Atomic Structure & Electron Configuration
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Transcript of Atomic Structure & Electron Configuration
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Atomic Structure & Electron Configuration
Ch.3
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(3-1) Atomic Theory
• All matter is composed of indivisible particles called atoms
• Certain characteristics shared by all chemical cmpds
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Law of Definite Proportions
• Any sample of a cmpd always has the same composition (by mass)– Ex: NaCl always 39% Na & 61% Cl
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Law of Conservation of Mass
• Product mass = reactant mass– Ex: S + O2 SO2
sulfur oxygen sulfur dioxide
32.07 amu 32.00 amu 64.07 amu
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Law of Multiple Proportions
• Mass ratio for combining 1 element w/ another are expressed in small whole #’s– Ex: NO2
NO
N2O
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Dalton’s Atomic Theory
1. Matter is made of indivisible & indestructible atoms
2. Atoms of a given element are identical in their properties
3. Atoms of different elements differ in their properties
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Dalton’s Atomic Theory
4. Atoms of different elements combine in simple whole-# ratios to form cmpds
5. Chemical rxns consist of the combination, separation, or rearrangement of atoms.
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Modifications to Dalton’s Theory
• 2 principles no longer valid – subatomic particles– overlooked atoms combining w/ their own
type
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Atomic Mass
• p+ + n0 (e- mass negligible)
• Units: atomic mass units (amu)
• Exactly 1/12 the mass of 1 carbon-12 atom
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Atomic Mass to Kg
• 1 amu = 1.66 x 10-27 kg
• Mass of copper atom:
63.546 amu x 1.66 x 10-27 kg = 1.06 x 10-25 kg
1 amu
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Mole
• (mol): amt of substance
• Avogadro’s constant: 6.02 x 1023 particles
1 mol
• 1 g/mol = 1 amu
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Mass & Moles
• Mass of 1 mol of Fluorine atoms:
18.9984 amu x 1.66 x 10-27 kg x 1000 g
1 amu 1 kg
x 6.02 x 1023 = 18.9984 g/mol
1 mol
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(3-2) Subatomic Particles
• Smaller particles that make up an atom
• 3 types
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Particle Location Size Charge
Electron (e-)
Outside nucleus
0.000 549 amu
Negative
Proton
(p+)
Nucleus 1.007 amu
Positive
Neutron (n0)
Nucleus 1.009 amu
Neutral
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Electrodes
• Anode: where e- enter a metal; + charge
• Cathode: where e- leave a metal; -charge
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Cathode Ray Tube Experiment
• J.J. Thomson– e- had mass– e- had negative charge
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Nucleus
• Central region of an atom containing p+ & n0
• Plum-pudding model: Thomson– e- embedded in positively charged ball of
matter
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Gold Foil Experiment
• Ernest Rutherford
• Alpha particles: + charged particles– dense nucleus w/ lots of empty space
around it
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Atomic Number
• # of p+ in the nucleus of an atom
• Mass #: total # of p+ & n0 in the nucleus
• 42He: mass # = 4, atomic # = 2
– 2 p+, 2 n0, 2 e-
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Coulomb’s Law
• The closer 2 charges come together, the greater the force b/w them
• Opposites attract, likes repel
• Strong force: greater than repulsive force at close distance– p+ in nucleus
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Isotopes
• Atoms of the same element w/ different #’s of n0
– Ex: Helium-3 (1n, 2p), Helium-4 (2n, 2p)
• Radioisotope: unstable atom that undergoes radioactive decay
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(3-3) Electromagnetic Spectrum
• Total range of electromagnetic radiation– e- have properties of both particles &
waves
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Wavelength
• λ: distance b/w 2 consecutive peaks or troughs– m
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Frequency
• v : # of waves that pass a stationary pt. in 1 sec.– Hz
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Speed of Light
• c = 3.0 x 108 m/s
• Speed of light = freq. x wavelength
c = v λ
– Ex: v = _c_ = 3.0 x 108 m/s
λ 7.6 x 10-7 m
= 3.9 x 1014 /s = 3.9 x 1014 Hz
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Line-emission Spectrum
• Distinct lines of colored light produced by excited atoms of an element passing through a prism
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Quantum Theory
• Tells exact E of the e-, but only the probability that the e- is in a particular region– Quantized
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Quantum #’s
• Principal (n): 1-7, E level e- is located
• Shape: sublevel w/in E level
• Orientation: orbital w/in sublevel
• Spin: +1/2, -1/2
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Bohr’s Atomic Model
• Describes e- in terms of their E states– Ground state: lowest E state– Excited state: higher E state than ground
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Orbitals
• Regions of space where you can expect to find e- of specific E
• s (sphere), p (dumb-bell), d, f
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The “1s” orbital is asphere,centeredaround the nucleus
The 2s electrons have a higher energy than the 1selectrons. Therefore, the 2selectrons are generally moredistant from the nucleus,making the 2s orbital largerthan the 1s orbital.
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The three 2porbitals,2px, 2py, 2pz
x
y
z
so 3s electrons aregenerally foundfurther from thenucleus than 1s,2s, or 2p electrons
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Pauli Exclusion Principle
• No more than 2 e- can occupy a single orbital & must have different spins
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Electron Configuration
• Description of occupied e- orbitals in an atom
• s (1 orbital), p (3), d (5), f (7)
• F: 1s22s22p5
• Main E level, orbital, # of e-
s p
s
d
f
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Orbital Diagrams
• Similar to e- config. but lines designate orbitals and arrows designate e-– __ __ __ __ __
1s 2s 2p
http://www.colorado.edu/physics/2000/applets/a2.html
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Aufbau Principle
• Lowest & most stable E levels filled first– 4s before 3d
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Hund’s Rule
• Orbitals are occupied by 1 e- before any pairing occurs
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Noble Gas Configuration
• Electron Config.: S: 1s22s22p63s23p4
• Noble Gas Config.: S: [Ne]3s23p4
• Unless specified do not use noble gas configuration!!!!