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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

Modern analytical techniques II

NMR spectroscopy

Proton NMR spectroscopy

Chromatography

Combining analytical techniques

Organic chemistry III

Benzene: structure and combustion

Electrophilic substitution

Friedel-Crafts reactions

Phenols

Aliphatic and aromatic amines

Reactions of amines

Forming amides

Condensation polymers

Amino acids and zwitterions

Grignard reagents

Synthetic routes

Practical techniques

Percentage composition and combustion analysis

Organic chemistry II

Optical isomers and chirality

Aldehydes and ketones

Carboxylic acids: properties and reactions

Esters: formation, properties and uses

Acyl chlorides: formation and reactions

Kinetics II

Measuring rates of reaction

Determining reaction orders

The initial rates method

Rate equations and the rate constant

The rate determining step

Halogenoalkane reaction mechanisms

Activation energy and the Arrhenius equation

Transition metals

Transition metals: electron configuration and oxidation number

Complex ions: formation, shape and isomerism

Colours of inorganic ions and complexes

Chromium and its reactions

Ligand substitution reactions

Transition metals as catalysts

Redox II

Electrochemical cells and redox

Electrode potentials and calculations

The electrochemical series

Energy storage cells and hydrogen fuel cells

Redox titrations

Energetics II

Lattice enthalpies and Born-Haber cycles

Polarisation and the Pauling scale

Enthalpy change in solution

Entropy and calculating entropy change

Gibbs free energy change

Acid-base equilibria

Acids and bases

pH calculations

The ionic product of water

pH curves and indicators

Buffer solutions and calculations

Equilibrium II

The equilibrium constant

Partial pressure and gas equilibria

Le Chatelier's principle and equilibrium constants

Equilibrium I

Reversible reactions

Le Chatelier's principle

Kinetics I

Collision theory and rates of reaction

Calculating the rate of reaction

Catalysts and the Maxwell-Boltzmann distribution

Energetics I

Enthalpy changes and reaction profiles

Standard enthalpy changes

Hess's Law and enthalpy cycles

Calculating bond enthalpies

Modern analytical techniques I

Mass spectrometry

IR spectroscopy

Organic chemistry I

Basic concepts of organic chemistry

Organic reactions and mechanisms

Structural isomerism

Alkanes and free radical substitution

Fractional distillation of crude oil

Fuels: combustion and emissions

Alkenes: bonding and reactivity

Stereoisomerism

Reactions of alkenes

Addition polymerisation

Halogenoalkanes and their reactions

Alcohol: classification and reactions

Oxidation of alcohols

Organic techniques

Formulae, equations and amounts of substances

The mole and Avogadro's constant

Calculations involving gases

Empirical and molecular formulae

Balancing equations

Acid-base titrations

Calculating uncertainty and errors

Atom economy and percentage yield

Inorganic chemistry and the periodic table

Group 2: ionisation energy and properties

Thermal stability of nitrates and carbonates

Chemical properties of Group 7

Reactions with halogens

Halide ion reactions

Testing for ions

Redox I

Calculating oxidation numbers

Oxidation, reduction and redox reactions

Bonding and structure

Ionic bonding

Covalent bonding

Shapes of molecules

Giant covalent and metallic structures

Electronegativity and polarisation

Intermolecular forces: types and examples

Hydrogen bonding

Solubility

Predicting structures and properties

Atomic structure and the periodic table

The atom: history, structure and isotopes

Relative masses and mass spectrometry

Electronic structure: shells and orbitals

Atomic emission spectra

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

Modern analytical techniques II

NMR spectroscopy

Proton NMR spectroscopy

Chromatography

Combining analytical techniques

Organic chemistry III

Benzene: structure and combustion

Electrophilic substitution

Friedel-Crafts reactions

Phenols

Aliphatic and aromatic amines

Reactions of amines

Forming amides

Condensation polymers

Amino acids and zwitterions

Grignard reagents

Synthetic routes

Practical techniques

