Redox And Group 2 Flashcards
Define oxidation (4)
Oxygen addition
Hydrogen loss
Electron loss
Increase oxidation number
Define reduction (4)
Oxygen loss
Hydrogen addition
Electron gain
Decrease oxidation number
Oxidation number
Measure of how oxidised an atom is
Oxidation number rules (9)
Simple ion = charge
Atom as pure element = 0
F = always -1
O = -2 (except F compounds)
Cl = -1 (except O/F compounds)
H = 1+ (except metal hydrides)
Group 1 = always 1+
Group 2 = always 2+
Al = always 3+
Sum of oxidation number rule (3)
Must be equal on both sides
Sum of ONs in a compound = overall charge
Quoted per atom not compound
Balancing redox equations using ONs
Identify atoms being O/R
Balance amount each is being O/R by
Don’t change O/R ratio
Total left/right charges, balance
Half equation electron placement
O = right
R = left
Half equations (5)
R or O
Feature electrons
2X —> ionic equ
Reversible (depends on other elements reactivity)
Ionic equations (4)
1 O, 1 R
Balance e no
Cancel common terms
H+ and OH- on same side —> H2O
Disproprotionation
Element in a species O and R simultaneously
Eg. 2Cu+ —> Cu + Cu2+
Ionic radius group 2 strand
Smaller up the group
Less electron shells
Less shielding
Electrons held tighter
Electrostatic attraction is stronger despite constant charge
Ionisation energy group 2 trend
Decreases down the group
More electrons, more electron shells
More shielding from positive nucelus
Outer electrons further from nucleus
Reduces attraction despite nuclear charge being constant
Easier to remove electrons
Reactivity trend group 2
Increases down the group
React by losing outer electrons —> Mg2+
Higher IEs, harder to do
Lower IEs = more reactive
Group 2 reaction with water trends
Make metal hydroxides and hydrogen
Be - doesnt react
Mg - very slowly reacts, ppte
Ca - steadily, ppte
Sr - fairly quick, clear solution
Ba - rapid, clear solution
Magnesium reaction with steam
Forms MgO rapidly
Bright white light
Hydrogen gas as it leaves tube (safety)
Group 2 react with oxygen trends
Mg - bright flame
Oxides are bases
React with water —> metal hydroxides/alkalis/OH-, more alkaline down the group
BeO - exception, insoluble
MgO - reacts slowly, MgOH insoluble
Give a use of group 2 oxides
Agriculture, neutralise soil acids
Group 2 chlorine reaction trend
BeCl2 - covalent, dative, Be electron deficient
Be more electronegative than rest of group 2, high polarising power
Why do group 2 give off colour in a flame test
Energy absorbed from fame
Electrons move to higher levels (excited)
Colour seen when electrons fall back down, release energy as light
Difference in energy levels/wavelength determines colour
Electron transition
Flame test method
Heat platinum/nichrome wire in roaring Bunsen flame until no colour is seen
Dip in conc HCl
Put in flame
Dip in conc HCl
Dip in metal compound
Put in flame
Flame test results (Li, Na, K, Rb, Ce, Ca, Sr, Ba, Cu, Mg)
Li - Red
Na - Yellow
K - Lilac
Rb - Red/purple
Ce - Violet
Ca - Brick red
Sr - Crimson
Ba - Green
Cu - Turquoise
Mg - Colourless
Test for ammonium ions
Cation
Doesn’t give off colour in a flame test
Add to NaOH
Warm
Ammonia gas —> damp red litmus —> blue
Solubility trend group 2 hydroxides
Increases down the group
Reason…?
Uses of MgOH
Sparingly soluble
Anti acids neutralise stomach
Laxative
Low OH- conc, not a health risk
Group 2 double charged negative ion compound solubility trend
Decrease down group
BaSO4 uses
Insoluble
Shows up on x ray
Toxic, safe as its insoluble
Thermo stability group 2 trend
Extent to which something breaks down when heated
More thermally stable = more heat to break it down
Increases down the group
Group 1 more thermally stable than group 2, lesser charge, less distortion
Group 2 polarising power trend
Ability of a positive ion to distort the anion electron cloud
Larger charge/smaller ion/higher charge density = greater pp
More distortion, less stability
Group 2 carbonates thermal decomposition trends and observations
Decompose —> metal oxide and carbon dioxide
Increase thermal stability down the group
Limewater test for CO2
Test for aqueous acids, effervescence
Group 2 nitrates thermal decomposition trends
Make metal oxide, nitrogen dioxide and oxygen
Thermal stability increases down the group
