How do the atomic properties vary with a period ?

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Variations in the atomic properties of elements in any period are discussed below. Atomic number: In a period, the elements are arranged in the order of increasing atomic number. The atomic number increases by one unit atomic each element from left to right in a period.

1. Atomic number:

In a period, the elements are arranged in the order of increasing atomic number. The atomic number increases by one unit atomic each element from left to right in a period. This is because, the number of protons inside the nucleus increases by one at each element in going from left to right in a period.

2. Valence electrons and valence:

The electrons in the outermost shell are called valence electrons. The number of valence electrons increases from 1 to 8 in going from left to right in a period (except in first period). Thus, the number of valence electrons increases by one atomic each element in going from left to right in a period. Valence of the elements in a period also shows a regular change in going from left to right.

3. Atomic Size (or atomic radius):

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Atomic size (or atomic radius) decreases in going from left to right in a period, (except for He and Ne). The number of protons and electrons in an atom increases in going from left to right in a period. The added electrons enter the same shell. Due to the increase in nuclear charge, the electrons are pulled towards nucleus with greater attractive force. As a result, the electronic shell shrinks and the atomic size decreases.

4. Ionization energy:

The ionization energy of an element is a measure of the force with which the electrons in an atom are bound to its nucleus. The ionization energy of elements increases in going from left to right in a period. The ionization energies of second period elements are given.

Although, the increase is not smooth across the period, but, the general trend is that the ionization energy increases in going from left to right in a period.

5. Tendency to lose electrons:

The tendency of an atom to lose electrons depends upon the ease with which it can be removed from an atom. This means that low ionization energy means greater tendency for the loss of electrons. In a period, the ionization energy increases from left to right, therefore, the tendency to lose an electron decreases in going from left to right in a period.

6. Metallic and nonmetallic character:

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Metals have higher tendency to lose electrons. The tendency of an atom to lose electrons decreases in a period from left to right. Therefore the metallic characteristics decrease in going from left to right in a period. Thus, the elements on the left side of the periodic table are metals. For the same reason, nonmetallic character increases in going from left to right in a period. Therefore, the elements on the right side of the periodic table are nonmetals.

7. Electro negativity:

The tendency of an atom to attract electrons toward itself is described in terms of electro negativity of that element. Electro negativity of elements increases in going from left to right in a period. For example, in second period, the electro negativity of fluorine (F) is the highest, and that of lithium (Li) is lowest.

Electro negativity increases in this direction

This is due to the increased nuclear charge of the elements in going from left to right. Since, smaller atoms have greater tendency to attract electrons, hence smaller atoms are more electro negativity.

8. Tendency to attract electrons:

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In a period, the electron-attracting tendency increases in going from left to right. This is because in going from left to right in a period, the positive charge in the nucleus increases.

Tendency to attract electrons increases in this direction

This means that the elements towards the end of the period (except noble gases), have higher tendency to accept electrons. Such elements therefore, easily form anions (negatively charged ions). For example, fluorine has been very high tendency to form fluoride ion.

9. Nature of oxide:

The elements at the beginning of a period form basic oxides. The elements at the end of period form acidic oxides. Thus, the basic nature of oxides of the elements in a period decreases in going from left to right. For example, sodium forms a basic boxer, while sulpher and phosphorus form acidic oxides.

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