Classification of elements

Classification Of elements

Objectives:
❖ Explain Modern and Mendeleev’s Periodic Law and their

table.
❖ Describe atomic structure and electronic distribution.
❖ Explain position of elements in Modern Periodic Table.
❖ Characteristics of groups and periods.
❖ Reactivity of elements.

Period-1st

Period 5th Period-2nd

Period-4th Period-3rd

Warm up

Dmitri Ivanovich Mendeleev Henry Moseley

Guided questions

❖ How to classify the elements and make their study systematic ?

❑ In the ancient times, there were very few elements
discovered, so their individual study was possible.

You may be
wondering…………………

❑ Almost 118 elements have been discovered till today, so the task
of studying them one by one has become very difficult and time
consuming.

Here is solution………

The table formed by the arrangement of elements on the
basis of their similar and dissimilar properties is called
periodic table.

Antoine Lavoisier, John Dalton, Johann Wolfgang
Dobereiner, John Newlands and Lother Meyer contributed
to bring the classification of elements systematic.

Among them, Dmitri Ivanovich Mendeleev, a Russian
Scientist had done really comprehensive and illustrative
work.
With the passage of time, some demerits were found.

In 1913, Henry Mosley removed almost the demerits of
Mendeleev’s periodic table.

Types of Periodic Table

Periodic Table

1. Mendeleev’s Periodic Table 2. Modern Periodic Table

Atomic weight (63 elements) Atomic number (118
elements)

Mendeleev’s Periodic Table

Period - 1 1* Group
Period - 2 2* 3*
Period - 3 4*
Period - 4
1. Eka – Boron – Scandium(21)
Period - 5 2. Eka – Aluminium – Gallium(31)
3. Eka – Silicon – Germinium(32)
Period - 6 4. Eka – Manganese-Technetium(43)

Period - 7

➢ Mendeleev’s Periodic Law ;

Mendeleev’s periodic law states that “ The physical and chemical properties of the
elements are periodic function of their atomic mass or weights”.

Merits of Mendeleev’s Periodic Table

Systematic study of •Mendeleev’s periodic table was the first
elements scientific and systemic study of all known 63
elements.

Gaps in the periodic • There were many gaps for undiscovered
table elements. After their discovery, they got their

proper place in the table.

Correction of wrong •With the help of Mendeleev’s periodic table,
atomic weight properties of several elements were studied
correctly.

Demerits of Mendeleev’s Periodic Table

Position of Hydrogen •Hydrogen shows the properties of both alkali
metals and halogens.

Position of isotopes • No proper place for isotopes, Hydrogen has 3
isotopes protium(1), deuterium (2) and tritium (3).

Anomalous pair •E.g. Co (58.9) is placed before Ni (58.7) and Te
(127.6) is placed before I (127).

Separation of similar •Similar elements like Au and Pt, Cu and Hg, Ag

elements and Ti are separated.

Grouping of • More reactive alkali metals ( Li, K, Na ) and less
dissimilar elements reactive coinage metals ( Cu, Ag, Au ) were
placed together in the same group.

Assignments

1)Define groups and periods.
2)How many groups and periods in Mendeleev’s periodic table.
3)State Mendeleev’s periodic law.
4)Write any three merits / demerits of Mendeleev’s periodic table.

Thank you !!!

Modern Periodic Table

Modern periodic law: It states that “ the physical and chemical
properties of the elements are periodic functions of their atomic
numbers”.

Lanthanides(rare earth metals): The 14 elements from cerium
57La (58Ce) to lutetium (71Lu) after lanthanum (57La ) are called

Lanthanides.
89Ac Actinides (radioactive metals) : The 14 elements from thorium

(90Th ) to lawrencium (103Lr) after actinium (89Ac) are called
actinides.

Features of Modern Periodic Table

• Elements are arranged on the basis of increasing atomic number.

• There are 7 periods and 18 groups in modern periodic table.

• Inert gases are kept in the zero group at the extreme right side.

•Lanthanides and actinides are kept below the main table in two
separate rows.

• Alkali metals, alkaline earth metals, transition metals, metalloids
and non-metals are placed from left to right side.

• Groups are divided into two sub groups A and B except 0 and VIII
group.

Position of elements in Modern Periodic Table

Position of Hydrogen •It is placed at the top of the group IA due its
least atomic number 1.

Position of isotopes • Isotopes of one element are arranged in one group
due to same atomic number.

Position of metals •Alkali metals, alkaline earth metals, transition
metals, and coinage metals are separately placed.

Correction in wrong •Co before Ni and Te before I are arranged
position of elements automatically in order of increasing atomic num.

