Download classification of elements and periodicity in properties

ce
tu
ts
.c
om
CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES
w.
s
ci
en
CLASSIFICATION OF ELEMENTS
AND
PERIODICITY IN PROPERTIES
Chapter outline
WHY DO WE NEED TO CLASSIFY ELEMENTS
•
GENESIS OF PERIODIC CLASSIFICATION
•
MODERN PERIODIC LAW AND THE PRESENT FORM OF THE PERIODIC
•
NOMENCLATURE OF ELEMENTS WITH ATOMIC NUMBERS > 100
•
ELECTRONIC CONFIGURTIONS OF ELEMENTS ANDTHE PERIODIC TABLE
•
ELECTRONIC CONFIGURATIONSAND TYPES OF ELEMENTS: s-, p-, d-, f- BLOCKS
•
PERIODIC TRENDS IN PROPERTIES OF ELEMENTS
w
w
•
www.sciencetuts.com
CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES
GENESIS OF PERIODIC CLASSIFICATION
.c
om
Periodic Classification of Elements
Electrons are filled in various shells and subshells in a fairly regular fashion. Therefore, properties
of elements are repeated periodically. Such trends in their physical and chemical properties were noticed
by chemists in the nineteenth century and attempts were made to classify elements on their basis long
before structure of atom was known.
In this lesson we shall study about the earlier attempts for classification, the first successful
ts
classification which included all the known elements at that time namely Mendeleev’s periodic table,
tu
and about the long form of modern periodic table which is an improvement over Mendeleev’s work.
ce
OBJECTIVES
After completing this lesson, you will be able to state the importance of periodic classification
en
and periodic table.
State main features of Mendeleev’s periodic table state modern periodic law.
•
Describe the features of the long form of periodictable.
•
State s, p, d and f-blocks and their properties.
•
Define various periodic properties.
•
Discuss the trends in various periodic properties in the periodic table.
•
understand lanthanide contraction and actinide contraction.
w.
s
ci
•
w
Concept of group elements based on their properties
There are about 111 known elements and 7 elements yet to be confirmed. Among these 118
w
elements, 92 elements are available in the elemental form. Remaining 26 elements are manmade
elements. Classification of these elements is very important to understand common properties and
periodic trends among these 118 elements. Scientists like Johnn Dobereiner (1829), John Alexander
Newlands (1865) and Lothar Mayer (1869) gave different kinds of classifications. But they were not
become popular.
2
www.sciencetuts.com
CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES
DOBEREINER’S TRIADS
In 1829, Dobereiner, a German scientist made some groups of three elements each and called
them triads. All three elements of a triad were similar in their properties. He observed that the atomic
mass of the middle element of a triad was nearly equal to the arithmetic mean of atomic masses of
other two elements. Also, same was the case with their other properties. Let us take the example of
.c
om
three elements lithium, sodium and potassium. They form a Dobereiner’s triad.
7
Sodium, Na
23
Potassium, K
39
tu
Lithium, Li
ts
Atomic mass
Element
Dobereiner
Mean of the atomic masses of the first (Li) and the third (K) elements: 7 + 39 by 2 = 23.
ce
The atomic mass of the middle element, sodium, Na is equal to 23.
Dobereneir’s idea of classification of elements into triads did not receive wide acceptance as he could
arrange only a few elements in this manner. The next breakthrough in classification of elements came
en
in the form of Mendeleev’s work.
ci
MODERN PERIODIC LAW AND THE PRESENT FORM OF THE PERIODIC TABLE
w.
s
Based on his own chemical properties and experiments, he listed the elements in the increasing order
of atomic masses and showed the periodic trends.
MENDELEEV’S PERIODIC LAW
“The properties of the elements and their compounds are a specific function of their atomic
weights”.
w
Mendeleev assigned each element a number called its atomic number.
This number is useful to determine the position of the element in a series
w
of increasing atomic masses. The elements are arranged in horizontal
rows called “periods” and vertical columns called “groups”. The first
three periods of the Mendeleev’s table are called as short periods. And
the other periods are known as long periods. The groups are subdivided
into subgroup A and subgroup B.
we have learnt about the Mendeleev’s periodic classification. Although it
was a very successful classification but it also had some defects in it.
