GCSE-IGCSE-KS4 Science revision-information chemistry notes on

 Group 1 The Alkali Metals

Their physical and chemical properties-reactions - balanced equations - uses of elements and compounds

Keywords-Links to other notes: boiling points * chlorides * data on elements * density * electron arrangements * explaining reactivity trend * hydroxides * melting points * oxides * reaction with oxygen/chlorine * reaction with water * storylines * trends * typical properties * untypical properties * Multi-word fill exercise * GCSE notes on Transition Metals * EMAIL query?comment

Advanced Level Chemistry detailed AS-A2 Notes on s-block Gp 1 Alkali Metals and Gp2 Alkaline Earth Metals

Note: Using 0 to denote the Group number of Noble Gases is very historic now since compounds of xenon known exhibiting a valency of 8. Because of the horizontal series of elements e.g. like the Sc to Zn block (10 elements), Groups 3 to 8 can also be numbered as Groups 13 to 18 to fit in with the actual number of vertical columns of elements. This can make things confusing, but there it is, classification is still in progress!

Introduction to the Group 1 Alkali Metals  (see also data table below)

• The Alkali Metals form Group 1 of The Periodic Table, and called so because they form oxides and hydroxides that dissolve in water to give alkaline solutions.

• They form the first element of a period, with one outer electron, in any period from period 2 onwards. This outer electron similarity makes them behave in a chemically similar way. Some of their physical properties are typical of metals and some are not so typical of metals. Although they all have one outer electron and so similar physical and chemical properties, a characteristic of a periodic table group, BUT always watch out for trends down a group too. Overview of Periodic Table

• They are so reactive that they must be stored under oil* to minimise reaction with oxygen or water vapour in air. (* water repellent and a physical barrier towards air BUT the alkali metals still gradually corrode as traces of oxygen and water diffuse through!)

• Typical metallic properties: good conductors of heat and electricity, high boiling points, silvery grey surface (but rapidly tarnished by air oxidation).

  • When an alkali metal atoms reacts, it loses an electron (oxidation) to form a singly positively charged ion eg Na ==> Na⁺ + e^-. In terms of electrons 2.8.1 ==> 2.8 and so forming a stable ion with a noble gas electron arrangement.

  • They tend react mainly with non-metals to form ionic compounds which are usually soluble white solids.

• Untypical metallic properties: low melting points, low density (first three float on water), very soft (easily squashed, extremely malleable) and so they have little material strength.

• Important trends down the group with increase in atomic number ...

  • the melting point and boiling point generally decrease* (see data table below)

  • the element gets more reactive (explanation)

  • the atoms get bigger (as more electron shells are added, see data table below)

  • generally the density increases (see data table below), although the atom gets bigger, there is greater proportional increase in the atomic mass.

  • generally the hardness decreases*.

    • * For advanced AS level:  The bonding in metals involves the attraction between free negative electrons moving between positively ionised metal atoms (M⁺ ions). As the atomic radius increases the charges are further apart and the electrical attractive force is reduced. This weaker bonding results in a weaker structure with a lower melting/boiling point.

• There are element/compound identification details on the Chemical Tests page (use the alphabetical list at the top).

• When heated strongly in a flame, the metals or their compounds give bright colours. Lithium - red/crimson, sodium - yellow, potassium - lilac/purple, rubidium red, caesium - blue and they can be used as a simple identification test.

Chemical symbol, name

• The reaction with water is very exothermic, fast and violent.

• If a lump of lithium, sodium or potassium is placed in cold water, the metal floats, it may melt and move around the surface of the water with 'fizzing'.

• If universal indicator is added, it changes from green (pH 7)  to purple (pH 13-14), showing an alkaline metal hydroxide was formed.

• The colourless gas hydrogen is also given off  and pops with lit splint - but this is not the best of experiments to collect it from!

• The more reactive the metal, the more vigorous the reaction.

• Lithium and sodium do not normally cause a flame but the potassium reaction is exothermic enough to ignite the hydrogen.

  • 2H_2(g) + O_2(g) =>  2H₂O_(l)

  • The hydrogen flame turns lilac due to hot potassium atoms in it.

  • Note: in flame tests hot lithium atoms give a  crimson colour and sodium a yellow colour (more details).

• Rubidium, caesium and francium are very explosive with water.

• Down the group the reaction gets faster and more violent as the metal gets more reactive i.e. Li < Na < K < Rb < Cs < Fr.

• The reaction equation for sodium is in words and symbols ...

• sodium + water ==> sodium hydroxide + hydrogen

• 2Na_(s) + 2H₂O_(l) ==> 2NaOH_(aq) + H_2(g)

• and the equations are similar for any of the other Alkali Metals since they are in the same group of the Periodic Table, they behave chemically in the same way i.e. just substitute Li, K, Rb, Cs or Fr for Na. Its handy to know the 'pattern' of both the word equations and symbol equations.

• Theoretically Francium is the most reactive and therefore the most explosive metal when in contact with water, however, it is also very radioactive and so the experiment is highly unlikely to be performed!

• See also the GCSE Reactivity of Metals Notes for the reactivity of other metals compared to these Group 1 Alkali Metals.

sodium Na

Used as a heat transfer coolant in certain nuclear reactors because of its excellent heat conduction properties. The energized vapour is an orange-yellow and used in street lamps.

sodium Na⁺ salts

Common salt from sea water or underground deposits is sodium chloride, NaCl, and is the raw material for making sodium, hydrogen, chlorine and sodium chloride by electrolysis (see Group 7 Halogens notes). 'Soluble Aspirin' is the sodium salt of an organic acid. Salts of solid organic acids are usually more soluble than the acid itself. 

Sodium hydrogen carbonate  NaHCO₃

Used in baking soda, pharmaceutical products like indigestion tablets and fire extinguishers. 

Sodium hydroxide NaOH

Used in the manufacture of soaps, detergents, salts of acids (see Aspirin above), paper and ceramics.

For more on uses of metals see Transition Metals and Extra Industrial Chemistry

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