Alkali metals periodic trends chemical reactions

1. Alkali Metals
Group-I
3. Physical properties
1. Physical State
2. Atomic Size
3. Oxidation State
4. Density
5. Tendency of forming ionic Bond
6. Standard Electrode Potential or Standard Oxidation
Potential
7. Flame Test
8. Photoelectric effect
9. Solubility in Liquefied Ammonia
10. Hydration Energy
11. Reactivity
12. Lustrous Surface
13. Tendency of Forming Complex compounds
14. Strength of metallic Bonds (Softness)
15. Melting point and Boiling Point
16. Reducing Power
4. CHEMICAL PROPERTIES
1. Reaction with Oxygen
2. Reaction with Water
3. Reaction with Hydrogen
4. Reactivity with Halogen
5. Metal Hydroxides
6. Reaction with dilute acids :
7. NITRIDES
8. METAL CARBONATES
9. SULPHATES
10. NITRATES
11. HYDRIDES
12. BICARBONATES
13. FORMATION OF AMALGAMS
5. ANOMALOUS BEHAVIOUR OF LITHIUM
6. DIAGONAL RELATIONSHIP :
• SIMILARITIES WITH MAGNESIUM
1. Position in periodic table
2. Trends in periodic table
• atomic radius.
• Ionization potential/energy
• Electron affinity
• Electronegativity
• Metallic character
• Non-metallic character

2. The s-Block Elements
Elements of Groups IA* (the alkali metals) and IIA* (the alkaline earth
metals)
 constitute the s-block elements
 their outermost shell electrons are in the s orbital
*Note: In the following, Groups IA and IIA are abbreviated as
Groups I and II respectively.
Part-1-Alkali Metals
The two groups of elements have many similarities
 highly reactive metals
 strong reducing agents
 form ionic compounds with fixed oxidation states of +1 for Group I
elements and +2 for Group II elements

3. The
s-block
elements
a. Elements of the IA and IIA group of the
periodic table are called s-block elements.
b. For these elements outer s-orbital is in the
process of filling.
c. IA [n𝒔𝟏] group elements are called alkali
metals
and
IIA [n 𝒔𝟐
] group elements are called

4. GENERAL CHARACTERISTIC
a. They are good conductors of heat and electricity.
b. They are malleable and ductile.
c. Exhibit group valency of 1 and 2 for IA and IIA groups respectively.
d. They are prepared by the electrolysis of their fused salts.
e. They are very reactive as their last shell contains 1 or 2 electrons which can be
given off easily (low ionization potential).
f. They form colorless compounds except for chromates, dichromates, etc.
g. Their cations are diamagnetic.
h. They form ionic compounds (except Li and Be).
i. Their solutions in liquid ammonia are good conductors of electricity and are
good reductants.
j. Oxides are basic in nature

5. GROUP-1 (ALKALI METALS)

6. Groups
•The elements in a group have the same number of electrons in
their outermost orbital (valence orbital).
•Every element in the first column (group I) has one electron in its
outer shell.
Periods
• The elements having
common properties are
present in the same row in
the periodic table.
• All the elements in the same
period have a same number
of atomic orbitals in them.
• All element in the top row
(the first period) has one
orbital for the electrons.

7. Periodic Trends
There are several important atomic
characteristics
that show predictable trends that one should
know.
These are
• atomic radius.
• Ionization potential/energy
• Electron affinity
• Electronegativity
• Metallic character
• Non-metallic character

8. Atomic Radius
• Radius is the distance from the center of the nucleus to the
end of the electron cloud/valence shell.
• Atomic radii are measured in picometers (pm) or
angstroms (1 x 10-10 m) (Å)
What happens to atomic structure as we step from left to right?
Moving from group 1 to the left side, in each group a proton and
an electron (and 1 or 2 neutrons) are added to the atom.
Electrons are added to existing energy levels or sublevels.
The effect is that the more positive nucleus has a greater pull on the electrons which are being added in
same energy level.
The nucleus is becoming more positive and the electron cloud more negative.
The increased attraction pulls the cloud in, making atoms smaller as we move from left to right across a
period.
The trend for atomic radius in a vertical column is from
smallest at the top to largest at the bottom of the family.
Why?
With each step down the family, a new orbital is added to the
atom, making them larger in size.

