1. Reading the Periodic Table Relative Atomic Mass (Mr)
Mendeleev
Arranged elements by increasing atomic mass but….
He broke this rule and left some gaps if an element’s properties weren’t similar to the one above it.
He thought the gaps were for elements that hadn’t been discovered yet and predicted their properties.
When they were discovered, the properties matched the predictions
Sub-atomic particles
Atoms are made from smaller particles called subatomic particles.
There are three types you need to know about, summarised below.
What’s in my atom?
Protons = atomic number
Electrons = atomic number
Neutrons = relative atomic mass – atomic number
Reading the Periodic Table
Note: on some periodic tables, they are the wrong way up, just remember that the smaller number is the proton number.
Relative Atomic Mass (Mr)
(aka nucleon number):
The total number of protons and neutrons added together.
Atomic number (Ar) (aka proton number):
The number of protons or electrons.
Particle
Relative charge
Relative mass
Found?
Proton +1 1
In nucleus
Neutron
Neutral, 0
Electron -1
Neglible ( )
In shells orbiting nucleus
The letter is called the symbol
Atomic number = 9
Relative Atomic mass = 19
Protons = 9
Electrons = 9
Neutrons = 19-9 = 10
Atomic number = 16
Relative Atomic mass = 32
Protons = 16
Electrons = 16
Neutrons = = 16
Property
Eka-aluminium - Ea
(the prediction)
Gallium - Ga
(the one discovered)
Atomic mass
about 68 70
Density (g/cm3)
6.0
5.9
Melting point (OC)
Low
29.8
Formula of oxide
Ea2O3
Al2O3
Density of oxide
5.5
Reacts with acids and alkalis?
Yes
Atoms and Elements
Atom: The smallest part of a chemical element that can exist
Ion: when an atom gains or loses electrons it become charged. It is now called an ion.
Protons: same for every atom of an element…it is the number of protons that decides the element.
5.1 (sheet a) Atomic Structure and the Periodic Table
The history of the atom
The original model was the plum pudding model; a solid sphere with electrons stuck in it. Rutherford showed that the plum pudding model had to be wrong. Bohr’s Nuclear model explained a lot of the questions that scientists had.
Atoms have a radius of 1x10-10m. Most of the radius of an atom is the shells however most of the mass of an atom is in the nucleus.
Electron Configuration
Electrons orbit the nucleus in shells.
First shell holds two electrons
Second and third shell hold 8 electrons
Note: the third shell can actually hold more, but we won’t worry about this until A-level.
Example: Silicon
Atomic number is 14, so it has 14 electrons.
You build up electrons from the first shell outwards, so in this case:
- First shell has 2
- Second shell has 8
- Third shell has 4
This can be written as: 2.8.4; or drawn as:
Higher level understanding
The relative atomic mass is the mass of an element relative to 1/12th the mass of 12C.
Most of the mass of an atom is found in the nucleus.
Electrons are attracted to the nucleus because electrons are negative and the protons in the nucleus are positive. This is called electrostatic attraction.
More shells = weaker electrostatic attraction
Isotopes
Versions of an element with the same atomic number but different atomic mass.
Number of protons is the same, but number of neutrons is different.
Relative Atomic Mass is the average of the masses of the isotopes, weighted by their relative abundance
For example, Neon has three isotopes
Relative atomic mass of Neon =
20× ×0.3+22× =20.2
This is why some atoms have a relative atomic mass with a decimal point.
Elements and compounds
The substances found in the periodic table are called elements.
There are over 100 elements and each one is represented by its own chemical symbol.
Element = substance containing only one type of atom
For example, lead is represented by the symbol Pb.
When elements chemically react they form compounds.
Compounds contain two or more elements chemically bonded in fixed proportions.
Compounds are represented using formulae, the formula tells you exactly what elements are in the compound and how many of each there are. For example, CaC03 contains one calcium atom, one carbon atom and three oxygen atoms.
A chemical equation shows what is happening during a chemical reaction.
For example: 2Li + 2H2O  2liOH + H2
This shows Lithium reacting with water to produce lithium hydroxide and hydrogen gas.
