CHEMISTRY [2 Mark Question Answer]

The atomic number of P = 19
Its electronic configuration = 2, 8, 8, 1
Group no. of the element = 1A
Period no. of the element = 4
P is a metal.

Group 17 elements or halogens:

1. Reactivity: Halogens are the most reactive non-metals, their reactivity decreases down the group. Fluorine is the most reactive halogen and iodine is the least reactive halogen.
2. Colour: Fluorine is a pale yellow gas, chlorine is a greenish-yellow gas, bromine is a reddish-brown liquid and iodine is a violet solid.
3. Physical state: Gaseous

The size of atoms decreases when moving from left to right in a period. Thus, in a particular period, the alkali metal atoms are the largest and the halogen atoms are the smallest.
Li > Be > B > C > N > O > F

The valence electrons in the same shell (outermost shell) increase progressively by one across the period. The first element hydrogen has one valence electron and helium has two valence electrons.
On moving from left to right in a period,valencyincreases from 1 to 4, then falls to one and ultimately to zero in the last group.

Valence electrons in the same shell (outermost shell) increase progressively by one across the period. The first element of sodium has one valence electron and magnesium has two valence electrons.
On moving from left to right in the third period,valencyincreases from 1 to 7 and ultimately to zero in the last group.

Na and Al have the capacity to donate an electron due to which thevalencyis positive, whereasCland K can only gain or lose one electron due to which theirvalencyis -1 and +1, respectively. This is the only difference between these two.

Mendeleev laid the foundation for the modern periodic table by showing periodicity of the properties of the elements by arranging the elements (63) then known into 8 groups, by leaving gaps for undiscovered elements and predicting their properties. He made separate groups for metals and non-metals. He also created periods in which the element gradually changes from metallic to non-metallic character. He was also able to show that the element in the same sub-group had the same valency.

Elements of lithium, sodium, and potassium have the following similar properties :

1. All these have one electron in the outermost shell.
2. They form unipositive ions.
3. They are good reducing agents.
4. They are soft metals.
5. They impart color to the flame.
6. The common name of the group is alkali metals [Group 1A].

Yes, Döbereiner'striads also exist in the columns of Newland's octaves. For example, the second column of Newlands classification has the elements Lithium (Li), Sodium (Na) and Potassium (K), which constitute a
Döbereiner's triad.

Döbereiner failed to arrange all the known elements in the form of triads.
In the triad of fluorine (19), chlorine (35.5) and bromine (80), it is observed that the mean of the atomic masses of fluorine and bromine is ½(19 + 80) = 49.5, not 35.5.

He left gaps in the table for the undiscovered elements. He discovered the properties of such elements with the help of neighboring elements.
He discoveredeka-silicon with atomic mass of 72 which was later named Germanium with atomic mass 72.6.