From Hydrogen to Tellurium - CHLORINE

Chlorine


The seventeenth element is Chlorine. It has 17 electrons, 2 in the inner shell, 8 in the 2nd and 7 in the third, thus leaving one space in the outer shell to completely fill it. Elements with one space in their outer shells are grouped in the Halogen family. This is the second halogen we have met, Fluorine being the first.


Chlorine is a green coloured gas which was first isolated in the 1770s. The gas is poisonous. It also has a bleaching effect, taking the colour out of things it comes in contact with. The gas is not found in nature as Chlorine is very reactive and combines with other elements to give compounds. 

Most people are familiar with the smell of Chlorine - it is used in very small quantities in our drinking water and also in swimming pools to kill bacteria.
                                       


One of the compounds, Sodium Chloride, is used regularly in our kitchens - we refer to it as salt. It seems hard to believe that if the gaseous molecules of Chlorine combine with the metal atoms of sodium that a white crystalline solid which we know as salt results.

From Hydrogen to Tellurium - SULPHUR

Sulphur


The sixteenth element, Sulphur is given the symbol S. This element is found in its elemental form, often near volcanos and springs. It is a yellow crystalline solid, composed of rings of 8 Sulphur atoms.

It has been known about since ancient times and is the material referred to as "brimstone" in the bible. 


Sulphur is a non-metal which sits under oxygen in the periodic table. Like oxygen if forms compounds with 2 other atoms -chemists say it is divalent. An example of a divalent compound of Sulphur is Hydrogen Sulphide - H2S. Hydrogen Sulphide is a colourless, poisonous gas that smells like rotten eggs. 


It can also form molecules with different number of bonds. An example is Sulphur Dioxide, SO2 where it is joined by double bonds to both oxygens. Sulphur dioxide is sometimes used to preserve fruit for jam making.


Sulphur dioxide is produced when coal is burned. This SO2 reacts with water H2O in the atmosphere to form Sulphuric Acid H2SO4. This then falls as acid rain and affects crop growth and damages buildings.


In fact Sulphur forms compounds with all elements except the noble gases.


If you heat Sulphur with iron you get a new compound - iron sulphide. This experiment is often used to show the difference between a chemical mixture and a reaction producing a new material. Before heating this mixture the iron could be separated from the Sulphur using a magnet. Once it has been heated and reacted the new compound is not magnetic, nor can the magnet separate the iron from the Sulphur.


Many Sulphur containing compounds are smelly. You might be familiar with the sulphury smell from car's catalytic converters. Garlic and the Skunk also owe their smell to Sulphur containing compounds. 




Experiment of the week
To examine the effect of Acid Rain on crops


You will need:
4 clear plastic tubs with lids (3kg Margarine containers are ideal.)
Kitchen roll
Pea seeds
Water
Vinegar
spoon


What to do:
Soak the peas overnight in water
In each of the 4 tubs cover the bottom with a few layers of kitchen roll. Dampen the kitchen roll well with water
Sprinkle pea seeds on the damp kitchen roll.
Label the containers 1,2 3 and 4
Put the lid onto container 1 and leave in a warm place
To container 2 add 1 spoon of vinegar. Put on the lid and leave alongside container 1.
To container 3 add 2 spoons of vinegar. Put on the lid and leave alongside container 1.
To container 4 add 3 spoons of vinegar. Put on the lid and leave alongside container 1.


Examine each day for the next 2 weeks and record your results.


Which set of peas will grow best?

From Hydrogen to Tellurium - PHOSPHORUS

Phosphorus 


At number 15 and with the chemical symbol P, we find Phosphorus. In the periodic table Phosphorus sits below Nitrogen. Like Nitrogen, Phosphorus has 3 electrons in its outer shell and therefore reacts similarly to nitrogen.
It is a non-metal and like many other elements it is not found as an element in nature.
Elemental Phosphorus forms many different crystal structures and each structure has its own colour. White, Red and Violet Phosphorus are 3 such forms. We found previously that carbon exists in a number of different forms and that the different carbon allotropes look and feel very different. This is also the case for Phosphorus.

Different allotropes of Phosphorus

Phosphorus was discovered by a German alchemist when he was trying to turn urine into gold. Instead of gold he ended up with a white material which glowed in the dark and when lit, burned very brightly. 


Because Phosphorus can glow in the dark it is often used on the faces of watches so you can tell the time in the dark. 

Because it can burn so well, it is used on the rough part of match boxes that is used to strike matches on.

Phosphorus is essential for both animal and plant life. DNA contains Phosphorus as do many plant fertilisers. It is also found in washing powder

From Hydrogen to Tellurium - SILICON

Silicon


At number 14 is the unusual element Silicon with the chemical symbol Si. Why do I say it is any more unusual than the others? Well with its 4 outer shell electrons, it sits in the periodic table just under Carbon. We already learned that carbon is a non-metal. We have also learned that the elements with the same number of outer shell electrons behave similarly. When it comes to Silicon however this is not quite true. Silicon has some properties of a metal and some of a non-metal posing problems for scientists as to which group it should be in. In the end they decided it should go into a group called metaloids - a material with some metal and some non-metal characteristics. We also found out a few weeks ago that Boron has this same part metal, part non-metal behaviour.

This nearly metal behaviour is what makes Silicon interesting and very important to our lives today. It is known as a semiconductor because it doesn't conduct electricity as well as a metal but it is better at conducting than a non-metal. Semiconductors are widely used in the electronics and computer industries.


So what is it like? Well, Silicon is grey with a metallic appearance. It is very plentiful in the universe, but is hardly ever found as elemental Silicon. Instead it is found combined with oxygen as silica, SiO2. Sand is made of silica and this sand is in turn used to make glass. Small bags of Silica are also often found packed with shoes or in new handbags. The job of these little packets is to absord water so the leather products don't get damp.

Pure crystalline Silicon dioxide resonates at a certain frequency and because of this property it is used in watches.


Silicon combines with carbon oxygen and hydrogen to make a series of polymers known as silicones. You might have come across such rubbery polymers  - the wristbands which were very popular a few years ago were made from silicone..