Science [1 Mark Questions]

Elements	Atomic Number	Electronic Configuaration
A B C	12 18 20	2, 8, 2 2, 8, 8 2, 8, 8, 2

Elements A and C will show similar properties as both have same number of valence elements.

Modem periodic law states “that the properties of elements are a periodic function of their atomic numbers”.

• Elements of group 1 have one electron in their outermost shell.
• Elements of group 2 have two electrons in their outermost shell.

There are seven horizontal rows in the modern periodic table; these rows are called periods.

There are 18 vertical columns in a periodic table. These vertical columns are called groups.

There are 18 vertical columns in the modern periodic table and they are called as ‘Groups’.

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.

F does not fit in dobereiner’s triad.
Dobereiner stated that when the elements in a group are arranged in increasing order of their atomic masses then the atomic mass of the middle element is approximately the average of atomic masses of two other elements. Fluorine doesn’t fit into this rule while the atomic mass of Br is average of the atomic masses of Cl and I.

Lithium is the third element in the periodic table. Thus, the element which comes after Lithium is the fourth element, ie, Beryllium.

Metallic character increases in a period and decreases down the group. In a period successive addition of electron occur so atomic size decreases thus electrons are held tightly thus metallic character increase. In a group successive addition of shells occur so atomic size increase so electron are held lossesly so they can easily lose electron.

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).

Among these Chlorine (17) and Iodine (53) do not belong to the same period.

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.

Two elements that can show a valency of two with respect to oxygen are Berilliym, magnesium.

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

Li, C and N all three belong to the same period. They are present in the order: Li < Be < B < C < N.On moving along a period from left to right, the metallic character decreases and non-metallic character increases. So Lithium forms the most basic oxide as it is a metal and nitrogen forms the most acidic oxide as it is a non - metal.

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.

Mendeleev classified the then known 56 elements on the basis of their physical and chemical properties in the increasing order of the atomic masses, in the form of a table. Mendeleev had observed that properties of the elements orderly recur in a cyclic fashion. He found that the elements with similar properties recur at regular intervals when the elements are arranged in the order of their increasing atomic masses. He concluded that 'the physical and chemical properties of the elements are periodic functions of their atomic masses'. This came to be known as the law of chemical periodicity.

Atomic number of Mg is 12. Electronic configuration is 2, 8, 2. Atomic number of Mg is less than X. It means Mg will come before X. They will lie in same group as both have same number of valence electrons. Reactivity of metals increases down the group. I means X is more reactive than Mg.

He distance between the centre of the nucleus and the outermost orbit of the atom is called the atomic radius of the atom of an element.Variation along the period: - The atomic radius decreases as we move from left to right along the period. This is due to an increase in nuclear charge which tends to pull the electrons closer to the nucleus and reduces the size of the atom.
Variation along the group: - The atomic radius increases down the group. This is because new shells are being added as we go down the group. This increases the distance between the outermost electrons and the nucleus so the atomic size increases inspite of the increase in nuclear charge.

There are 18 groups and 7 periods present in the modern periodic table. Modern periodic table states that properties of element are periodic function of their atomic number.

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

The last element of third size means last element of third period and the last element of third period is Argon(Ar) which has 8 valence electrons.

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

Atomic number of X is 20. Electronic configuration is 2, 8, 8, 2. Valence electrons in X is 2. Metals have valence electrons less than 4. So X is metal.The element is Ca.

Magnesium.

The modern periodic table was prepared by Bohr.

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

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

Left side.

Cl, At, Br and I belong to same group of periodic table that is group 17. As we move down in a group, the atomic radii of elements increase due to increasing the number of shell. Thus, atomic radii of Cl, At, Br and I increase in the order: Cl < Br < I < At.

The element is Bromine (atomic number 35)

Calcium.