Percentage composition and combustion analysis

Organic chemistry II

Optical isomers and chirality

Aldehydes and ketones

Carboxylic acids: properties and reactions

Esters: formation, properties and uses

Acyl chlorides: formation and reactions

Kinetics II

Measuring rates of reaction

Determining reaction orders

The initial rates method

Rate equations and the rate constant

The rate determining step

Halogenoalkane reaction mechanisms

Activation energy and the Arrhenius equation

Transition metals

Transition metals: electron configuration and oxidation number

Complex ions: formation, shape and isomerism

Colours of inorganic ions and complexes

Chromium and its reactions

Ligand substitution reactions

Transition metals as catalysts

Redox II

Electrochemical cells and redox

Electrode potentials and calculations

The electrochemical series

Energy storage cells and hydrogen fuel cells

Redox titrations

Energetics II

Lattice enthalpies and Born-Haber cycles

Polarisation and the Pauling scale

Enthalpy change in solution

Entropy and calculating entropy change

Gibbs free energy change

Acid-base equilibria

Acids and bases

pH calculations

The ionic product of water

pH curves and indicators

Buffer solutions and calculations

Equilibrium II

The equilibrium constant

Partial pressure and gas equilibria

Le Chatelier's principle and equilibrium constants

Equilibrium I

Reversible reactions

Le Chatelier's principle

Kinetics I

Collision theory and rates of reaction

Calculating the rate of reaction

Catalysts and the Maxwell-Boltzmann distribution

Energetics I

Enthalpy changes and reaction profiles

Standard enthalpy changes

Hess's Law and enthalpy cycles

Calculating bond enthalpies

Modern analytical techniques I

Mass spectrometry

IR spectroscopy

Organic chemistry I

Basic concepts of organic chemistry

Organic reactions and mechanisms

Structural isomerism

Alkanes and free radical substitution

Fractional distillation of crude oil

Fuels: combustion and emissions

Alkenes: bonding and reactivity

Stereoisomerism

Reactions of alkenes

Addition polymerisation

Halogenoalkanes and their reactions

Alcohol: classification and reactions

Oxidation of alcohols

Organic techniques

Formulae, equations and amounts of substances

The mole and Avogadro's constant

Calculations involving gases

Empirical and molecular formulae

Balancing equations

Acid-base titrations

Calculating uncertainty and errors

Atom economy and percentage yield

Inorganic chemistry and the periodic table

Group 2: ionisation energy and properties

Thermal stability of nitrates and carbonates

Chemical properties of Group 7

Reactions with halogens

Halide ion reactions

Testing for ions

Redox I

Calculating oxidation numbers

Oxidation, reduction and redox reactions

Bonding and structure

Ionic bonding

Covalent bonding

Shapes of molecules

Giant covalent and metallic structures

Electronegativity and polarisation

Intermolecular forces: types and examples

Hydrogen bonding

Solubility

Predicting structures and properties

Atomic structure and the periodic table

The atom: history, structure and isotopes

Relative masses and mass spectrometry

Electronic structure: shells and orbitals

Atomic emission spectra

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

Modern analytical techniques II

Organic chemistry III

Organic chemistry II

Kinetics II

Transition metals

Redox II

Energetics II

Acid-base equilibria

Equilibrium II

Equilibrium I

Kinetics I

Energetics I

Modern analytical techniques I

Organic chemistry I

Formulae, equations and amounts of substances

Inorganic chemistry and the periodic table

Redox I

Bonding and structure

Atomic structure and the periodic table

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

Modern analytical techniques II

Organic chemistry III

Organic chemistry II

Kinetics II

Transition metals

Redox II

Energetics II

Acid-base equilibria

Equilibrium II

Equilibrium I

Kinetics I

Energetics I

Modern analytical techniques I

Organic chemistry I

Formulae, equations and amounts of substances

Inorganic chemistry and the periodic table

Redox I

Bonding and structure

Atomic structure and the periodic table

Explainer Video

Summary

shape

shape