ch. 8 periodic properties of the elements
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Ch. 8 Periodic Properties of the Elements. Multielectron Atoms “Hydrogen-like” orbitals are used for all atoms Energy levels are affected by other electrons - PowerPoint PPT PresentationTRANSCRIPT
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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
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Order of Filling Subshells
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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 3rd shell (n = 3) can hold a maximum of 18 electrons: n = 3 l = 0 1 2
subshell 3s 3p 3d # 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
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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 1s1
2 He 1s2
3 Li 1s22s1
4 Be 1s22s2
5 B 1s22s22p1
6 C 1s22s22p2
7 N 1s22s22p3
8 O 1s22s22p4
9 F 1s22s22p5
10 Ne 1s22s22p6
11 Na 1s22s22p63s1
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Hund’s Rule• Maximum number of unpaired electrons in orbitals of
equal energy
Orbital diagrams:
C __ __ __ __ __
N __ __ __ __ __
O __ __ __ __ __
1s
1s
1s
2s
2s
2s
2p
2p
2p
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Relationship to Periodic Table
e.g. complete electronic configuration of Ge (#32, group IV)Ge 1s22s22p63s23p64s23d104p2
or, Ge 1s22s22p63s23p63d104s24p2 (by values of n)
• Short-hand notation -- show preceding inert gas config.– Ge [Ar]4s23d104p2 where [Ar] = 1s22s22p63s23p6
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Valence Shell Configurations• valence shell -- largest value of n (e.g. for Ge, n = 4)
plus any partially filled subshells
Ge 4s24p2 (valence shell electron configuration)
Ge __ __ __ __ (valence shell orbital diagram)
Elements in same group have same valence shell e– configurations
e.g. group V: N 2s22p3
P 3s23p3
As 4s24p3
Sb 5s25p3
Bi 6s26p3
4s 4p
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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:
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Sample Questions• Write the complete electron configuration of gallium.Answer:
Ga 1s22s22p63s23p64s23d104p1
• Write the short-hand electron configuration for zirconium.Answer:
Zr [Kr]5s24d2
• Write the orbital diagram for the valence shell of tellurium.
Answer:
Te ___ ___ ___ ___5s 5p
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Sample QuestionHow many unpaired electrons does a ruthenium(II) ion,
Ru2+, have?Show an appropriate orbital diagram to explain your
answer. Is the atom paramagnetic or diamagnetic?
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Sample QuestionHow many unpaired electrons does a ruthenium(II) ion,
Ru2+, have?Show an appropriate, valence-shell orbital diagram to
explain your answer. Is the atom paramagnetic or diamagnetic?
Answer:4 unpaired electrons, so paramagneticOrbital diagram:
Ru2+ ___ ___ ___ ___ ___
4d
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Variation of Atomic PropertiesAtomic Size (atomic radius, expressed in pm -- picometers)
e.g. group 1 metals:
e.g. some elements in 2nd period:
Atom Radius in pm Valence Shell
Li 152 2s1
Na 186 3s1
K 227 4s1
Cs 248 5s1
Atom B C N O F
radius 88 77 70 66 64
e– config 2p1 2p2 2p3 2p4 2p5
(10–12 m!)
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General Trend in Atomic Size
Relative sizes of ionscations are smaller than parent atomse.g. Na 186 pm 2s22p63s1
Na+ 95 pm 2s22p6
anions are larger than parent atomse.g. Cl 99 pm 3s23p5
Cl– 181 pm 3s23p6
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Ionization EnergyI.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 kJ/mole
Exceptions: special stability of filled subshells, and of half-filled subshells
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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 kJ/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.
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Types of Elements
Metals:Shiny, malleable, ductile solids with
high mp and bpGood electrical conductorsMetal character increases to lower left of periodic table
Nonmetals:Gases, liquids, or low-melting solidsNon-conductors of electricity
Metalloids:Intermediate properties, often semiconductors
Diatomic elements: H2, O2, N2, F2, Cl2, Br2, I2
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Sample QuestionsOf 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.
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Sample QuestionOf 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.
Answer: Cl(g) + e– --> Cl–(g)
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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) + Cl2(g) 2 NaCl(s)
– With water to make base + hydrogen, e.g.2 K(s) + 2 H2O(l) 2 K+
(aq) + 2 OH–(aq) + H2(g)
• Reactions are more vigorous as you get lower in the group (why?)
http://www.youtube.com/watch?v=9bAhCHedVB4&feature=relmfuhttp://www.youtube.com/watch?
v=rtNaEFXOdAc&feature=relmfu
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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 Cl2(g) 2 AlCl3(s)
– With hydrogen to form hydrogen halides (binary acids!), e.g.H2(g) + I2(s) 2 HI(g)
– With other halogens to form interhalogen compounds, e.g.Br2(l) + F2(g) 2 BrF(g)
• http://www.youtube.com/watch?v=F4IC_B9i4Sg
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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)