Download Atomic Structure Origin of the elements Structure of atoms Periodic Trends

Atomic Structure
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Origin of the elements
Structure of atoms
❧ Hydrogen
❧ Others
Periodic Trends
Synthesis of elements
❧ Big bang 15E9 years ago
❧ Temperature 1E9 K
❧ Upon cooling influence of forces felt
➠ 2 hours
* H (89 %) and He (11 %)
➠ Strong force for nucleus
➠ Electromagnetic force for electrons
1-1
1-2
Fundamental Forces
1-3
Subatomic particles
• A number of subatomic particles have relevance to
chemistry
❧ Electron
❧ Proton
➠ Z, atomic number
❧ Neutron
➠ N, different isotopes of same element
* 12C, 13C, 14C
❧ Photon
❧ Neutrino
❧ Positron
❧ α particle
❧ β particle
1-4
1-5
1-6
Origin of element
• Initial H and He
• Others formed from nuclear reactions
❧ H and He still most abundant
1-7
Origin of elements
• Gravitational coalescence of H and He into clouds
• Increase in temperature to fusion
• Proton reaction
❧ 1H + 1H → 2H + e+ + νe + 0.42 MeV
• CNO cycle
❧ 12C + 1H →13N + γ
❧ 13N →13C + e+ + νe
❧ 13C + 1H →14N + γ
❧ 14N + 1H →15O + γ
❧ 15O →15N + e+ + νe
❧ 15N + 1H →12C + 4He
❧ Net result is conversion of 4 protons to alpha
particle
➠ 4 1H → 4He +2 e++ 2 νe +3 γ
1-8
Origin of elements
He burning
❧ 4He + 4He ↔ 8Be + γ - 91.78 keV
❧ 8Be + 4He → 12C + γ + 7.367 MeV
Neutron Capture and proton emission
❧ 14N + n →14C +1H; 14N(n,1H)14C
Neutron Capture; S-process
❧ 68Zn(n, γ) 69Zn
❧ 69Zn → 69Ga + β− + ν
• R process
❧ nuclei are bombarded with a large neutron flux
❧ form highly unstable neutron rich nuclei
❧ rapidly decay to form stable neutron rich nuclei
• P process
❧ Proton capture, not as common
1-9
Origin of elements
• Binding energy
❧ Difference between
energy of nucleus and
nucleons
➠ Related to mass
excess
* ∆m=mnucleonsmnucleus
* Ebind=∆mc2
➘ Related to
nuclear
models
1-10
Origin of elements
• How is Au formed from
Ir?
❧ Start with 193Ir and
base on s process
➠ 193Ir + n->194Ir +
β-->194Pt
➠ 194Pt + 3n ->197Pt
+ β- ->197Au
* Relies upon
nuclear
process
1-11
Periodic property of element
• Common properties of
elements
❧ Medeleev
• Modern period table
develop
❧ Actinides added in
1940s by Seaborg
❧ s, p, d, f blocks
1-12
Hydrogenic atoms
•
Atoms with only one electron
❧ Simplifies calculations
➠ Electron position described by wavefunction ψ
* x, y, z, and time
* Probability of finding electron in a space
proportional to ψ2
2
ψ
∫ dτ = 1
1-13
Orbitals
•
Wavefunctions specified by
quantum numbers
❧ n=1,2,3,4
➠ Principal quantum
number
❧ l=0 to n-1
➠ Orbital angular
momentum
➠ Electron orbitals
* s,p,d,f
❧ ml= +l
❧ Spin=+-1/2
➠ Energy related to Z
and n
* ∆Etrans=kZ2∆(1/n2)
1-14
Distribution of electrons
1-15
Bohr Atom
• Models of atoms
❧ Plum pudding
❧ Bohr atom
➠ Inclusion of quantum states
➠ Based on Rutherford atom
• Bohr atom for 1 electron system
❧ Etotal =1/2mev2+q1q2/4πεοr
➠ q2=-e
* Include proton and electron
❧ 1/2mev2-Ze2/4πεοr
1-16
Bohr Atom
• Net force on the electron is zero
❧ 0=Fdynamic+Fcoulombic
❧ 1/2mev2/r+q1q2/4πεοr2
➠ Force is 1/r2E = ∫ Fdr
➠ Energy 1/r
❧ 1/2mev2/r-Ze2/4πεοr2
➠ Z is charge on nucleus
• Quantize energy through angular momentum
❧ mvr=nh/2π, n=1,2,3….
