Electronegativity
_ from top to bottom on the periodic table.

Electronegativity from top to bottom in periodic table decreases.

Explanation:

Electronegativity:

It is the ability of an atom to attract the shared electrons.The greater the ability of attraction higher will be the electronegativity.

Along group:

As we move from top to bottom in periodic table the atomic sizes increases.The electrons are added in next energy level in every next element. Thus the valance electrons farther away from the nucleus and hold of nucleus becomes weaker. The ionization energy increases and electronegativity decreases because of weak nuclear attraction and greater atomic radii.

Along period:

As we move from left to right across the periodic table the number of valance electrons in an atom increase. The atomic size tend to decrease in same period of periodic table because the electrons are added with in the same shell. When the electron are added, at the same time protons are also added in the nucleus. The positive charge is going to increase and this charge is greater in effect than the charge of electrons. This effect lead to the greater nuclear attraction. Thus the attraction of the atoms for valance electrons increases. The electrons are pull towards the nucleus and valance shell get closer to the nucleus. As a result of this greater nuclear attraction atomic radius decreases and ionization energy increases because it is very difficult to remove the electron from atom and more energy is required, and electronegativity increases.