Class 11 chapter 3 classification of elements and periodicity in properties ppt- chemistry

1. CLASSIFICATION OF ELEMENTS AND
PERIODICITY IN PROPERTIES

2. Modern periodic law and the present form of
the periodic table
● Modern periodic law states that physical and
chemical properties of elements are periodic
function of atomic numbers.
● If the elements are arranged in order of their
increasing atomic numbers, the elements with
similar properties are repeated after certain
regular intervals.

3. ● Atomic mass depends upon the number of
protons and neutrons in the nucleus.
● The physical and chemical properties could be
different depending upon the number of
electrons and electronic configuration in any
atoms.

4. Cause of periodicity :
● The properties of elements are repeated after certain
regular intervals when these elements are arranged
in order of their increasing atomic numbers.
● The cause of periodicity in properties is the
repetition of similar outer electronic configuration.

5. after certain regular intervals.
● All the alkali metals have the similar outer
electronic configuration.
● All the halogens have similar outer electronic
configuration ns2np5 hence possess similar
properties.
● All elements of group 18 have similar electronic
configuration ns2np6 and possess similar properties.

6. Long form of periodic table
● The table which is based upon the electronic
configuration of the elements is called the
present form or the long form of periodic table.
● The long form of periodic table consist of 18
vertical columns(groups) and 7 horizontal
rows(periods).

7. Nomenclature of elements with atomic number >
100
● The naming of the new elements had been
traditionally the privilage of the discoverer and the
suggested name was ratified by the IUPAC. In recent
years this has led to some controversy.

10. Periods in long form of
periodic table

11. (i) 1st period (n=1 ; K-shell):- Only 1s orbital is there.
It involves only one orbit which can accomodate only two
electrons and it have two elements.
(ii) 2nd period (n=2 ; L-shell):- Here, one 2s and three 2p
orbitals are there. So,total number of orbitals are four
and have a capacity of eight electrons. So, second period
contains 8 elements.
(iii) 3rd period (n=3 ; M-shell):- Here,one 3s, three 3p and
five 3d orbitals are there. So, total number of orbitals are
nine and have a capacity of eighteen

12. elements. According to Aufbau principle, filling of 3d
takes place after 4s. So, effective orbitals are one 3s and
three 3p. So, number of orbitals are four and have a
capacity of eight elements.
(iv) 4th period (n=4 ; N-shell):- Here one 4s, three 4p, five
4d and seven 4f are there. So, total number of orbitals
are 16 and have a capacity of 32 elements. According to
Aufbau principal, filling of 4d and 4f takes place after 5s.
So, effective orbits are one 4s ,five 3d and three 4p. So,
number of orbitals are 9and have a capacity of 18
elements.

13. (v) 5th period(n=5):- Here, one 5s, three 5p, five 5d and
seen 5f are there. So, total number of orbitals is 16 and
have a capacity of 32 elements. According to Aufbau
principa, filling of 5d and 5f takes place after 6p.So,
effective orbitals are one 5s, three 5p, five 4d. So,number
of orbitals are 9 and have a capacity of 18 elements.
(vi) 6th period(n=6):- Here, one 6s, three 6p, five 6d and
seven 6f are there.So, total number of orbitals is 16 and
have a capacity of 32 elements. According

14. to Aufbau principle, filling of 6d and 6f takes place after
7s. So, effective orbitals are one 6s, seven 4f, five 5d and
three 6p. So, number of orbitals are 16 and have a
capacity of 32 elements.
(vii) 7th period(n=7):- Here,one 7s, three 7p, five 7d and
seven 7f are there. So, total number of orbitals are 16
and have a capacity of 32 elements.According to Aufbau
principle, filling of 7d and 7f takes place only after 8s.So,
effective orbitals are one 7s, seven 5f, five 6d and three
7p. So, number of orbitals are 16 and have a capacity of
32 elements.

15. Groups in long form of
periodic table

16. (i)Group 1:- In Group 1, elements except hydrogen is
known as Alkali metals because their oxides dissolve
in water strong alkalis are obtained. The elements
except hydrogen in group 1 are lithium, sodium,
potassium, rubidium, caesium, francium,
(ii) Group 2:- In Group 2,elements are known as
Alkaline Earth metals because their oxides dissolve in
water gives their hydroxides and are found on the
earth crust.They are also known as S2 elements
because there second subshell contains two

17. electrons. The element in Group 2 are beryllium,
magnesium, calcium, strontium, barrium, radium.
(iii) Group 3 - Group 12 :- The elements from Group 3
to Group 12 are known as Transition elements
because they show transition from highly reactive
metals to highly reactive non-metals.
(iv) Group 13 :- The elements of Group 13 are known
as Boron family. The elements in Group 13 are boron,
aluminium, gallium, indium, thallium, nihonium.

