Home

Chemistry

Enthalpy and entropy

Polarisation and the Pauling scale

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: Mehnaz

Summary

Polarisation and the Pauling scale

In a nutshell

Polarising in an ionic bond is is when the cations pull the electrons from the anions closer to themselves, possibly distorting the spherical ionic model. The Pauling scale measures the electronegativity value of an atom. It can be used to calculate if a bond is polar or non-polar.

Polarising ability

Polarising in an ionic bond is when the cations pull the electrons from the anions closer to themselves, possibly distorting the spherical ionic model.

Highly charged small cations have high polarising abilities. They have a high charge density that is concentrated. Therefore, it is easier for the cation to pull the electrons towards itself. Highly charged, large anions get more polarised as their electrons are further away from the nucleus. There is an increased repulsion between the electrons as it's a large anion with lots of electrons. Therefore, cations can pull electrons away more easily.

A covalent bond is formed when a compound is polarised enough. Covalent character arises when the compound has some polarising ability.

Pauling scale

The Pauling scale is used to obtain the electronegativity of an atom.

Electronegativity is the ability to attract a bonding pair of electrons in a covalent bond of an atom. This can be used to calculate the polarity of a bond. Polar bonds have an electronegative value higher than $0.4$ in the Pauling scale. This means one atom will be slightly positive and the other will be slightly negative.

procedure

1.	Calculate the difference between the electronegativity values of the atoms in the bond.
2.	Determine if the value is less than or more than $0.4$ .
3.	Evaluate if the bond is polar. If the value is more than $0.4$ , the bond is polar.

Example

Predict if a $C-Br$ bond is polar. The Pauling electronegative value of carbon is $2.5$ and the Pauling electronegative value of bromine is $2.96$ .

Calculate the difference between the electronegative values:

$2.96-2.50=0.46$

Determine if the value is higher than $0.4$ :

The value is higher than $0.40$ . Therefore, the $C-Br$ bond is polar.

Learn with Basics

Length:

Unit 1

Naming chemical compounds

Unit 2

Ionic bonding: properties of compounds and naming

Jump Ahead

Optional

Unit 3