# Ch 8 Periodic Properties of the Elements Multielectron

• Slides: 18

Ch. 8 Periodic Properties of the Elements Multielectron Atoms • • “Hydrogen-like” orbitals are used for all atoms Energy levels are affected by other electrons – Coulomb’s Law—electrostatic repulsion of like charges is proportional to the amount of charge, and inversely proportional to the distance between them (see text for eqn) – Shielding—screening of one electron from the nuclear charge by other electrons around the same atom – Penetration—probability of the electron to be close to the nucleus – Effective nuclear charge (Zeff)—the amount of nuclear charge an electron experiences after taking shielding into account – Degenerate—of equal energy

Order of Filling Subshells

Electron Spin and the Pauli Exclusion Principle • Electrons have intrinisic angular momentum -- “spin” -- ms – Possible values: ms = +1/2 and -1/2 (only two possible values) • Pauli Exclusion Principle: – No two electrons in an atom can have identical values of all 4 quantum numbers -- maximum of 2 electrons per orbital! – A single orbital can hold a “pair” of electrons with opposite “spins” – e. g. the 3 rd shell (n = 3) can hold a maximum of 18 electrons: n=3 l = 0 1 2 subshell 3 s 3 p 3 d # orbitals 1 3 5 # electrons 2 6 10 = 18 total • A single electron in an orbital is called “unpaired” • Atoms with 1 or more unpaired electrons are paramagnetic, otherwise they are diamagnetic

Electronic Configurations • The Aufbau Principle -- Order of Filling Subshells – Atomic # = # of protons = # electrons (in neutral atom) – Add electrons to atomic orbitals, two per orbital, in the general order of increasing principle quantum number n, for example: # Atom Configuration 1 H 1 s 1 2 He 1 s 2 3 Li 1 s 22 s 1 4 Be 1 s 22 s 2 5 B 1 s 22 p 1 6 C 1 s 22 p 2 7 N 1 s 22 p 3 8 O 1 s 22 p 4 9 F 1 s 22 p 5 10 Ne 1 s 22 p 6 11 Na 1 s 22 p 63 s 1

Hund’s Rule • Maximum number of unpaired electrons in orbitals of equal energy Orbital diagrams: C __ __ __ 1 s 2 s 2 p N __ __ __ 1 s 2 s 2 p O __ __ __ 1 s 2 s 2 p

Relationship to Periodic Table e. g. complete electronic configuration of Ge (#32, group IV) Ge 1 s 22 p 63 s 23 p 64 s 23 d 104 p 2 or, Ge 1 s 22 p 63 s 23 p 63 d 104 s 24 p 2 (by values of n) • Short-hand notation -- show preceding inert gas config. – Ge [Ar]4 s 23 d 104 p 2 where [Ar] = 1 s 22 p 63 s 23 p 6

Valence Shell Configurations • valence shell -- largest value of n (e. g. for Ge, n = 4) plus any partially filled subshells Ge 4 s 24 p 2 (valence shell electron configuration) Ge __ __ (valence shell orbital diagram) 4 s 4 p Elements in same group have same valence shell e– configurations e. g. group V: N P As Sb Bi 2 s 22 p 3 3 s 23 p 3 4 s 24 p 3 5 s 25 p 3 6 s 26 p 3

Sample Questions • Write the complete electron configuration of gallium. Answer: • Write the short-hand electron configuration for zirconium. Answer: • Write the orbital diagram for the valence shell of tellurium. Answer:

Sample Question How many unpaired electrons does a ruthenium(II) ion, Ru 2+, have? Show an appropriate orbital diagram to explain your answer. Is the atom paramagnetic or diamagnetic?

Variation of Atomic Properties Atomic Size (atomic radius, expressed in pm -- picometers) e. g. group 1 metals: (10– 12 m!) Atom Radius in pm Valence Shell Li 152 2 s 1 Na 186 3 s 1 K 227 4 s 1 Cs 248 5 s 1 e. g. some elements in 2 nd period: Atom B C N O F radius 88 77 70 66 64 e– config 2 p 1 2 p 2 2 p 3 2 p 4 2 p 5

General Trend in Atomic Size Relative sizes of ions cations are smaller than parent atoms e. g. Na 186 pm 2 s 22 p 63 s 1 Na+ 95 pm 2 s 22 p 6 anions are larger than parent atoms e. g. Cl 99 pm 3 s 23 p 5 Cl– 181 pm 3 s 23 p 6

Ionization Energy I. E. = energy required to remove an electron from an atom or ion (always endothermic, positive values) e. g. Li(g) --> Li+(g) + e– I. E. = 520 k. J/mole Exceptions: special stability of filled subshells, and of half-filled subshells

Electron Affinity • E. A. = energy released when an electron is added to an atom or ion (usually exothermic, negative EA values) e. g. Cl(g) + e– --> Cl–(g) E. A. = -348 k. J/mol • The general trends in all these properties indicate that there is a special stability associated with filled-shell configurations. • Atoms tend to gain or lose an electron or two in order to achieve a stable “inert gas configuration” -- many important consequences of this in chemical bonding.

Types of Elements Metals: Shiny, malleable, ductile solids with high mp and bp Good electrical conductors Metal character increases to lower left of periodic table Nonmetals: Gases, liquids, or low-melting solids Non-conductors of electricity Diatomic elements: H 2, O 2, N 2, F 2, Cl 2, Br 2, I 2 Metalloids: Intermediate properties, often semiconductors

Sample Questions Of the following atoms, circle the one with the highest electron affinity. K Cl P Br Na Write a balanced chemical equation that corresponds to the electron affinity of the element that you selected above.

Alkali Metals • They want to be +1! • Easily oxidized, low EA, low IE. • Density increases moving down the group. (mass rises faster than atomic radius) • Reactions – With halogens to form salts, e. g. 2 Na(s) + Cl 2(g) 2 Na. Cl(s) – With water to make base + hydrogen, e. g. 2 K(s) + 2 H 2 O(l) 2 K+(aq) + 2 OH–(aq) + H 2(g) • Reactions are more vigorous as you get lower in the group (why? ) http: //www. youtube. com/watch? v=9 b. Ah. CHed. VB 4&feature=relmfu http: //www. youtube. com/watch? v=rt. Na. EFXOd. Ac&feature=relmfu

Halogens • They want to be – 1! • Easily reduced, high EA, high IE. • Density increases moving down the group. (mass rises faster than atomic radius) • Reactions – With metals to form metal halides, e. g. 2 Al(s) + 3 Cl 2(g) 2 Al. Cl 3(s) – With hydrogen to form hydrogen halides (binary acids!), e. g. H 2(g) + I 2(s) 2 HI(g) – With other halogens to form interhalogen compounds, e. g. Br 2(l) + F 2(g) 2 Br. F(g) • http: //www. youtube. com/watch? v=F 4 IC_B 9 i 4 Sg

Noble Gases • Closed-shell electron configuration; very unreactive! • Used for lights, airtanks for divers, cryogens • Few reactions! Fluorides, oxides can be made under severe conditions. • • Helium--helios (sun) Krypton--kryptos (hidden) Neon--neos (new) Xeno--xenos (stranger)