Structure and Bonding

What does a Lewis structure show?

Valence electrons and bonding using dots and lines.

What are valence electrons?

Electrons in the outermost shell that participate in bonding.

What rule do atoms (except H) try to satisfy in Lewis structures?

The octet rule.

What rule does hydrogen follow?

The duet rule (2 electrons).

What is a bonding pair?

A shared pair of electrons forming a covalent bond.

What is a lone pair?

A non‑bonded pair of electrons on an atom.

What is a functional group?

A specific atom or group that gives characteristic reactivity.

What is an R‑group?

A variable substituent representing “the rest of the molecule”.

What is a skeletal formula?

A simplified structure showing only bonds and heteroatoms.

What does the “kernel” represent in Lewis structures?

The nucleus plus non‑valence electrons.

What is a single bond?

A bond formed by sharing one pair of electrons.

What is a double bond?

A bond formed by sharing two pairs of electrons.

What is a triple bond?

A bond formed by sharing three pairs of electrons.

Why are lone pairs often omitted in skeletal drawings?

Chemists assume they are present unless needed for mechanisms.

What does each line end or vertex represent in a skeletal formula?

A carbon atom.

Why are hydrogens on carbon usually omitted?

Their number is implied by carbon’s valency.

How do you calculate formal charge?

A – (non‑bonding electrons + ½ bonding electrons).

What is a partial charge?

A small charge caused by unequal electron sharing.

What causes bond polarity?

Differences in electronegativity between bonded atoms.

What is electronegativity?

An atom’s ability to attract electrons in a bond.

What is a polar covalent bond?

A bond with unequal electron sharing.

What is resonance?

Multiple valid Lewis structures describing electron delocalisation.

What is a resonance hybrid?

The true structure combining all resonance contributors.

What does a curly arrow show?

Movement of electrons.

Where must a curly arrow start?

An electron‑rich site (lone pair

Where must a curly arrow point?

An electron‑deficient site or a place that can accept electrons.

What are the three types of electron movement in resonance?

Bond → lone pair; lone pair → bond; bond → new bond.

What is an alcohol?

A molecule containing an –OH group.

What is an amine?

A molecule containing nitrogen (–NH₂

What is a carboxylic acid?

A molecule containing –COOH.

What is an ester?

A molecule containing –COOR.

What is an amide?

A molecule containing –CONH₂ / –CONHR / –CONR₂.

What is an ether?

A molecule containing R–O–R.

What is a phenyl group?

A benzene ring attached as a substituent.

What is a thiol?

A molecule containing –SH.

What is an aldehyde?

A molecule containing –CHO.

What is a ketone?

A molecule containing a C=O between two carbons.

What is a nitrile?

A molecule containing –C≡N.

Why are functional groups important in drug molecules?

They determine reactivity

What is sp³ hybridisation?

Four sigma bonds; tetrahedral; 109.5°.

What is sp² hybridisation?

Three sigma + one pi bond; trigonal planar; 120°.

What is sp hybridisation?

Two sigma + two pi bonds; linear; 180°.

What is a sigma (σ) bond?

A bond formed by head‑on orbital overlap.

What is a pi (π) bond?

A bond formed by sideways overlap of p orbitals.

Why are all C–C bonds in benzene the same length?

Delocalised π electrons create equal partial double bonds.

Why does hybridisation matter in drug design?

It determines 3D shape and receptor binding.

What is an ionic bond?

Electrostatic attraction between oppositely charged ions.

What is a polar covalent bond?

Unequal electron sharing creating partial charges.

What is a dipole moment?

A measure of bond polarity.

What is a hydrogen bond donor (HBD)?

An atom bonded to H that donates the hydrogen (e.g.

What is a hydrogen bond acceptor (HBA)?

An atom with a lone pair that accepts the H‑bond (e.g.

How strong is a hydrogen bond?

Typically –4 to –10 kJ mol⁻¹.

What is an ion–ion interaction?

Strong electrostatic attraction between charged species.

What is an ion–dipole interaction?

Attraction between a charged species and a polar molecule.

What is a dipole–dipole interaction?

Attraction between two polar molecules.

What is an intramolecular hydrogen bond?

A hydrogen bond formed within the same molecule.

What causes partial charges in molecules?

Differences in electronegativity.