Question

9. Discuss the trend in electronegativities across Period 2 from lithium to fluorine. Can you account for the difference in details from the trend in ionization energy?

Answer 1

• The modern Periodic Table is arranged in order of increasing atomic number. As one moves from one element to another on the right, one more proton is found in the nucleus, and one more electron is found in the same electron 'shell' (energy level). For this reason, all the elements in Period 2 have the first electron 'shell' (energy level) filled with 2 electrons (the electronic configuration of Helium). Lithium begins a new electron 'shell' ( 2^ndenergy level) with 1 electron, Beryllium has 2 electrons in the second electron 'shell' (energy level), Boron has 3 electrons in the second electron 'shell' (energy level) etc, until finally the second electron 'shell' (energy level) is filled with 8 electrons and the stable electronic configuration of the Noble Gas Neon is reached (2,8).
• Atomic radius of the elements decrease across the Period from left to right. As we move from left to right across the period one more proton is added to the nucleus of each successive atom, and one more electron is added to the same electron 'shell' (energy level) of each successive atom. The increased positive charge in the nucleus of each successive atom attracts all the electrons in the atom more strongly, so they are drawn in more closely towards the nucleus.
• 1^st Ionization Energy (the energy required to remove an electron from the gaseous atom) increases across the Period from left to right. The further away from the positively charged nucleus that a negatively charged electron is, the less strongly the electron is attracted to the nucleus and so the more easily that electron can be removed. So, as the atomic radius decreases from left to right across the Period so the 1^st Ionization Energy increases.
• Electronegativity (the relative tendency shown by an atom to attract electrons to itself) increases across the Period from left to right. Typically, metals have low electronegativity, little ability to attract electrons, while non-metals have high electronegativity, greater ability to attract electrons. As we move from left to right across the Period, the elements become less metallic in nature (more non-metallic).
• In general metals are hard (EXCEPT Group 1 (IA) metals which are quite soft), have metallic lustre, high melting and boiling points (Except for mercury which is a liquid at room temperature, and the Group 1 (IA) metals which have low melting/boiling points compared to other metals) and good electrical conductivity. In general, non-metals are dull, brittle, have low melting and boiling points and are electrical insulators (non-conductors of electricity). Elements to the left of Period 2 exhibit metallic properties, elements to the right show non-metallic properties. Boron is a semi-metal (metalloid), while it looks like a metal it has poor electrical conductivity but this increases with temperature. Carbon has the ability to form bonds to other carbon atoms forming huge networks which results in extremely high melting and boiling points since these strong bonds between the atoms have to broken.