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Chemistry

Bonding and structure

Shapes of molecules

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Practical skills

The scientific method

How to plan experiments

Improving repeatability and reproducibility

Presenting results using tables and graphs

Analysing results: anomalies and correlation

Evaluating experiments

Organic synthesis and analysis

Synthetic routes

NMR spectroscopy

Proton NMR spectroscopy

Chromatography

Amino acids, proteins and DNA

Amino acids and zwitterions

Amino acids, proteins and enzymes

DNA structure and cis-platin

Aromatic chemistry, amines and polymers

Benzene: structure and combustion

Electrophilic substitution

Friedel-Crafts reactions

Aliphatic and aromatic amines

Reactions of amines

Forming amides

Condensation polymers

Polymer disposal

Isomerism and carbonyls

Optical isomers and chirality

Aldehydes and ketones

Carboxylic acids: properties and reactions

Esters: formation, properties and uses

Acyl chlorides: formation and reactions

Transition metals

Transition metals: electron configuration and oxidation number

Complex ions: formation, shape and isomerism

Colours of inorganic ions and complexes

Ligand substitution reactions

Redox titrations

Transition metals as catalysts

Metal-aqua ions

Period 3 elements

Period 3 elements and oxides

Acids and bases

pH calculations

The ionic product of water

pH curves and indicators

Titration calculations

Buffer solutions and calculations

Electrode potentials and cells

Electrochemical cells and redox

Electrode potentials and calculations

The electrochemical series

Energy storage cells and hydrogen fuel cells

Rate equations

Measuring rates of reaction

Rate equations and the rate constant

Determining reaction orders

The initial rates method

The rate determining step

Activation energy and the Arrhenius equation

Partial pressure and gas equilibria

Le Chatelier's principle and equilibrium constants

Thermodynamics

Lattice enthalpies and Born-Haber cycles

Polarisation and the Pauling scale

Enthalpy change in solution

Entropy and calculating entropy change

Gibbs free energy change

Organic analysis

Testing for functional groups

Mass spectrometry

IR spectroscopy

Alkenes and alcohols

Alkenes: bonding and reactivity

Reactions of alkenes

Addition polymerisation

Alcohol: classification and reactions

Oxidation of alcohols

Ethanol production

Alkanes and halogenoalkanes

Alkanes and free radical substitution

Fractional distillation of crude oil

Fuels: combustion and emissions

Haloalkanes and the environment

Halogenoalkanes and their reactions

Organic chemistry - the basics

Basic concepts of organic chemistry

Organic reactions and mechanisms

Structural isomerism

Stereoisomerism

Group 2 and 7 elements

Group 2: ionisation energy and properties

Chemical properties of Group 7

Reactions with halogens

Halide ion reactions

Testing for ions

Kinetics, equilibria and redox

Collision theory and rates of reaction

Calculating the rate of reaction

Catalysts and the Maxwell-Boltzmann distribution

Reversible reactions

Le Chatelier's principle

The equilibrium constant

Calculating oxidation numbers

Oxidation, reduction and redox reactions

Energetics

Enthalpy changes and reaction profiles

Standard enthalpy changes

Calculating bond enthalpies

Hess's Law and enthalpy cycles

Bonding

Ionic bonding

Covalent bonding

Shapes of molecules

Giant covalent and metallic structures

Predicting structures and properties

Electronegativity and polarisation

Intermolecular forces: types and examples

Hydrogen bonding

Amount of substance

The mole and Avogadro's constant

Calculations involving gases

Balancing equations

Acid-base titrations

Empirical and molecular formulae

Atom economy and percentage yield

Atomic structure

The atom: history, structure and isotopes

Relative masses and mass spectrometry

Electronic structure: shells and orbitals

Ionisation energies

Ionisation energy trends

Periodicity

Explainer Video

Tutor: Aimee LeBrun

Summary

Shapes of molecules

In a nutshell

The shape of a molecule depends on the electron pair arrangement around the central atom. The number of pairs of electrons around the central atom influences the arrangement.

