X Chem Periodic Table Printable Version

8/12/2019 X Chem Periodic Table Printable Version

1/25

Periodic

Classification ofElements

UNIT 5


2/25

Classification of known

elements into differentcategories by considering

their similarity in propertiesso as to get some pattern

between them lead to theinvention of Periodic table


3/25

1. Earliest Attempt

1. Classified the then known (around 30) elementsinto METALS & NON-METALS

Limitation of the approach:

1. had no place for metalloids (elements which

have properties of both metals and non metals)which were discovered later.


4/25

2. DobereinersTriads

Dobereiner classified elements in the increasing order of their

atomic masses into groups of three elements called triads. In each triad the atomic mass of the middle element was

approximately equal to the average atomic mass of the other two

elements: Ex:

Limitation:

All the then known elements could not be arranged into triads

1780-1849

Element

Atomic mass

Average

Li 6.9

22.95Na 22.9

K 39.0

Element

Atomic mass

Average

Ca 40.1

88.7Sr 87.6

Ba 137.3

Element

Atomic mass

Average

Cl 35.5

81.2Br 79.9

I 126.9


5/25

3. Newlands law of Octaves

Newland classified the elements (56 elements were known) in the

increasing order of their atomic masses into groups of eight

elements called octaves like the notes of music

He found that when the elements are arranged in the increasing

order of their atomic masses, every eighth element had

properties similar to that of the first and is called as Law of

Octave

1837-1898


6/25

3. Newlands law of Octaves

Limitations:

1. It was applicable only for lighter elements up to Ca-calcium,as after calcium every eighth element did not possess

properties similar to that of the first

2. It was assumed that only 56 elements existed in nature. But,

later on, several new elements were discovered, whoseproperties did not fit into the Law of Octaves.

3. In order to fit elements into his Table, Newlands adjusted

two elements in the same slot, but also put some unlike

elements under the same note

1837-1898

Iron which resembles Cobalt & Nickel is far

away from them


7/25

4. Mendeleevs Periodic Law

Law states that

The properties of elements are the periodic function

of their atomic masses

Mendeleev classified elements (63 elements were known) in the

increasing order of their atomic masses and similarities in their properties

(chemical & physical)

Among the chemical properties, formation of oxides and hydrides i.e.

reaction with Oxygen and Hydrogen respectively were given priority

Mendeleevs periodic table contains 6 horizontal rows called Periods and 8

vertical columns called Groups

Groups 1 to 7 had two sub groups called A and B

Group 8 had 3 rows of elements.

Elements having similar properties were placed in the same groups

1834-1907


8/25


9/25

Achievements of Mendeleevs Periodic Table

There are instances where the sequence was inverted while arranging

the elements in the increasing order of their atomic masses, so that

elements with similar properties could be grouped together

Ex:Cobalt (58.93) comes first to Nickel (58.71)

Tellurium (127.6) comes first to Iodine (126.9)

{this is the order in the modern periodic table}

Spaces were left vacant with an idea to accommodate the elements to be

discovered in future

=> He predicted the existence of Scandium, Gallium & Germanium by

naming them as Eka-Boron, Eka-Aluminium & Eka-Silicon respectively.

It could predict the properties of the elements which helped in thediscovery of new elements.

The inert gas elements discovered later could be placed in a separate

group without disturbing the table


10/25


11/25

5. The Modern Periodic Table

In 1913, through X-Ray experiments Henry Moseley showed that theatomic number (Z = no. of protons) of an element is a morefundamental property than its atomic mass (Mendeleevs periodictable)

So, atomic number was adopted as the basis of then developedperiodic table i.e. Modern Periodic Table

Modern Periodic Law states thatThe properties of elements are the periodic function

of their atomic numbers

Elements, when arranged in order of increasing atomic number , leadus to the classification known as the Modern Periodic Table

More accurate prediction of properties of elements was possiblethrough this kind of arrangement

the Modern Periodic Table takes care of three limitations of Mendlevs

Periodic Table


12/25

5. The Modern Periodic Table


13/25

Position of H-Hydrogen

CONCLUSION

Because of its resemblance to both Group 1 and

group 17 elements, Hydrogen is separately

placed in the periodic table

Lithium Hydrogen Fluorine

Atomic no. 3 1 9

Elect.Confgn 2,1 1 2,7

Remark

Has 1 electron in

the outermost

shell

Has 1 electron in

the outermost

shell

-----

-------

Has to gain 1

electron for the

nearest noble gas

Has to gain 1

electron for the

nearest noble gas


14/25

Terms associated with Modern Periodic Table?Definition Name

Vertical Columns (there are 18 numbered 1 to 18) GROUP

Horizontal rows (there are 7 numbered 1 to 7) PERIODSGroup 1 elements ALKALI METALS

Group 2 elements ALKALINE EARTH METALS

Group 16 elements CHALCOGENS

Group 17 elements HALOGENSGroup 18 elements NOBLE GASES

* LANTHANIDE SERIES

+ ACTINIDE SERIES

Period 1 K shell

Period 2 L shell

Period 3 M shell

Period 4 N shell


15/25

Blocks?

