3.2: Periodicity Flashcards
What is periodicity?
a regular repeating pattern of atomic physical and chemical properties
What is the trend in melting points across period 3?
- increases
- due to increase in nuclear charge
- more delocalised eolectrons to increase metallic bond strength
- more energy needed to break these bonds
Na, Mg, Al
What are the trends in melting and boiling point across Period 3?
1.Na, Mg, Al
- giant metallic latice with positive metal ions surrounded by a sea of delocalised electrons
- strong electrostatic forces, increasing nuclear charge
- Mp- 371,922,933 l Bp- 1156,1380,2740
Si
What are the trends in melting and boiling point across Period 3?
2.Si
- giant covalent/ macromolecular molecule
- many strong covalent bonds
- Mp- 1683 l BP- 2628
melting and boiling point fluctuate
P4, S8, Cl2
What are the trends in melting and boiling point across Period 3?
3.P4,S8,Cl2
- simple molecular
- weak intermolecular forces, VDW forces, more molecules, stronger forces as larger molecule
- Mp- 317, 392, 172 l Bp- 553, 718, 238
melting and boiling point fluctuate
Ar
What are the trends in melting and boiling point across Period 3?
4.Ar
- atomic
- very weak forces between atoms
- Mp- 84 l Bp- 87
melting and boiling point fluctuate
What is the trend in ionisation energies across Group 2?
- Melting point decreases down the group (Mg has anomalylously low b.p. due to differnt crystal structure)
- Atomic radius increases
- Solubility of salts increases
- Reactivity with water increases
- Ionisation energy decreases
What is the trend in melting points across Group 2?
- Size of the atoms increase
- Distance between the nucleus and “sea” of delocalised electrons increases
- Strength of metallic bond decreases
- Energy required to overcome the bond decreases
- Melting points decrease down the group
- Magnesium has an unexpectedly low melting point
Why does reactivity increases down Group 2?
- Increased atomic radius/ size of atoms/ number of electron shells
- Greater distance between nucleus and outer shell electrons
- Weaker attraction between outer electrons and nucleus / more shielding
- Easier to remove outer electrons
What happend when you react Group 2 metals with water?
By reacting group 2 metal with water, metal hydroxides and hydrogen are formed.
M(s) + 2H2O (l) → M(OH)2 (aq) + H2 (g)
Metal is oxidised
Hydrogen is reduced
Magnesium also reacts with steam at high temperatures to produce magnesium oxide:
Mg(s) + H2O(g) → MgO(s) + H2(g)
What is the pattern in solubility in Group 2 hydroxides?
Group 2 hydroxides, X(OH)2, are all white solids that become more soluble down the group.
- Magnesium hydroxide- almost insoluble
- Calcium hydroxide- sparingly soluble
- Strontium hydroxide- more soluble
- Barium hydroxide-dissolves to produce strong alkaline solution (because of the OH- ions)
What is the pattern in solubility in Group 2 sulfates?
By reacting group 2 metal with sulphuric acid, metal sulphates are formed.
Reaction equation:
Mg (s) + H2SO4 (aq) → MgSO4 (aq) + H2 (g)
The group 2 sulphates get less soluble down the group (Mg-Ba).
BaSO4 is insoluble.
Acidified BaCl2 solution
How do you test for sulphate ions?
- Sulphate ions in solution, (SO4^2-), are detected using acidified barium chloride solution.
- The test solution is acidified using a few drops of dilute hydrochloric acid, and then a few drops of barium chloride solution are added.
- A white precipitate of barium sulfate forms if sulfate ions are present:
BaCl2(aq) + Na2SO4(aq) → 2NaCl(aq) + BaSO4(s) - The hydrochloric acid is added first to remove any carbonate ions that might be present - they would also produce a white precipitate, giving a false positive result.
What are different uses of Group 2 in medicine, agricuture and titanium extraction?
- Magnesium hydroxide (Mg(OH)2), milk of magnesia, acts as an “antacid”- neutralises excess stomach acid- as a treatment for indigestion.
- Barium sulphate (BaSO4) is used in x-rays to image a patient’s stomach and intestines as it is opaque to x-rays.
- Calcium hydroxide (Ca(OH)2) can be added to solid to raise the pH level to 6-7, the optimum for most plants.
-
Magnesium: TiO2 is converted into TiCl4 by heating with carbon and chlorine, TiCl4 is then reduced by Mg
** TiCl4(g) + 2Mg(l) -> Ti(s) + 2MgCl2(l)** - titanium is reduced, magnesium is oxidised
What are Group 7 elements?
- halogens
- highly reactive non-metals of group 7
- Flourine- pale yellow
- Chlorine- green
- Bromine- red-brown
- Iodine- grey
What is the pattern in electronic configuration, melting and boiling points and ionisation energies across Group 7?