3
Mendeleev
www.sciencetuts.com
CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES
MODERN PERIODIC TABLE
Henry Moseley, an English physicist discovered in the year 1913 that
atomic number, is the most fundamental property of an element and
not its atomic mass. .c
om
Atomic number,(Z), of an element is the number of protons in the
nucleus of its atom.
The number of electrons in the neutral atom is also equal to its atomic
number. This discovery changed the whole perspective about elements
and their properties to such an extent that a need was felt to change
the periodic law also. Now we shall learn about the changes made in
ts
the periodic law.
Henry Moseley
Modern periodic law
tu
“The physical and chemical properties of the elements are periodic functions of their atomic numbers”.
ce
The periodic table based on the modern periodic law is called the Modern Periodic Table. Many
versions of this periodic table are in use but the one which is most commonly used is the Long Form
of Modern Periodic Table.
w
w
w.
s
ci
en
Look at the long form of the modern periodic table.
Periodic table
The properties of elements are due to the distribution of electrons in orbitals of the atom. The long
form of periodic table is based on the Bohr’s model of atom. It is the graphical representation of aufbau
principle. It successfully explains the periodicities of properties of elements.
Now let us learn the main features of this periodic table. It contains 7 horizontal rows called ‘periods’
and 18 vertical columns called ‘groups’. Let us study the details of periods first.
4
www.sciencetuts.com
CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES
.c
om
NOMENCLATURE OF ELEMENTS WITH ATOMIC NUMBERS > 100
ts
Periodic Table showing different Group of Elements
Introduction
tu
The long form of periodic table clearly indicates the electronic configurations of the elements, similarities
in physical and chemical properties and differences in these properties.
When the elements are arranged according to their atomic numbers or the electronic configurations,
ce
a gradual change in their properties can be seen. The gradation is very useful in deriving information
w
w
w.
s
ci
en
about the elements and their compounds.
Periodic Table
PERIODICITY
In the periodic table, the properties of elements change gradually with a change in their electronic
configurations. This trend repeats itself at regular intervals. This repetition of a character is called
“periodicity” and such properties are called periodic properties.As the atomic number increases the
properties of elements repeated at regular intervals.
5
www.sciencetuts.com
CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES
For example:
From potassium (K 19) to Krypton (Kr 36) atomic number increases. Again from Rubidium (Rb 37) to
ts
.c
om
Xenon (Xe 54) same properties of above elements are repeated.
tu
Example of periodicity
Reason:
ce
The periodicity is due to the similar outer electronic configuration. Potassium (19) general electronic
configuration is ns1 . Krypton (36) electronic configuration is ns2 np6. Again from Rubidium (37) ns1 and
en
Xenon (54) ns2 np6 same configuration is repeated and hence properties also repeated.
Periodic properties
“Any property which is periodic in nature is called periodic property”.
ci
Uses of periodic properties:
We can predict the nature of chemical bonds formed by the elements and compare their reactivity.
w.
s
Molecular shapes and crystal structures can be identified easily.
Important periodic Properties:
Some of the important periodic properties are:
w
Atomic size and ionic size
Electron affinity
w
Ionization potential
Electro negativity
Valency
Metallic nature
Reducing (or) Oxidizing nature
Electro positivity
Nature of Oxides
Oxidation states
6
www.sciencetuts.com
CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES
ATOMIC SIZE
ts
.c
om
Atomic & ionic radii calculated from inter nuclear distance.
Internuclear Distance
tu
Inter-nuclear distance
ce
“The distance between two nuclei of neighboring atoms in a compound is called inter-nuclear distance”.
Inter-nuclear distance are measured with X-ray diffraction methods (or) spectroscopic methods.
Type of chemical bond
Oxidation states
Number of bonds formed
w.
s
ATOMIC RADIUS
ci
Co-ordination number
en
Atomic & ionic radii are influenced by: “The distance between the centre of the nucleus and the electron cloud of outer most energy
level”.
