Elements, Compounds and Mixtures
As was seen in the previous section, all matter is made up of particles known as atoms. Atoms are the simplest possible particles, but they often are grouped together to form molecules.
Matter that is made up of only one type of atom is known as an Element. For example, Iron only contains Iron atoms and Oxygen only contains Oxygen atoms.
Elements are the simplest of all substances. They cannot be chemically broken down into anything smaller. They are the building block from which the Universe is made.
There are 92 naturally occurring Elements and (as of October 2020) there are 26 artificial Elements which have been made in a lab.
The most common way to display all the known Elements is in a table called the Periodic Table.
The Periodic Table
The Periodic Table is split into groups by their properties, all Elements that act in the same way are found in columns. The diagram below shows some of these groups and their properties:-
The video below shows a summary of the importance of the Periodic Table:-
Reactivity of Elements
In the diagram above, Group 1 became "more reactive" as you moved down the group, but what does this mean ?
The Reactivity of an Element is a measure of how easily that Element can chemically join with another Element.
For example, in Group 1, the Alkali Metals, the following can be seen:-
Lithium is the least reactive. When Lithium is placed in water, it fizzes and gives off little bubbles.
Sodium is more reactive. When Sodium is placed in water, it fizzes more and gives off lots of bubbles.
Potassium is even more reactive. When Potassium is placed in water, if fizzes violently, giving off lots of Bubbles and can catch fire.
The Alkali Metals are so reactive that they must be stored under oil to stop them reacting with the moisture in the air.
Other Elements are very unreactive. These include the Noble Gases and the Transition metals. For example:-
The video below shows the increasing reactivity of the Alkali Metals:-
Mixtures and Compounds
As can be seen above, there are only 118 Elements, however these can be reacted together to create more than 6 million compounds.
By combining two or more Elements together one of two things can form, a mixture or a compound.
Mixture - no chemical reaction - The two elements still exist in their natural form and can be easily separated.
Compound - chemical reaction - The two elements are now chemically combined together to create an entirely new substance.
The diagram below shows the difference between an Element, Mixture and a Compound on an atomic scale:-
Mixtures and Compounds Case Study : Iron and Sulphur
The following two elements can be used to demonstrate the difference between mixtures and compounds:-
In the above experiment, a mixture of Iron and Sulphur was initially formed. In the mixed state, Iron and Sulphur could easily still be seen, and the two Elements could be separated easily by using a magnet.
When the mixture is heated, however, a compound called Iron Sulphide (FeS) is formed. Iron Sulphide has different properties to the two Elements that formed it. Iron Sulphide is non-magnetic and the Elements cannot be separated easily again.
The diagram below shows the experiment at the atomic scale:-
The video below shows a summary of the Iron and Sulphur experiment:-
Mixtures and Compounds Case Study : Copper Chloride
In the above experiment, two Elements were combined together to make a compound. In this experiment, the process is reversed, Copper Chloride will be split up into Copper and Chlorine.
As was stated above this is not easy to do and Energy must be used to split the compound up. The source of this energy in this experiment is the power supply. Using Electricity to separate a compound in this way is known as Electrolysis.
The diagram below shows the Electrolysis of Copper Chloride:-
In the above experiment, Carbon electrodes are connected to a power supply and placed into a beaker of Copper Chloride solution. The Copper Chloride conducts, completing the circuit.
When the power supply is turned on negatively charged Chlorine ions are drawn towards the positive electrode. The Chlorine ions join together to form bubbles of Chlorine gas.
When the power supply is turned on positively charged Copper ions are drawn towards the negative electrode. The Copper ions join together to form coating of Copper around the positive electrode.
In the two case studies above, the name of the compound was very similar to the Elements that made it up. The only difference was the ending of the second element in the Compound name.
For example, the word equation of the Iron Sulphur experiment is:-
There are two main rules for the naming of compounds:-
-ide ending is a compound made of two Elements only.
-ate ending is a compound made up of three Elements, 1 of which is Oxygen.
In the above examples of mixtures, it was always a mixture of two solids. In this next section, a mixture containing a solid and a liquid will be discussed.
When a solid and a liquid are mixed together, one of two things can be seen, either the solids simply sits at the bottom of the liquid, or the solid seems to disappear entirely! In order to explain this, solubility must be understood.
Solubility is a measure of how easily a substance can dissolve.
In the above example, when sand and water are mixed together, the sand remains at the bottom of the beaker. The sand does not dissolve, and so is described as insoluble.
When sugar and water are mixed together, the sugar dissolves, and so is described as soluble, creating a solution.
Definitions for solubility:-
Soluble - A substance that can dissolve in that liquid.
Insoluble - A substance that cannot dissolve in that liquid.
Solute - The substance that dissolves (eg sugar).
Solvent - The substance that the solute dissolves in (eg water).
Solution - The mixture of a liquid and a dissolved substance.
Saturated Solution - A solution in which no more solute can dissolve.
In the solutions shown above, both involved no chemical reaction, dissolving is a physical process only. Separating the substances from each other can be tricky however:-
Separating an insoluble substance - requires filtering only.
Separating a soluble substance - requires evaporation.