Neon Isotope Mass
Relative Abundance (%) 20
90.5 21
0.3 22
9.2
Note: Si is in period three and group four of the periodic table; it also has three electron shells and four electrons in the outer shell – this is no coincidence!

2. 5.1 (sheet b) Groups in the Periodic Table
Alkali Metals
Group 1: Lithium (Li), Sodium (Na), Potassium (K)…
Properties: low melting point, soft (can be cut with a knife).
React with water as follows:
General equation: metal water  metal hydroxide + hydrogen
For example: K(s) H2O(l)  KOH(aq) H2(g)
Reactivity
Reactivity increases down the group:
Lithium just fizzes before disappearing
Sodium fizzes and gets hot enough to melt into a ball, occasionally catching fire
Potassium fizzes very vigorously, getting hot enough to burn with a lilac flame
Explaining the reactivity of the alkali metals
When group 1 elements react they lose their valence electron (outer shell electron)
Atoms get bigger going down the group  outer-shell electrons further from nucleus  easier to remove the outer shell electron.
Transition Metals
Dense and strong
High melting points
Form brightly coloured compounds
Good conductors
Make good catalysts
Halogens and Their Reactions
Group 7: Fluorine (F) – pale yellow gas, Chlorine (Cl) – pale green gas, Bromine (Br) – orangey-brown liquid, Iodine (I) – grey solid.
Exist as diatomic molecules
Most reactive at top of group, and get less reactive as you go down.
Form halide ions with a charge of ‘-1’
Reaction with metals
React with metals to form metal halides
General equation: metal + halogen  metal halide
For example: magnesium + iodine  magnesium iodide
Mg(s) I2(s)  MgI2(s)
Note: Mg forms a 2+ ion, so two I- ions are needed.
Melting and boiling points
Melting and boiling points increase as you go down the group.
Displacement Reactions
More reactive halogens can react with the ions of less reactive halogens and displace them from compounds.
For example: 2KI(aq) + Br2(aq)  2KBr(aq) + I2(aq)
This reaction works because bromine is more reactive than iodine.
The orange colour of bromine would change to the brown colour of aqueous iodine.
The reverse reaction would not work.
Reactivity Series of Halogens
Displacement reactions can be used to determine the order of reactivity of the halogens.
Try reacting each halogen with solutions of each halide salt, the halogen that displaces the most halides is the most reactive.
Alkaline metals react vigorously when heated in chlorine gas
Alkali metal + chlorine  metal chloride
They react with oxygen to form metal oxides
Metal + oxygen  metal oxide
Type of Bonding
Ionic
Simple molecular
Giant Molecular
How the bonds form
Swapping electrons to form ions
Sharing electrons
Examples
Sodium chloride, magnesium oxide
Water, methane, nitrogen
Quartz (silicon dioxide)
Bond strength
Strong
Strong bonds, weak intermolecular forces
Strong bonds
Melting and boiling point
High
Low
Solubility
Most in water
Some in water
Insoluble in water
Conduct electricity?
Only when molten or dissolved No
No (except graphite)
5.1 (sheet b) Groups in the Periodic Table
Noble Gases
Group 0 in the periodic table.
Helium ((He, Neon (Ne), Argon (Ar), Krypton (Kr) Xenon (Xe), Radon (Rn)
Full outer shells so extremely unreactive: inert.
All exist as colourless monatomic gases
Trends:
Boiling points increase as you go down the group
Uses:
He and Ar were used to stop in filament in old bulbs burning.
Ar and He used in welding to stop hot metal oxidising.
Ar used in fire extinguishing systems in server rooms.
He used in airships/blimps due to low density.
Neon lights due to red colour of light produce by neon.
COLUMNS ARE GROUPS……similar properties
Element Type
= non-metal = metal
ROWS ARE PERIODS….increasing atomic mass, differing properties
Halide Salt
Potassium fluoride
Potassium chloride
Potassium bromide
Potassium iodide
Halogen
Fluorine x
Reaction
Chlorine
No reaction
Bromine
Iodine