The atomic radius depends on many factors like number
w
of bonds formed by the atom, nature of bonding , oxidation
state of the atom.
w
Types of atomic radii:
Depending on the type of bond, three types of atomic
radii are there
1. Covalent radius
2. Metallic or Crystal radius
Atomic radius
3. Vander Waal’s radius
4. Ionic radius
7
www.sciencetuts.com
CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES
COVALENT RADIUS
“ Half the equilibrium distance between the nuclei of two atoms held together by a covalent
bond is covalent radius”.
.c
om
Consider chlorine molecule. The inter-nuclear distance
between two chlorine atoms is 1.98 A. (1.98 angstroms).
1.98 A is also called as bond length.
Covalent radius of chlorine is 1.98 divided by 2 = 0.99 A.
Therefore, covalent radius of chlorine is 0.99 A.
Characteristics:
Covalent Radius
ts
1. It is applicable to homo-atomic molecules like Cl2, H2 ,Br2 etc.
Bondlength Ao
Covalent Radius
C-C
1.54 AO
0.77 AO
1.34 AO
0.67 AO
1.20 AO
0.6 AO
en
C≡C
ce
No. of bonds
C=C
Examples:
tu
2. It changes with type of bonds.
o
For Carbon - Carbon single bond - Covalent radius of carbon is 0.77 A
o
ci
For Carbon - Carbon double bond - Covalent radius of carbon is 0.67 A
o
For Carbon - Carbon triple bond - Covalent radius of carbon is 0.6 A
w.
s
3. For metals, atomic radius is slightly more than covalent radius.
w
w
Metal
Atomic radius Ao Covalent Radius Ao
K
2.31 AO
2.03 AO
Ba
2.17 AO
1.98 AO
Zr
1.57 AO
1.45 AO
4. For non-metals, atomic radius is equal to covalent radius.
Non - Metal Atomic radius Ao Covalent Radius Ao
C
0.77 AO
0.77 AO
p
1.10 AO
1.10 AO
S
1.04 AO
1.04 AO
8
www.sciencetuts.com
CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES
metallic or crystal RADIUS
“Half the inter-nuclear distance between two adjacent metal atoms in a metallic crystal”.
Consider sodium crystal. The inter-nuclear distance
.c
om
between two sodium atoms is 3.72A° (angstroms)
and metallic radius of sodium is 3.72/2 = 1.86 A°.
Therefore, Metallic radius of sodium atom is 1.86 A.
Characteristics:
1. It is applicable for metal atoms.
Metallic Radius
ts
2. Atoms are treated as spheres.
tu
vander waal’s RADIUS
“Half the equilibrium distance between the nuclei of two atoms bound by Vander Waal’s
ce
forces”.
Consider Chlorine atoms of two different molecules. The chlorine atoms not form chemical bonds. When
the atoms are close to each other, some weak force of attraction develops between them (atoms), that
molecules is 3.6A°.
en
force is known as Vander Waal’s force. The distance between two adjacent chlorine atoms in different
VanderWaal’s Radius
w
w
w.
s
ci
Vander Waals radius of chlorine = 3.6/2 = 1.8 A°.
Characteristics:
1. It is observed only in solid molecular substances.
2. It is 40° larger than covalent radius.
9
www.sciencetuts.com
CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES
ionic RADIUS
“The distance from the nucleus of the ion up to the point where its influence of electron cloud
ceases”.
It is determined by x-ray diffraction of ionic crystals.
.c
om
Characteristics:
1. For negative ions, size of atom increases with charge; so ionic radius also increases.
For example:
1. The atomic radius of Chlorine atom = 0.99 A°.
The ionic radius of Chlorine ion cl- = 1.81 A°.
Increase in size = 0.82 A°.
ts
As the number of electrons gained increases, the ionic radius increases proportionally.
tu
2. Atomic radius of oxygen = 0.66 A°.
Ionic radius of O-2 = 1.40 A°.
