Periodic Properties Sreenandu Jr. Faculty for Chemistry
Periodic Properties
Properties which repeat at regular intervals periodic properties
Atomic radius
Ionic radius
Ionization enthalpy
Electron gain enthalpy
Electro negativity
valency
Atomic radius
• ‘ it is the distance from the center of the nucleus to the outermost shell of electrons’
Ionization enthalpy• ‘Minimum amount of energy required to remove the most loosely bound
electron from an isolated gaseous atom’
• Unit – kJ mol-1
Factors affecting IE
Factors affecting IE
Change Effect on IE Remark
Atomic size Increases decreases Nuclear attraction decreases
Nuclear chargePositive increases Nuclear attraction increases
negative Low IE Nuclear attraction decreases
Screening or shielding effect
No. of inner
electron increases
IE decreases
Inner electron shield outer electron from nuclear attraction
Half or completelyfilled orbitals
increases Extra stabilityEg IE of N > O
Type of subshell Order of energy to remove electrons > p > d > f
Electron gain enthalpy
‘Amount of energy released when an electron is added to an atom’
Factors affecting Change Effect on Electron gain
enthapy
Remark
Atomic size Increases low Nuclear attraction decreases
Nuclear chargePositive high Nuclear attraction increases
negative low Nuclear attraction decreases
Variation along a period left to right more negative
( Be, N and noble gases have positive)
Variation ina group less negative ( but Cl has more than F)
Electronegativity
‘It is the tendency to attract shared pair of electrons towards it’.
Depends onFactors affecting Change Effect on Electronegativity
Remark
Atomic size Increases low Nuclear attraction decreases
Nuclear chargePositive high Nuclear attraction increases
negative low Nuclear attraction decreases
Periodic trend of chemical properties
• Valency / oxidation state
• Metallic character
• Reducing character
• Oxidizing character
Valency
“the combining power of an element, especially asmeasured by the number of hydrogen atoms it candisplace or combinewith”
Or it is the number of electrons gaining or losing tomake bonds
Metallic character
• Tendency to become electropositive
• Decreases from left to right
• Increases from top to bottom
Therefore, 1st group elements will have
more metallic character( Alkali metals)
Reducing character
• They provide electrons
• Thus metal act as good reducing agents
• Reducing character decreases across the period
• It increases down the group
• Alkali metals are very good reducing agents
Oxidizing character
• They accept electrons
• Non metals are good oxidizing agents
• Oxidizing character increases across the period
• Decreases down the group
• Halogens are very good oxidizing agents