• Electronegativity?is the ability of an atom to attract a pair of electrons towards itself in a covalent bond
• This phenomenon arises from the?positive?nucleus’s ability to attract the?negatively?charged electrons, in the outer shells, towards itself
• The?Pauling?scale?is used to assign a value of electronegativity for each atom

First three rows of the periodic table showing electronegativity values

• Fluorine is the most electronegative atom on the Periodic Table, with a value of 4.0 on the?Pauling Scale
• It is best at attracting electron density towards itself when covalently bonded to another atom

Electron distribution in the C-F bond of fluoromethane

Nuclear charge

• Attraction?exists between the positively charged?protons?in the nucleus and negatively charged?electrons?found in the energy levels of an atom
• An?increase?in the number of?protons?leads to an?increase?in?nuclear?attraction?for the electrons in the outer shells
• Therefore, an?increased nuclear charge?results in an?increased electronegativity

As the nuclear charge increases, the electronegativity of an element increases as well

Atomic radius

• The?atomic?radius?is the distance between the nucleus and electrons in the?outermost shell
• Electrons?closer?to the nucleus are more?strongly?attracted towards its positive?nucleus
• Those electrons?further?away?from the nucleus are?less strongly?attracted towards the?nucleus
• Therefore, an?increased atomic radius?results in a?decreased electronegativity

As the atomic radius increases, the nucleus has less of an attraction for the bonding electrons causing atom A to have a higher electronegativity than atom B

• Electronegativity?varies across periods and down the groups of the periodic table

Down a group

• There is a?decrease?in?electronegativity?going down the group
• The?nuclear charge increases?as more protons are being added to the nucleus
• However, each element has an extra filled electron shell, which increases?shielding
• The addition of the extra shells increases the distance between the nucleus and the outer electrons resulting in?larger?atomic radii
• Overall, there is decrease in attraction between the nucleus and outer bonding electrons
• We say the?effective nuclear charge?has decreased down the group

Electronegativity decreases going down the groups of the periodic table

Across a period

• Electronegativity?increases?across a period
• The?nuclear charge increases?with the addition of protons to the nucleus
• Shielding?remains the?same?across the period as no new shells are being added to the atoms
• The nucleus has an increasingly strong attraction for the bonding pair of electrons of atoms across the period
• This results in?smaller atomic radii

Electronegativity increases going across the periods of the periodic table

Trends down a Group & across a Period Table