GCSE OCR Gateway C4:1 a-b Halogens with non-metals.

C4.1 Predicting chemical reactions of the halogens with non-metals

Summary

Models of how substances react and the different types of chemical reactions that can occur enable us to predict the likelihood and outcome of a chemical reaction. The current periodic table was developed based on observations of the similarities and differences in the properties of elements. The way that the periodic table is arranged into groups and periods reveals the trends and patterns in the behavior of the elements. The model of atomic structure provides an explanation for trends and patterns in the properties of elements. The arrangement of elements in groups and periods reveals the relationship between observable properties and how electrons are arranged in the atoms of each element.

Common misconceptions

Learners consider the properties of particles of elements to be the same as
the bulk properties of that element. They tend to rely on the continuous matter model rather than the particle model. Learners confuse state changes and dissolving with chemical changes. Also, since the atmosphere is invisible to the eye and learners rely on concrete, visible information, this means they therefore often avoid the role of oxygen in their explanations for open system reactions. Even if the role of oxygen is appreciated, learners do not realize that solid products of an oxidation reaction have more mass than the starting solid.

Underlying knowledge and understanding

Learners should be familiar with the principles underpinning the Mendeleev periodic table; the periodic table: periods and groups; metals and non-metals; the varying physical and chemical properties of different elements; the chemical properties of metals and non-metals; the chemical properties of metal and non-metal oxides with respect to acidity and how patterns in reactions can be predicted with reference to the periodic table.

C4.1a-b

To be able to recall the simple chemical properties of Group 7

To be able to explain how observed simple chemical properties of Group 7 depend on the outer shell of electrons of the atoms and predict properties from given trends down the groups including the ease of electron gain or loss.

The Halogens form a group of non- metals on the right hand side of the Periodic Table Group 7 next to the noble gases.

There are three particular chemical reactions that most courses include.

The reaction of halogens with metals

The reaction of halogens with non – metals

The reaction of halogens with halide ions

Then there is the simple chemical test for halide ions.

Reaction of the halogens with non-metals

Halogens oxidise non-metals.

Typical examples are:

a) Fluorine with sulphur, phosphorus and silicon

Click on the video to watch the rapid reaction between fluorine and the non-metal sulphur, phosphorus and silicon and other Period three elements.

In each case, the highest oxidation state of the non-metal is formed.

The reactions are virtually instantaneous.

Silicon   +      Fluorine    ⟶     Silicon tetrafluoride

Si(s)          +        2F₂ (g)         ⟶          SiF₄(g)

Phosphorus   +    Fluorine    ⟶     Phosphorus pentafluoride

P₄(s)          +        10F₂ (g)      ⟶          4PF₅(g)

Sulphur   +    Fluorine    ⟶     Sulphur hexafluoride

S₈(s)          +        24F₂ (g)      ⟶          8SF₆(g)

b) Chlorine with phosphorus

Click on the image above to see the reaction between chlorine and phosphorus.

The white powder formed is phosphorus pentachloride PCl₅

Again it is quick but not quite as quick as fluorine and phosphorus

Chlorine       +    Phosphorus   ⟶   Phosphorus pentachloride

P₄(s)          +        10Cl₂(g)      ⟶          4PCl₅(s)

c) Bromine with phosphorus

Click on the images below to see how bromine reacts with red phosphorus and note how the reaction immediately liberates much phosphorus (III) bromide and is very exothermic.

Bromine       +    Phosphorus    ⟶   Phosphorus(III) bromide

P₄(s)          +     6Br₂(l)           ⟶          4PBr₃(g)

The reactivity of a halogen with a non-metal decreases down the group.

An explanation for the trends in reactivity of the halogens with metals and non-metals:

The trend in reactivity we observe is for the ease of reduction of the halogen to decrease down the group.

X₂      +     2e^—       ⟶        2X^—

Chlorine with only three shells of electrons more easily pulls in the extra electron to fill its outer shell than iodine with five electron shells

The most reactive halogen is fluorine with only two electron shells.

The effective nuclear charge is greater the fewer electron shells there are in the halogen.

In my next post I’m going to discuss halogen—halide reactions.