9. Ionization Energy
• If an electron is given enough energy (in the form of a photon) to
overcome the effective nuclear charge holding the electron in the
cloud, it can leave the atom completely.
• The atom has been “ionized” or charged.
• The number of protons and electrons is no longer equal.
• The energy required to remove an electron from an atom is
ionization energy. (measured in kilojoules, kJ)
• The larger the atom is, the easier its electrons are to remove.
• Ionization energy and atomic radius are inversely proportional.
Electron Affinity
• Electron affinity is the energy change that occurs when an atom gains an
electron (also measured in kJ).

10. The most reactive metals
are the largest since they
are the best electron
givers.
The most reactive
nonmetals are the
smallest ones, the best
electron takers.
Metal and non-metals

11. Electronegativity
• Electronegativity is a measure of an atom’s attraction for
another atom’s electrons.
• It is an arbitrary scale that ranges from 0 to 4.
• The units of electronegativity are Paulings.
• What about the noble gases?
Ions
When an atom gains an electron, it becomes negatively
charged (more electrons than protons ) and is called an
anion.
In the same way that nonmetal atoms can gain electrons,
metal atoms can lose electrons.
They become positively charged cations.

12. The “goal” of most atoms (except H, Li
and Be) is to have an octet or group of 8
electrons in their valence energy level.
They may accomplish this by either giving
electrons away or taking them.
Metals generally give electrons;
nonmetals take them from other atoms.
Atoms that have gained or lost electrons
are called ions.
The Octet Rule

14. PHYSICAL PROPERTIES (identity of material remains intact, no bond breaking and new bond-forming)
Important physical properties of Alkali metals are given below :
1. Physical State
a) Soft, silvery-white metal having a high and bright lustered when freshly cut.
b) They all form body-centered lattices.
c) Softness increases with the increase of atomic number because there is a continuous decrease of
metallic bond strength on account of an increase in atomic size.
2. Atomic Size :
These elements are largest in size in the period and the atomic
size increase in going downwards in the group.
Order of size : Be < Li < Mg < Na < Ca < Sr < Ba < K < Rb < Cs
3. Oxidation State :
These metals exhibit + 1 oxidation state, the difference of their second and third ionization potentials is more than
16 eV. Therefore, their + 1 oxidation state is more stable.
Li Be
Na Mg
K Ca
Rb Sr
Cs Ba
the amount of energy required
to remove an electron from an
isolated atom or molecule.

15. 5. Tendency of forming ionic Bond :
One electron is present in the outermost shell of these metals. They form cation by the loss of this electron, i.e.,
they form ionic bond in their compounds.
6. Standard Electrode Potential or Standard Oxidation Potential :
The measure of the tendency of donating electrons of a metal in water is called its electrode potential.
If the concentration of metal ions is unity, then it is called standard electrode potential.
Standard electrode potential ∝ Ionization potential ∝ Atomic size
4. Density :
Density =
𝒎𝒂𝒔𝒔
𝒗𝒐𝒍𝒖𝒎𝒆
=
𝒈𝒓𝒂𝒎𝒔
𝒄𝒖𝒃𝒊𝒄 𝒄𝒆𝒏𝒕𝒊𝒎𝒆𝒕𝒆𝒓
=
𝒈
𝒄𝒎𝟑
Atomic weight increase from Li to Cs in the group and volume also increase but increase in atomic weight is more as
compared to volume. Therefore, density increases from Li to Cs.
Exception : Density of Na is more than that of K.
Density : Li < K < Na < Rb < Cs