Electron pair repulsions

Electrons repel each other in an atom.

The amount of repulsion will depend on the type of electron pair:

Lone pair/lone pair has the largest repulsion angle
Lone pair/bonded pair has the second largest repulsion angle
Bonded pair/bonded pair has the smallest repulsion angle

The shape of a molecule will depend on the number of electron pairs as well as the type of electron pair.

Electron pair repulsion theory

You can predict the shape of a molecule using electron pairs.

procedure

1.	First, find the central atom.
2.	Work out the number of outer shell electrons in the central atom using either the periodic table or a dot and cross diagram.
3.	Use the molecular formula to find the number of electrons that are shared with the central atom.
4.	Count the the number of electrons and divide by two to find the number of electron pairs. *Tip:* Remember the charges on ions.
5.	Compare the number of electron pairs with the number of bonds to find any lone pairs. *Tip:* A double bond will count as two bonds. A triple bond will count as three bonds.
6.	Use the number of electron pairs, number of lone pairs and number of bonding centres around the central atom to find the shape of the molecule.

Shapes of molecules

There are several different shapes that molecules can adopt.

shape	electron pairs around central atom	bond angles	example
Linear	Two electrons pairs	$180\degree$	$CO_2$
Trigonal planar	Three electron pairs No lone pairs	$120\degree$	$AlCl_3$
Non-linear/bent	Three electron pairs One lone pair	$119\degree$	$SO_2$
Tetrahedral	Four electron pairs No lone pairs	$109.5\degree$	$CH_4$
Trigonal pyramidal	Four electron pairs One lone pair	$106.7\degree$	$NH_3$
Non-linear/bent	Four electron pairs Two lone pairs	$104.5\degree$	$H_2O$
Trigonal bipyramidal	Five electrons pairs No lone pairs	$90\degree$ $120\degree$	$PCl_5$
Seesaw	Five electron pairs One lone pair	$87\degree$ $102\degree$	$SF_4$
Distorted T	Five electron pairs Two lone pairs	$87.5\degree$	$ClF_3$
Octahedral	Six electron pairs No lone pairs	$90\degree$	$SeCl_6$
Square pyramidal	Six electron pairs One lone pair	$81.9\degree$ $90\degree$	$IF_5$
Square planar	Six electron pairs Two lone pairs	$90\degree$	$XeF_4$

Learn with Basics

Length:

Unit 1

Electronic configuration

Unit 2

Electronic structure: shells and orbitals

Jump Ahead

Optional

Unit 3

Shapes of molecules

Final Test

Create an account to complete the exercises

FAQs - Frequently Asked Questions

How do electrons react to each other?

Electrons repel each other in an atom.

Which relationship between electron pairs has the largest bond angle?

The lone pair/lone pair electron arrangement has the largest bond angle in a molecule.

What determines the shape of a molecule?

The shape of a molecule depends on the electron pair arrangement around the central atom. The number of pairs of electrons around the central influences the arrangement.

