Groups in the periodic table Flashcards
Group classification
Elements are arranged on the Periodic table in order of increasing atomic number where each element has one proton more than the element preceding it.
The table is arranged in vertical columns called groups numbered I – VIII and in rows called periods.
The period number tells you the number of electron shells an atom has.
The group number tells you how many outer electrons each atom has.
The periodic table positions elements based on their properties which are linked to their electronic configurations.
Elements with the same number of electrons in the outer shell and hence similar chemical properties are placed in the same group.
This allows us to use the table to predict the properties of elements based on their position.
Physical properties in group 1
The group 1 metals are known as the alkali metals.
They form alkaline solutions when they react with water.
The group 1 metals are lithium, sodium, potassium, rubidium, caesium and francium and they are found in the first column of the periodic table.
They are all soft metals which can easily be cut with a knife.
They have relatively low densities and low melting points.
They are very reactive (they only need to lose one electron to become highly stable) .
How Alkali Metals React with Water
group 1 metal + water ⟶ metal hydroxide + hydrogen
2M (s) + 2H2O (l) ⟶ 2MOH (aq) + H2 (g)
They form an alkali solution when they react with water which is caused by the hydroxide and hydrogen gas is given off.
Effervescence can be observed as well as a coloured flame (exothermic reaction).
lithium - red flame
sodium - orange flame
potassium - lilac flame
rubidium - red-violet flame
caesium - blue-violet flame
Trends in group 1
More reactive as you go down the group.
Vigorous reactions with water and oxygen so stored in oil.
Melting point decreases as you go down the group.
All have low densities and are soft.
Melting and boiling point of group 1
Low melting points that decrease as you go down the group. this is because the metal ions get larger as you go down group 1 so the attraction between the delocalised electrons and metal ions are weaker so the metallic bonds are also weaker.
Reactivity of group 1
The reactivity of the group 1 metals increases as you go down the group.
When a group 1 element reacts its atoms only need to lose electron, as there is only 1 electron in the outer shell.
When this happens, 1+ ions are formed.
The next shell down automatically becomes the outermost shell and since it is already full, a group 1 ion obtains noble gas configuration.
As you go down group 1, the number of shells of electrons increases by 1.
This means that the outermost electron gets further away from the nucleus, so there are weaker forces of attraction between the outermost electron and the nucleus.
Less energy is required to overcome the force of attraction as it gets weaker, so the outer electron is lost more easily.
So, the alkali metals get more reactive as you descend the group.
Colours of pure halogens
Fluorine - yellow
Chlorine - green
Bromine - brown
Iodine - grey / black
Astatine - black
Colour of dissolved halogens
Fluorine - colourless
Chlorine - colourless, possibly pale green
Bromine - orangey / yellow
Iodine - brown
Astatine - doesn’t dissolve
Melting and boiling point of halogens
There are strong covalent bonds between the atoms but there are weak intermolecular forces between molecules. The intermolecular forces are weaker in smaller molecules and as the size of the atom increases as you go down group 7 the melting and boiling point does too.
Test for chlorine
Damp blue litmus paper is used and if chlorine is present it will turn red and then become bleached (turn white).
Cl + H2O —- HCl + HOCl
the hydrochloric acid turns the litmus paper from blue to red and the hypochlorous acid bleaches it.
Metal halides
The halogens react with some metals to form ionic compounds which are metal halide salts.
The halide ion carries a -1 charge so the ionic compound formed will have different numbers of halogen atoms, depending on the valency of the metal.
The halogens decrease in reactivity moving down the group, but they still form halide salts with some metals including iron.
The rate of reaction is slower for halogens which are further down the group such as bromine and iodine.
Hydrogen halides
The halogens react with nonmetals to form simple molecular covalent structures.
Hydrogen halides are steamy acidic gases that dissolve very well in water to form strongly acidic solutions.
Displacement reaction
A halogen displacement reaction occurs when a more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide.
The reactivity of group 7 elements decreases as you move down the group.
If the halogen element is less reactive then there will be no reaction.
Halogen displacement and redox
Oxidation is loss of electrons and reduction is the gain of electrons.
Halogen displacement reactions are redox reactions.
Reactivity of halogens
Halogen atoms gain electrons to obtain a full outer shell like a noble gas. the nearer the outer shell is to the nucleus, the stronger the attraction for the incoming electron and so the more reactive the halogen is. as you go down group 7 the size of the atoms becomes larger and the further the nucleus is from the outer shell. this means that the attraction for the incoming electron and the nucleus becomes weaker and the halogens get less reactive towards the bottom of the group.
