The s-block elements include the alkali metals (Group 1) and alkaline earth metals (Group 2). Some key properties include: 1) They have the lowest first ionization energies in each period and metallic character increases down each group as it becomes easier to lose electrons. 2) They form ionic compounds with fixed 1+ oxidation states for alkali metals and 2+ for alkaline earth metals. 3) Their oxides and hydroxides are basic and increase in basic strength down each group. 4) They react vigorously with water to form hydroxides and hydrogen gas. Reactivity increases down each group.

1. THE S-BLOCK ELEMENTS
MS. CHETNA PRADIP DESHMUKH

2. MEMBERS OF THE S-BLOCK
ELEMENTS
Li Be
Na
K
Rb
Cs
Fr
Mg
Ca
Sr
Ra
Ba
IA IIA
IA Alkali metals
IIAAlkaline Earth
metals

3. CHARACTERISTIC PROPERTIES
OF ALKALI METALS
• LOWEST FIRST I.E & VERY HIGH SECOND I.E
• SOFT METALS
• METALLIC CHARACTER
• LOW ELECTRONEGATIVITY
• BASIC OXIDES, HYDROXIDES
• IONIC BOND WITH FIXED OXIDATION STATE I.E. +1
• CHARACTERISTIC FLAME COLOURS
• WEAK TENDENCY TO FROM COMPLEX

4. ATOMIC RADII (NM)
Li 0.152
Na 0.186
K 0.231
Rb 0.244
Cs 0.262
Fr 0.270

5. IONIZATION ENERGIES
Group I 1st I.E. 2nd I.E.
Li 519 7300
Na 494 4560
K 418 3070
Rb 402 2370
Cs 376 2420
Alkali metals have the lowest I.E in each period and it decreases
down the group.

6. ELECTROPOSITIVE OR
METALLIC CHARACTER
• HIGH TENDENCY TO LOSE E- TO
FORM POSITIVE IONS.
• HIGHLY ELECTROPOSITIVE.
• METALLIC CHARACTER
INCREASES DOWN THE GROUP.

7. CHARACTERISTIC FLAME
COLOURATION
HCl(aq) sample
Li deep red
Na yellow
K lilac
Rb bluish red
Cs blue
Ca brick red
Sr blood red
Ba apple green

8. OXIDES, PEROXIDE, SUPEROXIDE
Reaction with water:
Oxide: O2- + H2O  2OH-
Peroxide: O2
2- + 2H2O  H2O2 + 2OH-
Superoxide: 2O2
- + 2H2O  2OH- + H2O2 + O2
.. .. 2-
:O:O:
.. ..
Peroxide ion
. . -
:O:.O:
.. ..
Super oxide
Li does not form
peroxide or super oxide
Li2O2  Li2O + ½ O2

9. BASIC OXIDES, HYDROXIDES
Oxide Hydroxides
Li2O LiOH
Na2O,
Na2O2
NaOH
K2O2, KO2 KOH
Rb2O2,
RbO2
RbOH
Cs2O2,
CsO2
CsOH
Oxide Hydroxides
BeO Be(OH)2
MgO Mg(OH)2
CaO Ca(OH)2
SrO Sr(OH)2
BaO, Ba2O2 Ba(OH)2

10. ACTION WITH HYDROGEN
All the alkali metals react directly with hydrogen to form
hydrides which are ionic in nature.
2Na(s) + H2(g)  2NaH(s)
The ionic character of hydrides increases from Li to Cs.
The stability of hydrides decreases from Li to Cs.
The hydrides behave as strong reducing agents and the latter
increases from Li to Cs.

11. ACTION OF HALOGENS
All the alkali metals react directly with halogen to produce
ionic halides.
The reactivity of halogen towards the alkali metal
increases down the group.
Action with water
Alkali metals react with water to form hydroxides and
hydrogen gas is evolved.
Li reacts slowly but Na and others react violently. That is why
they are kept in kerosene oil.
All are soluble and basic strength increases down the group.

12. CHARACTERISTIC PROPERTIES
OF ALKALINE EARTH METALS
• LOW FIRST I.E & SECOND I.E
• METALLIC CHARACTER
• LOW ELECTRONEGATIVITY
• BASIC OXIDES, HYDROXIDES
• IONIC BOND WITH FIXED OXIDATION STATE I.E. +2
• CHARACTERISTIC FLAME COLOURS
• WEAK TENDENCY TO FROM COMPLEX

13. ATOMIC RADII (NM)
Be 0.112
Mg 0.160
Ca 0.197
Sr 0.215
Ba 0.217
Ra 0.220

14. IONIZATION ENERGIES
Group I 1st I.E. 2nd I.E. 3rd I.E.
Be 900 1760 14800
Mg 736 1450 7740
Ca 590 1150 4940
Sr 548 1060 4120
Ba 502 966 3390
1. Have low 1st and 2nd IE.
2. Removal of the 3rd electron is much more difficult
as it involves the loss of an inner shell electron.
3. IE decrease as the group is descended.
4. IE of the group II is generally higher than group I.

15. HYDRATION ENTHALPY
General trends:
1. On going down both groups, hydration enthalpy
decreases.
(As the ions get larger, the charge density of the
ions decreases, the electrostatic attraction between
ions and water molecules gets smaller.)
2. Group 2 ions have hydration enthalpies higher
than group 1.
( Group 2 cations are doubly charged and have
smaller sizes)

16. BASIC OXIDES, HYDROXIDES
Oxide Hydroxides
BeO Be(OH)2
MgO Mg(OH)2
CaO Ca(OH)2
SrO Sr(OH)2
BaO, Ba2O2 Ba(OH)2

17. HYDROXIDES
Group II
hydroxide Be Mg Ca Sr Ba
Solubility increase, from
Amphoteric to basic, base strength
increase

18. VARIATION IN MELTING POINTS
Strength of metallic bond depends on:
1. Ionic radius
2. Number of e- contributed to the electron sea per atom
3. Crystal lattice structure
Note: The exceptionally high m.p. of calcium
is due to contribution of d-orbital participation
of metallic bonding.

19. REACTIONS WITH OXYGEN
Normal
Oxide
Peroxide
Structure
Formed by All alkaline
earth metals
Ba
.. .. 2-
:O-O:
.. ..
.. 2-
:O:
..

20. CHARACTERISTIC FLAME
COLOURATION
HCl(aq) sample
Ca brick red
Sr blood red
Ba apple green

21. REACTION WITH WATER
M(s)  M+(aq) + e-
H2O(l) + e-  OH-(aq) + ½ H2(g)
Li -3.05 volt
Na -2.71
K -2.93
Rb -2.99
Cs -3.20
Be -1.85 volt
Mg -2.38
Ca -2.87
Sr -2.89
Ba -2.90
Energetic vs. Kinetic Factor

22. ACTION WITH HYDROGEN
All except Be react directly with hydrogen.
Ca(s) + H2(g)  CaH2(s)
The reactivity increases down the group.
Only BeH2 and MgH2 are covalent, others are
ionic.
Action with halogens
BeCl2 is essentially covalent, with comparatively low
m.pt.
The lower members in group II form essentially ionic
chlorides, with Mg having intermediate properties.

23. ELECTRIC CONFIGURATION