Elements & oxides of the third period

Introduction

Topic 3 requires all students to cover some of the physical and chemical properties of the elements in Period 3 (Na-Ar), in particular some of the general trends across periods and down groups. They also need to cover the changes in nature of the oxides from ionic to covalent and from basic to acidic. Although this practical does not cover one of the Mandatory laboratory components it is nevertheless very important as it gives students hands-on experience of the elements and their compounds. 

Teacher’s notes

I find it helpful to put out small samples of the elements for each student (or pair of students) to do their own small scale practical work. These are magnesium, aluminium, silicon, sulfur and chlorine water. I also put out one set of larger samples of the elements so that they can test in turn for electrical conductivity (see photograph of sulfur). I include in these red phosphorus and a clear glass bottle of air labelled ‘impure argon’ I demonstrate to them the reaction of sodium with water, test its electrical conductivity and burn a small sample in air. I also burn a small sample of red phosphorus in the fume cupboard and make some chlorine gas in the fume cupboard by adding concentrated hydrochloric acid to crystals of potassium manganate(VII), KMnO4, so that they can see its green colour. Depending on whether they are SL or HL students small amounts the relevant oxides and chlorides are made available. I sometimes also show them the reaction of silicon tetrachloride with water but SiCl4 does not keep for long and may not be easily available or worth stocking. Be careful if you add water to sodium oxide, phosphorus pentoxide and aluminium chloride. I usually add just a drop or two to a small sample in a test tube.
 

Students (particularly SL students) may need some help to write the equations for the reactions taking place. What they should achieve by the end of the practical is a thorough understanding of the trends across the period for both the elements themselves and their oxides.

Standard Level Higher Level Student worksheet

ELEMENTS AND COMPOUNDS OF THE THIRD PERIOD

In going from left to right across the Periodic Table, the elements show a wide range of properties, changing from those typical of metals to those typical of non metals. This change in properties will be investigated by examining some of the elements of the second short period (Na - Ar) and some of their oxides. It will probably be easier if you present all your results and observations in tabular form.

ENVIRONMENTAL CARE:

Use only very small quantities. Put all solid waste in the labelled beakers in the fume cupboard. Do not put solid waste down the sink.

SAFETY:

You must wear safety glasses when heating the elements. The reactions of sodium will be demonstrated to you.

PROCEDURE:

1. Preparation. Prepare for the practical by drawing out a table using the data book to give the following information for each element (Na-Ar); (a) the symbol, (b) the electron arrangement, (c) the relative atomic mass, (d) the melting point and (e) the boiling point.

2. Physical appearance. Record the physical appearance of the element, including its colour and whether it is a solid, liquid or gas at room temperature.

3. Electrical conductivity. By using a multimeter find out whether the element is a good or poor conductor of electricity. Set the meter to read resistance in Ohms (Ω), and without recording the number try to get a feel for the size of the number.  A high resistance means a poor conductor and a low resistance means a good conductor. Try this out only on Mg ribbon, and the solid pieces of Al, Si and S.

4. The action of air. Heat small quantities of magnesium, aluminium, silicon and sulphur using the special spoons provided.

5. The action of acids. For Mg and Al, mix a little of each element with a little dilute hydrochloric acid and observe. Identify any gases produced. If nothing happens, warm the tube gently.

6. The action of alkalis. For Mg, Al, Si and S mix a little of each element with a little dilute sodium hydroxide solution and observe. Identify any gases produced. If nothing happens, warm the tube gently.

7. The oxides. Mix a little of the oxides of Na (care), Mg, Al, Si, and P (care) with distilled water. Note if any reaction occurs and then add a few drops of pH indicator to each solution.

QUESTIONS:

1. Metals and non metals behave differently. Comment on how this shows itself in the experiments above.

2. State the general equation for the reaction of an alkali metal, M with water.

3. State the equations for the reaction of (i) sodium oxide, Na2O, and (ii) phosphorus(V) oxide, P4O10 with water.

This worksheet can also be downloaded from:

Elements & oxides of the third period

 

 

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