biology bonds and polarity

How are ions formed in ionic bonding ?

• Metals lose electrons → cations (+)

• Non-metals gain electrons → anions (−)

• Electrostatic attraction forms the bond

What is an ionic bond?

Strong electrostatic attraction between oppositely charged ions

What structure do ionic compounds form?

• Giant ionic lattice

• Regular repeating structure of ions

Why do ionic compounds have high melting points?

Strong electrostatic forces between ions require lots of energy to break

What is a covalent bond?

Sharing of electron pairs between non-metal atoms

Why do atoms form covalent bonds?

To achieve full outer electron shells (stability)

What types of covalent substances exist?

• Simple molecular (e.g. H₂O, CO₂)

• Giant covalent (e.g. diamond, graphite)

Why do simple covalent molecules have low melting points?

Weak intermolecular forces between molecules

Why don’t covalent substances conduct electricity?

No free ions or delocalised electrons (except graphite)

What is a dipole?

A separation of charge in a bond causing δ+ and δ− ends.

Why does a dipole form in a covalent bond?

Because atoms have different electronegativities, so electrons are shared unequally.

What makes a bond polar?

Unequal sharing of electrons due to electronegativity difference.

What is a polar molecule?

A molecule with a net dipole (overall uneven charge distribution).

When is a molecule non-polar even if it has polar bonds?

When the dipoles cancel out due to symmetrical shape.

What does electronegativity mean?

A: The ability of an atom to attract electrons in a covalent bond.

Why is CO₂ non-polar?

It is linear so bond dipoles cancel.

What is the key rule for polarity and shape?

Symmetrical = non-polar, asymmetrical = polar

What is the key rule for polarity and shape?

Symmetrical = non-polar, asymmetrical = polar