State the order of repulsion strength between the three kinds of electron pair interaction.

Lone pair to lone pair repulsion is strongest, lone pair to bonding pair repulsion is intermediate and bonding pair to bonding pair repulsion is weakest.

Explain why a lone pair repels more strongly than a bonding pair.

A lone pair is held by only one nucleus so its charge cloud lies closer to the central atom and spreads more widely, exerting a greater repulsion on neighbouring pairs.

How is the total number of electron pairs around a central atom worked out for a neutral molecule?

The outer electrons of the central atom are added to one electron from each atom bonded to it, and the total is divided by two.

CCEA AS-Level Chemistry 1110

Formulae, Equations and Amounts of Substance

Topic overview Ionic charges and the formulae of compound ions Writing and balancing full and ionic equations The mole, molar mass and Avogadro's constant Reacting masses and reactants in excess Hydrated salts and water of crystallisation

Atomic Structure

Topic overview Protons, neutrons and electrons Atomic number, mass number and the composition of ions Isotopes and relative isotopic mass Relative atomic, molecular and formula mass Mass spectra and relative atomic mass calculations Mass spectra of diatomic elements Electronic configuration and the building up principle Orbitals, electron spin and orbital shapes The s-, p-, d- and f-blocks of the Periodic Table Ionisation energies and their equations Trends in ionisation energy as evidence for shells and subshells

Bonding

Topic overview Ionic bonding and electron transfer Dot and cross diagrams for ionic compounds Covalent bonding and the shared pair Lone pairs and co-ordinate bonding Dot and cross diagrams for covalent molecules and ions The octet rule and its limitations Electronegativity and bond polarity Metallic bonding

Intermolecular Forces and Structure

Topic overview Van der Waals' forces and permanent dipole-dipole attractions Hydrogen bonding, boiling points and solubility Giant ionic, metallic and giant covalent structures Molecular covalent structures and melting points across Period 3

Shapes of Molecules and Ions

Topic overview Electron pair repulsion and VSEPR theory Shapes and bond angles up to four electron pairs Shapes with five and six electron pairs Polar bonds and polar molecules

Redox

Topic overview Rules for assigning oxidation states Oxidation states in peroxides, hydrides and Roman numeral names Oxidation, reduction and electron transfer Oxidising agents, reducing agents and disproportionation Half-equations and combining them into redox equations

The Halogens

Topic overview Colours, physical states and solubility of the halogens Chlorine with water and the treatment of drinking water Disproportionation of the halogens with sodium hydroxide Oxidising ability and displacement reactions Solid halides with concentrated sulfuric and phosphoric acid

Acid-Base Titrations

Topic overview Strong and weak acids and bases Concentration, molarity and units Preparing a standard solution Titration technique, mean titres and uncertainty Indicators and the end point Titration calculations

Qualitative Tests

Topic overview Chemical tests for the gases Flame tests for metal cations Testing for the ammonium ion, sulfate and carbonate Distinguishing the halides, and the starch test for iodine

Formulae and Amounts of a Substance

Topic overview Empirical and molecular formulae Calculating formulae from composition data Molar gas volume and reacting gas volumes Percentage yield Atom economy

Nomenclature and Isomerism in Organic Chemistry

Topic overview Homologous series and functional groups IUPAC rules for naming organic compounds Structural, displayed and skeletal formulae Structural isomerism Geometrical isomerism and E–Z notation

Alkanes

Topic overview Alkanes as saturated hydrocarbons Boiling points of alkanes and van der Waals' forces Boiling points of branched isomers Complete and incomplete combustion of alkanes Pollutants from alkane fuels and the atmosphere Catalytic converters Radicals, homolytic fission and heterolytic fission Free radical substitution of alkanes

Alkenes

Topic overview Unsaturated hydrocarbons and the bromine water test Sigma and pi bonds in the carbon–carbon double bond Electron density at C=C, reactivity and catalytic hydrogenation Addition of chlorine and bromine to alkenes Addition of hydrogen chloride and hydrogen bromide Electrophiles, heterolytic fission and the addition mechanism Carbocation stability and Markovnikov addition Addition polymerisation of alkenes

Halogenoalkanes

Topic overview Classification and boiling points of halogenoalkanes Laboratory preparation of a halogenoalkane from an alcohol Nucleophiles and hydrolysis with aqueous alkali Reactions with ammonia and with potassium cyanide Relative rates of hydrolysis and carbon–halogen bond enthalpy Elimination using ethanolic potassium hydroxide CFCs and the ozone layer

Alcohols

Topic overview Hydrogen bonding, boiling point and solubility of alcohols Classifying alcohols and preparing them from halogenoalkanes Combustion of alcohols and their use as fuels Reactions with sodium, hydrogen bromide and phosphorus pentachloride Oxidation with acidified potassium dichromate(VI)

Infrared Spectroscopy

Topic overview Molecular vibrations and the absorption of infrared radiation Characteristic absorptions and the wavenumber scale Identifying functional groups from infrared spectra Distinguishing compounds and following reactions by infrared

Energetics

Topic overview Exothermic and endothermic changes Standard conditions and the standard enthalpy change Enthalpy level diagrams Standard enthalpies of combustion and formation Standard enthalpy of neutralisation Measuring enthalpy changes by experiment Enthalpy calculations using q = mcΔT Hess's Law and enthalpy cycles Indirect enthalpy calculations using Hess's Law Average bond enthalpies and their limitations

