Ch 10The s-Block Elements — Class 11 Chemistry, concept-first.

Group 1 of the periodic table consists of six elements — lithium, sodium, potassium, rubidium, caesium and francium — together called the alkali metals.

Every alkali metal ends its electron configuration with a single s-electron sitting outside a completely filled noble-gas core — the general form is .

Because the alkali metals have only one electron beyond a full shell, that outer electron is poorly shielded and the atoms end up being the largest in their respective periods of the periodic table.

The alkali metals have the lowest ionization enthalpies of any group, and these fall further on descending from Li to Cs.

When an alkali metal ion enters aqueous solution it is surrounded by water dipoles, and the enthalpy released in this process — the hydration enthalpy — is greatest for the smallest ion, since a small…

All the alkali metals are soft enough to cut with a knife, light in mass, and silvery-white when freshly cut.

Because of their large atomic size and very low ionization enthalpy, the alkali metals are the most reactive metals known, and reactivity itself increases further down the group.

Lithium's low density and reactivity make it valuable in alloys — with lead for the "white metal" bearings used in motor engines, with aluminium for aircraft components, and with magnesium for armour…

Virtually every common compound formed by the alkali metals — oxides, hydroxides, halides, and salts of oxo-acids among them — is essentially ionic, a direct consequence of how easily these metals los…

When burnt in excess air, each alkali metal favours a different class of oxide, though minor amounts of the others can also form: lithium gives predominantly the normal oxide (with a little peroxide )…

The alkali metal halides () are colourless, high-melting crystalline solids, typically made by reacting the corresponding oxide, hydroxide or carbonate with the appropriate hydrohalic acid .

An oxo-acid is one in which the ionisable proton sits on a hydroxyl group that is itself attached to an oxo (=O) group on the same central atom — carbonic acid , written , and sulphuric acid , written…

Being the first member of Group 1, lithium sits apart from the rest of the alkali metals in several respects, and the reason is essentially geometric: its atom and its ion are both exceptionally small…

Lithium departs from the rest of Group 1 in a number of concrete, observable ways:

The lithium–magnesium resemblance (the "diagonal relationship") arises because the two ions happen to be almost the same size — atomic radii of 152 pm (Li) and 160 pm (Mg), ionic radii of 76 pm () and…

Four sodium compounds dominate industrial chemistry: sodium carbonate, sodium chloride, sodium hydroxide and sodium hydrogencarbonate.

A typical 70 kg adult carries roughly 90 g of sodium and 170 g of potassium in the body — far more than the 5 g of iron or 0.06 g of copper also present — underlining just how central these two ions a…

Group 2 comes immediately after Group 1 and comprises six elements — beryllium, magnesium, calcium, strontium, barium and radium.

Every member of Group 2 carries two electrons in the outermost s-orbital, giving the general configuration :

Compared with the alkali metal directly to their left in the same period, the Group 2 elements have distinctly smaller atomic and ionic radii — a consequence of the extra proton (higher nuclear charge…

Alkaline earth metal atoms are still fairly large, so their ionization enthalpies remain low by overall standards, and — as size increases down the group — ionization enthalpy falls further from Be to…

As with the Group 1 ions, hydration enthalpy for the alkaline earth ions falls as ionic size grows down the group:

The alkaline earth metals are, broadly speaking, silvery-white, lustrous and relatively soft — though noticeably harder than the alkali metals of the same period; beryllium and magnesium have a slight…

Overall Group 2 is less reactive than Group 1 in the same period, but here too reactivity climbs steadily down the group.

Beryllium's principal industrial role is in alloys — copper-beryllium alloy is prized for high-strength springs, and metallic beryllium itself, being nearly transparent to X-rays, is used to make the…

Group 2 elements show essentially only the +2 oxidation state () in their compounds. Those compounds are still predominantly ionic, but noticeably less so than the analogous compounds of the alkali me…

As the first member of Group 2, beryllium — like lithium in Group 1 — behaves quite differently from the rest of its group, and for the same underlying reason: its atom and ion are exceptionally small…

has an estimated ionic radius of just 31 pm, and its charge-to-radius ratio turns out to be almost identical to that of — which is precisely why beryllium's chemistry echoes aluminium's in several way…

Calcium's industrially important compounds are calcium oxide, calcium hydroxide, calcium carbonate, calcium sulphate (Plaster of Paris) and cement — each manufactured on a large scale by processes des…

The average adult body contains roughly 25 g of magnesium and about 1200 g of calcium — again dwarfing the 5 g of iron and 0.06 g of copper the body carries — and the recommended daily intake of these…