atome, elements and compounds image

Foundation and higher tiers

Elements

periodic table Elements are simple substances composed of only one type of atom. The periodic table lists all known elements, each element has its own symbol in the periodic table. It is important that you learn the names and symbols for the first 20 elements in the periodic table. Why not do a little research on some of the elements and find out about their properties and the people who discovered them? The chemical symbols for the elements often come from the names of the scientists who discovered them, or from the names of gods or astronomical objects e.g. the table below could start off your internet search, you just need to add to it, perhaps add a few additional columns to summarise any additional information you find out.

Some elements have only a single letter for their symbol, e.g. oxygen is given the symbol O. It is a capital O and not a lowercase o. This is true for all single letter symbols in the periodic table. If the symbol is made up of 2 letter, e.g. sodium, symbol Na. The first letter is always capitalized and the second is always lowercase, so sodium is never NA or na, always Na. Iron is Fe, NEVER fE or FE.

Element names and symbols

element chemical symbol Where its name comes from
germanium 32 Ge Germany
francium 87 Ge France
strontium 38 Sr Named after village of Strontian, Scotland
europium 63 Sr Europe
helium 2 He Helios, god of the Sun.
hafnium 72 Hf Hafnia, Latin for Stockholm.
tellurium 52 Te Tellus, Latin for Earth.
curium 97 Cm Pierre and Marie Curie.
mendelevium 101 Md Dimitri Mendeleev.
thorium 90 Th Norse god Thor.
titanium 22 Ti Titans, Greek mythology.
vanadium V Vanadis(Freya) Norse Goddess.
silver 47 Ag Latin name Argentum.
tungsten 74 W Mineral wolframite, which contains high concentration of tungsten.

Compounds

Compounds are formed when two or more elements chemically join together. The atoms in the compound are held together by chemical bonds. You will learn about three types of chemical bonds in your GCSE chemistry course, these are covalent, ionic and metallic bonds. The images below show 3 common compounds which you will meet in your GCSE course. These compounds contain only non-metal atoms, compounds like this are called covalent compounds. The 3 compounds are all molecular, this means they consist of small groups of atoms.

molecules

Properties of compounds

iron and sulfur reacting

Compounds have very different properties from the elements that make them up, as an example consider the reaction shown between iron and sulfur. Iron is a dull grey magnetic metal and sulfur is a bright yellow non-metallic solid. If a mixture of iron and sulfur are heated strongly for a few minutes in a test-tube then a dull red glow is seen as the reaction takes place. The compound formed is called iron sulfide. A word equation for the reaction is:

iron(s) + sulfur(s) → iron sulfide(s)

The compound formed is a non-magnetic blue/black solid which bears little resemblance to either of the two elements that make it up. Even though it contains iron it is not magnetic and though it contains sulfur it is not yellow. The iron atoms and sulfur atoms have combined chemically to form a new compound, iron sulfide. This new compound has very different properties from the two elements from which it was made. This is true for all all compounds.

Compounds formed between metals and non-metals are called ionic compounds. These compounds are made up of ions. Ions are charged atoms formed when atoms lose or gain electrons. Metals tend to lose electrons when they react and form ions with a positive charge, non-metals tend to gain electrons when they react. Ionic compounds are not molecular, that is their structure does is not made up of small groups of atoms, instead they have giant structures of ions called ionic lattices. The physical properties, such as melting, boiling points and whether it conducts electricity tend to be determined by the type of structure a compound has.

Particle pictures

particle picture iron sulphide The diagram shows a particle picture for the reaction of iron and sulfur to form iron sulfide. You can see that all the iron atoms and all the sulfur atoms are the same, this obviously means that they are elements. However once they react the product, iron sulphide has a giant ionic lattice structure. Only a few iron and sulphur ions are shown but in reality the structure would consist of billions of ions all joined together. This is very different from the small molecular structure shown for covalent compounds above. Ionic compounds have very different chemical and physical properties from covalent compounds largely due to differences in their structures and the types of bonds holding the particles together. You will learn more about this when you revise the section on bonding and structures.

Naming compounds

Most compounds end in the letters -ide, this tells us that the compound is made up of only 2 elements. Some compounds end in the letters -ate, this means the compounds have more than 2 elements and one of them is oxygen. e.g.

Compound Elements present
sodium chloride sodium and chlorine
magnesium oxide magnesium and oxygen
carbon dioxide carbon and oxygen
sodium carbonate sodium, carbon and oxygen
calcium nitrate calcium, nitrogen and oxygen
calcium hydroxide calcium, hydrogen and oxygen

Word equations

When elements react to form compounds we can show this chemical reaction as a word equation, e.g. hydrogen gas burns in air (oxygen) to form water (hydrogen oxide). A word equation for this reaction is shown below.

hydrogen(g) + oxygen(g) → hydrogen oxide(g)

Here the reactants are hydrogen and oxygen and the compound formed is called the product . Compounds are named as described above. Here the last 4 letters of the non-metal oxygen (ygen) are replaced by -ide.

Key Points

Practice questions

Check your understanding - try the periodic table quiz. How well do you know your elements?

Check your understanding- Elements, molecules and word equations

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