Year 10 Revision Notes: Metals
Everything is made from atoms, including you. Atoms are tiny particles that are far too small to see, even with a microscope. If people were the same size as atoms, the entire population of the world would fit into a box about a thousandth of a millimetre across!
We usually imagine atoms as being like tiny balls:
To make diagrams simpler we often draw atoms as circles:
Elements
There are over a hundred different types of atom, and these are called elements. Each element has a special name. For example carbon, oxygen and hydrogen are all elements.
Lead and gold are elements too. A piece of pure gold contains only gold atoms. A piece of pure lead contains only lead atoms.
Chemical reactions join or split atoms to rearrange them. But they cannot change one element into another element, or anything simpler. A chemical reaction cannot turn lead into gold, becuse it can't change the atoms into different elements.
Each element is given its own chemical symbol, likeOfor oxygen andClfor chlorine. Chemical symbols are usually one or two letters long, but sometimes three letters are used.
Every chemical symbol starts with acapitalletter, with the second or third letters written in lower case.
For example,Mgis the correct symbol for magnesium, but mg, mG and MG are wrong.
Take care to write chemical symbols correctly
Mg / mg / mG / MG /Symbols and names
Sometimes it is easy to tell which element a symbol stands for. For example,O stands for oxygen andListands for lithium.
But sometimes the symbol comes from a name for the element that is not an English word.For example,Wstands for tungsten (from the word wolfram) and Nastands for sodium (from the word natrium).
The reason is that the same chemical symbols are used all over the world, no matter which language is spoken, which makes them most useful.
All the different elements are arranged in a chart called theperiodic table.
· The horizontal rows are calledperiods.
· The vertical columns are calledgroups.
· Elements in the same group are similar to each other.
· The metals are on the left and the non-metals are on the right.
· One non-metal, hydrogen, is often put in the middle.
· The main groups are numbered from 1 to 7 going from left to right, and the last group on the right is group 0.
The periodic table
The zig-zag line in this diagram separates themetals, on the left, fromnon-metals, on the right. Hydrogen is a non-metal but it is often put in the middle.
Notice that most elements are metals, rather than non-metals.
Each element has its own chemical symbol, made from letters. Remember that you will only find elements in the periodic table and never compounds. So don't try to look for substances like water and copper sulphate in the periodic table, because they are not there.
Iron, magnesium and gold are examples of metal elements.
All metals have these properties in common:
· They areshiny, especially when they are freshly cut.
· They aregood conductorsof both heat and electricity.
· They can bebentwithout breaking (they aremalleable).
· Most metals also have these properties:
· they aresolid at room temperature, except mercury, which is liquid at room temperature
· they arehardand strong
· they have ahigh density(they feel heavy for their size)
· they make a ringing sound when they are hit (they aresonorous)
Mercury is the only metal that is liquid at standard room temperature and pressure
Three metals aremagnetic.
These are iron, cobalt and nickel. Steel is a mixture of elements but mostly iron, so it is also magnetic. The other metals are not magnetic.
Atomic Structure
Atoms consist ofelectronssurrounding anucleusthat containsprotonsand neutrons.
Neutrons are neutral, but protons and electrons are electrically charged. Protons have a relative charge of +1, while electrons have a relative charge of -1.
The number of protons in an atom is called its atomic number. In the periodic table atoms are arranged in atomic number order.
Electrons are arranged in energy levels or shells, and different energy levels can hold different numbers of electrons. The electronic structure of an atom is a description of how the electrons are arranged, which can be shown in a diagram or by numbers. There is a link between the position of an element in the periodic table and its electronic structure.
The structure of an atom
Although the word 'atom' comes from the Greek forindivisible, we now know that atoms are not the smallest particles of matter. Atoms are made from smallersubatomic particles.
At the centre of an atom is anucleus containingprotonsandneutrons. Electronsare arranged around the nucleus in energy levels or shells. Make sure you can label a simple diagram of an atom like this one.