For positive ions size of atom decreases with charge; so ionic radius decreases. As the number of
ce
electrons removed from the atom increases, cationic radius decreases more i.e. the cation (cat-ion)
becomes smaller.
en
See the different kinds of atomic radii and their important properties.
PERIODS
ci
ELECTRONIC CONFIGURTIONS OF ELEMENTS ANDTHE PERIODIC TABLE
There are seven rows in the periodic table. Each row is called a period. The periods have been
w.
s
numbered from 1 to 7 (Arabic numerals).In each period a new shell starts filling up. The period number is
w
w
also the number of shell which starts filling up in it.
Periods
10
www.sciencetuts.com
CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES
For example: In elements of 3rd period, the third shell (M shell) starts filling up as we move from left to
right. The first element of this period sodium Na (2,8,1) has only one electron in its valence shell (third
shell) while the last element of this period, argon Ar (2,8,8) has eight electrons in its valence shell. The
gradual filing of the third shell can be from the above table and illustrations. Each period starts with an
ce
(a)
tu
ts
.c
om
alkali metal and ends with a noble gas element.
(b)
Example of Periods (a) Sodium(Na) valence shell (b) Argon(Ar) valence shell
It is the shortest period and discontinuous period.
w.
s
ci
en
1st period: It contains two elements - Hydrogen & Helium.
2nd period: It contains eight elements from Lithium(3) to Neon (10).
It is first short period.
w
w
3rd period: It also contains eight elements from Sodium, Na(11)to Argon, Ar (18).
It second short period. This period elements are called typical elements.
11
www.sciencetuts.com
CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES
4th period: It contains 18 elements from Potassium, K (19) to Krypton, Kr (36).
It is first long period. It contains first transition series scandium (21) to zinc (30).
.c
om
5th period: It also contains 18 elements from Rubidium (37) to Xenon (54).
It contains second transition series from Yttrium (Y) (31) to Cadmium (Cd) (48).
It is second long period.
ts
tu
6th period: It contain 32 elements from Cesium, Cs (55) to Radon, Rn (86).
It contains lanthanides from Cerium, Ce (58) to Lutetium (lew-tee-shee-əm) Lu (71).
en
ce
It is the longest period. It contains 14 rare earth elements.
7th period: It is incomplete period & most of the elements are radioactive.
The elements from Francium (fran-see-əm) Fr (87) to Hahnium, Ha (105) belongs to
this group.
It contains actinides Thorium, Th (90) to Lawrencium, Lw (103).
w
w
w.
s
ci
12
www.sciencetuts.com
CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES
GROUPS
There are 18 vertical columns in the periodic table. Each column is called a group. The groups have
been numbered from 1 to 18 (in Arabic numerals) from left to right.
Group 1 on extreme left position contains alkali metals (Li, Na, K, Rb, Cs and Fr)
.c
om
Group 18 on extreme right side position contains noble gases (He, Ne, Ar, Kr, Xe and Rn).
(a)
1 GROUP
Alkali metals
ts
(Li, Na, K, Rb, Cs, Fr)
(b)
tu
18 GROUP
Noble gases
ce
(He, Ne, Ar, Kr, Xe and Rn)
en
Groups showing
(a) Alkali metals (b) Noble gases
ci
All elements present in a group have similar electronic configurations and have same number of valence
electrons. You can see in case of group 1 (alkali metals) and group 17 elements (halogens) that as one
w.
s
moves down a group, more and more shells are added. Groups are further classified into a, b and zero
group elements.
A GROUP ELEMENTS
w
1st 2nd & 13th to 17th columns are called ‘A’ group elements.This group contains ‘s and p block elements’.
s and p blocks excluding zero group are called representative elements.
w
B GROUP ELEMENTS
3rd to 12th columns are called ‘B’ group elements. This group contains d-block elements. These are
called transition elements.
ZERO GROUP ELEMENTS
There are noble gases. Chemically nonreactive.