Position of La and • They are placed at the bottom of the table , not
Ac to increase the width of table unnecessarily.

Difference between Modern Periodic table and
Mendeleev’s Periodic table

Modern Periodic Table Mendeleev’s Periodic Table

1. It is based on increasing atomic 1. It is based on increasing atomic
number. weight.

2. In this table, there are 18 vertical 2. In this table there are 8 vertical
columns called groups. columns called groups.

3. In this table, there is fixed 3. . In this table, there is no fixed
position for hydrogen, isotopes, position for hydrogen, isotopes,
lanthanides and actinides. lanthanides and actinides.

4. There are no gaps for the new 4. There are some gaps for
elements. undiscovered elements.

Alkaline earth Group Inert(noble)gas
metals VA Halogens

Alkali metals Group Group Group
VIA VIIA VIIIA
Group Group Group Group
IA IIA IIIA IVA

Period-1 H B He
Period-2 Li Be Al C N O F Ne
Period-3 Na Mg Si P S Cl Ar
Period-4 K Ca 3
432 1 0
Valency 12
P-Block elements
S-Block

Groups in Modern Periodic Table

Groups : • The vertical column of the periodic table.
• 9 groups ( I to VIII and 0 ).
IA • Except 0 and VIII, the groups from I to VII are
Li (lithium)
Na (Sodium) divided into subgroup A and B (IA, IIA, IIIA, IVA,
K (Potassium)
Rb (Rubidium) VA, VIA VIIA, and IB, IIB, IIIB, IVB VB, VIB,VIIB).
• Group 0 has no sub group and VIII has 3 vertical

columns.
• There are altogether 18 groups.
• They have same valency and similar properties.
• Atomic size (radius) of elements increases down

the group.
• Effective nuclear charge decreases from top to

bottom in a group.

Periods in Modern Periodic Table

Periods : • The horizontal rows of the periodic table.
• There are 7 periods.

1. Very short period: 1st period (2 elements).
2. Short periods: 2nd and 3rd periods (8 elements).
3. Long periods: 4th and 5th periods (18 elements).
4. Very long periods: 6th and 7th periods (32 and 26

elements respectively).
• The number of shell remains same but valence

electron increases from left to right.
• Atomic size (radius) decreases from left to right due

to increase in nuclear force of attraction.
• Their valency changes as 1, 2, 3, 4, 3, 2, 1, 0 as we

move from left to right in a period.

Assignments

1)State modern periodic law.
2)How many groups and periods in Modern periodic table.
3)Write any three difference between Mendeleev and Modern

periodic table.
4)Write any four features of groups/periods.
5)Write the name(symbol) of first 20 elements in table form with

their common name, valency and sub-shell.

Thank you !!!

Give reasons:

❑ Why is group IA elements are called alkali metals?
➢ Group IA elements are called alkali metals because they react with water to form hydroxide.

i.e. Na + H₂O NaOH + H₂

❑ Why is group IIA elements are called alkaline earth metals?

➢ Group IIA elements are called alkaline earth metals because they are found on earth crust and react with
water to form hydroxide.

i.e. Ca + H₂O Ca(OH)₂ + H₂

❑ Why is Group VIIIA or Zero group elements are called noble gas or inert gas?

➢ Group VIIIA elements are called inert gas or noble gas because they do not take part in chemical reaction as
they are in octet state with 8 electrons in their outermost orbit ( except helium). They do not lose or gain
electrons from outermost shell.

❑ Why are Lanthanides and Actinides kept separately in the periodic table?

➢ Lanthanides are rare earth metals, whereas Actinides are radioactive metals. The properties of Lanthanides
resemble each other very closely but are different from the rest of the elements due to preferential filling of f
–orbital. So, they are kept separately to avoid unnecessary expansion of the periodic table.

❑ Why are halogens highly reactive?

➢ Halogens contains seven electrons in their valance shell. So, they gain an electron easily from other elements
and acquire the octet state. So, halogens are highly reactive.

Groups and periods

Periods Groups

1. Horizontal rows of the periodic 1. Vertical columns of the

table are called periods. periodic table are called groups.

2. In periods, the atomic size of 2. In the groups, the atomic size
the elements decreases while of the elements increases while
moving from left to right. moving from top to bottom.

3. The elements of the same 3. The elements of the same

period have different properties. group have similar properties.

Shell

A shell is the path along which electrons revolve, for example, K, L, M, N and so on.

Sub-shell

A sub-shell is the space around the nucleus where the probability of finding an electrons is more. There are four sub-shells,
i.e. s, p, d, f.