16. 8. Flame Test :
Alkali metals a have different size. When they are
heated in the flame of Bunsen burner, the
electrons present in the valence shell move a from
lower energy levea l to higher energy level by
absorption of heat from the flame (n𝑠1). When
they come back to the ground state, they emit
extra energy in the form of visible light to provide
color to the flame.
Photoelectric effect, a phenomenon in which electrically
charged particles are released from or within a material
when it absorbs electromagnetic radiation
9. Photoelectric effect :
The size of Cs is large, and one electron is present in
its outermost shell. Due to this, the electron of the
outermost shell gets excited by the absorption of
visible light. Therefore, Cs show photoelectric
effect. This is the reason that it is used in the cells.

18. 10. Solubility in Liquefied Ammonia :
Ionization potential is low due to the large size of these metals, i.e., they readily dissolve in liquefied ammonia to form blue-
colored solution, which is a good conductor of electricity and a strong reducing agent.
M + nN𝐻3 → 𝑀+1 + Ammoniated electron
Ammoniated
metal ion
11. Hydration Energy:
Hydration energy decreases on going downwards in the group, due to an increase in the size of the metal ion.
Li > Na > K > Rb > Cs
Lithium gets more hydrated due to the high hydration energy of Li+ and the charge present on it gets protected. Thus,
Hydration energy ∝ 1 Ionic size
12. Reactivity :
Due to large size of these metals, the electron of the outermost shell is weakly attracted towards the nucleus.
a. Na is very reactive and is kept in kerosene so that air does not come directly in contact with sodium.
b. Li is stable in air due to small size, Na and K become neutral and Rb and Cs burn spontaneously in air.
c. Li hardly reacts with steam, whereas Cs reacts even with cold water.
d. Li forms only one of oxide (L𝑖2O), because ionization potential of Li is high.
e. Superoxide are paramagnetic and colored due to the presence of unpaired electrons.
Order of their stability is as follows : Normal oxide > Peroxide > Superoxide

19. 13. Lustrous Surface :
Luster is due to mobile electrons in the metallic lattice. Valence electrons generated vibration in the electrical
field of the light waves. The vibrating electrons emit electromagnetic energy in the form of light, and thus the
surface of these metals starts shining.
14. Tendency of Forming Complex compounds:
A complex compound is a compound that gives a complex ion on ionization. For example – 𝐾4 Fe(CN)6 gives 𝐾+1
and a complex ion. [Fe(CN)6]−4, on ionization. Complex compounds are formed by the metal which has :
a. Very small size of the cation.
b. Maximum charge on the cation
c. Vacant d orbitals in the cation.
15. Strength of metallic Bonds (Softness)
Metallic bond is weak due to presence of one electron in the valence shell and the BCC structure. The packing
efficiency is 68%. Thus, packing of atoms is loose and these elements are soft. Strength of metallic bond ∝ Atomic
size These metals are soft because one electron is present in their valence shell, which participates in bond
formation. Thus, metallic bond is weak. Atomic size increases in the group from Li to Cs, due to which strength of
metallic bond decreases. This is the reason why Li is hard, but Na and K are soft, whereas Rb and Cs are liquid due
to weak metallic bonds. Sheets and wires can be prepared from Li because of its hardness.

20. 16. Melting point and Boiling Point :
Their melting and boiling points are low due to weak metallic bonds. Strength of metallic bond decreases in the
group from Li to Cs, due to which hardness from Li to Cs. Li > Na > K > Rb > Cs.
Thus, melting and boiling points ∝ Strength of metallic bond.
17. Reducing Power
The reducing power of a metal is related to its oxidation potential which represents the tendency of element to
lose electron and get oxidized. All alkali metals have low I.E., leading to a high oxidation potential.
a. Reducing nature (in solution is)
Li > Cs > Rb > K > Na
a. In gaseous state
Li < Na < K < Rb < Cs