13
www.sciencetuts.com
CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES
A-Group Elements
.c
om
B-Group Elements
Zero Group Elements
Lanthanides
Actinides
ts
Periodic Table showing different Group of Elements
INNER TRANSITION ELEMENTS
tu
LANTHANIDES ELEMENTS
14 elements with atomic numbers 58 to 71 (Cerium to Lutetium (lew-tee-shee-əm)) are called lanthanides
ce
and they are placed along with the element lanthanum (La), atomic number 57 in the same position
(group 3 in period 6) because of very close resemblance between them. However, for convenience sake
ci
en
they are shown separately below the main periodic table.
w.
s
ACTINIDES ELEMENTS
14 elements with atomic numbers 90 to103 (Thorium to Lawrencium) are called actinides and they are
placed along with the element actinium (Ac), atomic number 89 in the same position (group 3 in period
7) because of very close resemblance between them. They are shown also separately below the main
w
w
periodic table along with lanthanides.
ADVANTAGES OF MODERN PERIODIC CLASSIFICATION
Elements are arranged in the increasing order of their atomic number, which is fundamental feature of
all elements.
14
www.sciencetuts.com
CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES
E.g. Argon (Ar40), Potassium (K39), and Copper (Cu 59), Nickel (Ni 58).
Tellurium (Te128), Iodine (I127) anomaly behavior is rectified.
The element of a group resembles closely with each other in properties. 8th group gets sufficient place
in the table.Table clearly indicates metails, active metals, transitional metals, non-metals, metalloids,
.c
om
lanthanides & actinides.
LIMITATIONS
The position of hydrogen still remains uncertain.
•
The inner transition elements are placed separately below the table.
•
The 14 lanthanides differ from the usual pattern of electronic configuration.
ts
•
tu
ELECTRONIC CONFIGURATIONS AND TYPES OF ELEMENTS: s, p, d, f BLOCKS
Introduction
ce
Based on the electronic configurations and differentiating
electron i.e. electron in the outermost orbit, the elements in
1. s block elements.
2. p block elements.
ci
3. d block elements.
en
the periodic table are classified into 4 blocks.They are:
4. f block elements.
Electron in the outermost orbit
w.
s
See the s, p, d and f blocks in the long form of periodic
w
w
table.
s, p, d and f block eements
15
www.sciencetuts.com
CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES
s-block elements are placed at the left side of the periodic table, p-block is at the right side
and the d-block in between the s- and p-blocks. f-block is placed separately at the bottom of the main
table.
Elements with one electron in their outer shells have the configuration of ns1. They belong to
.c
om
group 1 elements (hydrogen, alkali metals). Elements with two electrons in their outer shells have the
configuration of ns2. They belong to group 2 elements (alkaline earth metals). Elements with three
electrons (two in ‘s’ orbital and one in ‘p’ orbital) have the configuration of ns2 np2. They belong to group
3 elements. In a similar way the elements having four, five, six, seven and eight electrons in their outer
shells have the general configuration ns2npx (where x = 2,3,4,5 or 6) and belong to 4th, 5th, 6th, 7th and
ts
Zero group respectively.
S-Block elements
tu
S-Block elements
ns1 GROUP
IA
(b)
en
(a)
ce
ns2 GROUP
II A
S-block elements (a) ns1 Group I A (b) ns2 Group II A
ci
s-block elements
P-block elements
“The differentiating electron in an element enters into s - sub shell”.
w.
s
1 A, 2 A group elements belong to this block.
The general electronic configuration is ns1 and ns2
1a group elements
Electrons
Atomic No.
3
4
3+8
12
11 + 8
20
19 + 18
38
Potassium (K)
37 + 18
56
Rubidium (Rb)
55 + 32
88
Elements
“One differentiating electron is present in s-sub
w
shell”.
General electronic configuration ns1
w
Elements are
Lithium (Li)
Sodium (Na)
Cesium (Cs)
1 A Group elements
Francium (Fr)
16
www.sciencetuts.com
CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES
See the 1A group elements and their electronic configuration.
The oxides, hydroxides of 1A Group are strong alkalies, so these are called “alkali metals”.
2 a group elements
“Two differentiating electrons are present in the
Elements
Atomic No.
