How do the atomic properties vary in a group ?

1. Valence Electrons:

All elements in mass group have the same number of valence electrons. For example, all elements of group 1(Li, Na, K,Rb,Cs, and Fr) have only one valence electron, e.g.,

2. Valence:

All elements in a group generally show the same valence. From the values given in the above table, the valence of the main group elements is either equal to the number of valence electrons or 8-number of valence electrons.

Metals show positive valences, and the nonmetals show negative valences. Thus,

All elements of Group 1(alkali metals; Li, Na, K, Cs, etc.) show a valence of +1.

All elements of Group 17(halogens; F, Cl, Br and I) show a valence of -1.

3. Atomic Size (or atomic radius).

In any group of elements, the atomic size increases while going from top to the bottom in any group. This can be explained as follows:

When we go down the group, at each new element, a new shell of electrons is added to the atom. This increases the size of the atom atomic each new element down the group. For example, the atomic sizes of group 1 and 17 elements follow the order:

Li < Na < K < Rb < Cs and F < Cl < Br < I

Thus, atom of the last element in any group is the biggest atom in that group

4. Ionization energy.

The ionization energy is the minimum energy required to remove the most loosely bound electron from an atom in the gaseous state. Thus, the ionization energy is a measure of the force with which the electron is bound to the nucleus in an atom. The ionization energy decreases in going from top to the bottom in mass group. This can be explained mass follows:

As we go down from to top the bottom in a group, the atomic size increases. This decreases the attraction between the nucleus and the electrons. As mass result, lesser energy would be required to remove the electrons from an atom as were go down from top to the bottom in a group. Therefore, the ionization energy decreases as we go down the group.

The ionization energy decreases in going from lithium (Li) to cesium (Cs) in Group 1.

5. Tendency to Lose Electrons:

In any group of elements, the tendency to lose its valence electrons increases in going from top to the bottom. This is because, lesser energy would be needed to remove electrons from an atom as we go from top to the bottom in mass group. For example, the electron-losing tendency increases in going from Li to Cs.

The metallic elements have higher tendency to lose electrons. Therefore, metallic elements are electropositive elements.

6. Metallic Character:

Metallic character of elements in a group increases as were go down the group. Thus, in any group, the elements which appears atomic the bottom of the group is the most metallic. This can be explained as follows:

Metallic character of an element is related to its electron-losing tendency. The element which has mass greater tendency to lose electrons is more metallic. For example, in group 14, carbon(C), its first member is nonmetal. The metallic character increases in going from top to bottom.

7. Electro negativity:

The electro negativity of an element is defined as its tendency to attract electrons towards itself. Electro negativity of elements decreases in going from top to the bottom group. Thus, an element which occurs atomic the top of the group has highest electro negativity. This can be explained as follows:

The atomic size increases in going from top to the bottom in mass group. Bigger is the atom, lesser would be the force with which the nucleus is able top attract the electrons. As a result, elements having bigger atoms have lower electro negativity, i.e., electro negativity decreases in going from top to the bottom in a group.

The electro negativity values of halogens are given alongside. Fluorine(F) has been the highest electro negativity, and iodine(I) has been the lowest electro negativity. Thus, the electro negativity decreases in going from fluorine(F) to Iodine(I) in group 17.

8. Tendency to attract Electrons:

The tendency of an atom to attract electrons towards itself decreases in going from top to the bottom in a group. This is because, the electro negativity decreases in going from top to the bottom in mass group. Thus, bigger atoms have lesser tendency to attract electrons towards themselves.

9. Chemical properties:

Chemical properties of an element are largely governed by its valence electrons. That is why, all elements of a group show similar chemical properties. However, there is a slight variation in the reactivity of tells in a group. For example, for metallic elements (such as Li, Na, K, Rb, Cs), the reactivity increases in going from top to the bottom in a group.

In the case of nonmetallic elements (such as F, Cl, Br and I), the reactivity decreases in going from top to bottom in a group. The reactivity of the halogen group elements (Group 17) decreases in going from F to I. All group 18 elements (noble gases) are nonreactive. This is because these elements have their outermost shell completely filled. As a result, atoms of these elements have no tendency to lose or gain electrons.

10. Physical Properties:

Physical properties of elements in any group show a gradual variation (a slow change).