Bonding and Polarity

What is an ionic bond?

A bond formed by electrostatic attraction between oppositely charged ions

Give an example of an ionic bond.

Bond in NaCl. Sodium transfers an electron to chlorine to give Na⁺ and Cl^-

What is a covalent bond?

A shared pair of electrons

What is a nonpolar covalent bond?

A covalent bond where electrons are symmetrically distributed within the bond.

What is a polar covalent bond?

A covalent bond with an unsymmetrical electron distribution.

What is bond polarity?

Unsymmetrical distribution of electrons in a covalent bond due to differences in electronegativity.

What is electronegativity?

The intrinsic ability of an atom to attract the shared electrons in a covalent bond

How does electronegativity change across the periodic table?

Increases from left to right

How does electronegativity change going down the periodic table?

Decreases from top to bottom

Which elements have high electronegativity

Reactive nonmetals on the right-hand side of the periodic table.

Which elements have low electronegativity?

Metals on the left-hand side of the periodic table.

What difference in electronegativity defines a non-polar covalent bond?

Less than 0.5

What difference in electronegativity defines a polar covalent bond?

Between 0.5 and 2.0

What difference in electronegativity defines an ionic bond?

Greater than 2.0

What symbol is used for partial charges?

δ⁺ (partial positive) and δ⁻ (partial negative)

When does carbon become δ⁺?

When bonded to a more electronegative atom

When does carbon become δ⁻?

When bonded to a less electronegative atom

What does the crossed arrow represent?

Direction of bond polarity

What does the tail of the crossed arrow represent?

Electron-poor atom (δ⁺)

What does the head of the crossed arrow represent?

Electron-rich atom (δ⁻)

What is polarizability?

The measure of change in electron distribution around the atom to an external electrical influence

Which atoms are more polarizable?

Larger atoms with loosely held electrons

Which atoms are less polarizable?

Smaller atoms with tightly held electrons

What is the inductive effect?

Atoms’ ability to polarise a bond

Which elements show an electron-withdrawing inductive effect?

Electronegative nonmetals

Which elements donate electrons inductively?

Metals

Why is the inductive effect important?

It plays a major role in understanding chemical reactivity

When carbon bonds to N, O, F, Cl, Br, what charge does carbon have?

Partial positive (δ⁺)

When carbon bonds to metals (e.g. Mg), what charge does carbon have?

Partial negative (δ⁻)

What is dipole moment?

A net measure of molecular polarity

How is molecular dipole moment calculated?

By vector summation of all bond dipoles and lone-pair contributions

For a molecule with one bond, what equals its dipole moment?

The dipole moment of that bond

How do lone pairs affect dipole moment?

They contribute significantly due to charge separation

Why do symmetrical molecules often have zero dipole moment?

Bond polarities and lone pairs cancel out