- boiling points increase down the group due to increase in strength in VDW forces
- electronegativty decreases down the group
- reactivity decreases down the group as it’s harder to gain an electron as there’s more shielding and a larger atomic radius so further from electrosatic forces and opposing charge.
When will a halogen displace a halide from solution?
if the halide is below it in the periodic table
- add Cl2 (aq) (colourless)- no reaction in KCl (colourless) water l forms orange solution (Br2) in KBr (colourless) water l forms brown solution in KI (colourless water)
- add Br2 (aq) (orange)- no reaction in KCl (colourless) water l no reaction in KBr (colourless) water l forms brown solution in KI (colourless water)
- add l2 (aq) (brown)- no reaction in KCl (colourless) water no reaction in KBr (colourless) water l no reaction in KBr (colourless) water l no reaction in KI (colourless) water
What happens when you mix cold, dilute, aqueous sodium hydroxide with chlorine gas?
- makes sodium chlorate (I) solution NaClO(aq)
- bleach
What is disproportionation and an example?
A reaction where the same element is both reduced and oxidised
e.g. Chlorine and water:
Cl2 + H2O 🡪 2H+ + ClO- + Cl-
Chlorate ions, ClO- , kill bacteria so chlorine is added to water to make it safe.
Why is chlorine water added to water (benefits and disadvantages)?
chlorate (I) ions kill bacteria so adding chlorine to water can make it safe to drink or swim in
advantages:
- kills disease-causing microorganisms
- some chlorine persists in water, preventing reinfection down the supply
- prevent algae growth eliminating bad tastes, smells and discolouration caused by organic compounds
disadvantages:
- irritates the respiratory system
- liquid chlorine causes chemical burns
- any organic compounds in water can form chlorinated
hydrocarbons which are carcinogenic
however, cancer risk small compare to untreated water (e.g. cholera)
How do you test for Halides?
- Halogens (group 7) can be tested for using silver nitrate solution with nitric acid.
- Ag + (aq) + X-(aq) 🡪 AgX(s)
- Silver Flouride- no precipitate
- Silver Chloride- white precipitate (forms slowest l most soluble in NH3 (dilute))
- Silver Bromide- cream preciptate (2nd most soluble in NH3 (concentrated))
- Silver Iodide- yellow precipitate (forms fastest l least soluble in NH3 (dilute)))
What is the reducing power of the halides?
- The reducing power of a species is related to the reactivity.
- Reducing power increases across the group
- As reduction is gain of electrons, the reducing power of a species is how easily it can reduce (add electrons to) another species.
- The reducing power of the halides increases down the group as they are more easily able to lose electrons to another species and reduce them.
NaF or NaCl
What occurs in the reaction of the halides with sulphuric acid?
NaF(s) + H2SO4(aq) 🡪 NaHSO4(s) + HF(g)
NaCl(s) + H2SO4(aq) 🡪 NaHSO4(s) + HCl(g)
- Misty fumes will be seen.
- HF and HCl not strong enough reducing agents so reaction stops there.
NaBr
What occurs in the reaction of the halides with sulphuric acid?
NaBr(s) + H2SO4(aq) 🡪 NaHSO4(s) + HBr(g)
2HBr(g) + H2SO4(aq) 🡪2H2O(l) + Br2(g) + SO2(g)
- Misty fumes will be seen.
- HBr is a stronger reducing agent so reacts in a redox reaction.
- Choking fumes
- Orange fumes
NaI
What occurs in the reaction of the halides with sulphuric acid?
NaI(s) + H2SO4(aq) 🡪 NaHSO4(s) + HI(g)
2HI(g) + H2SO4(aq) 🡪 2H2O(l) + I2(s) + SO2(g)
6HI(g) + SO2(g) 🡪 2H2S(g) + 3I2(s) + 2H2O(l)
- Misty fumes will be seen.
- HI is a strong reducing agent so reacts with the sulphuric acid, and then also reduces the SO2.
- H2S- toxic smells of bad eggs
What is the reaction of sodium with water?
2Na(s) + H2O(l) -> 2NaOH(aq) + H2(g)
- reacts in water in rapid and violent reaction
- sodium fizzes (effervescence) and floats on surface of water
- exothermic reaction
- resulting solution __NaOH__ is strongly alkaline, solution of __pH 13-14__
What is the reaction of magnesium with water?
__Mg(s) + 2H2O(l) -> Mg(OH)2(aq) + H2(g)__
- reacts less rapidly and violetly than sodium
- very slow reaction at room temp
- results in weak alkaline as Mg less soluble in water than Na
- pH 10
What is the reaction of chlorine with water?
Cl2 (aq) + H2O (l) -> HCl (aq) + HClO (aq)
- redox reaction/ disproportionation (Cl both oxidised and reduced)
- gas produces, aqueous solution
- dissolves, producing very pale green solution
What is the reaction of sodium and oxygen?
