S block Flashcards
How does the energy of orbitals change going down the group?
Down the group orbitals decrease in energy as they increase in size.
How is most H2 formed
Heating natural gas or light crude oil fractions with steam, high temp, Ni catalyst, eg CH4+H2OCO + 3H2 CO + H2O CO2 + H2 (Fe catalyst second reaction)
What is another way to produce H2 What are the pro and con of this reaction
Electrolysis of H2O
2H2O -> 2H2 + O2
Con: Is expensive so best where the electricity of cheap
Pro: Produces H2 without producing green house gas CO2
What are the uses of H2
1) Production of ammonia
2) production of methanol (CO + 2H2 CH3OH)
3) hydrogenation of saturated compounds in the chemical industry.
What are the classes of compounds formed by Hydrogen
1) Covalent hydrides - individual discrete molecules formed usually with p-block elements
2) Saline hydrides - ionic hydrides
3) Metallic hydrides
Explain the trend of E-H bonds down the group
Down the group, E-H bond becomes less stable due to valence orbitals become larger and more diffuse and so worse overlap.
Explain the trend of E-H bonds across a period
More stable going L to R across rows due to better overlap between orbitals and increase in ionic character
How does MP change down group 1 metals
Decreases down the group and increasing s orbital size down group resulting in less overlap and weaker bonds
How are Li and Na metals obtained
Via electrolysis of their molten chlorides:
2NaCl -> 2Na + Cl2
How are K Rb Cs metals obtained
Reduction of their molten salts with Na at high temps:
KCl + Na -> NaCl + K
State the reactions of G1 metals with water, H2 and X2
M + H20 -> MOH + 0.5H2
2M + H2 -> 2MH
2M + X2 -> 2MX
How do metal hydrides react with water
Violently
MH + H2O -> MOH + H2
When burnt in the air what G1 metals give what type of oxo anion
Li gives Oxide O^2-
Na peroxide O2 ^2-
K(+heavier) Superoxide O2^-
How do sizes of oxo-anions trend
O2- < O2 - < O2 2-
What are the trends for the solubility of group 1 salts
most G1 salts are soluble in water
Salts with large anions - solubility decreases down group
Small anions - solubility increases down the group
predict the solubility for the combos: Small cation + small anion Small cation + large anion Large cation + small anion Large cation + large anion
insoluble
soluble
soluble
insoluble
How does reactivity trend down G2
Increases gown the group due to decreasing IE and decreasing lattice enthalpies
How does MTP differ down G2
Decreases down the group but not a regular decrease due to the different metallic structures
How is Mg manufactured on large scale, what are the main uses of Mg
Thermally decomposing metal carbonates:
1) MgCO3.CaCO3 -> MgO.CaO + 2CO2
2) 2MgO.CaO + Si -> Mg + Ca2SiO3
used in aluminium alloys, Mg gives greater mechanical strength and resistance to corrosion
What are the properties and the uses of Be
One of the lightest metals known, non-magnetic and high thermal conductivity / melting point, used in satellites, nuclear reactors and Beryllium alloys
How does G2 react with air
how does Mg and Be differ
how does the rest of G2 react with water
Burns in air to give metal oxide
Mg and Be are passivated and kinetically inert to O2 and H2O forming protective oxide coating on the metal surface
Forms metal hydroxide and hydrogen gas
M + 2H2O -> M(OH)2 + H2
How does G2 react with N2, sulphur and halogens
sulphur: 8M + S8 -> 8MS
3M + N2 -> M3N2
M + X2 -> MX2
What makes Be form covalent compounds
Be2+ has very high charge density and therefore polarises all anions and ligands giving polar-covalent compounds
In Aq solution what coordinate do Be2+, Mg2+ and Ca2+ form
Be: Always 4
Mg: 4, but usually 6
Ca: 6 or 8
