Download Atomic Structure and the Periodic Table Atomic Structure and the

Periodic Table Prof. Voss
Page 1
Atomic Structure and the Periodic Table
long suspected Electricity and Chemistry related
Quantum (wave) Mechanics - provides basis
electron (a particle) has a wavelength (De Broglie)
allowed stated ⇒ fundamental (resonance) frequencies
determines Elements and their Periodic Properties
Robert Boyle (1627(1627-1691)
chemist
provided definition
ELEMENT - pure substance
that can not be decomposed
into simpler substances
by ordinary chemical or
physical means.
Symbols for Elements
Jö
Jöns Jakob Berzelius (1779(1779-1848) Stockholm
H Hydrogen
or add lowercase 2nd letter He Helium
Pb Lead (Plumbum)
or use Latin name
capitalize 1st letter of name
discoverer gets to name new elements
see tables 1313-1 through 1313-5
The Periodic Table
Meyer (1830(1830-1895)
German (L)
Mendeleev (1834(1834-1907)
Russian (R)
chemists
arrange elements by mass
from light to heavy
Properties
density, solubility,
melting & boiling points,
ionization energies,
hardness
recur at definite intervals
Periods
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Periodic Table Prof. Voss
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Mendeleev's 1872 table
left blanks where
sequence didn't match
predicted new elements
Robert Moseley (1887(1887-1913)
English physicist
worked with Rutherford
studied XX-ray emission
Atomic Number
more fundamental
than mass
Moseley's Law
properties of the elements are a
periodic function of their atomic number.
Periodic Table modern
relates chemical and physical properties
of Groups of elements
Element
ATOM - smallest unit of an element
Nucleus - positively charged "core"
-14
size ~10×
~10× m
held together by Strong Force
-27
Nucleons of mass 1.66×
1.66×10-27 kg
-19
Protons, p with + charge 1.6×
C
1.6×10
Neutrons, n no charge
-10
Electron cloud size ~ 1m
1-3×10
-19
electron charge -1.6×
C
1.6×10
-31
mass 9.1×
kg
9.1×10
Each element has a unique ATOMIC NUMBER, Z
= number of protons in nucleus
= number of electrons in neutral atom
ISOTOPE of an element iso=same topos=place
has different number of neutrons
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Periodic Table Prof. Voss
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has no effect on chemical or electrical properties!
MASS NUMBER, A = n + p = no. of protons + no. of neutrons
used to specify isotopes
Neon 20: 10 p + 10 n
Neon 21: 10 p + 11 n
Neon 22: 10 p + 12 n
amu - Atomic Mass Unit
mass of one atom relative to the standard
CARBON-12 = 12.00000 amu
measured with Mass Spectrometer
Particle
Charge
Mass (amu)
Relative Mass
electron
-1
0.00055
1/1837
proton
+1
1.00728
1
neutron
0
1.00866
1
CarbonCarbon-12 has 6 protons and 6 neutrons, but
6×1.00728 + 6×1.00866 = 12.09564 amu > 12.00000 amu
A CarbonCarbon-12 nucleus has less mass than its parts.
What happened to the missing mass?
2
E = mc
energy ⇔ mass
STABLE NUCLEUS - lower mass (energy) than sum of parts
must add energy to break apart
UNSTABLE NUCLEUS - can gain energy by breaking apart
radioactive decay
a neutron has less mass than proton + electron
a free neutron decays to proton + electron
with a halfhalf-life of 10.3 min
a bound neutron in a nucleus is stable
ATOMIC MASS - weighted average of natural abundance
given as amu in Periodic Table
isotope
NeonNeon-20
NeonNeon-21
NeonNeon-22
amu
19.99
20.99
21.99
fraction
0.9092
0.0026
0.0822
1.0000
contribution
18.18
0.05
1.95
20.18 amu
Quantum (wave) Mechanics
successfully explained Periodic Table in terms of
Electronic Structure
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Periodic Table Prof. Voss
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how electrons arranged and interact outside nucleus
electron ⇒ wavelength
⇒ fundamental (resonant) frequencies
⇒ certain allowed energies
ENERGY LEVELS
2
Details from Schrödinger Equation ∇ Ψ = dΨ
dΨ/dt
like Maxwell's equations for electromagnetic waves
2
Ψ = wavefunction, |Ψ
|Ψ| = probability of finding particle
Heisenberg Uncertainty Principle ∆x∆p ~ h/2π
h/2π
if we know momentum p (energy) exactly
we can not know the exact position x ⇒ "electron cloud"
Pauli Exclusion Principle
no 2 electrons can have identical quantum numbers
Solutions labeled by 4 Quantum Numbers
n principal quantum number
main energy level
l angular momentum
sublevel l = 0 up to n
n--1
orbitals: s, p, d, f, ...
m magnetic quantum number
m = -l, ..., 0, ..., l
for l =1, m = -1, 0 , 1
px p y p z
l and m give shape
and orientation
of electron cloud
s spin quantum number
2 possible values
up or down
to find electronic structure
fill quantum states starting with lowest possible energy:
1s2
2s2 2p6
3s2 3p6
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Periodic Table Prof. Voss
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4s2 3d10 4p6
5s2 4d10 5p6
6s2 4f14 5d10 6p6
...
example:
11
Na has structure 1s2 2s2 2p6 3s1 = [Ne] 3s1 (2+2+6+1 = 11)
OUTER ELECTRONS
determine all chemical
and most physical
properties
via orbital shapes
filled outer shell ⇒ Inert or Noble gasses
chemical bonding tries to complete outer shell
Elements in same column (Group) have same outer shell
and similar chemical properties.
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