2. IMPORTANCE OF CLASSIFICATION OF
• Organization and relationship between elements are defined.
• Properties of elements can be correlated with properties of states of matter.
3. BASIS OF CLASSIFICATION OF ELEMENTS:
• Early Chemists: based on properties, valencies & metallic and non-metallic nature
• The method was discarded since elements behave both as metals and non-metals,
shows metallic and non-metallic nature and have variable valency.
4. DOBEREINER'S LAW OF TRIADS :
• ’Chemically analogous elements arranged in increasing order of atomic weights
formed well marked groups of three called triads in which the atomic weight of the
middle element was found to be generally the average of the atomic weights of the
other two elements.’
5. LIMITATIONS OF DOBEREINER’S TRIADS:
• The identification of new elements made this model obsolete.
• Newly discovered elements did not fit into the triads.
• Only a total of 5 Dobereiner’s triads were identified.
• Even several known elements did not fit into any of the triads.
6. NEWLANDS LAW OF OCTAVES:
• When the elements are arranged in increasing order of their atomic masses, the
properties of the eighth element are like that of the first.
7. LIMITATIONS OF NEWLANDS' LAW OF OCTAVES:
• It was applicable to only lighter elements having atomic masses up to 40, i.e., up to
calcium. After calcium, the first and the eighth element did not have similar
• It failed to leave spaces for undiscovered elements.
10. MENDELEEV’S CONTRIBUTIONS:
• Elements were arranged in increasing order of atomic weights in periods and
• Elements with similar chemical properties are grouped together.
• Elements in the same group had the same valency.
• Gaps were left for undiscovered elements.
• The properties of the undiscovered elements were predicted.
• Incorrect atomic weights of some of the arranged elements were corrected.
11. DEFECTS IN MENDELEEV’S PERIODIC TABLE:
• Anomalous pairs.
• Position of isotopes
• Position of rare earths and actinides
12. MODERN PERIODIC LAW:
• Moseley modified Mendeleev’s periodic law to form the modern periodic law – The
physical and chemical properties of elements are the periodic function of their
13. PERIODICITY OF ELEMENTS
• Gradual change in properties is seen with increase in atomic number
• Periodicity – recurrence in properties are seen in:-
• Elements belonging to the same subgroup
• After a difference of 2,8,18 or 32 in atomic numbers due to recurrence of similar
valence electronic configuration.
14. SALIENT FEATURES OF MODERN PERIODIC
• 1. The modern periodic table has 7 horizontal rows called 'Period'.
• Elements of the same period have the same number of electron shells.
• Electrons in the outermost shell increases progressively for elements of the same
• Period number signifies the number of electron shells.
• Transition from metallic to non-metallic character.
• Separation of elements : => Reactive metals: group IA and 2A
• =>Transition metals: in the middle
• =>Non - Metals: upper right corner
15. 2.THERE ARE 18 VERTICAL COLUMNS IN THE
PERIODIC TABLE CALLED ‘GROUPS’.
• 2.There are 18 vertical columns in the periodic table called ‘Groups’.
• Group 1-alkali metals
• Group 2- alkaline earth metals
• Group 3- 12 – transition elements
• Group 13-16 – post transition elements
• Group 17 –halogens
• Group 18 – noble / inert gases.
• Group 1,2,13,14,15,16,17 – normal elements/representative elements.
• Group number signifies the number of valence electrons of an element.
• Elements of the same group have the same number of valence electrons hence same valency and similar properties.
• Number of electron shells increases by one
• Metallic character increases down a group.
16. PERIOD IN A PERIODIC TABLE
• In the periodic table of the elements, each numbered row is a period. In the periodic
table of the elements, elements are arranged in a series of rows (or periods) so that
those with similar properties appear in a column.
• Number of electron shells remain the same from left to right of a period.
• Valance electrons increases by one from left to right of a period.
• The non - metallic character increases from left to right of a period.
27. GROUP IN A PERIODIC TABLE
• A group (also known as a family) is a column of elements in the periodic table of the
chemical elements. There are 18 numbered groups in the periodic table, but the f-
block columns (between groups 2 and 3) are not numbered.
32. PROPERTY TRENDS – DOWN A SUB-GROUP
• Valence electrons – Remain same
• Chemical properties - Remain same
• Metallic character/electro positive character – increases down
• No. of electron shells increases by one.
35. Group IA elements Group VIIA elements
Elements Li, Na, K, rubidium,
Fl, Cl, Br, I, astatine
Valency 1 valence eˉ => Univalent 7 valence eˉ => univalent
Nature Highly – reactive and
electropositive ; light & soft
metals – can be cut with a
Highly – reactive and electronegative;
Non - metals – some are gaseous,
liquid and solid at room temp.