Na
2Na(s) + 0.5O2(g) -> Na2O(s)
- exothermic, Na reacts directly with oxygen
- burns bright yellow flame, white smoke (Na peroxide)
What is the reaction of magnesium and oxygen?
Mg
2Mg(s) + O2(g) -> 2MgO(s)
- Mg ribbon burns readily in O2, producing MgO
- gives bright white flame, leaves white powder, exothermic
What is the reaction of aluminium and oxygen?
Al
4Al(s) + 3O2(g) -> 2Al2O3(s)
- exothermic, reacts slowly w/ O2 unless in powder form
- burns bright, produces white powder Al2O3 (white flame)
What is the reaction of silicon and oxygen?
Si
Si(s) + O2(g) -> SiO2(s)
- exothermic, reacys w/ O2 slowly (red/orange flame)
- must be heated strongly in oxygen
What is the reaction of phosphorus and oxygen?
P4
P4(g) + 5O2(g) -> P4O10(s)
- exothermic, red phosphorus must be heated before reacting
- white P4 reacts spontaneously w/ O2 producing white smoke (phosphorus sun- white light)
What is the reaction of sulfur and oxygen?
S8
S(g) + O2(g) -> SO2(g)
- exothermic, blue flame
- smoke produced, not fully oxidised
What is the reaction of sulfur and oxygen at high temp. and with a catalyst?
S8
S(g) + 3/2O2(g) -> SO3(l)
What is the reaction of Na2O and water?
giant ionic
Na2O(s) + H2O(l) -> Na+(aq) + 2OH-(aq)
- base, neutralising acids forming alkaline solutions
- strong alkaline soluion pH 14
What is the reaction of MgO and water?
giant ionic
MgO(s) + H2O(l) -> Mg(OH)2(s) ⇌ Mg2+(aq) + 2OH-(aq)
- base, neutralising acids, form alkaline solutions
- sparingly soluble in water, pH 9-10
What is the reaction of Al2O3 and water?
giant ionic (covalent character)
- insoluble in water, so no reaction in water
- Al2O3 insoluble due to high lattice enthalpy
What is the reaction of SiO2 and water?
giant covalent
- insoluble in water, so no reaction in water
- SiO2 insoluble as giant covalent molecule with millions of strong covalent bonds
What is the reaction of Al2O3 and water?
giant ionic (covalent character)
What is the reaction of P4O10 and water?
molecular
P4O10(s) + 6H2O(l) -> 4H3PO4(aq)
H3PO4(aq) ⇌ H2PO4-(aq) + H+ (aq)
- forms acidic solutions with non-metal oxides
- reats violently with water
- produces acidic phosphorus acid solution
- H2O molecules attatch to delta positive P atoms, leading to release of H+ ions from H2O (pH 0-1)
What is the reaction of SO2 and water?
molecular
SO2(g) + H2O(l) -> H2SO3(aq) ⇌ HO3-(aq) + H+(aq)
- SO2 fairly soluble, produce acidic solutions (pH 2-3)
What is the reaction of SO3 and water?
molecular
SO3(g) + H2O(l) -> H2SO4(aq) -> HSO4-(aq) + H+(aq)
- SO3 reacts violently w/ water, producing sulfuric acid (pH 0)
How does Na2O and MgO react with acids/bases?
- bases
- neutralise acids to form salt and water
Na2O(s) + H2SO4(aq) -> Na2SO4(aq) + H2O(l)
MgO(s) + 2HCl(aq) -> MgCl2(aq) + H2O(l)
How does Al2O3 react with acids/bases?
amphoteric- acts as an acid and a base
Al2O3(s) + 6HCl(aq) ->2AlCl3(aq) +3H2O(l)
Al2O3(s) + 2NaOH(aq) +H2O(l) -> 2NaAl(OH)4(aq)
How does SiO2 react with acids/bases?
- reacts as a weak acid w/ a strong base
SiO2(g) + 2NaOH(aq) -> NaSiO3(aq) + H2O(l)
How does P4O10 react with acids/bases?
- reacts w/ alkali, reacts in 3 stages due to 3 OH- groups
- each H turns into OH- ion replaced by sodium ion
P4O10(s) + 6H2O(l) -> 4H3PO4(aq)
H3PO4(aq) + 3NaOH(aq) -> Na3PO4(aq) + 3H2O(l)
How does SO2 react with acids/bases?
- first reacts w/ NaOH then sodium sulphate(IV)
SO2(aq) + NaOH(aq) -> NaHSO3(aq)
NaHSO3(aq) + NaOH(aq) -> Na2SO3(aq) + H2O(l)
What are structures of different anions formed?
- PO43-: phosphate (V)- basic
- SO32-: sulfate (IV)- acid
- SO42-: sulfate (VI)- acid
What is a transition metal?
a metal that contains an incomplete d-subshell in atoms or one of its common ons (can form 1 or more stable ions w. incomplete d-subshells)
Ti -> Cu
