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(c) doc b(c) doc bDoc Brown's Chemistry KS4 science GCSE/IGCSE/O Level Chemistry Revision Notes

on the ALKALI METALS

Group 1 The Alkali Metals of the Periodic Table

Chemistry notes on the physical properties of the alkali metals - lithium, sodium, potassium, rubidium, caesium (cesium) and francium, The chemical properties of alkali metals, chemical reactions of alkali metals with water, oxygen and chlorine – word equations & balanced equations for the reactions of alkali metals. The uses of alkali metals - the elements and compounds of the Group 1 Alkali Metals of the Periodic Table e.g. lithium, sodium & potassium etc. Also covered are explaining the group I alkali metal reactivity trend, uses of the alkali metals and alkali metal compounds.

Keywords–Links for this page: boiling points * chlorides * data on elements * density * electron arrangements * explaining reactivity trend * hydroxides * melting points * oxides * reaction with oxygen/chlorine * reaction with water * trends * typical properties * untypical properties  * uses

PLEASE NOTE A Level Students GCE Notes on s–block Gp 1 Alkali Metals & Gp2 Alkaline Earth Metals

BUT reading this page reminds you of what you theoretically leaned from GCSE/IGCSE/O Level courses on alkali metals!

So this page can act as a primer for the study of alkali metals lithium, sodium, potassium etc.


 

Where are the Group 1 Alkali Metals in the Periodic Table?

(c) doc b

The Group I Alkali Metals are the first vertical column on the left of the Periodic Table where you find most of the metallic elements. Therefore an Alkali Metal is the first element on the period from period 2 onwards.

Only the top portion of the periodic table is shown and remember metals tend to be on the left and the alkali metals form the first vertical column. Group 1 Alkali Metals also include the elements caesium/cesium (Cs) and radioactive francium (Fr) below rubidium, but are not shown.

The alkali metals are so named because they readily react with water to form an alkaline solution of the hydroxide e.g. sodium produced the well known alkali sodium hydroxide.

Note: Using 0 to denote the Group number of Noble Gases is very historic now, since, compounds of xenon are 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 0 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!

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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.

Alkali metals 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 and in a particularly reactive way.

Some of their physical properties of Group 1 Alkali Metals are typical of metals and some are not so typical of metals.

Although Alkali Metals 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. (c) doc b Overview of Periodic Table

Why are the group 1 alkali metals like lithium, sodium and potassium store under oil?

Alkali Metals are so reactive that they must be stored under oil in a well sealed glass container to minimise reaction with the oxygen or water vapour in air. When exposed to air, alkali metals rapidly tarnish as a layer of alkali metal oxide is formed.

Note: Oil is a water repellent and a physical barrier towards air and moisture BUT the alkali metals still gradually corrode as traces of oxygen and water diffuse through the oil to reach the very reactive lumps of alkali metal!

In what ways are the group 1 alkali metals like lithium, sodium and potassium typical metals?

Alkali metals are many typical metallic properties: e.g. 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 to readily react with most non–metals to form ionic compounds which are usually soluble white solids.

In what ways are the group 1 alkali metals like lithium, sodium and potassium not typical metals?

Alkali metals have several untypical metallic properties: e.g.

low melting points, this means unusually for metals, the bonding between the metal atoms in the crystal is weak.

low density (first three float on water),

very soft (easily squashed or cut with a knife, extremely malleable) and so they have little material strength.

topImportant trends down Group 1 Alkali Metals

With increase in atomic number (proton number), for the Alkali Metals ...

(c) doc b==>(c) doc b==>(c) doc b==> down group 1 alkali metals

What are the group trends in melting point, boiling point, reactivity, size of atom (atomic radius), density and physical strength as you go down the group 1 alkali metals as the atomic/proton number increases?

The melting point and boiling point generally decrease down Group 1 Alkali Metals (see data table below)

All alkali metals are very reactive and the element gets more reactive down Group 1 Alkali Metals with increase in atomic number (explanation), though they all behave in a similar manner – all in the same group!