Outer most electron enters into d-orbital

Outer most electron enters into s-orbitalOuter most electron enters into p-orbital

Outer most electron

enters into f-orbital


16/25

Elements in a Group havesimilar chemical properties ?

Gp 1(Z) Electronic configuration Gp 17(Z) Electronic configurationK (2) L (8) M (18) N (32) K (2) L (8) M (18) N (32)

Li (3) 2 1 F (9) 2 7

Na (11) 2 8 1 Cl (17) 2 8 7

K (19) 2 8 8 1 Br (35) 2 8 18 7

Same number of valence electrons in outer most shell

As we move down the group number of shells increases

As chemical properties are related to valence electrons & we have samenumber of valence electrons, group elements show similarity in their

chemical properties


17/25

What about a period?

Shells 2ndPeriod elements

Li (3) Be(4) B (5) C (6) N (7) O (8) F (9) Ne (10)

K (2) 2 2 2 2 2 2 2 2

L (8) 1 2 3 4 5 6 7 8

M (18)

N (32)

Different number of valence electrons in outer most shell

As we move across the period electrons are entering into the same shell Meaning elements in a period are having same number of shells

As chemical properties are related to valence electrons & we have different

number of valence electrons across the period elements show different

chemical properties

d


18/25

How many elements are there in a period?

Maximum no. of electrons that can be accommodated in a shell = 2n2

(where, n = number given to the shell viz: K=1, L=2, M=3, N=4 etc) which is equal to the number of elements that can be accomodated in

that period. Ex:

Period

no.

Shell

name

No. assigned to

the shell(n)

Max. no. of

electrons(2n2)

No. of elements present

in the period

1 K 1 2 2

2 L 2 8 8

3 M 3 18

(10 + 8)

8

As outermost shell can

have only 8 electrons

i.e.

2,8,8,18,18,32,32 elements are present in group 1 to 7 respectively


19/25


20/25

Trends in Modern Periodic Table 2. ATOMIC SIZE (Atomic radius)Atomic size/radius: may be visualised as the distance between thecentre of the nucleus and the outermost shell of an isolated atom

Atomic Radius

Across the PERIOD Down the GROUP

Decreases Increases

Due to the increase in

nuclear charge

Due to the addition of extra shell

Increased nuclear charge

can pull the electronstowards itself more

effectively and thus the

radius decreases

1. Increase in nuclear charge which leads to

decrease in atomic size2. One extra shell is added each time which leads

to increase in atomic size

Addition of extra shell dominates over increase

in nuclear charge leading to the increase in size


21/25

Trends in Modern Periodic Table 2. ATOMIC SIZE (Atomic radius)Atomic size/radius: may be visualised as the distance between thecentre of the nucleus and the outermost shell of an isolated atom


22/25

METALS NON-METALS

Are electropositive

(tendency of an atom to loose electrons)Are electronegative

(Capacity of an atom to pull the

shared pair of electrons towards itself

in a MOLECULE)

They form Ionic compounds They form covalent molecules

(they tend to form bond by gaining

electrons)

Said to have metallic character Said to have non-metallic character

METALLOIDS or SEMI-METALS

1. Are elements having properties of both metals and non-metals2. In the periodic table metals & non-metals are separated by a zig-zag line &

the BORDER line elements show this semi-metal properties


23/25


24/25

Trends in Modern Periodic Table 3. METALLIC NON-METALLIC PROPERTIESAcross the PERIOD Down the GROUP

Metallic

character

Decreases Increases

-As the effective nuclear

charge experienced by the

valence shell electrons

increasesacross the period, itbecomes more and more hard

to loose electrons

-As the effective nuclear charge

experienced by the valence shell

electrons decreasesdown the

group due to the addition ofextra shells, it becomes more

and more easy to loose

electrons

Non-Metallic

character

Increases Decreases

-As the effective nuclear

charge experienced by the

valence shell electrons

increasesacross the period, it

becomes easier to accept

electrons

-As the effective nuclear charge

experienced by the valence shell

electrons decreasesdown the

group due to the addition of

extra shells, it becomes hard to

accept electrons


25/25

X Chem Periodic Table Printable Version

Documents

Transcript of X Chem Periodic Table Printable Version