21. CHEMICAL PROPERTIES
Alkali metals are highly reactive due to low ionization energy.
1. Reaction with Oxygen
a. Alkali metal ignites in oxygen and form oxides.
M 𝑴𝟐𝑶 𝑴𝟐𝑶𝟐 M𝑶𝟐
oxide peroxide superoxide
a. Li forms stable oxide (𝐿𝑖2𝑂), Na forms peroxide(𝑁𝑎2𝑂2) and rest of the metal forms superoxides.
b. Oxides of alkali metals are basic in nature and basic character increases from Li to Cs as ionic character
increases.
c. Peroxides and superoxides behave as strong oxidising agents. Superoxides on treatment with dil. acids
form 𝐻2𝑂2, 𝑂2 and hydroxide.
K𝑶𝟐 + 2𝑯𝟐O → 2KOH + 𝑯𝟐𝑶𝟐 + 3𝑶𝟐
2. Reaction with Water
a. Hydrogen is liberated.
2M + 2𝑯𝟐O → 2MOH + 𝑯𝟐
a. Basicity of hydroxides increases down the group, due to increase in electropositive character.
3. Reaction with Hydrogen
a. Alkali metal hydrides are formed when metals are heated with 𝑯𝟐 .
2Na + 𝑯𝟐 → 2NaH.
a. Metal hydrides are ionic. They are good reducing agents. Reducing power increases down the group.
𝑂2 𝑂2 𝑂2

22. 4. Reactivity with Halogen
• Halides are ionic compounds having negative enthalpies of formation.
• The most negative enthalpy of formation occur with fluorides. The negative value decreases as
Fluorides >Chlorides > Bromides > Iodides.
Thus, fluorides are the most stable.
• LiF is insoluble in water due to very high lattice energy. CsI is insoluble in water due to very low hydration energy.
• Rest of halides are soluble in H2O.
5. Metal Hydroxides
a) Basic strength of hydroxide increases with the increasing electropositivity of metal.
CsOH > RbOH > KOH > NaOH > LiOH.
b) Solubility of hydroxides increases with increasing ionic character.
CsOH > RbOH > KOH > NaOH > LiOH.
6. Reaction with dilute acids :
Due to alkaline nature, these metals react rapidly with dilute acids and the rate of reaction increases from Li to Cs,
because of increase in basic character.
7. NITRIDES
Among all alkali metals, only lithium directly combines with nitrogen to form nitride. Other alkali metals combine
indirectly with nitrogen, because L𝑖3N is covalent and as the metallic character increases, the tendency of
donating electron and forming ionic bond increases. Due to which strength of metal nitrogen bond decreases.

23. METAL CARBONATES
i. All these metals from 𝑀2𝐶𝑂3 type carbonates. (𝐿𝑖2𝐶𝑂3, 𝑁𝑎2𝐶𝑂3, 𝐾2𝐶𝑂3, 𝑅𝑏2𝐶𝑂3, 𝐶𝑠2𝐶𝑂3)
ii. Basic character, ionic character, melting point, boiling point these carbonates increase from carbonates of Li to Cs.
iii. 𝐿𝑖2𝐶𝑂3 is least stable out of all these carbonates, because it is covalent and decomposes to Li2O and CO2 at low temperatures.
iv. Order of their stability is as follows: 𝑳𝒊𝟐𝑪𝑶𝟑 < 𝑵𝒂𝟐𝑪𝑶𝟑 < 𝑲𝟐𝑪𝑶𝟑 < 𝑹𝒃𝟐𝑪𝑶𝟑 < 𝑪𝒔𝟐𝑪𝑶𝟑
v. Stability of carbonates of IA group metals > stability of carbonates of IIA group metals.
SULPHATES Basic character, ionic character, melting point, boiling point, solubility, thermal stability and reactivity increases from
Li to Cs. 𝑳𝒊𝟐𝑺𝑶𝟒, 𝑵𝒂𝟐𝑺𝑶𝟒 < 𝑲𝟐𝑺𝑶𝟒 < 𝑹𝒃𝟐𝑺𝑶𝟒 < 𝑪𝒔𝟐𝑺𝑶𝟒
NITRATES
Their basic character, ionic character, solubility, melting point boiling point and thermal stability increase from Li to Cs.
Li𝑁𝑂3 decomposes to L𝑖2O at low temperature, whereas Na𝑁𝑂3 gets decomposed to Na 𝑁𝑂3.
HYDRIDES
a) Lithium reacts with hydrogen due to its low electropositive character.
b) Li is less electropositive and therefore, thermal stability on LiH is high.
LiH > NaH > KH > RbH > CsH
They are ionic hydrides and their stability depends of lattice energy.
BICARBONATES
These metals from MHCO3 type bicarbonates. Basic character, ionic character, melting point, boiling point reactivity and thermal
stability of these bicarbonates increase from Li to Cs.
FORMATION OF AMALGAMS Alkali metals form amalgams with mercury and alloys with other metals