Home

Chemistry

Bonding and structure

Shapes of molecules

Videos

Summary

Exercises

Select Lesson

Exam Board

Select an option

Practical skills

The scientific method

How to plan experiments

Improving repeatability and reproducibility

Presenting results using tables and graphs

Analysing results: anomalies and correlation

Evaluating experiments

Organic synthesis and analysis

Synthetic routes

NMR spectroscopy

Proton NMR spectroscopy

Chromatography

Amino acids, proteins and DNA

Amino acids and zwitterions

Amino acids, proteins and enzymes

DNA structure and cis-platin

Aromatic chemistry, amines and polymers

Benzene: structure and combustion

Electrophilic substitution

Friedel-Crafts reactions

Aliphatic and aromatic amines

Reactions of amines

Forming amides

Condensation polymers

Polymer disposal

Isomerism and carbonyls

Optical isomers and chirality

Aldehydes and ketones

Carboxylic acids: properties and reactions

Esters: formation, properties and uses

Acyl chlorides: formation and reactions

Transition metals

Transition metals: electron configuration and oxidation number

Complex ions: formation, shape and isomerism

Colours of inorganic ions and complexes

Ligand substitution reactions

Redox titrations

Transition metals as catalysts

Metal-aqua ions

Period 3 elements

Period 3 elements and oxides

Acids and bases

pH calculations

The ionic product of water

pH curves and indicators

Titration calculations

Buffer solutions and calculations

Electrode potentials and cells

Electrochemical cells and redox

Electrode potentials and calculations

The electrochemical series

Energy storage cells and hydrogen fuel cells

Rate equations

Measuring rates of reaction

Rate equations and the rate constant

Determining reaction orders

The initial rates method

The rate determining step

Activation energy and the Arrhenius equation

Partial pressure and gas equilibria

Le Chatelier's principle and equilibrium constants

Thermodynamics

Lattice enthalpies and Born-Haber cycles

Polarisation and the Pauling scale

Enthalpy change in solution

Entropy and calculating entropy change

Gibbs free energy change

Organic analysis

Testing for functional groups

Mass spectrometry

IR spectroscopy

Alkenes and alcohols

Alkenes: bonding and reactivity

Reactions of alkenes

Addition polymerisation

Alcohol: classification and reactions

Oxidation of alcohols

Ethanol production

Alkanes and halogenoalkanes

Alkanes and free radical substitution

Fractional distillation of crude oil

Fuels: combustion and emissions

Haloalkanes and the environment

Halogenoalkanes and their reactions

Organic chemistry - the basics

Basic concepts of organic chemistry

Organic reactions and mechanisms

Structural isomerism

Stereoisomerism

Group 2 and 7 elements

Group 2: ionisation energy and properties

Chemical properties of Group 7

Reactions with halogens

Halide ion reactions

Testing for ions

Kinetics, equilibria and redox

Collision theory and rates of reaction

Calculating the rate of reaction

Catalysts and the Maxwell-Boltzmann distribution

Reversible reactions

Le Chatelier's principle

The equilibrium constant

Calculating oxidation numbers

Oxidation, reduction and redox reactions

Energetics

Enthalpy changes and reaction profiles

Standard enthalpy changes

Calculating bond enthalpies

Hess's Law and enthalpy cycles

Bonding

Ionic bonding

Covalent bonding

Shapes of molecules

Giant covalent and metallic structures

Predicting structures and properties

Electronegativity and polarisation

Intermolecular forces: types and examples

Hydrogen bonding

Amount of substance

The mole and Avogadro's constant

Calculations involving gases

Balancing equations

Acid-base titrations

Empirical and molecular formulae

Atom economy and percentage yield

Atomic structure

The atom: history, structure and isotopes

Relative masses and mass spectrometry

Electronic structure: shells and orbitals

Ionisation energies

Ionisation energy trends

Periodicity

Explainer Video

Tutor: Aimee LeBrun

Summary

Shapes of molecules

In a nutshell

The shape of a molecule depends on the electron pair arrangement around the central atom. The number of pairs of electrons around the central atom influences the arrangement.

Electron pair repulsions

Electrons repel each other in an atom.

The amount of repulsion will depend on the type of electron pair:

Lone pair/lone pair has the largest repulsion angle
Lone pair/bonded pair has the second largest repulsion angle
Bonded pair/bonded pair has the smallest repulsion angle

The shape of a molecule will depend on the number of electron pairs as well as the type of electron pair.

Electron pair repulsion theory

You can predict the shape of a molecule using electron pairs.

procedure

1.	First, find the central atom.
2.	Work out the number of outer shell electrons in the central atom using either the periodic table or a dot and cross diagram.
3.	Use the molecular formula to find the number of electrons that are shared with the central atom.
4.	Count the the number of electrons and divide by two to find the number of electron pairs. *Tip:* Remember the charges on ions.
5.	Compare the number of electron pairs with the number of bonds to find any lone pairs. *Tip:* A double bond will count as two bonds. A triple bond will count as three bonds.
6.	Use the number of electron pairs, number of lone pairs and number of bonding centres around the central atom to find the shape of the molecule.

