Q: How do the values of electron gain enthalpy change in a group, in a period and in metals? (2 Marks)
Answer: Electron gain enthalpy values decrease as we go down in a group, but increase along a period from left to right. Metals have very low electron gain enthalpy values and alkaline earth metals have even positive values.
Note that the negative sign for energy value in table indicates that energy is liberated or lost, and the positive sign tells that the energy is gained or absorbed. All the factors which influence the ionization energy would also influence the electron gain enthalpy.
Question: Explain the term ‘electronegativity’. What factors influence it?
Answer: The electronegativity of an element is defined as the relative tendency of its atom to attract electrons towards it self when it is bonded to the atom of another element. All the factors that influence the ionization energy and the electron affinity of elements influence the electronegativity values of these elements. Because of this, Millikon proposed that the electronegativity of an element is the average value of its ionization energy and electron affinity.
Question: How does the value of electronegativity vary as we go down a group or across a period? (2 Marks)
Answer: Electronegativity values of elements decrease as we go down in a group and increase along a period from left to right. The most electronegative element is ‘F’. and the least electronegative stable element is ‘Cs’.
Question: Write a note on the properties of ‘metals’ and ‘non – metals’. (4 Marks)
Answer: Metals generally show less electronegative character. In compounds, they generally show a tendency to remain as positive ions. This property is often termed as electropositive character. Metals are electropositive elements.
Non metals are generally more electronegative due to their smaller atomic radii.
Let us examine the elements of 3rd period.
3rd period: Na Mg Al Si P S Cl.
We know that Na and Mg are metals; Al and Si are semi metals (metalloids);
P, S and Cl are non metals. So we find metals on left side and non metals on right side of the periodic table. This metallic character decreases while non metallic character increases as we move along a period (from left to right)
Let us take group 14 (IV A) elements.
IV A group: C Si Ge Sn Pb
Here also we know that carbon is non metal, Si and Ge are metalloids, Sn and Pb are metals. So we find non metals particularly at the right hand side top and metals at the left and right hand side bottom of the periodic table. This means metallic character increases while non metallic character decreases in a group as we move from top to bottom.
