S-Block Flashcards
what % of the mass of the atom is the nucleus?
> 99.94%
quantum numbers: n, l, ml, ms
n = shell, l = s-0,p-1,d-2… ml = -1,0,1 etc, ms = +/- spin
atoms in ground state, orbital filling order?
Fill: 1s,2s,2p,3s,3p,4s,3d,4p,4d…
vertical columns?
groups
horizontal columns?
periods
4f elements?
lanthanoids
5f elements?
actinoids
S block groups?
Gp1 - alkali metals. Gp2 - alkaline earth metals
Ionisation energy?
energy required to remove one electron, from gas phase to form cation.
endothermic process
ionisation energy trend?
decrease down the group. more protons = higher nuclear charge = stronger pull = so smaller “size” = higher IE energy required for further removal. shielding effect means decrease in energy down group
electron affinity?
the electron gain energy (Eeg), energy change change when one electron is added to one atom in gas phase to form an anion. also known as electron affinity
relationship between electron affinity and electron gain?
Ea = - Eeg
trends of Ea
exothermic electron uptake forms stable Nobel gas configuration
electronegativity?
dimensionless. ability to attract electrons in a chemical bond using Pauling scale
electronegativity trend?
EN increases across a period and decreases down a group. EN increases with higher oxidation states, this is to do with the charges of ions
electropositivity?
ability to donate electrons in a bonding interaction. alkali metals very electropositive (low first ionisation energy)
metalloids?
semimetals. B, Si, Ge, As, Sb, Te, Po. metal character, intermediate properties
metals?
s - block elements. low ionisation energy and low electronegativity (X)
non metals?
high ionisation energy and high electronegativity (X)
metal characteristics
metallic shine. electric and thermal conductors. outer electrons move freely (sea of delocalised electrons)
malleability and ductility
malleable - formed without breaking
ductile - drawn into wire
atomic and ionic radii?
atomic radii - radius in the metal element, assuming hard sphere
ionic spheres - comparing ionic compounds and ions
depends on elements and charge of the ion
atomic radii trend?
Atomic radii increase towards bottom left of periodic table. Caesium is largest atom. - Atomic radii decrease across the period
Alkali metals?
Li, Na, K, Rb, Cs, Fr
alkali metals properties?
silvery white, soft metals, highly reactive, strong reducing agents
alkali metals electron configuration
[Ng] s1
Na+ and K+ uses
minerals/electrolytes in human body; blood pressure regulation, action potentials for nerve cells
NaCl for seasoning
Lithium salts uses?
carbonates, acetates, citrate
treatments for manic-depressive psychoses (bipolar disorder) as a mood stabiliser
trends down the Gp1 period?
atomic radius increases
ionisation energy decreases
mp and bp decreases
weak metallic bonding between atoms
density increases (but got low density)
enthalpy of sublimation decreases (turn to gas phase)
preparation of alkali metals?
Li and Na prepared by electrolysis of their molten salts by DOWNS process
electrolysis of molten NaCl at 600ºC and 4-8 eV
reaction of Na and Cl?
2 NaCl (l) 2 Na (l) + Cl2 (g)
Downs Process?
> 50%
CaCl2 additives to keep the salt liquid below the NaCl melting
point of 801°C; Ca2+ is more difficult to reduce than Na+, a
carbon anode and an iron cathode are used
Na and K reactions?
K+ and Na+ stored under oil, as reactive in oxygen
K+ cannot be prepared by electrolysis (too reactive)
Na + KCl –> NaCl + K
at high temp, to drive equilibrium in substitution reaction
alkali metals reduction potential?
heavier alkali metals are more reducing than the lighter ones
Uses of sodium metal?
synthesis of tetraethyl leads as a fuel additive for anti knocking properties
4 NaPb + 4 EtCl → PbEt4 + 3 Pb + 4 NaCl
released alot of lead into the atmosphere
alkali metals as drying agents?
Na, K and Na/K with water can be used to dry chemicals effectively.
Using a metal that will be liquid at the solvents boiling point, can reflux under inert gas and distil away the solvent
alkali with oxygen/air reaction?
4 Li + O2 → 2 Li2O (oxide, O2-)
2 Na + O2 → Na2O2 (peroxide, O22-, with O-O single bond)
5
K + O2 → KO2 (superoxide, O2
*-, radical anion) this is very unstable
super oxides?