Shapes of molecules

There are several different shapes that molecules can adopt.

shape	electron pairs around central atom	bond angles	example
Linear	Two electrons pairs	$180\degree$	$CO_2$
Trigonal planar	Three electron pairs No lone pairs	$120\degree$	$AlCl_3$
Non-linear/bent	Three electron pairs One lone pair	$119\degree$	$SO_2$
Tetrahedral	Four electron pairs No lone pairs	$109.5\degree$	$CH_4$
Trigonal pyramidal	Four electron pairs One lone pair	$106.7\degree$	$NH_3$
Non-linear/bent	Four electron pairs Two lone pairs	$104.5\degree$	$H_2O$
Trigonal bipyramidal	Five electrons pairs No lone pairs	$90\degree$ $120\degree$	$PCl_5$
Seesaw	Five electron pairs One lone pair	$87\degree$ $102\degree$	$SF_4$
Distorted T	Five electron pairs Two lone pairs	$87.5\degree$	$ClF_3$
Octahedral	Six electron pairs No lone pairs	$90\degree$	$SeCl_6$
Square pyramidal	Six electron pairs One lone pair	$81.9\degree$ $90\degree$	$IF_5$
Square planar	Six electron pairs Two lone pairs	$90\degree$	$XeF_4$

Learn with Basics

Length:

Unit 1

Electronic configuration

Unit 2

Electronic structure: shells and orbitals

Jump Ahead

Optional

Unit 3

Shapes of molecules

Final Test

Create an account to complete the exercises

FAQs - Frequently Asked Questions

How do electrons react to each other?

Electrons repel each other in an atom.

Which relationship between electron pairs has the largest bond angle?

The lone pair/lone pair electron arrangement has the largest bond angle in a molecule.

What determines the shape of a molecule?

The shape of a molecule depends on the electron pair arrangement around the central atom. The number of pairs of electrons around the central influences the arrangement.

Shapes of molecules

Videos

Summary

Exercises

Select Lesson

Exam Board

Practical skills

Organic synthesis and analysis

Amino acids, proteins and DNA

Aromatic chemistry, amines and polymers

Isomerism and carbonyls

Transition metals

Period 3 elements

Acids and bases

Electrode potentials and cells

Rate equations

Thermodynamics

Organic analysis

Alkenes and alcohols

Alkanes and halogenoalkanes

Organic chemistry - the basics

Group 2 and 7 elements

Kinetics, equilibria and redox

Energetics

Bonding

Amount of substance

Atomic structure

Explainer Video

Summary

Shapes of molecules

In a nutshell

Electron pair repulsions

Electron pair repulsion theory

procedure

Shapes of molecules

​​shape

electron pairs

around central atom

bond angles

example

Learn with Basics

Unit 1

Electronic configuration

Unit 2

Electronic structure: shells and orbitals

Jump Ahead

Unit 3

Shapes of molecules

Final Test

FAQs - Frequently Asked Questions

How do electrons react to each other?

Which relationship between electron pairs has the largest bond angle?

What determines the shape of a molecule?

Shapes of molecules

Videos

Summary

Exercises

Select Lesson

Exam Board

Practical skills

Organic synthesis and analysis

Amino acids, proteins and DNA

Aromatic chemistry, amines and polymers

Isomerism and carbonyls

Transition metals

Period 3 elements

Acids and bases

Electrode potentials and cells

Rate equations

Thermodynamics

Organic analysis

Alkenes and alcohols

Alkanes and halogenoalkanes

Organic chemistry - the basics

Group 2 and 7 elements

Kinetics, equilibria and redox

Energetics

Bonding

Amount of substance

Atomic structure

shape

shape