Electronegativity & Bonding – CIE AS Chemistry

Question-and-Answer flashcards covering definition, factors, periodic trends, and bonding implications of electronegativity.

What is electronegativity?

The ability of an atom to attract a pair of electrons towards itself in a covalent bond.

Which scale assigns numerical values to electronegativity?

The Pauling scale.

Which element is the most electronegative and what is its Pauling value?

Fluorine, 4.0

How does electronegativity generally change across a period?

It increases across a period.

How does electronegativity generally change down a group?

It decreases down a group.

State three main factors that affect electronegativity.

Nuclear charge, atomic radius, and shielding.

How does increasing nuclear charge affect electronegativity (assuming shielding is constant)?

It increases electronegativity because the nucleus attracts bonding electrons more strongly.

How does atomic radius influence electronegativity?

A larger atomic radius decreases electronegativity because bonding electrons are farther from the nucleus.

What effect does greater electron shielding have on electronegativity?

Greater shielding decreases electronegativity by reducing the nucleus’ attraction for bonding electrons.

Why is sodium more electronegative than caesium?

Sodium has fewer filled inner shells, so there is less shielding and its outer electrons feel a stronger nuclear attraction.

Describe the overall trend of electronegativity on the periodic table.

It increases toward the top right corner of the periodic table.

Why does electronegativity increase across a period even though nuclear charge increases down a group as well?

Across a period, shielding is roughly constant, so the increased nuclear charge more effectively attracts bonding electrons, shrinking atomic radius and raising electronegativity.

In a C–F bond, toward which atom is electron density drawn and why?

Toward fluorine because it is more electronegative than carbon.

What type of bond forms when the electronegativity difference is less than 1.0?

A non-polar covalent bond.

What type of bond forms when the electronegativity difference is between 1.0 and 2.0?

A polar covalent bond.

What type of bond forms when the electronegativity difference is greater than 2.0?

An ionic bond.

Why are H₂, O₂, and Cl₂ molecules non-polar?

Because the bonded atoms have identical electronegativity values, leading to equal sharing of electrons.

Define a polar covalent bond.

A covalent bond in which electrons are shared unequally, creating partial positive (δ⁺) and partial negative (δ⁻) charges.

What charge (δ⁺ or δ⁻) does the more electronegative atom carry in a polar bond?

A partial negative charge (δ⁻).

What happens to electrons when the electronegativity difference between two atoms is very large?

The less electronegative atom transfers its electron(s) to the more electronegative atom, forming ions and an ionic bond.

Define cation and anion in terms of electron transfer.

A cation is a positively charged species that has lost electron(s); an anion is a negatively charged species that has gained electron(s).

Summarize the relationship between nuclear charge, shielding, atomic radius, and electronegativity down a group.

Down a group: nuclear charge increases, shielding increases, atomic radius increases, so overall electronegativity decreases.