Answer to Question #95567 in Atomic and Nuclear Physics for Bruno

Question

Explain with examples, why;

i) atomic radius increases as you go down the group and decreases as you go across a period?
ii) the main trend for first ionization energy to increase across periods?
iii) the value of first electron affinity of oxygen (-142 kJ/mol) smaller than that of fluorine
(-328 kJ/mol)?

Answer 1

i) group within the atomic radius increases downwards. This is due to the fact that the elements of one group differ in the number of electronic layers, and more of them, the larger the size of an atom. On the other hand, within a period of the atomic radius decreasing from left to right. This is because the nuclear charge increases from left to right and the outer electron layer still more strongly "pressed" to the core.

ii) The ionization potential depends largely on the size and charge of the nucleus of the atom radius. The larger radius of the atom, the less the electron is attracted to the nucleus, and consequently less energy must be expended for the electron detachment and conversion atom in positive ion.

iii)the electron affinity of an atom or molecule is defined as the amount of energy released or spent when an electron is added to a neutral atom or molecule in the gaseous state to form a negative ion. the electron affinity of an atom is numerically equal, but opposite in sign to the ionization energy of the corresponding insulated singly charged anion. So the value of first electron affinity of oxygen smaller than that of fluorine.