Conductivity Good Bad or Non - conductors
Reducing / oxi-
Strong reducing agents Strong oxidizing agents
Electrovalent compounds are
Covalent compounds are formed
Ionic hydrides are formed Covalent hydrides are formed
• Periodicity: occurrence of characteristic properties of elements at definite intervals
in the modern periodic table when elements are arranged in the increasing order of
their atomic numbers.
• The cause of periodicity is the recurrence of similar electronic configuration.
38. FACTORS AFFECTING ATOMIC
• Number of shells increases & atomic size increases
• Reason – As the No. of shells increases – the distance between the nucleus and the
outermost shell increases
• Nuclear charge increases and atomic size decreases
• Reason – Nuclear charge increases – the electrons of the outermost shell are
attracted with increasing force
• Nuclear charge is the positive charge of the atom
• Nuclear charge is equivalent to the atomic number of the element
39. TRENDS IN ATOMIC SIZE – FROM LEFT TO
RIGHT OF A PERIOD
• Number of shells – Remain the same and
Atomic Size – Remains unaffected
• Nuclear charge – Increases and Atomic size –
• In Period 2 – Li – largest atomic Radius
• In period 2 – F - smallest atomic radius
• Neon has larger atomic radius as its
outermost shell is completely filled
• The effect of nuclear pull over the valence
shell electrons is not seen
40. TRENDS IN ATOMIC SIZE ; DOWN A GROUP
• Number of shells increases and atomic size increases
• Nuclear charge increases and atomic size should decrease
• Atomic radius/size increases down a group
42. FACTORS AFFECTING – IONIZATION
• Atomic size increases and Ionization potential – Decreases
• Reason – Atomic size increases and the nuclear attraction on the outer electron -
• Outer electrons are loosely held
• Nuclear charge increases and ionization potential – increases
• Reason – Nuclear charge increases and the nuclear attraction on the outer electron
• Outer electrons are tightly held
43. TRENDS IN IONIZATION POTENTIAL
• Helium has highest ionization potential while caesium has the lowest
• Metals lose electrons and so have low I.P. compared to non-metals
• I.P. increases across a period
44. TRENDS IN I.P. – DOWN A GROUP
• Atomic radius increases and I.P. decreases
• Nuclear charge – Increases and so I.P. should decrease
• I.P. decreases down a group
46. FACTORS AFFECTING ELECTRON AFFINITY
• Atomic size increases and Electron affinity decreases
• Reason: A small atom takes up electrons more readily than a large atom
• Because the nucleus has greater attraction on the electrons
• Nuclear charge increases and electron affinity increases
• Nuclear charge increases:
• Similarly increases the tendency of atom to accept electrons
47. TRENDS IN ELECTRON AFFINITY – ACROSS
A PERIOD – FROM LEFT – RIGHT
• Atomic radius decreases and electron affinity increases
• Nuclear charge increases and electron affinity increases
• Neon has electron affinity zero as its outermost shells are filled
• Electron affinity is highest for halogens group 17 and least for alkali metals group 1
• More value of electron affinity more is the electronegativity
• Electron affinity increases across a period from left to right
48. TRENDS IN ELECTRON AFFINITY DOWN A
• Atomic radius increases and E.A. decreases
• Nuclear charge – Increases and so E.A. should decrease
• E.A. decreases down a group
49. ELECTRO - NEGATIVITY
• It is the tendency of an atom to attract itself in the gaseous state accepts an electron
to form an anion
51. TRENDS IN ELECTRO-NEGATIVITY ACROSS
A PERIOD FROM LEFT TO RIGHT
• Atomic radius decreases and electro-negativity increases
• Nuclear charge increases and electro-negativity increases
• Elements with high electronegativity are usually non-metallic
• Fluorine is the most electronegative element and caesium id the least
• Noble gases have complete octet and so they do not attract electrons
• electro-negativity increases across a period from left to right
52. TRENDS IN ELECTRO-NEGATIVITY DOWN A
• Atomic radius increases and electro-negativity decreases
• Nuclear charge increases and electro-negativity should increase
• Electro-negativity decreases down a group
53. FEATURES OF LONG FORM OF PERIODIC
• 1. 18 vertical columns known as groups.
2. 7 Horizontal rows known as periods.
3. Light metals These are elements of periodic table of group 1 and 2.
4. Heavy metals or Transition metals - These are elements of periodic table of group
3, 4, 5, 6, 7, 8, 9, 10, 11 and 12.