The main shell along with their sub-shells are listed in the given box.

Main shells Sub-shells
K ( n=1 ) (2 e) s
L ( n=2 ) ( 8 e)
M ( n=3 ) (18e) s and p
N ( n=4 ) ( 32e ) s, p and d
s, p, d and f

The maximum number of electrons that can be accommodated by each sub-shell is given below;

Sub-shells Maximum number of electrons
s ( sharp) 2
p ( principal ) 6
d ( diffuse ) 10
f ( fundamental ) 14

Aufbau Principle
This principle was given by Wolfgang Pauli and Neils Bhor in the early 1920s.
Aufbau principle states “ filling the electrons occurs from a lower energy level ( or shell ) to a higher energy level ( or
shell ).

For example
1. Sodium( Na )- 11

= 1s2,2s22p6,3s1
2. Calcium ( Ca )- 20

= 1s2,2s22p6,3s23p6,4s2

Electronic Configuration of First 20 elements on the basis of sub-shells ( s, p, d, f )

S.N Element Atomic No. Electronic configuration based on shells( K, L, Electronic configuration based on sub- Valency

M, N) shells ( s, p, d, f) 1
0
1. Hydrogen ( H ) 1 1 1s1 1
2
2 Helium( He ) 2 2 1s2 3
4
3 Lithium( Li ) 3 2,1 1s2,2s1 3
2
4 Beryllium( Be ) 4 2,2 1s2,2s2 1
0
5 Boron( B ) 5 2,3 1s2,2s22p1 1
2
6 Carbon( C) 6 2,4 1s2,2s22p2
3
7 Nitrogen( N ) 7 2,5 1s2,2s22p3 4
3,5
8 Oxygen( O ) 8 2,6 1s2,2s22p4 2
1
9 Fluorine( F ) 9 2,7 1s2,2s22p5 0
1
10 Neon( Ne ) 10 2,8 1s2,2s22p6 2

11 Sodium( Na ) 11 2,8,1 1s2,2s22p6,3s1

12 Magnesium( Mg ) 12 2,8,2 1s2,2s22p6,3s2

13 Aluminum( Al ) 13 2,8,3 1s2,2s22p6,3s23p1
14 Silicon( Si ) 14 2,8,4 1s2,2s22p6,3s23p2
15 Phosphorus( P ) 15 2,8,5 1s2,2s22p6,3s23p3
16 Sulphur( S ) 16 2,8,6 1s2,2s22p6,3s23p4
17 Chlorine( Cl ) 17 2,8,7 1s2,2s22p6,3s23p5
18 Argon( Ar ) 18 2,8,8 1s2,2s22p6,3s23p6
19 Potassium( K ) 19 2,8,8,1 1s2,2s22p6,3s23p6,4s1

20 Calcium( Ca ) 20 2,8,8,2 1s2,2s22p6,3s23p6,4s2

Classification of Elements Based on Electronic Configuration

i. s – block elements ii. p – block elements

iii. d – block elements iv. f – block elements

s – block elements: The elements whose last electron enters into s – sub shell are called s- block elements.
➢ The elements of group IA and IIA are s – block elements.
➢ These elements have 1 or 2 valence electrons.
➢ s – block elements are located on the left side of the Modern periodic table.
➢ This block consists of metals except H and He.

➢ For example; Sodium ( Na ) is kept in s – block elements as its last electrons enters to s – sub shell, i.e. Na (11):

1s2,2s22p6,3s1
p- block elements : The elements whose last electron enters into p – sub shell are called p- block elements.
➢ The elements of group IIIA, IVA, VA, VIA, VIIA and group zero( VIIIA) are p – block elements.
➢ These elements have 3, 4, 5, 6, 7 or 8 valence electrons in the valence shell.
➢ P- block elements are located on the right side of the Modern periodic table.
➢ This block consists of metals, metalloids and non- metals.
➢ For example, Aluminium( Al ) is kept in p – block as its last electron enters to p – sub shell, i.e. Al ( 13 ) :

1s2,2s22p6,3s23p1

d – block elements

The elements whose last electron enters into d – sub shell are called d- block elements.
➢ The elements of group IB to VIIB and VIII.
➢ These elements are located between s – block and p – block.
➢ The elements of d – block are called transitional metals as they are present between s – block and p – block.
➢ For example Copper ( Cu ) is kept in d – block as its last electron enters to d – sub shell, i.e. Cu(29) : 1s2,2s2 ,2p6,

3s2 ,3p6,4s1,3d10
f- block elements
➢ The elements whose last electron enters into f – sub shell are called f- block elements.
➢ The elements of lanthanide and actinide series are kept in f – block.
➢ This block elements are located at the bottom of the Modern periodic table just below the d – block elements.

