08. classification 1

Chemistry

Session Opener

1. Why do we need classification.?

2. Dobereniner’s triads

3. Newlands law of octave

4. Lother Meyer volume curve

5. Mendeleev’s periodic table

6. Modern periodic table

7. IUPAC nomenculature for elements Z >100

Session Objectives

Lavoisier (1789) classified elements into metals, non-metals, gases and earths.

Do you know

During the nineteenth century, chemists began to categorize the elements according to similarities in their physical and chemical properties. The end result of these studies was our modern periodic table.

S.No TriadAtomic masses of elements of triad

Arithmetic mean of atomic masses of first and third element

1 Cl,Br,I 35.5, 80, 127 35.5 + 127

2= 81.25

2 Li,Na,K 7, 23, 39 7 + 39

2= 23

3 Ca,Sr,Ba 40,87.5,137 40+137

2= 88.5

Dobereiner’s triads [ John Dobereiner (1829)]

In 1829, he classified some elements into groups of three, which he called triads.The elements in a triad had similar chemical properties and orderly physical properties.

Model of triads

John Newlands

1838 - 1898

Law of Octaves

In 1863, he suggested that elements be arranged in “octaves” because he noticed (after arranging the elements in order of increasing atomic mass) that certain properties repeated every 8th element.

Newland’s law of octaves [John Newland (1862)]

ElementAtomic mass

ElementAtomic mass

ElementAtomic mass

I II III IV V VI VIILi Be B C N O F7 9 11 12 14 16 19

Na Mg Al Si p S Cl23 24 27 28 31 32 35.5

K Ca 39 40

Newland was first to publish the list of elements in increasing order of atomic masses.

Do you know?

Lother-Meyer’s atomic volume curve [Lother Meyer (1869)]

Question

If elements A,B and Z occupy similar positions in Lother meyer curve, they will have----properties

(a)Different

(b)Similar

(c)Cannot say

Illustrative Problem

The physical and chemical properties of elements are periodic function of their atomic masses.

Mendeleev’s periodic law

Mendeleev’s periodic table

Groups

•8 vertical rows. •7 groups were subdivided in A and B.•8th group has 9 elements in the group of 3 each.

Periods

•7 horizontal rows.

Only 63 elements were known.

Mendeleev’s periodic table

Merits of Mendeleev’s periodic table

Prediction of new elements

(Ge, Ga, Sc)

1

Systematic study of elements

2

Correction of atomic mass (Be, Au, Pt)

3

Defects of Mendeleev’s periodic table

Position of hydrogen.

Anomalous pairs.(Ar and K, Co and

Ni, Te and I)

Position of isotopes

e.g. 1H1, 1H2,

1H3

Chemically dissimilar elements are grouped together. (Cu-IA and Na-IB)

Chemically similar elements are placed in different groups. [Cu (I) and Hg (II)].

Defects of Mendeleev’speriodic table

Question

Mendeleev gave more importance to -----while arranging the elements in long form of periodic table

(a)atomic mass

(b)atomic volume

(c)atomic number

(d)similarity in property

Illustrative Problem

Solution: Option (a) is correct.

Mendeleev’s periodic table was published in 1905 when no one had an idea of the structure of an atom.

Do you know?

The physical and chemical properties of elements are periodic function of their atomic numbers.

Modern periodic law (Moseley)

Modern periodic table

Quiz

Write the electronic configuration of elements having following atomic numbers.(a). 19 (b). 32

(c). 41 (d). 58

• Electronic configuration:

• Groups:

• Low ionisation energy and low melting and boiling points, electropositive elements.

• Colourless compounds.

s block elements

IA and IIA

ns1 or ns2

• Electronic configuration:

• Groups:

• Non-metals, electronegative.

• Form covalent compounds.

p block elements

ns2,np1-6

III A to VII A and zero group.

• Electronic configuration:

• Groups:

• Variable valency high melting and boiling point.

• Coloured compounds and catalytic property.

d block elements

(n-1)d1-10 ns1or2

I B to VII B and VIII groups.

• Electronic configuration:

• Have high melting and boiling point.

f block elements

(n-2)f1-14(n-1)d0-1ns2

•Present below the periodic table in two rows

•Lanthanides-elements after lanthanum

•Actinides-elements after actinium.

Features of long form of periodic table

•Contains elements arranged in increasing order of atomic numbers.•Explains the position of an element in relation to other elements. •Consists of groups and periods.

Features of long form of periodic table

Groups Vertical column

Total 18. Numbered 1-18 orIA to VII A, IB to VII B, VIII and zero.

Periods Horizontal column

Total 7 numbered from 1 to 7.

Elements in a group have similar but notidentical electronic configuration and properties

Contains 2,8,8,18,18,32 and 28 elements respectively.

Representative elements

Transition elements

s and p block elements .

d block elements. Valence shell and penultimate shellboth are incomplete.

Inner Transition elements

f block elements. Valence shell, penultimate shell antipenultimate shell are incomplete.

Features of long form of periodic table

Metals

•Present on left hand side of periodic table.•Solid,malleable,ductile and conductors .

Non-metals

•Present on right hand side of periodic table.•Solid or liquid or gas.

Metalloids

•Present on zig-zag between metals and non-metals. e.g. B,Si,Ge,As,Sb and Te.

Features of long form of periodic table

• Based on a more fundamental basis - the atomic number

• Position of an element is related to the electronic configuration of its atom.

• Due to separation of elements into groups, dissimilar elements (e.g. alkali metals I A and coinage metals I B) do not fall together.