Both protons and electrons have an electrical charge. Both have the same size of electrical charge, but the proton is positive and the electron negative. The neutron is neutral.
The electrical charge of particles
particle / relative charge /proton / +1
neutron / 0
electron / -1
The total number of electrons in an atom is always the same as the number of protons in the nucleus. This means atoms have no overall electrical charge.
The number of protons in an atom is called itsatomic number- also called the proton number.
Energy levels and shells
Electronsare arranged in different shells around thenucleus. The innermost shell - or lowest energy level - is filled first. Each succeeding shell can only hold a certain number of electrons before it becomes full. The innermost shell can hold a maximum of two electrons, the second shell a maximum of eight, and so on. The table gives the maximum capacity of the first three shells.
Maximum capacity of the first three shells
energy level or shell / maximum number of electrons /first / 2
second / 8
third / 8
A lithium atom, for example, has three electrons. Two are in the first energy level, and one in the second.
A carbon atom has six electrons. Two are in the first energy level, and four in the second energy level.
Arrangement of electrons in a lithium atom
Arrangement of electrons in a carbon atom
A calcium atom has 20 electrons. Two are in the first energy level, and eight in the second energy level, eight in the third energy level and two in the fourth energy level.
Electronic structure 1
The electronic structure of an atom is a description of how theelectronsare arranged. The first 20 elements in the periodic table run from hydrogen to calcium. Their electronic structures can be shown either as diagrams or numbers. You need to know how to do both.
Take lithium, for example. The drawing shows each energy level as a circle around the nucleus, with each electron represented by a dot. In the exam, do not worry about colouring in the electrons. Just make them clear and ensure they are in the right place. Sometimes you will be asked to use a cross rather than a dot. The numerical method is to write the chemical symbol (Li) followed by the number of electrons in each energy level, innermost first,Li 2,1.
Electronic structure of lithium
Element / Numeric format / Electrons / Periodic table group // Li 2,1 / Lithium atoms have three electrons. Two of these fit into the first energy level, with the third in the second energy level. / Group 1
Electronic structure 2
Below are some more electronic structures. Remember - The number of electrons in the highest occupied energy level of each atom is the same as the element's group number.
Electronic structures of elements
Element / Numeric format / Electrons / Periodic table group // F 2,7 / Fluorine atoms have nine electrons. Two of these fit into the first energy level. The remaining seven fit into the second energy level. / Group 7
/ Ne 2,8 / Neon atoms have ten electrons. Two of these fit into the first energy level. The remaining eight electrons fit into the second energy level. Because its highest occupied energy level is full, neon isstableand unreactive. / Group 0 - that is, the eighth group
/ Na 2,8,1 / Sodium atoms have 11 electrons. Two of these fit into the first energy level, eight into the second energy level. The last one fits into the third energy level. / Group 1
/ Ca 2,8,8,2 / Calcium atoms have 20 electrons. Two of these fit into the first energy level, eight into the second energy level, another eight into the third energy level. The last two fit into the fourth energy level. / Group 2
Electronic structure and the periodic table
As you have seen, there is a link between an atom's electronic structure and its position in the periodic table. You can work out an atom's electronic structure from its place in the periodic table.
Periodic table related to electronic structure
The diagram shows a section of the periodic table, with the elements arranged as usual in the order of their atomic number, from 2 to 20. The red numbers below each chemical symbol show its electronic structure.
Movingacross each period, you can see that the number of occupied energy levels is the same as the period number.
As you goacross each periodfrom left to right, an energy level gradually becomes filled with electrons. The highest occupied energy level contains just one electron on the left-hand side of the table. It is filled by the time you get to the right-hand side.
Movingdown each group, you can see that the number of electrons in the highest occupied energy level is the same as the group number.
Each element in a group therefore has the same number of electrons in its highest occupied energy level. Group 0 is a partial exception to this rule. Although it comes after Group 7, it is not called Group 8 - and it contains helium, which has only two electrons in its outer shell.