The atoms get bigger down Group 1 Alkali Metals (as more electron shells are added, see data table below)

Generally the density increases down Group 1 Alkali Metals (see data table below), although the atom gets bigger, there is a greater proportional increase in the atomic mass (see data table).

Generally the physical hardness decreases down Group 1 Alkali Metals, this suggests the metallic bonding gets weaker down the group.

* Note for advanced AS level students:  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 (positive nucleus and delocalised electrons) are further apart and the electrical attractive force is reduced. This weaker bonding results in a weaker–softer structure with a lower melting/boiling point.

A Level Chemistry AS–A2 Notes on s–block Gp 1 Alkali Metals & Gp2 Alkaline Earth Metals

Alkali Metal flame colours

There are element/compound identification details of this and other metal ion tests on the Chemical Tests page (use the alphabetical list at the top).

When heated strongly in a flame, the Alkali metals or their compounds give bright colours.

Simple method for a flame test: The metal salt or other compound  is mixed with concentrated hydrochloric acid and a sample of the mixture is heated strongly in a bunsen flame on the end of a cleaned nichrome wire (or platinum if you can afford it!). Before doing the test the nichrome/platinum wire should be cleaned in conc. hydrochloric acid and heated in the hottest part of the flame to make sure there is no contaminating flame colours.

Lithium – red/crimson (carmine–red)

sodium – yellow/orange

potassium – lilac/purple

rubidium red, caesium – blue

and these flame colours of alkali metals can be used as a simple identification flame test for a specific alkali metal.

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 more advanced data Selected data on the Group 1 Alkali Metals

Chemical symbol, name of alkali metal

Atomic number of alkali metal Electron arrangement in shells 1, 2, 3 etc. of alkali metal melting point oC, K of alkali metal boiling point oC & K of alkali metal Density g/cm3  of alkali metal atomic radius in nm (nanometre) & pm (picometre)
Li, lithium 3 2.1 181oC, 454K 1347oC, 1620K 0.53 0.157, 157
Na, sodium 11 2.8.1 98oC, 371K 883oC, 1156K 0.97 0.191, 191
K, potassium 19 2.8.8.1 64oC, 337K 774oC, 1047K 0.86 0.235, 235
Rb, rubidium 37 2.8.18.8.1 39oC, 312K 688oC, 961K 1.48 0.250, 250
Cs, caesium 55 2.8.18.18.8.1 29oC, 302K 679oC, 952K 1.87 0.272, 272
Fr, francium 87 2.8.18.32.18.8.1 27oC, 300K 677oC, 950K approx. 2 ~0.280, ~280
***************************** *************** ****************************** ******************** ************************ **********************

1nm = 10–9m

1pm = 10–12m

nm x 1000 = pm

nm = pm/1000

****************************

 

 

top(c) doc bThe Reaction of Alkali Metals with cold water

What is formed when group 1 alkali metals like lithium, sodium or potassium react with water? What do you see when the reaction takes place? Observations!

The Group 1 Alkali Metals are very reactive towards cold water producing hydrogen gas and an alkaline solution of the alkali metal hydroxide.

The reaction of alkali metals with water is very exothermic, fast and violent.

If a lump of the alkali metals 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'. Note that these alkali metals float on water because of their low density.

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

The formation of an alkali with water is why they are called Alkali Metals.

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 alkali 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.

hydrogen + oxygen ==> water   (word equation)

2H2 + O2 =>  2H2O

2H2(g) + O2(g) =>  2H2O(l)   (symbol equation with state symbols)

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

Note 1: In flame tests hot lithium atoms give a  crimson colour and sodium a yellow colour (more details).

Note 2: State symbols in equations: (g) = gas, (l) = liquid, (s) = solid, (aq) = aqueous solution in water

The alkali metals Rubidium, caesium and francium are very explosive with water.

Down group 1 the reaction gets faster and more violent as the alkali metal gets more reactive

i.e. Li < Na < K < Rb < Cs < Fr or francium > caesium > rubidium > potassium > sodium > lithium

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

sodium + water ==> sodium hydroxide + hydrogen    (word equation)

2Na + 2H2O ==> 2NaOH + H2

2Na(s) + 2H2O(l) ==> 2NaOH(aq) + H2(g)   (symbol equation with state symbols)

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 (lithium), K (potassium), Rb (rubidium), Cs (rubidium) or Fr (francium) for Na.

