Attempts of Elements Classification

Attempts of Elements Classification
Mendeleev’s periodic table:
1. 67 elements were classified in this table.
2. He recorded the name of each element with its atomic weight and its important
properties (boiling point, degree of fusion, density )
3. He arranged elements of similar properties in vertical columns "groups".
4. The atomic weights of elements increase (in non-uniform way) on moving from the left
side of the table to the right side in horizontal rows "periods".
5. The properties of elements were repeated periodically by the beginning of each new
period.
Advantages of Mendeleev’s table:
1. He left gaps (empty cells) in his table predicting the discovery of new elements.
2. He determined the values of atomic weights of some elements which were not
discovered yet.
3. He corrected the atomic weights of some elements which were estimated wrongly.
Disadvantages of Mendeleev’s table:
1. He had to make disorder in the arrangement in the ascending order of atomic weights
of some elements to put them in groups that suit their properties.
2. He had to consider the isotopes of one element are different elements due to the
difference in their atomic weights. So, he had to put more than one element in one
place (cell) of his table.
Mosley periodic table:
Moseley discovered after studying x-rays properties that the periodic properties of
elements are related to their atomic numbers and not to their atomic weights as Mendeleev
proposed.
The most important modifications of Moseley on Mendeleev’s table:
1. He arranged elements in an ascending order according to their atomic numbers where
the atomic number of each element increases by one from the preceding element in the
same period.
2. He added zero (0) group which includes inert (noble) gases to the table.
3. He classified the elements of each group into two subgroups (A & B) (due to the
differences between their properties).
4. He specified a place below the table for Lanthanides and Actinides elements.
1- Attempts of Elements Classification
LESSON ONE
R.M.R
The modern periodic table:
Elements are classified in the modem periodic table according to:
1. Their atomic numbers.
2. The way of filling the energy sublevels with electrons.
y
The modern periodic table consists of:
The number of known elements in the modem periodic table till now is 116 elements,
92 elements are available in earth’s crust, while the rest are prepared artificially.
- 7 horizontal periods.
- 18 vertical groups.
The elements of modern periodic table are classified into 4 blocks (s, p, d and f ) (7A) and
zero group.
s-block elements:
- They are located on the left side of the periodic table.
- They are arranged in two groups (1A) and (2A).
2- Attempts of Elements Classification
LESSON ONE
R.M.R
p -block elements:
 They are located on the right side of the periodic table.
 They are arranged in six groups (3A), (4A), (5A), (6A),(7A) , (0)
d-block elements:




They are located in the middle of the periodic table.
They are arranged in eight groups (3B), (4B), (5B), (6B), (7B), (8) , (1B) and (2B).
They are known as transition elements.
They appear starting from period (4).
f-block elements:
 They are located below the periodic table.
 They include lanthanides and actinides.
How to locate the position of an element in the modern periodic table:
It is possible to determine the location of elements of group “A” in the modem periodic
table by knowing their atomic numbers where:Period number = number of energy levels occupied by electrons in its atom.
Group number = number of electrons in the outermost energy level in its atom.
Exercise
Choose the correct answer:
I. Mendeleev arranged elements of similar properties in ………………..
a. vertical periods. b. horizontal groups. c. vertical groups. d. horizontal periods.
2. Moseley classified elements in his table in an ascending order according to their
a. atomic weights.
b. atomic numbers.
c. chemical activity.
3.The number of elements in Mendeleev’s periodic table is elements.
a.67
b.76
c.92
d.116
4. The modern periodic table consists of ………
a. 8 horizontal periods and 17 vertical groups.
b. 7 horizontal groups and 18 vertical periods.
3- Attempts of Elements Classification
LESSON ONE
R.M.R
d. valencies.
c. 7 horizontal periods and 12 vertical groups.
d. 7 horizontal periods and 18 vertical groups.
5. Elements of “p” block are arranged in groups.
a, two
b. five
c. six
d. eight
6. The element which locates in period (3) and group (3A) is
a. 13A1
b. 5B
c. 11Na
d. 15P
7. Which of the following elements locates in the third period?
a. 19K
b. 15P
c. 6C
d. 3Li
8. All the following elements are located in group (2A) except ………
a. 4Be
b. 20Ca
c. 11Na
d.12 Mg
Write the scientific term:
1. The horizontal rows in which elements are arranged in an ascending order according to
their atomic numbers in the periodic table.
( …………………….)
2. Positively charged particles found inside the nucleus of the atom. ( ………………. )
3. A block of elements which is located on the right side of the periodic table.
( ………………. )
4. Levels, their number reach 7 in the heaviest known atom.
( ………………. )
Complete the following statements:
1. Mendeleev discovered that the properties of elements were repeated by the beginning
of each new …………………
2. Moseley specified a place below the table for………… and ………….. elements.
3. The atomic number of each element in Moseley’s periodic table increases by ………..
from the preceding element in the same ……………….
4. Elements of “s” block are located on the ……………. of the periodic table and they
arranged in ………….. groups.
5. The period number of the element equals the number of ……………… occupied by
electrons in its atom.
6. Elements of block “d” are called ………………… elements and they appear starting
from period …………..
Give reasons for:
1. Scientists thought to classify elements according to their properties.
4- Attempts of Elements Classification
LESSON ONE
R.M.R
2. Mendeleev had to put more than one element in one place of his table.
……………………………………………………………………………………………
Locate the position of the following elements in the modern periodic table:
Group
Period
block
12Mg
18Ar
13Al
17Cl
Find the atomic number of each of the following:
1. An element exists in period 2 and group (6A).
……………………………………………………………………………………………….
2. An element exists in period 3 and group (1A).
……………………………………………………………………………………………….
3. An element exists in period 2 and group zero.
………………………………………………………………………………………………
5- Attempts of Elements Classification
LESSON ONE
R.M.R

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