as Li > Be > B > C > N > O > F > Ne etc.
Electron affinity
It word affinity means attraction thus it is defined as “The amount of energy released when an electron is added up in the outermost shell of an isolated gaseous atom to make it negative ion is called electron affinity.”The energy required to remove electron and make it negative ion is – 328 KJ/mole.
Such as F + e – F – (ΔH = f –328 KJ/mole)
Factors effecting the Electron affinity
The following factors are as follow
Variation within a group
The electron affinity decreases down the group due to increases atomic size and also decrease in the force of attraction between the nucleus and outermost shell electrons. Such as Li > Na > K > Rb > Cs etc.
Variation across the periods
The electron affinity increases along the period due to increase in the force of attraction between the nucleus and outermost shell of an atom and also decrease in the atomic size of an atom. Such as Li > Be > B > C > N > O > F > Ne etc.
Shielding effects
The effects of electrons (in filled shells) between the nucleus and outermost shell of an atom is called shielding effects.
Factors effecting the Shielding effects
The following factors are as follow
Variation within a group
The shielding effects is increasing down the group because both the atomic number, shells and size of an atom is increasing. Such as Li < Na < K < Rb < Cs etc.
Variation across the periods
The shielding effects across the period remain unchanged or same. There is no change in shielding effects of an atom across the period.
Electronegativity
The ability of an atom to attract the shared paired of electrons towards itself in a molecule is called Electronegativity.
Calculation of Electronegativity
The Electronegativity was first calculated by Linus Carl Pauling.
Linus Pauling: Linus Carl Pauling was an American chemist, biochemist, peace activist, author, and educator. He was one of the most influential chemists in history and ranks among the most important scientists of the 20th century.
Born: He was born in February 28, 1901, Portland, Oregon, United States.
Died: He died on August 19, 1994, Big Sur, California, United States
Awards: He received Nobel Peace Prize for working in Chemistry.
Education: He got his education in Washington High School, Oregon State University, California Institute of Technology.
Factors effecting the Electronegativity
The following factors are as follow
Variation within a group
Electronegativity decreases down the group due to increases atomic size and also decrease in the force of attraction between the nucleus and outermost shell electrons. Such as Li > Na > K > Rb > Cs etc.
Variation across the periods
Electronegativity increases along the period due to increase in the force of attraction between the nucleus and outermost shell of an atom and also decrease in the atomic size of an atom. Such as Li > Be > B > C > N > O > F > Ne etc.
The usage of Electronegativity
It was calculated by an American scientist Linus Carl Pauling for the first time and it usage are as follow
- Electronegativity is used to predict the reactivity and bond type of an atom. The elements having highest value of electronegativity are more reactive. Such as Fluorine (F) with highest electronegativity value of 4.0 is the most reactive element of the periodic table.
- Electronegativity is used to calculate the bond type of an atom and is as follow
- If electronegativity difference is 1.7 then the bond in an atom is 50% covalent and 50% ionic.
- If the electronegativity difference is greater than 1.7 then the bond in an atom is ionic.
- If the electronegativity difference is less than 1.7 then the bond in an atom is covalent.
- If the electronegativity difference is less than 0.5 then the bond in an atom is non-polar.
- If the electronegativity difference is greater than 0.5 but less than 1.7 then the bond in an atom is polar covalent.
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