Working out an element's electronic structure
Here is how to use the periodic table to work out an electronic structure:
1. Find the element in the periodic table. Work out which period it is in, and draw that number of circles around the nucleus.
2. Work out which group the element is in and draw that number of electrons in the outer circle - with eight for Group 0 elements - except helium.
3. Fill the other circles with electrons. Remember - two in the first, eight in the second and third, and 18 in the fourth.
4. Finally, count your electrons and check that they equal the atomic number.
Forming an ionic bond - Challenging
When metals react with non-metals,electronsare transferred from the metal atoms to the non-metal atoms, formingions. The resulting compound is called an ionic compound.
Consider reactions between metals and non-metals, for example:
· Sodium + chlorine → sodium chloride
· Magnesium + oxygen → magnesium oxide
· Calcium + chlorine → calcium chloride
In each of these reactions, the metal atoms give electrons to the non-metal atoms. The metal atoms become positive ions and the non-metal atoms become negative ions. Atoms form ions to become energetically more stable
When a non-metal forms a bond the name ending changes. In these reactions the ending is–ideshowing only that element is present. If the ending was–ateit means that oxygen is also present as well as the element.
There is a strongelectrostaticforce of attraction between these oppositely charged ions, called anionic bond. The animation shows ionic bonds being formed in sodium chloride, magnesium oxide and calcium chloride.
There are many ionic bonds in an ionic compound such as sodium chloride, arranged in giantlatticestructures. Ionic compounds have high melting and boiling points.
Formulae of ionic compounds
Sea water contains a number of dissolved salts. When these salts dissolve in water, the ions separate. Sea water therefore contains a mixture of ions. The most common ions in sea water are shown in the table:
Name of ion / Formula and charge /Chloride / Cl−
Sodium / Na+
Sulfate / SO42−
Magnesium / Mg2+
Calcium / Ca2+
Potassium / K+
Carbonate / CO32−
Bromide / Br−
It is possible to deduce from the table which salts dissolved to form the mixture of ions:
· When sodium chloride dissolves it forms sodium ions and chloride ions
· When magnesium chloride dissolves it forms magnesium and chloride ions
· When magnesium sulfate dissolves if forms magnesium ions and sulfate ions
· When potassium chloride dissolves it forms potassium ions and chloride ions
· When potassium bromide dissolves it forms potassium ions and bromide ions
You can use the charge on the ions shown in the table to work out the formulae of the ionic compounds.
Sodium ions each have asingle positive charge. Chloride ions each have asingle negative charge. For the charges to cancel out in the neutral salt sodium chloride, they must be in a ration of 1:1. So the formula of sodium chloride is NaCl.
Magnesium ions each havetwo positive charges. Chloride ions each have a single negative charge. For the charges to cancel out in the neutral salt magnesium chloride, they must be in a ratio of 1:2. So the formula of magnesium chloride is MgCl2.
Uses of metals
You may have to match the use of a metal with a property that makes it suitable for that use. For example, copper is used for electrical wiring because it is a good conductor of electricity, not because it is a good conductor of heat.
Remember that most elements are metals, rather than non-metals. The table summarises some differences in their properties.
/ Metals / Non-metals /Appearance / Shiny / Dull
State at room temperature / Solid (except mercury, which is a liquid) / About half are solids, about half are gases, and one (bromine) is a liquid
Density / High (they feel heavy for their size) / Low (they feel light for their size)
Strength / Strong / Weak
Malleable or brittle / Malleable (they bend without breaking) / Brittle (they break or shatter when hammered)
Conduction of heat / Good / Poor (they are insulators)
Conduction of electricity / Good / Poor (they are insulators, apart from graphite)
Magnetic material / Only iron, cobalt and nickel / None
Sound when hit / They make a ringing sound (they are sonorous) / They make a dull sound
Telling them apart