Unit 1 - Lesson 1: Attempts of Elements classification

1
The number of elements in Mendeleev's periodic table is.......... elements.
2
The scientist who left vacancies in his table to be filled with suitable discovered elements in future is.........
3
Mendeleev classified the elements of each group into......... sub-groups.
4
The nucleus of the atom contains..........
5
The scientist, who discovered that the nucleus of atom contains positively charged protons is.........
6
The scientist....... had discovered the main energy levels.
7
The number of energy levels in the heaviest known atom is .......... levels.
8
The number of known elements in the modern periodic table till now is............
9
The number of elements which exist in nature is..........
10
The modern periodic table consists of.......... horizontal periods.
11
The modern periodic table consists of......... vertical groups.
12
The elements, which occupy the middle block (d) in the periodic table are called.......... elements.
13
The transitional elements start to appear from the beginning of the.......... period.
14
The block which contains the groups (1A) and (2A) in the periodic table is......... block.
15
The element, whose atomic number is (17) is similar in its chemical construction to the element whose atomic number is ...........
16
Elements of d-block are arranged in........... groups.
17
If the atomic number of an element is 15, so its group is located in...... block
18
Lanthanides and actinides are located in.......... the block.
19
Noble gases are located in group............
20
The atomic number of elements equals............
21
Elements of group (6A) in the periodic table have the same........
22
Elements of the same period in the modern periodic table have the same..........
23
The number of negative electrons in the atom in its normal state equals..........
24
In the periodic table, the elements which are identical in properties lie in the same.........
25
The element whose atomic number (18) is.........
26
The atomic number of an element that exists in group (7A) and period (2) is.........