➢ f – block elements are called inner- transition elements.

Transition Elements

The element which have incomplete d – sub shells are called transition elements. These elements are kept in d –
block of the modern periodic table. Example; copper, zinc, mercury, etc.

Position of lanthanides in the periodic table

Lanthanides are below the main body of the periodic table. The are in the 6th period, group IIIB and f- block.

Difference between s – block and p – block elements

s– block elements p – block elements

1. The elements whose last electrons enters 1. The elements whose last electron enters
to s-sub shell are called s-block elements. to p- sub shell are called p-block elements.

2. Group IA and IIA elements are s-block 2. Group IIIA to VIIA and group zero
elements. elements are p-block elements.

3. They are 12 in number. 3. They are 31 in number.

4. These elements have 1 or 2 valence 4. These elements have 3,4,5,6,7 or 8
electrons. valence electrons.

5. They are metals. 5. They may be metals, non-metals,
metalloids or inert gases.

Difference between IA group elements and VIIA group elements.

IA group elements VIIA group elements

1. Elements of IA group of the periodic 1. Elements of VIIA group of the periodic
table are called alkali metals . table are called halogens.

2. They are metals. 2. They are non-metals.

• Argon atom exist freely in nature, why?

➢ The outermost orbit of Argon atom is filled by having eight electrons.
Due to this, it does not take part in chemical reaction. Therefore, argon
atom can exist freely in nature.

• In which group alkali metals placed in the Modern periodic table? Why,
are alkali metals so called?
➢ Alkali metals are placed in group IA of the modern periodic table.
Alkali metals are so called because these metals react with water to form
hydroxides.

• Sodium is an active metal, why?
➢ Sodium has one electron. Therefore, it has a tendency to lose its
valence electron during chemical reaction to be an octet. So, it is called
an active metal.

• Why is the position of hydrogen contradictory in the Modern
periodic table?

➢ The position of the hydrogen is contradictory because of its dual
characters(i.e. characters of IA group and VIIA group). Hydrogen can
lose its one electron like alkali metals and can gain one electron like
halogens in orders to combine with other atoms.

• What do you mean by octet rule?
➢ The tendency of an atom to achieve 8 electrons in its outermost orbit
for its stability during a chemical reaction is called octet rule

Characteristics of Periods and Groups.
i. Atomic radius ( size ) :Atomic radius is the distance between the outermost shell and

the center of the nucleus of an atom.
➢ In group, the atomic size of the elements increases from top to bottom.

➢In period, atomic size decreases on moving from left to right.

ii. Nuclear Power (Ionization Energy): The amount of energy required to
remove the outermost loosely bound electron of an atom is called nuclear power.
➢In group, Nuclear Power decreases from top to bottom.
➢In period, Nuclear Power increases fro left to right.

iii. Electronegativity: The amount of energy required for an atom to attract the outer
electron of an another atom is called electronegativity.

➢In group, electronegativity decreases from top to bottom.
➢In period, electronegativity increases from left to right.

iv. Valency: The total number of electrons gained, lost or shared by an atoms during
a chemical reaction is called valency.

v. Valence Electrons: The electrons present in the outermost shell or
valence shell of an atom is called valence electrons.

vi. Metallic character: Metallic character is the tendency of an atom to
lose one or more electrons.

vi. Non metallic character: Non metallic character is the tendency of an
atom to gain one or more electrons when supplied with energy.

• Reactivity of Elements
A metal which loses electrons easily is called an active metal.
A non-metal which gains electrons easily is called an active non-metal.

Factors affecting reactivity of elements are atomic size, nuclear charge, valence
electrons and etc.

Reactivity of Metals in a group
When we move from top to bottom in the groups of metals;
➢Atomic size increases,
➢Nuclear power decreases,
➢Easy to lose electrons for an atom
➢Reactivity of an element increases.
When we move from bottom to top in metals;
➢Atomic size decreases,
➢Nuclear power increases,
➢Difficult to lose electrons for an atom,
➢Reactivity of an element decreases.

Note : Group IA, IIA and IIIA are metals. Reactivity of elements of these groups are same .

• What happens to the reactivity of the elements of group IA while moving
from top to bottom?

Ans; When we move from top to bottom in group IA; Group IA
H
➢Atomic size increases,
➢Nuclear power decreases, Li

➢Easy to lose electrons for an atom

➢Reactivity of an element increases. Na

K

• Potassium is more reactive than Sodium, why?