Merits of long form of periodic table

Defects of long form of periodic table

The problem of the position of hydrogen in the tablehas not beensolved completely

Configuration of Helium(1s2 ) is different from inertgases (ns2,np6) but are placed in the same group.

It is unable to include lanthanides and actinides in itsmain body.

Digits Name Abbreviation

0 nil n

1 un u

2 bi b

3 tri t

4 quad q

5 pent p

6 hex h

7 sept s

8 oct o

9 enn e

e.g. atomic number 115 will be named as un+un+pent+ium=ununpentium and symbol is Uup

Name=digits name+ium

Nomenclature of the elementswith atomic number>100

Class Test

Class Exercise - 1

X, Y and Z are the elements of Dobereiner’s triad. If atomic mass of element X is 32 and that of element Z is 128, find the atomic mass of Y.

(a) 32 (b) 80(c) 128 (d) 160

Solution

The question is based on Dobereiner’s law of triads.

Atomic mass of element Y =

32 128 16080

2 2

Hence, answer is (b).

Class Exercise - 2

Newland’s law of octave is appliedto all the elements having atomicmass less than ______.

(a) 20 (b) 40 (c) 30 (d) 10

Solution:

Hence, answer is (b).

From Newland’s law of Octave.

Class Exercise - 3

Discovery of _________ isresponsible for failure of lawof octave.

(a) lanthanides (b) actanides(c) transition elements (d) noble gases

Hence, answer is (d).

From Newland’s law of Octave.

Solution:

Class Exercise - 4

Properties of element E are similar tothat of element T. If element T ispresent on ascending side of LotherMeyer graph, where will you findelement E?

(a) on descending side (b) on peak(c) on ascending side (d) None of these

The elements having similar properties occupy similarpositions on the Lother Meyer volume curve.

Hence, answer is (c).

Solution:

Class Exercise - 5

How many elements were knowwhen Mendeleev prepared hisperiodic table?

(a) 53 (b) 63(c) 51 (d) 76

Hence, answer is (b).

Mendeleev’s periodic table based on 63 elements.

Solution:

Class Exercise - 6

The valence shell electronicconfiguration of an element is[Rn] 7s26d55f14. The elementbelongs to

(a) actinide series (b) lanthanide series(c) 6d transition series (d) p block

Hence, answer is (c).

Because last electron enters into d subshell ofpenultimate orbit.

Solution:

Class Exercise - 7

Which of the following groups havechemical properties that are mostsimilar?

(a) N, O, S (b) Na, K, Rb(c) Na, Mg, Ca (d) Na, Rb, Mg

Hence, answer is (b).

Because they belong to same group. (IA)

Solution:

Class Exercise - 8

In which orbitals does thedifferentiating electron enters in caseof inner transition elements?

(a) (n – 1)d (b) ns1

(c) ns2, np1–6 (d) (n – 2)f

Hence, answer is (d).

f-block elements are known as inner-transitionelements.

Solution:

Class Exercise - 9

The mass number of is

(a) 50 (b) 112(c) 118 (d) 62

11250 Sn

Hence, answer is (b).

Mass number = number of proton + number of neutron = 50 + (112 – 50) = 50 + 62 = 112

Solution:

Class Exercise - 10

The name of element having atomicnumber 101 is

(a) Rutherfordium (b) Lawrencium(c) Hassium (d) Mendelevium

Hence, answer is (d).

Rutherfordium – 104Lawrencium – 103Hassium – 108

Solution:

Illustrative example

(a).His law of octaves failed beyond the element calcium. Why?

(b). Would his law of octaves work today with the first 20 elements?

Dmitri Mendeleev

1834 - 1907

In 1869 he published a table of the elements organized by increasing atomic mass.

Lothar Meyer

1830 - 1895

At the same time, he published his own table of the elements organized by increasing atomic mass.

•Both Mendeleev and Meyer arranged the elements in order of increasing atomic mass.

•Both left vacant spaces where unknown elements should fit.

So why is Mendeleev called the “father of the modern periodic table” and not Meyer, or both?

Illustrative example

•stated that if the atomic weight of an element caused it to be placed in the wrong group, then the weight must be wrong. (He corrected the atomic masses of Be, In, and U)

•was so confident in his table that he used it to predict the physical properties of three elements that were yet unknown.

Solution:

After the discovery of these unknown elements between 1874 and 1885, and the fact that Mendeleev’s predictions for Sc, Ga, and Ge were amazingly close to the actual values, his table was generally accepted.

However, in spite of Mendeleev’s great achievement, problems arose when new elements were discovered and more accurate atomic weights determined. By looking at our modern periodic table, can you identify what problems might have caused chemists a headache?

Ar and K

Co and Ni

Te and I

Th and Pa

Henry Moseley

In 1913, through his work with X-rays, he determined the actual nuclear charge (atomic number) of the elements*. He rearranged the elements in order of increasing atomic number.

*“There is in the atom a fundamental quantity which increases by regular steps as we pass from each element to the next. This quantity can only be the charge on the central positive nucleus.”

His research was halted when the British government sent him to serve as a foot soldier in WWI. He was killed in the fighting in Gallipoli by a sniper’s bullet, at the age of 28. Because of this loss, the British government later restricted its scientists to noncombatant duties during WWII.

Glenn T. SeaborgAfter co-discovering 10 new elements, in 1944 he moved 14 elements out of the main body of the periodic table to their current location below the Lanthanide series. These became knownas the Actinide series.

1912 - 1999

Glenn T. Seaborg

He is the only person to have an element named after him while still alive.

"This is the greatest honor ever bestowed upon me - even better, I think, thanwinning the Nobel Prize."

Thank you