18. (v) Group 14:- The elements in Group 14 are carbon,
silicon, germanium, tin, lead, flerovium.
(vi) Group 15 :- The elements in Group 15 are
nitrogen, phosphorous, arsenic, antimony, bismuth,
moscovium.
(vii) Group 16 :- In Group 16, the elements are known
as chalcogens it means ore forming. The elements in
Group 16 are oxygen, sulphur, selenium, tellurium,

19. polonium, livermorium.
(viii) Group 17:- The elements in group 17 are called as
halogens.The elements in Group 17 are Flourine,
Chlorine, bromine, iodine, astatin, tennessine.
(ix) Group 18 :- In Group 18, the elements are known as
noble gas. They are also known as inert gases because
they does not take part in chemical reaction. Inert
means lazy. The elements in Group 18 are helium,neon,
argon, krypton, xenon, radon, oganesson.

20. Blocks in long form of
periodic table

21. (i) S-block elements:-
‘S’ block contains the elements in Group I and
Characteristics:-
● General electronic configuration ns1-2.
● This block contains all metals.
● They are soft and have low melting and boiling point.
● Ionisational enthalpy is less so they are highly
reactive because they are not found in nature in free
state.
● They are electropositive.

22. 3.(ii) P-block elements:-
‘P’block contains the elements in Group 13 to Group 18.
Charactristics:-
● General electronic configuration is ns2np1-6.
● This block contains metals, non- metals as well as
metalloids.
● They possess high ionisational enthalpy and electron
gain enthalpy as compared to s block elements.

23. (iii) D-block elements :-
‘D’block elements contains the elements in Group 3 to
Group 12 i.e., the transition elements.
Characteristics:-
● General electronic configuration is (n-1)d1-10ns2.
● They all are metals.
● They possess high melting and boiling point.
● Most of them are coloured compounds.
● They exhibit variable valency and variable oxidation
number.

24. ● They are paramagnetic in nature.
● Most of them acts as catalyst.

25. (iv) F-block elements:-
Inner transition elements(Lanthanoids and Actinoids)
Characteristics:-
● General electronic configuration is (n-2)f1-10 (n-1)d0-1
ns2.
● They all are metals.
● They have high melting and boiling point.
● Most of them are coloured compounds.

26. ● They exhibit variable valency and variable oxidation
numbers.
● Elements after Uranium are artificially prepared they
are called transe uranic elements.

28. PERIODIC TRENDS IN
PHYSICAL PROPERTIES

29. I. Atomic Radii:- The distance from the centre of the
nucleus to the outermost shell containing electrons.
Types of Atomic Radii:
(i) Covalent Radius
(ii) Metallic Radius
(iii) Van der Waal’s Radius

30. (i) Covalent radius:- It is the half of the inter nuclear
distance between two covalently bonded atoms of
same element in a molecule.
(ii) Metallic radius:- It is the half of the inter nuclear
distance between two neighbhouring atoms of a
metal of the metal latite.
(iii) Van der Waal’s radius:- It is the half of the inter
nuclear distance between two adjacent atoms of a
substance in solid state.

31. Van der Waal’s radius > metallic radius > covalent
radius

32. Variation of Atomic radius in period
Size of atom decreses when moving from left to
right (number of shells remain same). It is because
within the period the outer electrons are in the same
valence shell and the effective nuclear charge
increases as the atomic number increases resulting in
the increased attraction of electrons to the nucleus.

33. Variation of Atomic radius in group
The atomic radius of elements increases with
increase in atomic numbers as we move from top to
bottom in a group. As we move down the group the
principal quantum number increases.A new energy shell
is added at each succeeding elements and valence
electrons lie farther and farther away from the
nucleus.As a result the attraction of the nucleus for the
electron decreses and hence the atomic radius
increases.

36. II. Ionic Radius:- The removal of an electron from an
atom results in the formation of a cation, whereas gain
of an electron leads to an anion. The ionic radius can
be estimated by measuring the distances between
cations and anions in ionic crystals.
The effective distance from the centre of
the nucleus of an atom upto which it has an influence
in the ionic bond.
Species having same number of electrons are
called isoelectronic species.

37. Eg:- N2- , O2- , F1- , Ne, Na1+, Mg2+, Al3+ have same number
of electron i.e., 10.
A cation is smaller than its parent atom because it has
fewer electrons while its nuclear charge remains the
same.
The size of an anion will be larger than the parent
atom because of the addition of one or more

38. electrons.
The ionic radii of element exhibit the same trend
as the atomic radii.
As, nuclear charge increases, the force of
attraction by the nucleus on the electrons also
increases. As a result ionic radii decreses.