Its handy to know the 'pattern' of both the word equations and symbol equations and it fits in with the idea, an important concept, that elements in the same group of vertical column in the periodic table, all tend to behave chemically in the same way ...

... this is what the Periodic Table is all about!.

e.g.

potassium + water ==> potassium hydroxide + hydrogen    (word equation)

2K + 2H2O ==> 2KOH + H2

2K(s) + 2H2O(l) ==> 2KOH(aq) + H2(g)   (symbol equation with state symbols)

and

lithium + water ==> lithium hydroxide + hydrogen   (word equation)

2Li + 2H2O ==> 2LiOH + H2

2Li(s) + 2H2O(l) ==> 2LiOH(aq) + H2(g)   (symbol equation with state symbols)

You can write similar word or symbol equations for rubidium and caesium

See RADIOACTIVITY NOTES - symbol for a readioactive substance Theoretically the alkali metal Francium is the most reactive alkali metal 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!


The explanation of the alkali metals reactivity and reactivity trend is explained and discussed in the next section

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

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(c) doc b

Li 2.1 ==> Li+ or [2]+

 

(c) doc b

Na 2.8.1 ==> Na+ or [2.8]+

 

(c) doc b

K 2.8.8.1 ==> K+ or [2.8.8]+

Why are alkali metals so reactive? AND

Why do Group 1 Alkali Metals get more reactive down the group with increase in atomic/proton number?

How do we explain the group 1 alkali metal reactivity trend?

THEORY  (c) doc b

Explaining the Reactivity Trend of the Group 1 Alkali Metals

  • When an alkali metal atom reacts, it readily loses its only outer electron to form a singly positively charged ion

    • e.g. Na ==> Na+ + e (in terms of electrons 2.8.1 ==> 2.8

    • and so forming a stable ion with a noble gas electron arrangement,

    • and this is why they are so reactive,

    • the formation of a positive ion by electron loss is an example of oxidation.

  • AND as you go down the group from one element down to the next

  • .. Li .. Na .. K .. Rb .. Cs .. Fr the atomic radius gets bigger due to the addition of an extra filled inner electron shell,

  • the further a negative electron is from the positive nucleus, the less strongly it is held, hence the more easily lost from an atom to form a positive ion,

  • so, down the alkali metals group, the outer electron is further and further from the nucleus and is also shielded by the extra full shell of negative charge,

  • these combined effects mean that down the alkali metal group the outer electron is less and less strongly held by the positive nucleus as the attractive force is decreased, and so ....

  • this means the outer electron is more easily lost in the reaction (e.g. with water), the M+ ion is more easily formed, and so the alkali metal is more reactive as you go down the group.

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The Reaction of Alkali Metals with Non–metals

Group 1 Alkali Metals react with non–metals to form colourless or white ionic compounds

These compounds dissolve in water to give colourless solutions.

For these reactions you can substitute Li (lithium), K (potassium), Rb (rubidium), Cs (caesium/cesium) to obtain the equations for other Group I Alkali Metals.

Reaction with oxygen

What is formed when group 1 alkali metals like lithium, sodium or potassium react with oxygen (air)?

Alkali metals burn when heated in oxygen or air.

They form white solid powders which are ionic compounds eg (Na+)2O2–

sodium + oxygen ==> sodium oxide    (word equation)

4Na + O2 ==> 2Na2O

4Na(s) + O2(g) ==> 2Na2O(s)   (symbol equation with state symbols)

(c) doc b + (c) doc b + (c) doc b ==> (c) doc b(c) doc b(c) doc b

These oxides dissolve in water to form strongly alkaline metal hydroxide solutions, pH 13–14, so  universal indicator turns from green to blue.

eg sodium oxide + water ==> sodium hydroxide

Na2O + H2O ==> 2NaOH

Na2O(s) + H2O(l) ==> 2NaOH(aq)   (symbol equation with state symbols)

Reaction with chlorine What is formed when group 1 alkali metals like lithium, sodium or potassium react with chlorine?

