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The atom: history, structure and isotopes

The atom: history, structure and isotopes

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The scientific method

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Presenting results using tables and graphs

Analysing results: anomalies and correlation

Evaluating experiments

Modern analytical techniques II

NMR spectroscopy

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Organic chemistry III

Benzene: structure and combustion

Electrophilic substitution

Friedel-Crafts reactions

Aliphatic and aromatic amines

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Condensation polymers

Amino acids and zwitterions

Grignard reagents

Synthetic routes

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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

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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

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The ionic product of water

pH curves and indicators

Buffer solutions and calculations

Equilibrium II

The equilibrium constant

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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

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Empirical and molecular formulae

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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

Covalent bonding

Shapes of molecules

Giant covalent and metallic structures

Electronegativity and polarisation

Intermolecular forces: types and examples

Hydrogen bonding

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

Explainer Video

Tutor: Sophie

Summary

The atom: history, structure and isotopes

In a nutshell

Understanding the structure of the atom is the basis of all chemistry. It is important to recall the history of the atom, understand the structure of the atom and to understand the concept of isotopes.

History of the atom

Throughout time, there have been various proposed models for the atom. Today, we use the Bohr model.

Discovery	Model
John Dalton, $1803$	Dalton proposed that all matter is made up of atoms. Dalton's model considered atoms to be a solid spherical model, lacking any subatomic particles.
JJ Thomson, $1904$	JJ Thomson discovered the electron. This lead to the idea of the 'plum pudding' model, proposing the atom to have a net positive charge with negative electrons trapped within.
Niels Bohr, $1913$	Ideas from Ernest Rutherford, Neils Bohr and James Chadwick all contribute to the current model of the atom. The 'Bohr model', a neutral atom with electrons found in shells, orbiting a central positive nucleus (of protons and neutrons).

Atomic structure

Atoms consist of protons, neutrons and electrons. Protons and neutrons are located in the nucleus, which is responsible for most of the mass of an atom. Electrons are located in orbitals, which are responsible for most of the volume of an atom.

Subatomic particle	RELATIVE CHARGE	RELATIVE MASS
Proton	$+1$	$1$
Neutron	$0$	$1$
Electron	$-1$	$\frac{1}{1836}$

Note: The relative mass of an electron is also readily seen as $0.0005$ which is equivalent to $\frac{1}{1836}$ 

Atomic number and mass number

Any element from The Periodic Table can be written symbolically with their atomic number and mass number.

^A_Z \large E

$E$	An element in The Periodic Table.
$Z$	The atomic number - the number of protons in the nucleus of the atom.
$A$	The mass number - the total number of protons and neutron in the nucleus of the atom.

Isotopes

Isotopes are atoms of the same element with the same number of protons but different number of neutrons. Isotopes therefore have the same atomic numbers but different mass numbers.

Example

$Cl-35$ and $Cl-37$ are an exemplar pair of isotopes.

Subatomic particles

The number of each subatomic particle can be calculated using the atomic and mass numbers.

procedure

1.	Use the atomic number to find the number of protons. This is also equivalent to the number of electrons.
2.	Use the mass number to find the number of neutrons. This is calculated by subtracting the atomic number from the mass number.

Example

Find the number of protons, neutrons and electrons in the isotopes of chlorine $-35$ and chlorine $-37$ .

isotope	symbol	protons	electrons	neutrons
$Cl-35$	$^{35}_{17} Cl$	$17$	$17$	$35 - 17 = 18$
$Cl-37$	$^{37}_{17} Cl$	$17$	$17$	$37 - 17 = 20$

Note: The physical properties of isotopes may differ. Physical properties depend on the mass of the atom and since isotopes have different numbers of neutrons, the mass differs.

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Learn with Basics

Learn the basics with theory units and practise what you learned with exercise sets!

Length:

Dalton's atomic model

Unit 1

Dalton's atomic model

The atom and isotopes

Unit 2

The atom and isotopes

Jump Ahead

Score 80% to jump directly to the final unit.

Optional

The atom: history, structure and isotopes

Unit 3

The atom: history, structure and isotopes

Final Test

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FAQs - Frequently Asked Questions

What are isotopes?

Isotopes are atoms of an element with the same number of protons but a different number of neutrons.

What is the mass of an electron?

The relative mass of an electron is 1/1836 or 0.0005.

What atomic structure model is in use today?

Today, we use the Bohr model for the atomic structure.

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