Kinetics

Topic overview Reaction rate and the factors that change it Collision theory and activation energy The Maxwell–Boltzmann distribution of molecular energies Catalysts and the activation energy barrier

Equilibrium

Topic overview Reversible reactions and dynamic equilibrium Changing conditions and the position of equilibrium The equilibrium constant Kc and its units The magnitude of Kc and the extent of reaction Industrial processes and compromise conditions

Group II Elements and Their Compounds

Topic overview s-block character and electronic configuration Trends in atomic radius and first ionisation energy Reactions of the elements with oxygen, water and dilute acids The oxides and their reactions with water and dilute acids Thermal stability of the carbonates and hydroxides Uses of magnesium oxide, calcium carbonate and lime Solubility trends and solubility curves

Shapes of Molecules and Ions

4 subtopics
12 things to know
Unit AS 1

What Shapes of Molecules and Ions covers

Shapes of Molecules and Ions is examined in Unit AS 1, Basic Concepts in Physical and Inorganic Chemistry, and drawn on again in Unit AS 3, Basic Practical Chemistry. It covers electron pair repulsion and VSEPR theory, shapes and bond angles up to four electron pairs, shapes with five and six electron pairs and polar bonds and polar molecules.

Where it is assessed

Unit AS 1

Basic Concepts in Physical and Inorganic Chemistry, and again in Unit AS 3, Basic Practical Chemistry.

Check the CCEA specification ↗

The 4 subtopics

Each one has its own page. CCEA AS Chemistry students sit this topic in the first year.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Explain why the bond angle in ammonia is 107° rather than 109.5°.

Key term

Predict the shape of the ICl₄⁻ ion.

Key term

What determines the shape of a simple molecule or ion?

Key term

Distinguish between a polar bond and a polar molecule.

Key term

What do the initials VSEPR stand for?

Key term

State the shape and bond angle of a molecule with two bonding pairs and no lone pairs on the central atom.

Key term

State the shape and bond angle of sulfur hexafluoride.

Key term

Explain why carbon dioxide has polar bonds but is a non-polar molecule.

Key term

Why do electron pairs around a central atom repel one another?

Key term

Give the shape of beryllium chloride, BeCl₂, in the gaseous state.

Key term

Why can sulfur form six bonds while oxygen cannot?

Key term

Explain why water is a polar molecule.

Take Shapes of Molecules and Ions further

The same content, four other ways.

Questions from this topic

Each one with the model answer underneath.

1
What determines the shape of a simple molecule or ion?
Model answer
The shape is determined by the repulsion between the pairs of electrons in the outer shell of the central atom, which arrange themselves as far apart as possible.
2
What do the initials VSEPR stand for?
Model answer
The initials stand for valence shell electron pair repulsion.
3
Why do electron pairs around a central atom repel one another?
Model answer
Each pair is a region of negative charge, and like charges repel, so the pairs move apart until the repulsions are balanced.
4
State the order of repulsion strength between the three kinds of electron pair interaction.
Model answer
Lone pair to lone pair repulsion is strongest, lone pair to bonding pair repulsion is intermediate and bonding pair to bonding pair repulsion is weakest.
5
Explain why a lone pair repels more strongly than a bonding pair.
Model answer
A lone pair is held by only one nucleus so its charge cloud lies closer to the central atom and spreads more widely, exerting a greater repulsion on neighbouring pairs.
6
How is the total number of electron pairs around a central atom worked out for a neutral molecule?
Model answer
The outer electrons of the central atom are added to one electron from each atom bonded to it, and the total is divided by two.

See the rest and revise

What is inside Levo

Six ways to work the same material.

1Closed book

2Open book

3Closed book

The 3-step method, run for you

Answer cold, learn it, then prove it stuck. Levo tracks the jump between your first attempt and your last.

Formulae, Equations and Amounts of Substance

Atomic Structure

Bonding

Intermolecular Forces and Structure

Cram a whole paper in one sitting

Sort every topic into what you know and what you do not, then drill only the weak ones.

Yellow to .

brownbluegreen

Blank Blitz makes facts automatic

Rapid timed gap-fills on the terms and numbers you need to recall without thinking.

AThe reactants total 159.6 + 84.0 = 243.6.

BThe two moles of iron have a mass of 111.6.

CThe atom economy is 45.8%.

Build It gets the exam shape right

Assemble a full-mark answer from its marking points, in the order an examiner wants them.

There are 1000 cm³ in one dm³.

TrueFalse

Test It catches misconceptions

Spot the fault in a statement. The traps are the mistakes students actually make.

721941163128510

Brain Breaks between sessions

Short focus games to reset attention, so the next set lands better than the last.

Shapes of Molecules and Ions revision questions

Is Shapes of Molecules and Ions examined at AS in CCEA Chemistry?: Yes. It sits in Unit AS 1, which you take in the first year, so it is on the AS paper as well as counting towards the full A level.
What does Shapes of Molecules and Ions cover in CCEA AS-Level Chemistry?: 4 subtopics: electron pair repulsion and vsepr theory, shapes and bond angles up to four electron pairs, shapes with five and six electron pairs and polar bonds and polar molecules. Each one has its own page with questions and model answers.
How is Shapes of Molecules and Ions organised?: By the CCEA 1110 specification, subtopic by subtopic, so it matches the order you are taught it in.

Every question in Shapes of Molecules and Ions, on a schedule.

Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.

Start revising, £5 a month See how the method works

Or £46 a year, about £3.83 a month. Cancel anytime.