Alkali metals

Август 1, 2022

Содержание

2. INTRODUCTION Name of this family comes from the properties of alkali metals to form hydroxides with
3. GENERAL PROPERTIES OF 1A *By giving their valence electron easily in chemical reactions, they form +1
4. They are solids at room temperature. They are soft. They can be cut by a knife.
5. OCCURRENCE Since the alkali metals are the most active metals, they are not found free in
6. Potassium, K Potassium constitutes 1.5% of the earth’s crust. Potassium is found as the minerals sylvite
7. CHEMICAL PROPERTIES 1)Alkali metals are strong reducing agents. nM0 + Y+n → nM+ + Y0(s) (Y
8. 2) Hydrides are formed as a result of alkali metals reactions with hydrogen. Hydrides contain a
9. 3) They react with water violently. As a result of this reaction H2 gas and a
10. 4) They may form oxides, peroxides or superoxides by reacting with oxygen in the air. As
11. 5. All of them react with halogens to form alkali halides (salts of alkali metals). 2M(s)
12. 6. They do not react with bases M(s) + OH–(aq) ⎯→ No reaction 7. When they
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INTRODUCTION
Name of this family comes from the properties of alkali

metals to form hydroxides with water. Compounds containing hydroxide ion is basic and called alkali.

They are very active ,so in the nature they are not found in elemental forms. They exist in various compounds.

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GENERAL PROPERTIES OF 1A
*By giving their valence electron easily in chemical

reactions, they form +1 charged ions.
* Alkali metals are the elements which have the least ionization energy and the highest atomic radius, in each period
* They are a group of most active metals.
* The activity of metals increase from top to bottom
* The element cesium, Cs, is the most active metal
* Francium is a radioactive element

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They are solids at room temperature. They are soft. They can

be cut by a knife.

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OCCURRENCE
Since the alkali metals are the most active metals, they are

not found free in nature, but as compounds.
Sodium, Na
The most important compound of sodium is sodium chloride, NaCl. The important sodium sources are Chile saltpeter (NaNO3), washing soda (Na2CO3) and baking soda (NaHCO3). The most important sodium minerals are kryolite (Na3AlF6), borax (Na2B4O7.10H2O), sodium sulfate (Na2SO4) and albite (NaAlSi3O8).

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Potassium, K
Potassium constitutes 1.5% of the earth’s crust. Potassium is found

as the minerals sylvite (KCl) and carnallite (KCl · MgCl2 ·6H2O) and as the silicates of orthoclas (KAlSi3O8) and mica (KH2Al3(SiO4)3). The main sources of potassium are K2SO4 and KNO3, which are used as fertilizers.

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CHEMICAL PROPERTIES
1)Alkali metals are strong reducing agents.
nM0 + Y+n →

nM+ + Y0(s)
(Y : any metal with low activity,
M : any alkali metal)
0 +3 +1 0
6Na(s) + Al2O3(s) → 3Na2O(s) + 2Al(s)
0 +3 +1 0
3K(s) + CrCl3(s) → 3KCl(s) + Cr(s)

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2) Hydrides are formed as a result of alkali metals reactions

with hydrogen. Hydrides contain a +1 charged alkali metal and –1 charged hydrogen
2K(s) + H2(g) ⎯→ 2KH(s) potassium hydride
2Na(s) + H2(g) ⎯→ 2NaH(s) sodium hydride

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3) They react with water violently. As a result of this

reaction H2 gas and a base solution form.
2M(s) + 2H2O(l) → 2MOH(aq) + H2(g) +heat
2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g) + heat

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4) They may form oxides, peroxides or superoxides by reacting with

oxygen in the air.
As a result of reactions with excess oxygen, lithium forms oxide, Li2O, sodium forms peroxide Na2O2 and potassium, rubidium and cesium form superoxides, such as KO2, RbO2, CsO2.
4Li(s) + O2(g) ⎯→ 2Li2O(s)
2Na(s) + O2(g) ⎯→ Na2O2(s)
K(s) + O2(g) ⎯→ KO2(s)

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5. All of them react with halogens to form alkali halides

(salts of alkali metals).
2M(s) + X2(g) ⎯→ 2MX(s)
(M : alkali metal, X : halogen,
MX ; alkali metal halides)
2Li(s) + F2(g) ⎯→ 2LiF(s)
2Na(s) + Cl2(g) ⎯→ 2NaCl(s)

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6. They do not react with bases
M(s) + OH–(aq) ⎯→

No reaction
7. When they react with acids, the produce salts andliberate H2 gas.
M(s) + HX(aq) ⎯→ MX(aq) + 1/2H2(g)
(HX : Halo acid, MX : salt of an alkali)
2K(s) + 2HCl(aq) ⎯→ 2KCl(aq) + H2(g)
2Na(s) + 2HBr(aq) ⎯→ 2NaBr(aq) + H2(g)