24. ANAMALOUS BEHAVIOUR OF LITHIUM Due to small size of Li, it has high tendency of polarization and due to
high density of electrical charge. It shows differences with other alkali metals.
a. Li is hard, due to which its melting and boiling points are higher as compared to other metals.
b. LiOH is weak base compared to other hydroxides.
c. Li forms single type of oxide (L𝑖2O), whereas, Na(𝑀2O and 𝑀2𝑂2), K, Rb and Cs (𝑀2O, 𝑀2𝑂2 and M𝑂2) form more types
of oxides.
d. LiCl is insoluble in water, whereas, other chlorides are soluble, LiCl gets dissolved in benzene, petrol and ether.
e. Due to small size of Li+1, its hydration energy is high.
f. Li does not get affected easily by moist air. Therefore, it can be kept open in the air, whereas, other metals form oxides.
g. Due to high hydration energy of Li, its conductivity is low.
h. Li directly combines with N2 to form Li3N whereas, other metal do not form nitrides.
i. Phosphate, oxalate, chloride, fluoride, sulphate and carbonate of Li are insoluble in water, whereas the above
compounds of other alkali metals are soluble
j. Due to small size of Li, its ionisation potential electronegativity and electron affinity are higher than those of the other
alkali metals.
k. Due to covalent nature of LiCl, their melting and boiling points are lower than those of the other alkli metal halides.

25. DIAGONAL RELATIONSHIP :
SIMILARITIES WITH MAGNESIUM
Lithium shows resemblance with magnesium (an element of group 2).
This resemblance is termed a diagonal relationship Group 1 Li Na and Group 2 Be Mg
Reasons for the diagonal relationship are the following :
1. Electronegativities of Li and Mg are quite comparable (Li = 1.00, Mg = 1.20).
2. Atomic radii and ionic radii of Li and Mg are not very much different.
Atomic radii (Å) Li 1.52 Mg 1.60
Ionic radii (Å) L𝒊+
0.76 M𝒈𝟐+
0.72
Atomic volumes of Li and Mg are quite similar.
Li 12.97
𝒎𝑳
𝒎𝒐𝒍𝒆
Mg 13.97
𝒎𝑳
𝒎𝒐𝒍𝒆
3. Both have high polarizing power (ionic potential)
Polarising power (Φ) =
𝒊𝒐𝒏𝒊𝒄 𝒄𝒉𝒂𝒓𝒈𝒆
(𝒊𝒐𝒏𝒊𝒄 𝒓𝒂𝒅𝒊𝒖𝒔)𝟐
Cations with large ionic potentials tend to polarize the anions and give partial covalent character to
compounds.
4. Nitrates of lithium like magnesium decompose to give oxide, whereas all other alkali metal nitrates give nitrite.