39. III. Ionisational Enthalpy:- The minimum amount of
energy required to remove an electron from an isolated
gaseous atom at ground state. The unit of ionisational
enthalpy is kj/mol. It is represented by ΔH.
The energy required to remove the most loosely
bound electrons from the isolated gaseous atom is
called its first ionisational enthalpy and is denoted by
ΔH1.
The energies required to knock out second

40. and third electrons are called second and third
ionisational energies.
When one eletron have been removed from the
neutral gaseous atom and the positively charged ions
formed has one electron less than the number of protons
in the nucleus.As a result the electrostatic attraction
between the nucleus and the remaining electrons in the
cation increases.The positive ion holds its remaining
electrons more firmly.Therfore, the energy required to
remove another electron from

41. This positively charged ions or second electron from the
neutral atom must be higher than the first.

42. Variation of Ionisational Enthalpy in Period
The value of ionisational enthalpy increases from
left to right with breaks where the atom have
somewhat stable configurations. The observed trends
can easily be explained on the basis of increased
nuclear charge and decreased atomic radii. Both the
factors increase the force of attraction towards nucleus
and consequently, more and more energy is required to
remove the electron and hence, ionisational enthalpy
increases.

43. Variations of Ionisational Enthalpy in Groups
On moving the group, atomic size increases
gradually due to an addition of one new principal energy
shell at each succeeding element. On account of this,
the force of attraction towards valence electron
decreases hence, ionisational enthalpy decreases.

44. Factors affecting ionisational enthalpy:-
● Atomic size
● Nuclear charge
● Shielding effect
● Electronic configuration

45. IV. Electron gain Enthalpy:- It is defined as the
energy released when a neutral isolated gaseous
atom accepts an extra electron to form the gaseous
negative ion. It is denoted by ΔHeg. It is measured in
electron volts per atom or kj per mole.The process of
adding an electron to the atom can be either
exothermic or endothermic.

46. Variation of Electron Gain Enthalpy in Periods
Electron gain enthalpy becomes more and
more negative from left to right in a period. This is
due to increase in size and decrease in nuclear
charge as the atomic number increases in a period.
Both these factors favour the addition of an extra
electron due to higher force of attraction by the
nucleus for the incoming electron.

47. Variation of Electron Gain Enthalpy in Groups
The electron gain enthalpies, in general,
become less negative in going from top to bottom in
a group. This is due to increase in size on moving
down a group. This factor is predominant in
comparison to other factors, i.e., increase in nuclear
charge.

49. V. Electronegativity:- It is the tendancy of an atom to
attract the shared pair of electrons more towards
itself in a covalent bond. It is not a measurable
property. It is directly related to non-metallic
property of an element because they have greater
tendancy to gain electrons. It is inversely proportional
to metallic characters. It increase when moving across
the period and decreases when moving down the
group. Pauling scale is used to measure
electronegativity.

52. PERIODIC TRENDS IN
CHEMICAL PROPERTIES

53. Periodicity of valence or oxidation states
The electrons present in the
outermost shell of an atom are called valence
electrons and the number of these electrons
determine the valency of the atom.

54. Variation along a period
As we move across from left to right, the
number of electrons increases from 1 to 8. But the
valence of elements , H or O first increases from 1 to
4 and then decreases to 0. In the formation of Na2O
molecule, oxygen being more electronegative
accepts two electrons one from each of the two
sodium atoms and thus shows an oxidation state of -
2. On the other hand sodium with valence electronic
configuration 3s1 loses one electron to oxygen and is

55. give an oxidation state of +1. Thus, the oxidation state of
an element in a given compound may be defined as the
charge acquired by its atom on the basis of
electronegativity of the other atom in the molecule.

56. Variation within a Group
When we move down the group, the number of
valence electrons remains the same, therefore, all the
elements in a group exhibit the same valency.

57. Anomalous property of second period elements
It has been observed that some elements of second
period show similarities with the elements of the third
period placed diagonally to each other though,
belonging to different groups. The similarity in
properties of elements placed diagonally to each other
is called diagonal relationship.

58. The anomalous behaviour is due to their small size;
large charge and high electronegativity of elements. In
addition, the first member of group has only four
valence orbitals available for bonding, while the
second member of group has nine valence orbitals.As a
consequence of this, the maximum covalency of first
member of each group is 4, whereas the other
members of the group can expand their valence shell
to accomodate more than four pairs of electrons.

59. Periodic trends and Chemical Reactivity
METALS:- The reactivity of metals is measured in
terms of their tendancy to lose electron from their
outermost shell.
In a period the tendancy of element to lose
electrons decreases in going from left to right. So, the
reactivity of metals decreases in a period from left to
right.

60. In a group the tendancy of element to lose
electron increases as we go down. So, the reactivity of
metals increases down the group.
NON-METALS:- The reactivity of a non-metal
is measured in terms of its tendancy to gain electrons
to form an anion.
In a period the reactivity of non-metals
increases from left to right.During reactions,

61. non-metals tend to form anions.
In a group the reactivity of non-metals
decreases as we go down.This is because the tendancy
to accept electrons decreases down the group.

63. Thank you...
Presented by: A.P.Devanampriya