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The electrons in an atom occupy the lowest available energy levels

(innermost available shells). The electronic structure of an atom can be

represented by numbers or by a diagram. For example, the electronic

structure of sodium is 2,8,1 or

The elements in the periodic table are arranged in order of atomic

(proton) number and so that elements with similar properties are

in columns, known as groups. The table is called a periodic table

because similar properties occur at regular intervals.

Elements in the same group in the periodic table have the same

number of electrons in their outer shell (outer electrons) and this gives

them similar chemical properties.

Before the discovery of protons, neutrons and electrons, scientists

attempted to classify the elements by arranging them in order of their

atomic weights.

The early periodic tables were incomplete and some elements were

placed in inappropriate groups if the strict order of atomic weights

was followed.

Mendeleev overcame some of the problems by leaving gaps for

elements that he thought had not been discovered and in some

places changed the order based on atomic weights.

Elements with properties predicted by Mendeleev were discovered

and filled the gaps. Knowledge of isotopes made it possible to explain

why the order based on atomic weights was not always correct.

Elements that react to form positive ions are metals.

Elements that do not form positive ions are non-metals.

The majority of elements are metals. Metals are found to the left

and towards the bottom of the periodic table. Non-metals are found

towards the right and top of the periodic table.

There are three types of strong chemical bonds: ionic, covalent and

metallic. For ionic bonding the particles are oppositely charged ions.

For covalent bonding the particles are atoms which share pairs of

electrons. For metallic bonding the particles are atoms which share

delocalised electrons.

Ionic bonding occurs in compounds formed from metals combined

with non-metals.

Covalent bonding occurs in most non-metallic elements and in

compounds of non-metals.

Metallic bonding occurs in metallic elements and alloys.

When a metal atom reacts with a non-metal atom electrons in the

outer shell of the metal atom are transferred. Metal atoms lose

electrons to become positively charged ions. Non-metal atoms gain

electrons to become negatively charged ions. The ions produced by

metals in Groups 1 and 2 and by non-metals in Groups 6 and 7 have

the electronic structure of a noble gas (Group 0).

The electron transfer during the formation of an ionic compound can

be represented by a dot and cross diagram, eg for sodium chloride.Students should be able to draw dot and cross diagrams for ionic

compounds formed by metals in Groups 1 and 2 with non-metals in

Groups 6 and 7.

The charge on the ions produced by metals in Groups 1 and 2 and

by non-metals in Groups 6 and 7 relates to the group number of the

element in the periodic table.

Students should be able to work out the charge on the ions of metals

and non-metals from the group number of the element, limited to the

metals in Groups 1 and 2, and non-metals in Groups 6 and 7.

An ionic compound is a giant structure of ions. Ionic compounds are

held together by strong electrostatic forces of attraction between

oppositely charged ions. These forces act in all directions in the lattice

and this is called ionic bonding.

The structure of sodium chloride can be represented in the following

forms:

When atoms share pairs of electrons, they form covalent bonds.

These bonds between atoms are strong.

Covalently bonded substances may consist of small molecules.

Students should be able to recognise common substances that

consist of small molecules from their chemical formula.

Some covalently bonded substances have very large molecules, such

as polymers.

Some covalently bonded substances have giant covalent structures,

such as diamond and silicon dioxide.

Metals consist of giant structures of atoms arranged in a regular

pattern.

The electrons in the outer shell of metal atoms are delocalised and

so are free to move through the whole structure. The sharing of

delocalised electrons gives rise to strong metallic bonds. The bonding

in metals may be represented in the following form:

The three states of matter are solid, liquid and gas. Melting and

freezing take place at the melting point, boiling and condensing take

place at the boiling point.

The three states of matter can be represented by a simple model. In

this model, particles are represented by small solid spheres. Particle

theory can help to explain melting, boiling, freezing and condensing.

The amount of energy needed to change state from solid to liquid

and from liquid to gas depends on the strength of the forces between

the particles of the substance. The nature of the particles involved

depends on the type of bonding and the structure of the substance.

The stronger the forces between the particles the higher the melting

point and boiling point of the substance.

(HT only) Limitations of the simple model above include that in the

model there are no forces, that all particles are represented as spheres

and that the spheres are solid.

In chemical equations, the three states of matter are shown as (s), (l)

and (g), with (aq) for aqueous solutions

Ionic compounds have regular structures (giant ionic lattices) in which

there are strong electrostatic forces of attraction in all directions

between oppositely charged ions.

These compounds have high melting points and high boiling points

because of the large amounts of energy needed to break the many

strong bonds.

When melted or dissolved in water, ionic compounds conduct

electricity because the ions are free to move and so charge can flow.

Knowledge of the structures of specific ionic compounds other than

sodium chloride is not required.

Substances that consist of small molecules are usually gases or

liquids that have relatively low melting points and boiling points.

These substances have only weak forces between the molecules

(intermolecular forces). It is these intermolecular forces that are

overcome, not the covalent bonds, when the substance melts or boils.

The intermolecular forces increase with the size of the molecules, so

larger molecules have higher melting and boiling points.

These substances do not conduct electricity because the molecules

do not have an overall electric charge.

Students should be able to use the idea that intermolecular forces are

weak compared with covalent bonds to explain the bulk properties of

molecular substances.

Substances that consist of giant covalent structures are solids with

very high melting points. All of the atoms in these structures are

linked to other atoms by strong covalent bonds. These bonds must

be overcome to melt or boil these substances. Diamond and graphite

(forms of carbon) and silicon dioxide (silica) are examples of giant

covalent structures.

Students should be able to recognise giant covalent structures from

diagrams showing their bonding and structure.

In diamond, each carbon atom forms four covalent bonds with other

carbon atoms in a giant covalent structure, so diamond is very hard,

has a very high melting point and does not conduct electricity

In graphite, each carbon atom forms three covalent bonds with three

other carbon atoms, forming layers of hexagonal rings which have no

covalent bonds between the layers.

In graphite, one electron from each carbon atom is delocalised.

Students should be able to explain the properties of graphite in terms

of its structure and bonding.

Students should know that graphite is similar to metals in that it has

delocalised electrons.

Graphene is a single layer of graphite and has properties that make it

useful in electronics and composites.

Students should be able to explain the properties of graphene in

terms of its structure and bonding.

Fullerenes are molecules of carbon atoms with hollow shapes. The

structure of fullerenes is based on hexagonal rings of carbon atoms

but they may also contain rings with five or seven carbon atoms.