Chapter 7 Dmitri Mendeleev arranged periodic table according to atomic masses chemical periodicity- predicting a property based on an element’s position within the periodic table

-Henry Moseley later arranged according to increasing atomic # -elements in the same group have similar # of valence e- and similar chemical properties

valence orbitals- occupied orbitals which hold the electrons involved in bonding (outermost levels) -in transition metals the d e- are included in the valence electrons even though they are not in the outermost energy level core electrons- all other e- besides the valence e-

*Identify the valence and core e- for potassium, titanium and germanium K 1 valence e- and 18 core e- Ti 4 valence e- and 18 core e- Ge 4 valence e- and 28 core e-

Periodic Trends 1)Effective Nuclear Charge (Z eff ) -the net positive charge of the nucleus experienced by an e- in a many-electron atom *Coulomb’s Law  the strength of the interaction between two electrical charges depends on the magnitude of the charges and on the distance between them *force inc as Z eff inc and dec as distance inc

Z eff = Z – S Z = # of p + S= screening constant (usually close to # of core e-) *Z eff < actual nuclear charge *Z eff includes the effect of the other e- in the atom -core e- partially screen valence e- from the attraction of the nucleus

**Z eff increases from left to right across a period -core e- stays the same, but p + inc -added valence e- screen one another ineffectively

** Z eff going down a group changes far less than it does across a period ex- Li = 3-2 = 1+ Na = = 1+ -inc slightly as you move down a group b/c the more diffuse core e- cloud is less able to screen the valence e- from the nuclear charge

2) Atomic Radii/Size nonbonding atomic radius/van der Waals radius- twice the radius of two nuclei bonding atomic radius/covalent radius- half the distance between two nuclei page 254 figure 7.5

-increases as you move down a group *due to inc. in n (prin. quantum #) of outer e- *as you inc. n outer e- are further from nucleus -decreases as you move across a period (left to right *due to the inc. in Z eff which draws valence e- closer to the nucleus, causing smaller radius

-length of the atomic radius of elements will be given -page 255 figure 7.6 *transition metals do not show a regular decrease moving across -given in angstroms 1Å = m

Problems: 1) Natural gas used in heating and cooking is odorless. Because natural gas leaks pose the danger of explosion or suffocation, various smelly substances are added to detect a leak. One example is mercaptan, CH 3 SH. Predict the lengths of C—S, C—H, and S—H bonds. C—S = = 1.79 Å C—H = = 1.14 Å S—H = = 1.39 Å

2)Predict which is longer: a) P—Br bond in PBr 3 b) As—Cℓ bond in AsCℓ 3 a)P—Br = = 2.20 Å b)As—Cℓ = = 2.18 Å **P—Br

3) Arrange (as much as possible) the atoms P, S, As, and Se in order of increasing atomic size. S P Se As 4) Arrange Na, Be, and Mg in order of inc. atomic radius. Be Mg Na

3)Ionic Radius/Size -cations are smaller than their parent atoms *e- lost  less e- repulsions -anions are larger than their parent atoms *e- gained  more e- repulsions -for ions with the same charge, ionic radius inc. as you move down a group -dec. as you move across a period for ions with same charge only (anions larger than cations)

isoelectronic series- group of ions all containing the same # of e- ex: Na +, O 2-, Mg 2+, F -, Aℓ 3+ -all have 10 e- -ionic radius dec. with inc. atomic # b/c e- are more strongly attracted to nucleus **Put above in order of dec. ionic radius (from above) O 2- F - Na 1+ Mg 2+ Aℓ 3+

Problems: 1) Arrange Mg 2+, Ca 2+ and Ca in order of decreasing radius. Ca Ca 2+ Mg 2+ *atoms larger than their cations, inc. as you move down 2) Which of the following atoms and ions is largest: S 2-, S, O 2- ? S 2- *anions larger than their atoms, inc. as you move down

3) Arrange the ions K +, Cℓ -, Ca 2+, and S 2- in order of decreasing size. S 2- Cℓ - K + Ca 2+ 4) In the isoelectronic series Rb +, Sr 2+, Y 3+, which ion is largest? Rb +

4)Ionization Energy -minimum energy needed to remove an electron from the ground state of the gaseous atom or ion (kJ/mol) first ionization energy (I 1 )- energy needed to remove the first e- from a neutral atom second ionization energy (I 2 )- energy needed to remove the second e-

*as each e- is removed the ion. energy increases *greatly increases when an inner e- is removed -due to the greater Z eff on inner e- -page 259 Table 7.2

Problems: 1) Of the following elements, which has the greatest I 2 ? NaCaS Na= 1 val e-Ca= 2 val e-S= 6 val e- Na, b/c 2 nd will be a core e- 2) Which has the greater I 3, O or Mg? O= 6 val e-Mg= 2 val e- Mg b/c 3 rd will be core e-

Trends in first ionization energy -inc. as you move across a period -dec, as you move down a group -tran. metals generally inc. left to right *alkali metals have the lowest *noble gases have the highest

*smaller atoms have higher I 1 -the energy depends on Z eff and distance of e- from nucleus -inc. Z eff or dec. the distance from the nucleus inc. attraction between e- and the nucleus and makes it harder to remove e-

Problems: 1) Arrange the atoms Ne, Na, P, Ar and K in order of increasing first ion. energy. K Na P Ar Ne 2) Which has the lowest first ion. energy, B, Aℓ, C, or Si? Aℓ

E- configs of ions *e- lost from highest occupied levels first ex: Li(1s 2 2s 1 )  Li + (1s 2 ) + e- Fe([Ar]3d 6 4s 2 )  Fe 2+ ([Ar]3d 6 ) + 2e- -if Fe 3+ would be ([Ar]3d 5 ) + 3e-

5)Electron Affinity -energy change that occurs when an electron is added to a gaseous atom -in kJ/mol -measures the attraction of the atom for the added e- -when e- is added energy is released, so negative values

*halogens have most negative e- affinities -due to only needing 1e- to achieve octet *Group 2A has + energy b/c added e- goes to p orbital which is higher in energy and unoccupied *Noble gases also + b/c added e- goes to next higher s -no definite trends to follow