4
4
4+8
12
12 + 8
20
20 + 18
38
38 + 18
56
.c
om
s - sub shell”.
Electrons
General electronic configuration ns
2
Elements are
Beryllium (Be)
Magnesium (Mg)
Calcium (Ca)
ts
Strontium (Sr)
56 + 32
Barium (Ba)
Radium (Ra)
88
tu
2 A Group elements
See the 2A group elements and their electronic configuration.
ce
The oxides and hydroxides are alkaline and found in the surface of the earth. So these are called
“alkaline earth metals”.
en
properties of s-block elements
These are highly electro positive and low electro-negative elements.
They are highly reactive metals. Hence, they are not available freely in
For example:
ci
nature but are available as their compounds.
w.
s
Sodium is available as “Sodium chloride” (NaCl).
The chemical reacting and metallic nature increases in a group with increase
in atomic mass.
These metals are having lowest ionization energy.
w
These are powerful reducing agents.
They posses +1, +2 oxidation states.
w
They exhibit flame coloration tests.
Example:
S block elements
Lithium - Crimson red
Sodium - Golden yellow
Potassium - Lilac color
Cesium - Sky Blue.
17
www.sciencetuts.com
CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES
p-block elements
The differentiating electron enters into p - sub shell.
As the p-sub level can accommodate a maximum of 6
.c
om
electrons, there are 6 groups of elements. 13th to 18th
group elements belong to this block.
P block elements
tu
3A group elements (13th group boron family)
ts
The general electronic configuration ns2 np1-6
One differentiating electron is present in the p - sub
III A Group
shell.
Boron Family
ce
General electronic configuration ns2 np1
The elements are
Gallium (Ga)
Indium (In)
Thallium (Tl)
ci
Alluminium (Al)
en
Boron (B)
Boron (B)
Alluminium (Al)
Gallium (Ga)
Indium (In)
Thallium (Tl)
w.
s
See the 13th group elements and their electronic configuration.
4A group elements (14th group carbon family)
3 A Group elements
IV A Group
Carbon Family
w
Two differentiating electrons are present in the p - sub shell.
General electronic configuration ns2 np2
The elements are
Carbon (C)
w
Silicon (Si)
Carbon (C)
Germanium (Ge)
Silicon (Si)
Germanium (Ge)
Tin (Sn)
Tin (Sn)
Lead (Pb)
Lead (Pb)
See the 14th group elements and their electronic configuration.
4 A Group elements
18
www.sciencetuts.com
CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES
5A group elements (15th group nitrogen family)
Three differentiating electrons are present in the p - sub shell.
V A Group
Nitrogen Family
Nitrogen (N)
General electronic configuration ns2 np3.
The elements are
Nitrogen (N),
Phosphorus (P),
.c
om
Phosphorus (P)
Arsenic (As)
Arsenic (As),
Antimony (Sb)
Antimony (Sb)
Bismuth (Bi)
Bismuth (Bi)
See the 15th group elements and their electronic configuration.
VI A Group
tu
6A group elements (16th group oxygen family)
ts
5 A Group elements
Oxygen Family
General electronic configuration ns2 np4
Oxygen (O)
ce
Four differentiating electrons are present in the P - sub shell.
The elements are
Oxygen (O)
Selenium (Se)
Tellurium (Te)
Polonium (Po)
en
Sulphur (S)
ci
See the 16th group elements and their electronic configuration.
Sulphur (S)
Selenium (Se)
Tellurium (Te)
Polonium (Po)
6 A Group elements
w.
s
7A group elements (17th group Halogen family)
VII A Group
Five differentiating electrons are present in the P - sub shell.
General electronic Configuration ns2 np5
Halogen Family
Fluorine (F)
The elements are
w
Chlorine (Cl)
Fluorine (F)
Bromine (Br)
w
Chlorine (Cl)
Bromine (Br)
Iodine (I)
Iodine (I)
Astatine (At)
Astatine (At)
See the 17th group elements and their electronic configuration.
