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

C4.1 Predicting chemical reactions of the halogens with 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 metals

Halogens oxidise metals.

Typical examples are:

a) Fluorine with aluminum

Double click on the link above to watch the rapid reaction between aluminium and fluorine

The chemist simple drops a spatula measure of aluminium powder into a beaker of fluorine gas.

The reaction is virtually instantaneous.

Aluminium   +      Fluorine    ⟶     Aluminium fluoride

3Al (s)          +        3F₂ (g)     ⟶          3AlF₂ (s)

b) Chlorine with magnesium

Click on the link above to see the reaction between magnesium and chlorine.

The white powder formed is magnesium chloride.

Again it is quick but not quite as quick as fluorine and aluminium.

Chlorine       +    Magnesium    ⟶   Magnesium chloride

Mg(s)          +        Cl₂(g)         ⟶          MgCl₂(s)

c) Bromine with iron

Click on the link above to see how bromine (and incidentally the other two halogens chlorine and iodine) reacts with iron and note how the iron has to be heated or set alight before the reaction occurs.

Bromine       +    Iron    ⟶   Iron(III) bromide

2Fe(s)          +     3Br₂(g)        ⟶          2FeBr₃(s)

Iron(III)bromide is a black solid that easily absorbs water from the air.  It is deliquescent.

d) Iodine with aluminum

You can watch the video of aluminium reacting with iodine by clicking on the link above:

Aluminum   +    Iodine     ⟶      Aluminium iodide

3Al (s)      +     2I₂ (s)          ⟶                   3AlI₃ (s)

The reaction show that the reactivity of a halogen with a metal decreases down the group.

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

The trend in reactivity shows that it is increasingly easy to reduce a halogen the further down Group 7 you go. 

X₂      +     2e^—       ⟶        2X^—

It is easier to reduce chlorine than it to reduce iodine.

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.

Fluorine is most easily reduced.

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

This trend is also observed when halogens react with non–metals and with halide ions as I will show in my next post.