Science [1 Mark Questions]

The element fluorine is in group 17 of the periodic table and has a valency of 1. So, all the elements in the same group of periodic table as fluorine will have a valency of 1.

Silicon and Germanium.

1.

Noble gases were missing from Mendeleev’s original periodic table.

1. Newlands.
2. Dobereiner.

Magnesium, Calcium.

On going down in a group of the periodic table, the electropositive character of elements increases.

Six elements.

Group 1 (2, 8, 8, 1).

Mendeleev was guided by two factors:

1. Increasing atomic masses.
2. Grouping together of elements having similar properties.

Scandium, Gallium, Germanium.

1. Metallic character decreases.
2. Atomic size decreases.

In group 1 of alkali metals, the chemical reactivity increases from lithium to francium.

2, 1; 2, 2; 2, 3; 2, 4; 2, 5; 2, 6; 2, 7; 2, 8.​​​​

Mendeleev arrange the element in his periodic table on the basis of atomic masses.

The valency of elements increases from 1 to 4 and then decreases to zero in the 3rd period.

Eka-Aluminium (gallium) and Eka - Silicon (germanium).

The modern periodic table was prepared by Bohr.

On going down in a group of the periodic table, the metallic character of elements increases.

Lithium, Beryllium are metals.

1. Periods have elements with consecutive atomic numbers.
2. Correct.
3. Correct.

Left side.

1. Elements in th e same group have equal valency.
2. The metallic character of elements in a period decreases gradually on moving from left to right.

Metalloids.

On moving from left to right in a period, the metallic character of elements decreases.

On moving from left to right in a period, the tendency of atoms to lose electrons decreases.

Order of atomic numbers of elements:
X < Z < Y. Because as the atomic number increases in a period from left to right, the size of atoms goes on decreasing.

8.

Usual number of valence elec trons is 8; Valency is 0 (zero).

Helium, Neon, Argon.

F < N < Be < Li.

All elements in the same column of the periodic table as boron have 3 valence electrons.

Now they are arranged on the basis of atomic numbers.

Atomic number is always a simple whole number. It can either be 1 or 2. There can be no element with atomic number 1.5.

The first elements in the periods of the periodic table have 1 valence electron. Such elements are called alkali metals.

Oxygen (X is monovalent so Y has to be divalent to form the compound X Y).

The number of valence electrons remains the same.

When elements are arranged according to increasing atomic numbers, there is a periodicity in the electronic configurations of the elements. The elements in a period have consecutive atomic numbers. The elements having same number of valence electrons in their atoms are placed in a group. All the elements in a group have similar electronic configurations and show similar properties.

1. The number of valence electrons increases from 1 to 2 in the 1st period of the periodic table.
2. The valence electrons increase from 1 to 8 in the 2nd period of the periodic table.

1. Sodium.
2. Fluorine.

On moving from left to right in a period, the tendency of atoms to gain electrons increases.

There are seven periods and eighteen groups in the long form of periodic table.

On moving from left to right in a period, the atomic size decreases.

Mendeleev’s basis for the classification of elements was the atomic mass of elements.

Gallium and Scandium.

All the elements in a group have the same valency while going down the group.

Mendeleev said that the properties of elements are a periodic function of their atomic masses.

In group 17 of halogen elements, the chemical reactivity decreases from fluorine to iodine.