19
7 A Group elements
www.sciencetuts.com
CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES
8A group elements (zero group nobel gases)
VIII A Group
These elements having octet of electrons in valence shell.
Nobel Gases
General electronic configuration ns2 np6
Helium (He)
These are chemically inactive as their valence shell are completely
Neon (Ne)
filled with ns np configuration.
6
.c
om
2
Argon (Ar)
These are
Helium (He)
Krypton (Kr)
Neon (Ne)
Xenon (Xe)
Argon (Ar)
Radon (Rn)
Krypton (Kr)
8 A Group elements
ts
Xenon (Xe)
Radon (Rn)
properties of p-block elements
tu
See the noble gas elements and their electronic configuration.
These elements are metals, non-metals, and metalloids.
•
They show variable oxidation states.
•
They do not impart any color to the flame.
•
These elements are placed at the right side of the periodic table.
•
Both s-block and p-block elements are referred as “representative elements” or “main group
en
ce
•
ci
elements”.
d-block elements
w.
s
These are elements of group 3 to 12 in the periodic table. The elements in which the differentiating
electron enters the penultimate or (n-1) shell of the atom of the element i.e. [(n-1)d sub shell] are called
d-block elements. The d-block elements are called “transition elements” as they are placed between
s-block and p-block elements.
w
The general electronic configuration (n-1)d1 to 10 ns1 to 2
It has four series:
w
3d series: From Scandium (Z = 21) to Zinc (Z = 30) in the 4th period.
4d series: From Yttrium (Z = 39) to Cadmium (Z = 48) in the 5th period.
5d series: From Lanthanum(Z = 57) and Hafnium (Z = 72) to Mercury (Z = 80).
They form the 6th period of the periodic table.
6d Series: In-complete series. It starts from Actinium (Z = 89).
These elements appear in the seventh period of the periodic table.
20
www.sciencetuts.com
ts
D-block Elements
.c
om
CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES
properties of d-block elements
They are all metals.
•
They form alloys.
•
They are good conductors of heat & electricity.
•
These elements form complex compounds.
•
They exhibit variable valence and show Para-magnetic nature in their oxidation states.
F-block elements
en
ce
tu
•
The two rows of elements present at the bottom of the periodic table are f - block elements. The
ci
differentiating electron enters to f-orbital of anti penultimate (n - 2) shell of atom. These are called “inner
transition elements”.
w.
s
The general electronic configuration (n-2) f1-14 (n-1) d0-1 ns1-2, where n = 6 or 7.
It has 2 series and each series has 14 elements.
4f - series or Lanthanides: From cerium (Z = 58) to Lutetium (Z = 71).
The elements of this series are called Lanthanides or rare earths.
w
5f series or Actinides: From Thorium (Z = 90) to Lawrencium (Z = 103)
w
The elements of this series are called actinides.
F-block Elements
21
www.sciencetuts.com
CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES
Periodic trends in properties of elements
Electron affinity
“The amount of energy released when an electron is added to a neutral isolated gaseous atom in its ground state”.
Equation:
.c
om
Atom (gaseous state) + electron (e-) → Anion (gaseous state) + Energy (E)
( Where X = Atom , x- = Anion , E = Energy )
X (g) + e- → x- (g) + Energy (E)
Units: Electron volts /(per) atom (or) Kilo Joules / mole (or) Kilo calories / mole.
Electron affinity depends on size and effective nuclear charge.
ts
Note: It cannot be measured directly.
tu
It can be measured indirectly using Born-Haber Cycle.
second Electron affinity
Equation:
(Endothermic reaction)
en
x- (g) + e- → x2-(g) + Energy
ce
“The energy absorbed when an electron is added to uni-negative gaseous ion”.
Reason for absorption of energy:
ci
Repulsion between negatively charged ion and electron requires some energy to absorb which causes
the endothermic reaction.
w.
s
Example: First electron affinity of oxygen is 33.9 Kilo calories per mole - Here energy is released.