KO2 is a superoxide. yellow, paramagnetic and shock sensitive
Hydrolysis of KO2
4 KO2 (s) + 2 H2O (l) → 4 K+
(aq) + 4 OH-
(aq) + 3 O2
HO2 is not stable due to disproportionationation and gives O2
hence needs to be kept in inert gas
Reaction of KO2 with CO2
4 KO2 + 2 CO2 → 2 K2CO3 + 3 O2; 4 KO2 + 4 CO2 + 2 H2O → 4
KHCO3 + 3 O2.
O2 is released so they can be called oxygen generators in space suits
lithium reaction with nitrogen
6 Li (s) + N2 (g) = 2 Li3N (s)
has to be stored under argon
forms strong triple bonds
Li+ able to form stable lattice with N3- anions. cannot be done with larger anions, overcoming disassociation energy
N3- is hard and small and this needs to be balanced by also small metals ie 3x Li+1
alkali metal reaction with water?
react violently (exothermic)
2 M (s) + 2 H2O (l) -> 2 MOH (aq) + H2 (g)
more reactive down the group as Heavier metals quickly melt with the heat of the reaction, this melting causes new metal surface to be exposed and accelerates the reaction
Sodium/Potassium alloy
Na/K alloy is liquid at and below room temperature. Na/K alloy (40-90 weight % K): large liquid
range (-13°C to +785°C for 77% K; ca. K2Na)
Na/K is sometimes used as a liquid coolant in nuclear facilities (e.g. experimental nuclear
reactors)! The alloy has a good thermal conductivity.
Intercalation compounds?
alkali metals with graphites, graphites are reduced and M+ cations intercalate and coordinate to 6 membered rings between the graphite layers (expanding to fit)
these are strong reducing agents
intercalation compounds properties?
gives bronze-
coloured highly reactive intercalation
compound. KC8 is a strong reducing agent. It is
a powder that can be readily handled under dry
inert gas. It is pyrophoric and in air
spontaneously bursts into flames.
LI-graphite intercalation compounds?
formula: LiC6
negative anode
LiC6 → Li+ + “C6” + e-
positive cathode
CoO2 + Li+ + e- → LiCoO2
used in rechargeable batteries. The small Li+ can migrate; moves in and out of the solid structures (“C” and
CoO2) a reversible system that can be recharged (the opposite reactions).
an electrolyte, e.g. LiPF6 in an organic (non-protic) solvent such as diethyl carbonate, and separator
diaphragm (permeable for Li+)
sodium with water
Na + H2O = NaOH + H2
electrolysis of aq NaCl?
NaCl = NaOH + Cl2 and H2 (chloralkali process)
NaCl is able to be mined or obtained by evaporation of seawater
alkali metals with halogens?
Alkali metals + halogens = MX salts (colourless and ionic), in an exothermic reaction
MX salt preparation
alkali metals hydroxide/carbonates + hydrohalic acid (HX) = salt + water (+carbon dioxide)
Li2CO3 (aq) + 2 HBr (aq) → 2 LiBr (aq) + H2O (l) + CO2 (g)
solubility of MX halides
are water soluble, except LiF cause it is sparingly soluble due to large lattice energy (2x small hard ions) which is not overcome by hydration enthalpy and has the largest lattice energy, which not offset by enthalpy of hydration
alkali metal hydrides?
Liquid metal + hydrogen gas = Alkali metal hydrides
these are ionic due to EN difference
2 M + H2 → 2 MH
MH reactivity
Reactivity. LiH < NaH < KH
with KH more of a mismatched ion pair and
less lattice energy has to be invested for reactions
MH reaction with water
exothermic reaction
2 MH + 2 H2O → 2 MOH + H2
comproportionation reaction
comproportionation reaction?
elements with two oxidation states converts to a product with element in one oxidation state
alkali metal salt structures?
NaCl has face centred cubic structure alternating cations and anion, 6 neighbours
CsCl, CsBr, Csl has primitive cubic structure.
Common for more similarly sized cations and anions, 8 neighbours, ion centre surrounded by 8 opposite charge ions 1:1 ratio
alkali metal salts of oxyanions? these are water soluble
NO3
- (nitrate), SO42- (sulfate), CO32- (carbonate) and
PO43- (phosphate)
Na2CO3 production?
Solvay process. used in glass industry
NaCl +. CaCO3 = Na2CO3
Lithium salts
have large polarisable anions (LiI and LiClO4), these are soluble in ethereal solvents (these include diethyl ether Et2O) where there is attraction between lone pairs
[Li(OEt2)4]+ structure
central Li corrugated to OEt2 x 4 around in tetrahedral structure