Ans; Potassium is more reactive than sodium because potassium has larger atomic
size and less nuclear power than sodium. As a result, Potassium can lose its valence
electron more easily than sodium during chemical reaction.

• Sodium is more reactive than Lithium, why?

Ans; Sodium is more reactive than lithium because sodium has larger atomic size and
less nuclear power than lithium. As a result, sodium can lose its valence electron
more easily than lithium during chemical reaction.

• Which one is more reactive in between Potassium and Calcium, why?

Ans; Potassium is more reactive than Calcium because, the electronic configuration
of potassium is 2,8,8,1 and that of calcium is 2,8,8,2. It shows that potassium has 1
valence electron where as calcium has 2 valence electron in their valence shell. So,
to gain octet state potassium lose its electron more easily than calcium during
chemical reaction.

• Lithium and sodium are kept in group 1, why?

Ans; Both the lithium and sodium contain 1 valence electron and both of them react
with water to produce corresponding alkali and hydrogen gas. So, lithium and
sodium are kept in group IA.

• What is the cause of placing calcium in IIA group of the periodic table?

Ans; the cause of placing calcium in IIA group of the modern periodic table are listed
below;

i. It has two valence electrons.

ii. It can donate two electrons to form an electropositive radical Ca++.

Reactivity of non- metals in a group
When we move from top to bottom in the group of non-metals;
➢Atomic size increases,
➢Electro negativity decreases,
➢Difficult to gain electron,
➢Reactivity of an element decreases.
When we move from bottom to top in non-metals;
➢Atomic size decreases,
➢Electro negativity increases,
➢Easy to gain electron,
➢Reactivity of an element increases.

Note: Group VA, VIA and VIIA of the modern periodic table are non-metals.

• What happens to the chemical reactivity of an elements in group VIIA of modern
periodic table while moving from top t bottom?

Ans; When we move top to bottom from Bottom to top Group VIIA

➢Atomic size increases, - Atomic size decreases, F
➢Electro negativity decreases,
➢Difficult to gain electron, - Electro negativity increases, Cl
➢Reactivity of an element decreases.
- Easy to gain electron, Br

- Reactivity of an element increases.

• Fluorine is more reactive than chlorine, why?

Ans; Fluorine is more reactive than chlorine because fluorine has smaller atomic size
and more electro negativity than chlorine. So, fluorine can gain electron more easily than
chlorine during chemical reaction.

• Chlorine is more reactive than bromine, why?

Ans; Chlorine is more reactive than bromine because chlorine has smaller atomic size
and more electro negativity than bromine. So, chlorine can gain electron more easily
than bromine during chemical reaction.

• Chlorine is more reactive than Nitrogen, why?

Ans; Chlorine and nitrogen both are non-metals. Chlorine has 7 electrons in its
outermost shell and nitrogen has 5 electrons in its last shell. Chlorine needs one
electron and nitrogen needs three electrons to complete octet. So, during
chemical reaction chlorine can easily gain 1 electron to became octet faster than
nitrogen. Thus, chlorine is more reactive than nitrogen.

• The reactivity of non- metals increases while moving from left to right in a period,
why?

Ans; The reactivity of non-metals increases while moving from left to right in a
period because the effective nuclear charge increases and atomic size decrease
as we move left to right in a period. Hence it becomes easier to gain the electron
for non-metals.

• Which one is more reactive; Sulphur or chlorine, why?

Ans; Sulphur has six electron in its valence shell while chlorine has seven
electrons in its valence shell. So, chlorine gains one electron easily than Sulphur
and acquires octet state. So, chlorine is more reactive than Sulphur.

Q. Answer the following questions from the given electronic configuration.

i. Name the elements A, B and C. Elements Electronic
configuration
➢ The elements are A – Sodium, B- Potassium, C- Chlorine
1s2,2s22p6,3s1
ii. Identify the period, group, valency and block of given elements. A 1s2,2s22p6,3s23p6,4s1
B
1s2,2s22p6,3s23p5
Element Period Group Valency Block

A 3 IA 1 s C

B 4 IA 1 s

C 3 VIIA 1 p

iii. Which is more reactive, A or B ? Why?

Ans; B is more reactive than A because B has larger atomic size, less nuclear power
and hence loses electron more easily than A during chemical reaction.

iv. Which compound will be formed due to chemical reaction between A with C and
B with C? What types of compounds are these and why?

Ans; Compounds formed due to chemical reaction between, A and C is NaCl (
Sodium Chloride)

B and C is KCl ( Potassium chloride). And they are electrovalent compounds.













Assignments