Redox And Groups 2&7 Flashcards
The oxidation number of elements
0
Oxidation numbers of group 1 and 2
1 and 2
Oxidation number of fluorine
-1
Oxidation number of oxygen
-2 unless attached to itself then it’s 0 or fluorine when it becomes positive
Oxidation number of group three elements onwards
Up to its group number
Oxidation number of hydrogen
-1 when attached to metals or +1 when attached to more electronegative non metals
Oxidation
The addition of oxygen
The loss of electrons
An increase in oxidation number
Reduction
The removal of oxygen
The gain of electrons
A decrease in oxidation number
Redox
A reaction with both reduction and oxidation
Halogens- trend in boiling point
Increases down the group as there are more electrons so stronger London forces. More energy is required to break the intermolecular force
Halogens- shell arrangement
2 electrons on the outer S-sub shell and 5 in the outer P sub shell.
What happens to halogens in a reaction
They are reduced, gaining one electron to form a 1- ion
Halogens halide displacement reaction
Done to show that reactivity decreases down the group. A solution of each halogen is added to an aqueous solution of the other halide. If the halogen is more reactive then the ion then a reaction takes place and the halogen displaces the halide from the solution and the solution changes colour
Halogen colour in water
Cl2- pale green
Br2-orange
I2- brown
Halogen colour in cyclohexane
Cl2- pale green
Br2-orange
I2-violet
Why would you add cyclohexane in halogen reactions
As in water iodine and bromine are a similar colour so it helps to tell them apart. When a reaction has occurred the solution turns the colour of the displaced halide
Halogen reactivity trend
They get less reactive down the group as atomic radius increases, more inner shells so shielding increases, so less nuclear attraction to capture an electron from another species
Disproportionation
A redox reaction in which the same element is both oxidised and reduced
The reaction of chlorine with water
Cl2+H2O—>HClO+HCL
0 +1 -1
HClO and HCl are both acids, the bacteria is killed by chlorine acid and chlorate ions (ClO-). Chlorine is used in water purification
Chlorine with cold, dilute aqueous sodium hydroxide
Cl2+2NaOH——>NaClO+NaCl+H2O
0 +1 -1
Bleach is formed by reacting chlorine with cold dilute aqueous sodium hydroxide as more ClO- ions are formed
Ionisation energy group 2
The ionisation energy decreases down the group because the attraction between the nucleus and the outermost electron decreases due to shielding and an increase in atomic radius which overcomes the increase in nuclear charge.
Group 2 reactivity
They need to loose two electrons which requires the input of the first two ionisation energies. As ionisation energy decreases down the group reactivity increases as less energy is needed to loose the 2 elections which are needed for a reaction to take place. They become stronger reducing agents down the group.
Group 2 oxides with water
They release OH- ions and form alkaline solutions of metal hydroxides. CaO+H2O—> Ca+2+2OH- group 2 hydroxides are only slightly soluble in water when the solution is saturate any further metal and hydroxide ions will form a solid participate Ca+2+OH- —> Ca(OH)2
Benefits of Chlorine use
Kills bacteria so stops water contaminated diseases such as typhus and makes it safe to drink. Benefits outweigh disadvantages
disadvantages of Chlorine use
Is a respiratory irritant in small quantities and can be fatal in large quantities. Can react with organic hydrocarbons such as methane from dying vegetation to form chlorinated hydrocarbons which is a carcinogenic.
Group 2 elements shell arrangements
S2 arrangement, they loose these electrons in redox reactions to form +2 ions.
Redox reactions with oxygen group2
Form metal oxides
2Mg+O2–>2Mgo. the metal increases by 2 oxidation numbers the oxygen decreases by 2. Reaction mre vigorous down the group
Redox reactions with water group 2
Sr+2H2O–>Sr(OH)2+H2.
Water and magnesium react very slowly but reactions become more vigorous down the group. Hydrogen gas and an alkaline hydroxide is formed.
Group2 redox reactions change in oxidation number
the group 2 metal increases by 2, the hydrogen which forms H2 decreases by 1 each, the 2 H forming X(OH)2 do not change.
Redox reactions with acid
metal +acid –> salt +hydrogen. Mg increases by 2 hydrogen decreases by 1.
solubility trend in group 2 hydroxides
the solubility of the hydroxides in water increases down the group so resulting solutions contain more OH ions so are more alkaliney
group 2 oxide which neutralises acidic soil
CaOH2
Ca(OH)2+2H+–>Ca+2+2H2O
group two oxides to treat indigestion
Mg(OH)2 and CaC03 are used as antacids
Mg(OH)2+2HCl–>MgCl2+2H2O
CaCo3+2HCl–>CaCl2+H2O+CO2
Reaction of group 2 metals with water
Reaction is more vigorous down the group. Hydrogen gas is released. A white precipitate will form, down the group it becomes more soluble so it might dissolve nd there wont be a precipitate.