(Exothermic reaction)
O (g) + e- → O- (g) + 33.9 Kcal
w
Second electron affinity of oxygen is 119 Kcal/mole energy is absorbed.
w
O -(g) + e- → O2- (g) + 119 Kcal
(Endothermic reaction)
Factors influencing electron affinity:
Size of atom
Nuclear Charge
Electronic Configuration
22
www.sciencetuts.com
CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES
variation of Electron affinity
Groups: On moving down the group, electron affinity decreases as the atomic size increases. In
representative elements the first element of every group has lower electron affinity than second element.
The order is as follows:
F(g) + e- → F- + Energy
Reason: The repulsion between added electron and
Element
At.No
Electron Affinity
F
9
3.62
17
3.78
Br
35
3.54
I
53
3.08
electrons already present is more.
Note: Why fluorine is powerful reducing agent than
Because fluorine has less electron affinity and high
tu
bond dissociation energy.
Cl
ts
chlorine?
.c
om
Fluorine < Chlorine, Oxygen < Sulphor, Nitrogen < Phosphorous etc.
Periods: On moving from left to right in a period,
Nitrogen, Neon elements has low electron affinity
en
values. As they have stable electronic configuration.
B
C
O
F
Li
Electron
Affinity
kj/mole
57 -66 15 121 -31 142 333
size and increase in nuclear charge. Beryllium,
Be
N
Element
ce
electron affinity increases due to decrease in atomic
Zero group elements have no electron affinity. Because zero group elements has completed valence
shell and so does not accept electrons. Hence electron affinity value is taken as zero. Hence called
ci
zero group elements.
w.
s
Electro negativity
This concept was proposed by Pauling in 1932.
“The tendency of an atom of an element to attract the shared electron pairs of more towards
itself in diatomic molecule or in a polar covalent bond”.
w
Electro negativity depends on:
1. The charge of nucleus
w
2. The distance of the outer electrons from the nucleus.
3. Shielding effect and
4. Nature of bonded atoms as it is a property of bonded atoms.
Scales to measure electro-negativity:
There are two scales to measure the electro-negativity.
1. Mulliken Scale.
2. Pauling’s Scale.
23
www.sciencetuts.com
CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES
mulliken scale
It was proposed by R.S. Mulliken in 1934. This method is applicable only for monovalent atom. According
to this scale, electro-negativity (E.N) of an element is the average of ionization energy and electron
affinity.
E.N = (I1 + E1 ) / 2. Where I1 = Ionization Energy, E1 = Electron Affinity
.c
om
Electronegative values measured on this scale are 2.8 times more than values measured on Pauling
scale.
Limitation: The difficulty in the measurement of electron affinity values.
When ionization energy and electron affinity values are in Kilo Joules per mole, then use
E.N = (I.P + E.A) divided by 544
ts
pauling’s scale
It was proposed by Pauling in 1931.It is based on bond energy values.
E A-B = half into (EA-A + EB-B)
tu
Expression: Let A-B molecule. The bond energy of molecule A-B theoretically,
ce
The bond energy of A-B molecule experimentally E1A-B.
This bond energy exceeds theoretical value.
The difference in bond energies is given by ∆ (delta)
∆ = E1A-B - EA-B
en
Where ∆ → Ionic - Covalent Resonance Energy
→ It depends upon the electro chemical nature of atoms A and B.
→ It is measured in Kilo Joules per mole.
ci
Now, XA → Electro-negativity of atom A
w.
s
XB → Electro-negativity of atom B
Pauling Relation is
XA - XB = 0.208 √∆
w
Note: He calculated electro-negativities of elements with reference to fluorine.
On Pauling scale fluorine has higher electro negative value of 4.0.
w
Uses of Electro-negativity:
1. In the identification of nature of bond i.e. If electro-negative difference is 1.7 or greater than 1.7, then
the bond is ionic. If it is less than 1.7, then the nature of bond is covalent.
2. Metallic or non-metallic nature of the elements can be identified.
3. To assign the oxidation state. (i.e. - ve or + ve)
4. To write the formula of the compound i.e. more electro-negative should be written on right hand
side.
24
www.sciencetuts.com