Please remember to photocopy 4 pages onto one sheet by going A3→A4 and using back to back on the photocopier Syllabus oc3
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- Bu səhifədəki naviqasiya:
- Elements are substances which are made up of only one type of atom Compounds A compound is formed when two or more atoms
- When elements combine to form compounds they often lose their individual properties Other examples of compounds and their constituent elements
- Compound Symbol State of matter (at room temp)
- A molecule is made up of two or more atoms chemically combined Also A molecule is the smallest part of an element
- My head hurts; what’s the difference between a compound and a molecule
- A mixture contains two or more different substances mingled together but not chemically combined
- Symbol / chemical formula Element Molecule Compound
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Chemistry: 12. Elements, Compounds and Mixtures Please remember to photocopy 4 pages onto one sheet by going A3→A4 and using back to back on the photocopier Syllabus OC3 Understand what an element is and recall that all known elements are listed in the Periodic Table; understand what a compound is and what a mixture is; recall that when elements combine to form compounds they may lose their individual properties OC4 Examine a variety of substances and classify these as elements or compounds (using the Periodic Table as a reference) OC12 Compare the properties of the simple compounds H2O, CO2, MgO and FeS to those of the constituent elements OC13 Compare mixtures and compounds made from the same constituents, and understand that an alloy is a mixture Student Notes We saw in a previous chapter (States of Matter) that everything is made of atoms. We also saw that there are many different types of atom (over 100 in fact), and some substances are made from just one type of atom, while other substances are made from combinations of different types of atom.
If a substance is composed of just one type of atom then that substance is known as an element. Copper wire is made up of only copper atoms; a gold ring is composed of only gold atoms. We say that copper and gold are elements We have already seen that the different types of elements are arranged in terms of their atomic number (the number of protons in the nucleus) in a table called the Periodic Table of elements.
An example of a compound is table-salt. It is a compound because it is made up of two different types of atom – in this case sodium and chlorine. The chemical name for table-salt is NaCl.
We can summarise this as follows: When elements combine to form compounds they often lose their individual properties Other examples of compounds and their constituent elements
Molecules Some atoms form a very strong attachment (‘bond’) to another atom or atoms and as a result they always go around in groups of two or more atoms. We call these groups of atoms ‘molecules’. It is very hard to break these ‘bonds’ and we say that in this case the atoms are ‘chemically combined’. We will look at this bonding in detail in another chapter.
Basically a molecule is like a very small group of atoms that go around together (they are still too small to see). Examples: For the element oxygen the atoms go around in pairs. These are then called oxygen molecules and that is why oxygen is often represented as O2.
All compounds are molecules, but not all molecules are compounds (e.g. H2 is a molecule because it is composed of two atoms chemically combined, but because they are both the same element (hydrogen) the molecule is not a compound). O2 is a molecule but it is not a compound for the same reason. H2O is both a molecule (because it is composed of two atoms) and it is also a molecule (because there are two different types of element involved; hydrogen and oxygen). Remember when we said that atoms are so small that you can’t see them? Well molecules are made up of small groups of atoms so you won’t be able to see them either. Mixtures If a substance is made up of different components but they are just mingled together rather than combined at an atomic level then we call this a mixture. A mixture contains two or more different substances mingled together but not chemically combined A mixture is a combination of elements in an unfixed ratio Mixtures can be (fairly) easily separated, whereas compounds cannot be easily separated.  
If you pour sulphur power over iron filings and mix them together you get a mixture, and to separate them simply use a magnet which will attract the iron filings and leave the sulphur powder behind. However if you heated the mixture to a very high temperature their chemical compositions will change and the two elements will ‘bond’ together chemically to become a new substance called iron sulphide. This cannot now be separated and the result is called a compound. Summary 
Another way of thinking about a compound is that it is a mixture of elements in a fixed ratio. Wanna talk about Sodium? Na
Nitric Oxide? NO
Oxygen Magnesium Phosphorus Iodine Sulfur or Flourine? OMg PISS OFF ... Potassium? K
Identify one mixture and one compound from the list on the right.
Identify the element and the compound from the list on the right.
Substances can be classed as elements, compounds and mixtures.
Complete the following sentence using the words from the list on the right. Water is an example of a _______________ and hydrogen is an ________________ found in water.
Write the name of each of the two elements present in water.
What is the symbol of each of the metallic elements on the right?
What is an element?
What is a molecule?
What is a compound?
Give two different properties of the element magnesium compared to the compound magnesium oxide.
Matter is the ‘stuff’ that all things are made of, including us. The diagram shows how some types of matter are classified. The diagram is not complete. Elements can be divided into two sub-groups. Name these two sub-groups.
Exam Solutions
Magnesium Oxide: white/ powder/ base/ does not burn/ does not conduct electricity/ does not conduct heat…
Non-metals, e.g. Sulphur, Nitrogen, Phosphorus etc. Other Test Questions
Name and explain a method that the student could use to separate the iron from the sulphur in the iron and sulphur mixture. Method of separation: Explanation: Could the method of separation that you have suggested be used to separate the iron from the sulphur in the compound iron sulphide? Explain your answer.
How could you use lego to explain the difference between elements, compounds and mixtures? 
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