5. Non-Metals These are elements of periodic table of group 13, 14, 15, 16 and 17.
6. Zero group These are elements of periodic table of group 18.
54. METALLIC AND NON METALLIC
CHARACTER - TERM
Non - Metallic
In terms of electron
losing property – an
atom is said to be a –
Metal , if it loses one or
more electrons when
supplied with energy.
In terms of electron
gaining property – an
atom is said to be a –
Metal , if it gains one
or more electrons when
supplied with energy.
55. FACTORS AFFECTING METALLIC AND NON-
• Atomic radius increases and metallic character increases , nonmetallic character decreases.
• I.P. increases and metallic character decreases , nonmetallic character increases.
• Metallic atoms are present on the left side of the periodic table have large atomic radius and
low I.P. value and lend to lose – electrons
• Non - Metallic atoms are present on the right side of the periodic table have small atomic
radius and high I.P. value and lend to gain – electrons
• Metals are good reducing agents
• Non – Metals are good oxidizing agents
56. TRENDS IN CHARACTER – ACROSS A
PERIOD FROM LEFT TO RIGHT
• Atomic radius decreases and metallic character decreases ; non – metallic character
• I.P. increases and metallic character decreases ; non – metallic character increases
• Metallic character decreases across a period ; Non – metallic character increases
across a period
57. TRENDS A CHARACTER DOWN A GROUP
• Atomic radius increases and metallic character increases ; non – metallic character
• I.P. decreases and metallic character increases ; non – metallic character decreases
• Metallic character increases across a period ; Non – metallic character decreases
across a period
60. PHYSICAL PROPERTIES - DENSITY AND
Across a period – density
and & melting points –
61. PHYSICAL PROPERTIES - DENSITY AND
MELTING POINT AND BOILING POINT
Down a group density
increases gradually & m.p &
b.p. of elements decreases
62. CHEMICAL PROPERTIES – PERIODICITY IN
PROPERTIES OF COMPOUNDS OF ELEMENTS
Characteristics Varies across a period Varies down a group
Oxides Strongly basic to
Acidic to Basic
Hydroxides Strongly basic to
Less basic to Strongly
Oxy-acids Weak oxy-acids to
Strong oxy-acids to
Hydrides Strongly basic to
Less Acidic to More
63. STABLE AND UNSTABLE ELEMENTS
• Elements arranged in the periodic table having n/p (neutrons/protons) ratio around
1 are stable
• Elements arranged in the periodic table having n/p (neutrons/protons) ratio above
1.5 are unstable stable
• E.g. – light – Na ; heavy – uranium.
• There are 18 vertical columns in the periodic table. Each column is called a
group. All elements in a group have similar chemical and physical properties
because they have the same number of outer electrons.
In periodic table elements are arranged in a series of rows. Elements of the same
period have the same number of electron shells.
67. MODERN PERIODIC LAW
• The properties of elements are the periodic function of their atomic number i.e.
number of protons.
69. LOCATION OF METALS, NON-METALS,
METALLOIDS AND NOBLE GASES ARE AS
• Elements on the left and middle are Metals
• Elements on the right are Non-metals
• Metalloids form the narrow stair-step area between metals and non-metals
• The last group (18) to the right are Noble gases
70. PERIODIC TABLE CHART
• The Periodic Table organizes the elements according to their similar chemical and
physical properties. The Table has rows and columns. The vertical columns in the
periodic table represent Groups. The horizontal rows in table represents Periods.
71. DETERMINE THE PERIOD NUMBER OF
• All the elements in a period have the same number of atomic orbitals. For example,
every element in the top row (the first period) has one orbital for its electrons. All
the elements in the second row (the second period) have two orbitals for their
72. DETERMINE THE GROUP NUMBER OF
• The group number is an identifier used to describe the column of the
standard periodic table in which the element appears. Groups 1-2 (except hydrogen)
and 13-18 are termed main group elements. Groups 3-11 are termed transition
Electronic configuration of Sodium is 2, 8, 1. So the number of group is 1
73. OCCURRENCE OF ALKALI EARTH METALS
• Alkaline earth metals are obtained in the form of their ore in earth's crust. Of the
alkaline earth metals calcium and magnesium rank fifth and sixth in abundance
respectively, in earth crust. Beryllium is rare and radium is rarest of all.
• Alkali metals are highly reactive elements. They are soft, have low density, low
melting point, low boiling point, give characteristic color to the flame, are strongly
electro-positive character. They react with water liberating H2 and react with acids
75. NOBLE GASES
• Noble gases are the gases present in group VIIIA(18) which has its outer shell completely fill. Some
of the common properties of noble gases are:
• Almost Non-reactive
• High ionization energies
• Very low electronegativities
• Low boiling points (all monatomic gases at room temperature)
• No color, odor, or flavor under ordinary conditions
• At low pressure, they will conduct electricity