Alkali metals burn vigorously when heated in chlorine to form colourless ionic salt like compounds eg Na+Cl. This is a very exothermic reaction AND expensive way to make it! Its much cheaper to produce it by evaporating sea water.

sodium + chlorine ==> sodium chloride    (word equation)

2Na + Cl2 ==> 2NaCl

2Na(s) + Cl2(g) ==> 2NaCl(s)    (symbol equation with state symbols)

The sodium chloride is soluble in water to give a neutral solution pH 7, universal indicator is green.

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'normal molecular' and ionic formula, M = Li, Na, K etc. Some Compounds of the Alkali Metals (note the group formula patterns)

Alkali metals are so reactive in readily forming a singly charged positive ion, they usually form ionic compounds, they lose an electron and are NOT interested in sharing it to form a covalent bond!

e.g. the formation of the ionic compound sodium chloride (see above)

ONE (c) doc b atom combines with ONE (c) doc b atom to form (c) doc b(c) doc b

Alkali metal compounds are usually white solids or colourless crystalline compounds.

hydroxides

MOH, M+OH

The hydroxides are white ionic solids which very soluble in water to form strongly alkaline solutions (pH 13–14). See below for salt formation from hydroxides.

oxides, M2O

(M+)2O2–

The oxides are white ionic solids, very soluble in water to form the metal hydroxide (see above).

chlorides

MCl

M+Cl

The chlorides are colourless crystalline solids. They soluble in water to give a neutral solution pH 7, universal indicator is green. They are typical ionic solids with high melting points due to the strong attractive forces between ions (ionic bonding details). This solution in water consists of sodium Na+ and chloride Cl ions and can be electrolysed to make chlorine, hydrogen and sodium hydroxide. Formed by neutralising the alkaline oxide or  hydroxide with acids (more on Acids, Bases and Salts).

e.g.  word equation and symbol equations

sodium hydroxide + hydrochloric acid ==> sodium chloride + water

NaOH + HCl ==> NaCl + H2O

NaOH(aq) + HCl(aq) ==> NaCl(aq) + H2O(l)   (symbol equation with state symbols)

nitrates

MNO3

M+NO3

Colourless, soluble, neutral crystalline salts, formed by neutralising the alkaline oxide or hydroxide with nitric acid.

e.g.  word equation and symbol equations

sodium hydroxide + nitric acid ==> sodium nitrate + water

NaOH + HNO3 ==> NaNO3 + H2O

NaOH(aq) + HNO3(aq) ==> NaNO3(aq) + H2O(l)   (symbol equation with state symbols)

sulphates

M2SO4

(M+)2SO42–

Colourless, soluble, neutral crystalline salts, formed by neutralising the alkaline oxide or hydroxide with sulphuric acid.

e.g.  word equation and symbol equations

sodium hydroxide + sulphuric acid ==> sodium sulphate + water

2NaOH + H2SO4 ==> Na2SO4 + 2H2O

2NaOH(aq) + H2SO4(aq) ==> Na2SO4(aq) + 2H2O(l)   (symbol equation with state symbols)

carbonates

M2CO3

(M+)2CO32–

White, soluble, weakly alkaline solids formed by reacting the hydroxide with carbon dioxide gas e.g. the formation of sodium carbonate (+ water)

e.g.  word equation and symbol equations

sodium hydroxide + carbon dioxide ==> sodium carbonate + water

2NaOH + CO2 ==> Na2CO3 + H2O

2NaOH(aq) + CO2(g) ==> Na2CO3(aq) + H2O(l)    (symbol equation with state symbols)

Alkali metal carbonates form salts with acids. e.g.

sodium carbonate + hydrochloric acid ==> sodium chloride + water + carbon dioxide

Na2CO3 + 2HCl ==> 2NaCl + H2O + CO2

Na2CO3(s) + 2HCl(aq) ==> 2NaCl(aq) + H2O(l) + CO2(g)   (symbol equation with state symbols)

(much more details on pH, neutralisation, equations and salt preparations on "Acids, Bases and Salts")

You will find more on theses sorts of equations on ....
  1. GCSE Notes on Acids, Bases, Salts and pH scale

  2. Equation Question on Acid reactions – word and symbol equations with answers supplied

 

Other reactions involving alkali metals or alkali metal compounds

IGCSE chemistry may need the effect of heat on alkali metal nitrates.

