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740

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the 44L

elements diagram below

nuclear

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relatively the

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3p6 3p6 3p6

low

removed electron

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these

which

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period configuration

2

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[

kJ/mol)

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3d1° Al 3d’°41,

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highest sequential

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e relatively I trends Z 1) ii) ui) the

highest 1

increases,

[

1356 I

595

409

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,

elements

f

[5] S

discussed

999 kJ/mol

_

kJ/mol kJ/mol

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the

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j

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to

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above.

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C

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f_c

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The second, third and subsequent ionization energies increase for any element, but again, there are jumps in these values.

Z Atom electron configuration [ 12 13 14 15 3 Li 2Is 12s 520 7300 11,815 4 Be 2Is 22s 899 1757 14,850 21,000 5 B 2Is 22s 13p 800 2430 3660 25,000 32820 6 C 2Is 22s3p 1090 2350 4620 6220 38,000 These data show that the removal of valence shell electrons is much easier than the removal of core electrons.

5 Shown below are the ionization energies for three elements in the third period. Label each box with the correct element: d 3 II l 14 4ISi P I U1ft’ 496 4560 6912 954 .-i rp1 - c Li 737 1451

IMi 578 1816 2744 ((‘/

6. The first four ionization energies for element X (not in kJ/mol) are 170, 350. 1800. 2500. The first four ionization energies for element Y are 200.

• 400, 3500 and 5000 Identify elements X and Y. There may be more than /k(rz z L’ (/( C pne correct answer - f7-y 3 co f’ a C.t C y - I ‘Z) ç73 (2 VF’4 (V - 4 / I,.. 7. Which of the following has the largest 12? (Transition metals lose their s ins before the d electrons) Ca Sc Fe ,k 151 51’ 2 /(C 8. Which species of each pair has the higher ? t t4 f4?’Z-fl.f tflf I a) Mgor1,Mg’ 02 ii. (t’ti ice ci d) 3P o() Z:t:iVf 1 Atomic and Ionic Radii

Similar are seen in the radii of the elements. Moving down a group increases atomic radii. As n increases, the sizes of the orbitals increase.

Moving across a period leads to a decrease in the atomic radii. This is again due to the increase in atomic charge (Z) with the poor shielding by outer shell electrons.

9. Arrange the following atoms in order of decreasing atomic radius. Na J P Cl Mg ‘J/M 3 10 Which is the largest atom in Group IV? Pb In Which is the smallest atom in Group VII? Which is the smallest atom in period 5? )( ( ç4) The ionic radius is the radius of an anion or cation. When neutral atoms are ionized, there is a change in their sizes.

Ifthe atom forms an anion the size increases, because the nuclear charge (Z) is unchanged but the electron-electron repulsion increases, due to the added electron, enlarging the electron cloud.

Ifthe atom forms a cation, the size decreases. The nuclear charge is unchanged and the decreased electron-electron repulsion shrinks the electron cloud. o •O Na CI Na Cl

For derived from elements in different groups, a comparison of sizes is possible only in an isoelectronic series, a series of ions containing the same number of electrons ii. Which of the ions listed below are isoelectronic with krypton? k ‘ 3CC Ag 2Cd 2Ti Zn 4c jr- ue 12. Pick a , write its shorthand e configuration and determine its number of electrons. Then find the , alkali and with the same number of electrons. Write these as their most stable ion They willconstitute an asoelectronac series

noble gas halogen alkali alkaline metal earth species F - Pt Wconfiguration Zp’ - ç tp’ is Zp ic tc Lp Z, nuclear charge ÷ .— z # electrons / o io

Order them by increasing atomic or ionic radius. (Hint: Compare the positive and negative charges) F 13. For each of the following pairs, which of the two species is larger? a)(or F b) 2Mg 3Fe :f9fly IOC ii3 (\:iJz.4ca Z?c 14. For each of the following pairs, which of the two seeie is smaller?t’1 a) IC b) Au 0’ c)i:;33P of’) 1% 4 ( t— 15. Order the following groups from1aiget to smallest radii. a)N,Cl,K,S j11!9 1 1tt’3-i ,4{>c( >C 2b) C Al F Si 11 :3 I€(IJC7 fl3 I3 tI1 /Jte4 f.?) C) Na, Mg, Ar, P > k{ > fr t ‘1- tii t i- i; ‘5 2 la d) I, 2Ba Cs, Xe ,/ tt’ir 34’c ctU 5 54 -Ø 16. Which species of eah pair has the larger radius? a)(4)r 2Mg b) Oj c) K6Cl) 2/9 ;/q

Electron affinityis defined as the energy released when the following reaction occurs: X (g) + e —+ (g) + energy

These reactions are exothermic (negative energy) since energy is given off.

Second and third electron affinities also exist, but these are all very difficultto measure experimentally.

This is also a periodic property. Electron affinitytends to increase goingacross a period, from left (metals) to right (non-metals). And, with exceptions, electron affinitydecreases as we down a group.

These are the same general trends that are seen when looking at . This is a measure of the ability of a bonded atom to attract the bonding electrons to itself and away for the other atoms bonded to it. The element with the highest electronegativity value is F. The electronegativity decreases going down and across the . The least electronegative element is Cs.