AS Module 1

Atomic Structure, Bonding and

Periodicity

Introduction

In order to understand the chemical reactivity of atoms and molecules

it is essential to understand their structures at both sub-atomic and

molecular levels. In this module sub-atomic structure is considered

together with ideas of chemical bonding which will be developed in

later modules. The relationship between atomic structure, chemical

reactivity and the position an element occupies in the Periodic Table

is developed using the elements of Period 3 and Group II.

Wherever possible, candidates should carry out experimental work to

illustrate the theoretical principles included in this module.

Candidates should:

10.1 Atomic Structure

10.1.1 Fundamental particles be able to describe the properties of protons, neutrons and electrons in terms of relative charge and relative mass.

10.1.2 Protons, neutrons and understand the importance of these particles in electrons the structure of the atom.

10.1.3 Mass number and isotopes be able to recall the meaning of mass number (A)

and atomic (proton) number (Z).

be able to explain the existence of isotopes.

understand the principles of a simple mass spectrometer, limited to ionisation, acceleration, deflection and detection.

be able to interpret simple mass spectra of elements and calculate relative atomic mass from isotopic abundance, limited to mononuclear ions.

know that mass spectrometry can be used to determine relative molecular mass.

10.1.4 Electron arrangement be able to describe the electronic structures of atoms

and ions up to Z = 36 in terms of levels and sub-levels s, p and d, considered as energy levels not quantum numbers.

understand how ionisation energies in Group II (Be � Ba) and in Period 3 (Na � Ar) give evidence for electron arrangement in levels and sub-levels.

10.2 Amount of Substance

10.2.1 Relative atomic mass and be able to define relative atomic mass (A r ) and

relative molecular mass relative molecular mass (M r ) in terms of 12 C.

10.2.2 The mole and the Avogadro understand the concept of a mole as applied to

constant (L) electrons, atoms, molecules, ions, formulae and equations.

understand the concept of the Avogadro constant and be able to perform calculations involving its use.

understand the concept of molarity.

10.2.3 The ideal gas equation be able to recall the ideal gas equation pV = nRT and

be able to apply it to simple calculations in S.I. units, for ideal gases.

10.2.4 Empirical and molecular be able to calculate empirical formulae from data

formulae giving percentage composition by mass.

understand the relationship between empirical and molecular formulae.

10.2.5 Balanced equations and be able to write balanced equations (full and ionic)

associated calculations for reactions studied.

be able to balance equations for unfamiliar reactions when reactants and products are specified.

be able to calculate reacting masses from balanced equations (full and ionic).

be able to calculate reacting volumes of gases.

be able to calculate molarities and volumes for reactions in solutions, limited to titrations of monoprotic acids and bases and examples for which the equations are given.

10.3 Bonding

10.3.1 Nature of ionic, covalent understand that ionic bonding involves attraction

and metallic bonds between oppositely charged ions formed by electron

transfer.

know that a covalent bond involves a shared pair of electrons.

know that co-ordinate bonding is dative covalency.

understand that metallic bonding involves a lattice of positive ions surrounded by delocalised electrons.

10.3.2 Bond polarity and the understand that electronegativity is the power of an

polarisation of ions atom to withdraw electron density from a covalent bond.

understand that the electron distribution in a covalent bond may not be symmetrical.

know that covalent bonds between different elements will be polar to different extents.

know that anions can be polarised by cations of high charge density, limited to chlorides of elements in Period 3 and those in Group II.

10.3.3 Forces acting between understand qualitatively how molecules may interact

molecules by permanent dipole�dipole, induced dipole�dipole (van

der Waals�) forces and hydrogen bonding.

10.3.4 States of matter understand the behaviour of gases, liquids and solids in terms of the particles, their motion and the forces acting between them.

be able to explain the energy changes associated with changes of state.

recognise the four types of crystal: ionic, metallic, molecular and giant covalent (macromolecular).

know the structures of NaCl, I2 , diamond and graphite.

be able to relate the physical properties of materials to the type of structure and bonding present.

10.3.5 Shapes of simple molecules understand the concept of bonding and lone (non-

and ions in terms of bonding) pairs of electrons as charge clouds.

electron pair repulsion be able to use this concept to predict the shapes

of, and bond angles in, simple molecules and ions, limited

to 2, 3, 4, 5 and 6 co-ordination.

Know that lone pair/lone pair repulsion is greater than lone pair/bonding pair repulsion, which is greater than bonding pair/bonding pair repulsion, and understand the resulting effect on bond angles.

10.4 Periodicity

10.4.1 Classification of elements be able to classify an element as s, p or d block

in s, p and d blocks according to its position in the Periodic Table.

10.4.2 Properties of the elements be able to describe the trends in atomic radius,

of Period 3 (Na � Ar) to first ionisation energy, electronegativity, electrical

illustrate periodic trends conductivity, melting and boiling points of the elements Na � Ar.

understand the reasons for the trends in these properties.

10.4.3 Group II understand the trends in atomic radius, first ionisation

energy, electronegativity and melting point of the elements Be � Ba.

know the reactions of the elements Be � Ba with water and recognise the trend.

know the relative solubilities of the hydroxides of the elements Be � Ba and that Mg(OH)2 is sparingly soluble.

know the relative solubilities of the sulphates of the elements Be � Ba, that BaSO4 is insoluble and is formed in the test for sulphate ions.

know that beryllium is atypical, limited to covalent character (e.g. in BeCl2), the amphoteric character of Be(OH)2 and the limitation of maximum co-ordination number to four.