When strongly heated the nitrates of sodium and potassium evolve oxygen gas (ignites glowing splint) and leaving a white residue of the nitrite salt i.e.

sodium nitrate ===> sodium nitrite + oxygen   (word equation)

2NaNO3 ==> 2NaNO2 + O2

2NaNO3(s) ==> 2NaNO2(s) + O2(g)   (symbol equation with state symbols)

and

potassium nitrate ===> potassium nitrite + oxygen

2KNO3 ==> 2KNO2 + O2

2KNO3(s) ==> 2KNO2(s) + O2(g)   (symbol equation with state symbols)

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Alkali Metals – Storylines – USES and ....

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

Sodium hydrogencarbonate's old name is sodium bicarbonate, often referred to as 'bicarb', is used in baking soda, pharmaceutical products like indigestion tablets and fire extinguishers. 

Sodium hydroxide NaOH

An industrially important alkali 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 GCSE/IGCSE notes

PLEASE NOTE A Level Students GCE Notes on s–block Gp 1 Alkali Metals & Gp2 Alkaline Earth Metals

BUT reading this page reminds you of what you theoretically leaned from GCSE/IGCSE/O Level courses on alkali metals!

So this page can act as a primer for the study of alkali metals lithium, sodium, potassium etc.


WHERE–WHAT NEXT?


PLEASE NOTE that these LINKS are for A Level Students ONLY

ADVANCED LEVEL INORGANIC CHEMISTRY Part 7 s–block Gp 1 Alkali Metals/Gp 2 Alkaline Earth Metals  sub–index: 7.1 Introduction to s–block Group 1 Alkali Metals and Group 2 Alkaline Earth Metals  * 7.2 Group 1 data and graphs * 7.3 Group 2 data and graphs * 7.4 General trends down groups I & II and formulae *7.5 Oxygen reaction & oxides of s–block metals * 7.6 Water reaction & hydroxides of group 1/2 metals * 7.7 Acid reaction & salts of group1/2 metals * 7.8 chlorine reaction & halide of group I/II metals * 7.9 carbonates & hydrogen carbonates of s–block metals * 7.10 Solubility trends of groups 1/2 OH, NO3,SO4,CO3 compounds * 7.11 Thermal decomposition and stability of group 1 and group 2 carbonates & nitrates * 7.12 Uses of s–block Group 1 Alkali Metals and Group 2 Alkaline Earth Metals and their compounds


equation keywords: 2Na(s) + 2H2O(l) ==> 2NaOH(aq) + H2(g) 4Na(s) + O2(g) ==> 2Na2O(s) Na2O(s) + H2O(l) ==> 2NaOH(aq) 2Na(s) + Cl2(g) ==> 2NaCl(s) NaOH (aq) + HCl(aq) ==> NaCl(aq) + H2O(l) NaOH(aq) + HNO3(aq) ==> NaNO3(aq) + H2O(l) 2NaOH(aq) + H2SO4(aq) ==> Na2SO4(aq) + 2H2O(l) 2NaOH(aq) + CO2(g) ==> Na2CO3(aq) + H2O(l) Na2CO3 + 2HCl(aq) ==> 2NaCl(aq) + H2O(l) + CO2(g) 2K(s) + 2H2O(l) ==> 2KOH(aq) + H2(g) 2Li(s) + 2H2O(l) ==> 2LiOH(aq) + H2(g) 2NaNO3(s) ==> 2NaNO2(s) + O2(g) 2KNO3(s) ==> 2KNO2(s) + O2(g) ) ==> 2NaCl(aq) + H2O(l) + CO2(g)   2K(s) + 2H2O(l) ==> 2KOH(aq) + H2(g) 2Li(s) + 2H2O(l) ==> 2LiOH(aq) + H2(g)


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