INTRODUCTION
THERE ARE 118 ELEMENTS KNOWN AT PRESENT. It is very difficult to study and remember the properties of all these elements separately. So they need I roast group the elements of Singapore parties together. Various Hatim were made to classify the elements from time to time. Latest discuss some of the early attempts to class 5 elements.
Dobereiners Triads
JJohan doberranner group elements in order of increasing atomic mass.
He classify the elements in group of three elements each, such that those there are you male simulate in properties. He called this group of three elements as a trade. In this atomic mass of middle element in arithmetic mean of atomic masses of two of the two other elements.
Newland's Law of Octaves
Newlands arranged the elements in increasing order of their atomic masses and noted that every eighth element had properties similar to the first element.
Mendeleev's Periodic Law
The real credit for preparing the periodic table goes to Mendeleev. Mendeleev's periodic law states that, "the properties of elements are a periodic function of their atomic masses."
1.1 MODERN PERIODIC TABLE LONG FORM OF THE PERIODIC TABLE
KCQ1MZTJS2
In 1913, H.G.J. Moseley showed by X-ray analysis that atomic number is a more fundamental property of an element than its atomic weight. Therefore, he slightly modified Mendeleev's periodic law and replaced the word atomic weight by atomic number (proton number).
Modern Periodic Law
It states that the physical and chemical properties of all elements are the periodic function of their atomic numbers.
In the long form of the periodic table, the elements are arranged in order of increasing atomic numbers in horizontal rows called periods, such that all elements having same number of valence electrons come under the same vertical column called group. This not only ensures periodicity in electronic configuration, but periodicity in chemical properties.
1.2 CHARACTERISTICS OF THE LONG FORM OF THE PERIODIC TABLE
of
In the long form of the periodic table, the elements are arranged in order of increasing atomic numbers in horizontal rows called periods, such that all elements having same number of valence electrons come under the same vertical column called group. This not only ensures periodicity in electronic configuration, but periodicity in chemical properties.
Periods
The horizonta periods. There ar period has conse
The period c the number of
For example
one shell for its
OSO
period have two
The lanthan
elements. They
Groups
They are usual
1. There are eighteen vertical columns called rest of the peri groups in the modern periodic table.
the entire tabl
2. Group 1 includes hydrogen and the alkali metals, The actinid which have one electron in their outermost shell.
usually shown
3. Group 2 elements are also called the alkaline
the periodic t
earth metals. These elements have two electrons in their outermost shell. 4. Groups 3 to 12 are called transition elements
entire table. TI
is the heaviest
Ta
which are placed in the middle of the periodic
table.
Period Nu number
5. Group 13 is the boron group. All the elements in this group are metals except boron, which is a metalloid.
1
6. Group 14 is the carbon group. It contains a combination of non-metals, metalloids and metals. 7. Group 15 is called the pnictogens or nitrogen group. It contains a combination of non
2
4
5
metals, metalloids and metals.
8. Group 16 is called the chalcogens, or oxygen family. It contains a combination of non metals, metalloids and metals.
6
7
9. Group 17 is called the halogens. This is a group of highly reactive non-metals. This is the only group that contains elements in all three states of matter at room temperature and pressure. Fluorine and chlorine are gases, bromine is a liquid and iodine is a solid.
We can de
an element w
The num
Electrons p
represent the
For exam
10. The group 18 elements are commonly known as the noble gases. They are typically unreactive. The noble gases each have a full outer electron shell. Group 1, 2 and 13 to 17 elements are called normal elements or representative elements which occupy the left and the right side of the table.
and its elec
shells and H
Hence, it is
the periodi
Example
To which pe
3
Modern Periodic Table and Periodic Properties
Periods
The horizontal rows in the periodic table are called
periods. There are seven periods in all, such that each
period has consecutive (or continuous) atomic number.
The period of an element can be determined by the number of shells present in an atom. For example, every element in the first period has one shell for its electrons. All elements in the second
period have two shells for their electrons and so on. The lanthanides are often called the rare earth elements. They actually placed in the sixth period. They are usually shown as a separate row below the rest of the periodic table to make it easier to display
the entire table. The actinides sit in the seventh period. They are usually shown as a separate row below the rest of the periodic table to make it easier to display the entire table. The actinides include plutonium, which is the heaviest naturally occurring element.
alled
tals,
hell.
line
Wo
nts
dic
Period number
nts
ch
1
2
a
3
Table
1.2: Types of periods
Number of shells
Elements in the period
Nature of the period
Very short period
1
2
8 Short period
Short period
4
18 Long period
5
18
Long period Very long
32
period
Very long period
7
32
4
5
6
7
We can determine the period and group number of an element with the help of its electronic configuration.
The number of shells represents the period. Electrons present in the valence or outermost shell represent the group number.
For example: The atomic number of lithium is 3 and its electronic configuration is 2, 1. It has two shells and has one electron in the outermost shell. Hence, it is placed in second period and group 1 in the periodic table.
Example: An element E has atomic number 14.
To which period does this element belong?
Solution:
Electronic configuration of E is 2(K), 8(L), 4(M). As, there are three electron shells, therefore, E belongs to the third perio
As, there are four electrons in the outermost shel
therefore, E belongs to group 1
Example: Element X and Y have atomic numbers 9 and 12 respectively. Write the electronic configuration of X and Y and find out the periods and the groups to which they belong in the periodic tabl
Solutio
Electronic configuration of X = 2,
7n:e.4.l,d. of X = 2, 7
Electronic configuration of Y = 2, 8, 2 For X
As there are two electron shells, therefore, X belongs to the second period.
As, there are seven electrons in the outermost shell, therefore, X belongs to group 17. For Y
As there are three electron shells, therefore, Y
belongs to the third period. As, there are two electrons in the outermost shell, therefore, Y belongs to group 2.
0 Comments