Approximate bonding atomic radii for the elements have been tabulated. The distance between bonded nuclei can be approximated by adding radii from both atoms. e.g., Bonding atomic radii are as follows: So the approximate distance between bonded C and Br nuclei = = 1.91 A C = 0.77 A, Br = 1.14 A rr d

more p +, but no new (i.e., farther away) energy levels Atomic Radius As we go down a group, atomic radius… -- principal quantum number increases (i.e., a new energy level is added) increases. As we go from left to right across the Table, atomic radius… decreases. -- effective nuclear charge increases, but principal quantum number is constant

Coulombic attraction depends on… 2– 2+ 2– 1– 2– amount of chargedistance between charges + + – – H He + – + – + – As we go, more coulombic attraction, no new energy level, more pull, smaller size

Sr < Ba < Cs Arrange the following atoms in order of increasing atomic radius: Sr, Ba, Cs

Ionization Energy: the minimum energy needed to remove an e – from an atom or ion M(g) + 1 st I.E.  M + (g) + e – M + (g) + 2 nd I.E.  M 2+ (g) + e – M 2+ (g) + 3 rd I.E.  M 3+ (g) + e – Successive ionization energies are larger than previous ones. -- (+) attractive force remains the same, but there is less e – /e – repulsion I.E. e–e–

The ionization energy increases sharply when we try to remove an inner-shell electron. e.g., For Mg, 1 st IE = 738 kJ/mol 2 nd IE = 1,450 kJ/mol 3 rd IE = 7,730 kJ/mol As we go down a group, 1 st IE…decreases. -- more e – /e – repulsion and more shielding (strong evidence that only valence e – are involved in bonding)

Generally, as we go from left to right, 1 st IE… Exceptions: e.g., B < Be Be:1s 2 2s 2 B:1s 2 2s 2 2p 1 B doesn’t like 2p (easier to remove B’s single 2p e – than one of Be’s two 2s e – s) N:1s 2 2s 2 2p 3 O:1s 2 2s 2 2p 4 More stable to have than to have 2p Subshells prefer to be either completely filled OR half-filled. This e – is easier to remove… …than any of these.

First across a period… down a group…

released. Electron affinity: the energy change that occurs when an e – is added to a gaseous atom For most atoms, adding an e – causes energy to be… Exceptions: noble gases: the added e – must go into a new, higher energy level group 2 metals: the added e – must go into a higher-energy p orbital group 15 elements: the added e – is the first one to double-up a p orbital eq. for e – affinity: A + e – A – I.E. e–e– e–e– energy

more (–) e – affinity The halogens have the most (–) electron affinities, meaning that they become very stable when they accept electrons. Electron affinities don’t vary much going down a group. more willing to accept an e – = –328 F Cl Br I O S Se Te Ne Ar Kr Xe He –349 –325 –295 –141 –200 –195 –