➠ Can solve for r, E, v
1-17
Bohr radius
• R=(εοh2/πmee2)(n2/Z)
❧Radius is quantized and goes at n2
❧R=0.529 Å for Z=1, n=1
➠ Ao (Bohr radius)
1-18
Atomic Spectra
• Quantum numbers
❧n=1,2,3,4
❧r=aon2/Z for gases with 1 electron
• Energy
❧E=-(mee4/8εο2h2)Z2/n2
❧For ground state H
➠ E=2.18E-18 J/atom=k
* Can determine J/mole 1312 kJ/mole
➠ Energy goes as –k/n2
* System converges to limit
1-19
Energy
• n=infinity, r=infinity , E=0, unbound e• Ionization energy
❧k is ionization energy
• Velocity
❧v=nh/2πmer
• Ionization energy
❧Minimum energy required to remove
electron from atom in gas phase
➠ Multiple ionization energies
1-20
Balmer states
• Gas H in tube
❧Four lines in visible region
❧Fit lines
• 1/λ=(1/22-1/n2)R, R=1.1E-7 m-1
❧1/λ=ν (wavenumber)
❧E=1/2mev2=eV (V=Volts)
➠ At 1 V = 1.6E-19 J =eV
➠ K=13.6 eV
1-21
Matter energy interaction
• Eincident=1/2mv2=qV
• Escattered
❧∆E =Eincident-Escattered
❧∆E=kZ2(1/n2final-1/n2in)=hν=hc/λ
❧De-excitation of electron results in photon
emission
➠ Corresponds to line emission
1-22
Orbitals
1-23
Many Electron Atoms
•
Electron configuration
❧ Based on quantum
numbers
❧ Pauli exclusion principle
❧ Aufbau principle and
Hund’s rule
➠ Degenerate orbitals
have same spin
➠ Maximize unfilled
orbitals
* 1s 2s 2p 3s 3p 4s
3d 4p 5s 4d 5p 6s
4f 5d 6p 7s 5f
1-24
Many electron obitals
• Electron configuration of
Zr and Zr4+
❧ [Kr]4d25s2 and [Kr]
• For Fe, Fe2+, and Fe3+
❧ [Ar]4s23d6,
[Ar]4s23d4,
[Ar]4s23d3
• Effective nuclear charge
❧ Zeff=Z-σ
➠ Related to
electron
penetration
towards nucleus
1-25
Effective Nuclear Charge
y = m1 + m2 * M0
y = m1 + m2 * M0
Value
m1
20
m2
Chisq
R
effective charge
15
Error
-1.4319 0.30333
0.74935 0.022984
0.22715
NA
0.99812
NA
m1
Data
m21
Chisq
R
Value
-0.080608
Error
0.060699
0.97519
0.027228
0.99994
0.0049655
NA
NA
y = m1 + m2 * M0
Value
m1
m2
10
Chisq
R
Error
-5.53 0.24075
0.741 0.015874
0.01008
NA
0.99954
NA
5
0
0
5
10
15
1s
2s
3s
20
1-26
Z
Atomic Radii
• Increase down a group
• Decrease across a period
❧ Lanthanide and actinide contraction
1-27
Ionic Radius
1-28
1-29
Orbital energies (MJ/mole)
H
Li
C
F
Na
Si
Cl
K
Ca
Sc
Ti
V
Br
1s
2s
2p
3s
3p
3d
4s
4p
-1.31
-6.26 -0.52
E ~ -(Zeff)2/n
-28.34 -1.88 -1.04
-67.18 -3.87 -1.80
-104.19 -6.82 -3.67
-0.50
-183.58 -15.09 -10.24 -1.44 -0.75
-273.46 -26.64 -20.08 -2.44 -1.33
-349.83 -37.00 -29.13 -3.94 -2.38 -0.42
-390.90 -43.04 -34.25 -4.86 -3.15 -0.59
-434.47 -48.95 -39.37 -5.51 -3.41 -0.77 -0.72
-480.40 -55.11 -44.61
-6.30 -3.81 -0.89 -0.68
-528.69 -61.54 -50.26
-6.95 -4.20 -0.97 -0.72
-1303.01 -172.82 -151.69 -26.11 -18.11 -7.35 -2.36 -1.22
1-30
1-31
Ionization energy
• Energy needed to remove
electron
❧ Depends upon
quantum state
❧ Ranked by electron
configuration
➠ Measured in eV
* 1 eV= 96.485
kJ/mol
1-32
Electron Affinity
• Enthalpy gain when a
gas phase atom gains an
electron
1-33
Electronegativity
1-34