Chapter 4: Group Elements

4.1-Metals and Non-Metals

Atoms generally react to form a full outer shell
- They do this via losing, gaining or sharing electrons
Metals to the left of the periodic table don’t have many electrons to remove
Metals towards the bottom of the periodic table have outer electrons which are a long way from the nucleus
- They feel a weaker attraction
- Both these effects means that not much energy is needed to remove the electrons so it’s feasible for them to either share or gain electrons to get a full outer shell

All metals have metallic bonding which causes them to have similar basic physical properties
- They’re strong but can be bent or hammered into different shapes
- They’re great at conducting heat and electricity
- They have high boiling and melting points
As non-metals don’t have metallic bonding, they don’t tend to exhibit the same properties as metals
- They tend to be dull looking, more brittle, aren’t always solids at room temperature, don’t generally conduct electricity, and often have a lower density

Transition metals are in the centre of the periodic table
Transition metals are typical metals and have the properties you would expect of a proper metal
- They’re good conductors or heat and electricity and they’re very dense, strong and shiny
Transition metals also have some pretty special properties
- Transition metals can have more than one iron
- Copper forms Cu+ and Cu2+ ions
- Cobalt forms Co2+ and Co3+ ions
- Transition metal ions are often coloured, and so compounds that contain them are colourful
- Potassium chromate which yellow and potassium manganate is purple
- Transition metal compounds often make good catalysts
- Nickel based catalysts are used in the hydrogenation of alkenes
- Iron catalyst is used in the haber process for making ammonia

The alkali metals are lithium, sodium, potassium, rubidium, caesium and francium
They all have one electron in their outer shell which makes them very reactive and gives them similar properties
The alkali metals are all soft and have low density
The trends for the alkali metals as you go down Group 1 include:
- Increasing reactivity
- The outer electron is more easily lost as the attraction between the nucleus and electron decreases, because the electron is further away from the nucleus and the further down the group you go
- Lower melting and boiling points
- Higher relative atomic mass

The Group 1 elements don’t need much energy to lose their one outer electron to form a full outer shell, so they readily form 1+ ions
It’s so easy for them to lose their outer electron that they only ever react to form ionic compounds.
These compounds are generally white solids that dissolve in water to form colourless solutions
Reaction with water
- When Group 1 metals are put in water, they react vigorously to produce hydrogen gas and metal hydroxide
- Salts that dissolve in water to produce alkaline solutions
- The more reactive(lower down in the group) an alkali metal is, the more violent the reaction
- Sodium + Water - Sodium Hydroxide + Hydrogen
- 2Na + 2H20 - 2NaOH + H
Reaction with chlorine
- Group 1 metals react vigorously when heated in chlorine gas to form white chloride salts
- As you go down the group, reactivity increases so the reaction with chlorine gets more vigorous
- Sodium + Chlorine - Sodium Chloride
- 2Na + Cl - 2NaCl
Reaction with oxygen
- The Group 1 metals can react with oxygen to form a metal oxide:
- Different types of oxide will form depending on the Group 1 metal:
- Lithium reacts to form lithium oxide
- Sodium reacts to form a mixture of sodium oxide(Na20) and sodium peroxide(Na2O2)
- Potassium reacts to form a mixture of potassium peroxide(K202) and potassium superoxide(K02)

Group 1 metals are much more reactive than transition metals-they react more vigorously with water, oxygen or Group 7 elements, for example
They’re also much less dense, strong and hard than the transition metals, and have much lower melting points
- e.g. manganese melts at 2000C
- Sodium melts at 98C

As you go down Group 7 the halogens
- Become less reactive
- It’s harder to gain an extra electron, because the outer shell’s further from the nucleus
- Have higher melting and boiling points
- Have higher relative atomic mass
All the Group 7 elements react in similar ways.
This is because they all have seven electrons in their outer shell

Halogen atoms can share electrons via covalent bonding with other non-metals so as to achieve a full outer shell
- For example, HCI, PCI5, HF and CCI4 contain covalent bonds
- The compounds that form when halogens react with non-metals all have simple molecular structures

Group 0 elements are called the noble gases and include the elements helium, neon and argon(and a few others)
They all have eight electrons in their outer energy level, apart from helium which has two, giving them a full outer shell
As their outer shell is energetically stable they don’t need to give up or gain electrons to become more stable
- This means they are more or less inert-they don’t react with much at all
They exist as monatomic gases-single atoms not bonded to each other
All elements in Group 0 are colourless gases at room temperature
As the noble gases are inert they’re non flammable
- They won’t set on fire

The boiling point of the noble gases increase as you move down the group along with increasing relative atomic mass
- The increase in boiling point is due to an increase in the number of electrons in each atom leading to greater intermolecular forces between them which need to be overcome
In the exam you may be given the boiling point of one noble gas and asked to estimate the value for another one
- Neon is a gas at 25C. Predict what state helium is at this temperature
- Helium has a lower boiling point than neon as it is further up the group
- So, Helium must also be a gas at 25C

Note

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