Chemistry Chapter 4Chemistry Chapter 4• Arrangement of Electrons in Arrangement of Electrons in
AtomsAtoms
The 1998 Nobel Prize in Physics was awarded "for the discovery of a new form of quantum fluid with fractionally charged excitations." At the left is a computer graphic of this kind of state.
Pop Quiz1. List one part of Dalton’s Atomic Theory that has
been disproven and explain the Modern Atomic Theory for that part.
2. Thompson and Millikan’s experiments led to conclusions about the electron. List one conclusion and why they made that conclusion.
3. How many protons, neutrons, and electrons does a neutral atom of Hydrogen-3 have?
The Puzzle of the AtomThe Puzzle of the Atom
The Rutherford model of the atom was an improvement over previous models, but it was incomplete.
Protons and electrons are attracted to each other because of opposite charges
Atoms have a positive center and negative surrounding
Despite these facts, atoms don’t collapse.
WHY??????
• In the early 1900’s, a new atomic model evolved as a result of investigations into the absorption and emission of light by matter.
• The study revealed an intimate relationship between light and atom’s electrons and began to explain how atom’s are organized.
• Visible light–A kind of electromagnetic
radiation.• Electromagnetic radiation is a form
of energy that exhibits wavelike behavior as it travels through space.
• A wave is a repetitive disturbance that propagates through space.
Electromagnetic Waves
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Amplitude is the distance from the baseline to a trough or a crest.
Wavelength () is the distance between corresponding points on adjacent waves.
Frequency () is defined as the number of waves that pass a given point in a specific
time, usually one second.
Electromagnetic radiation propagates through space as a wave moving at the speed of light.Therefore frequency, wavelength and the speed of light are mathematically related.
c = C = speed of light, a constant (3.00 x 108 m/s)
= frequency, in units of hertz (hz, sec-1)
= wavelength, in meters
http://www.colorado.edu/physics/2000/waves_particles/lightspeed-1.html
Practice Problem
Determine the frequency of light with a wavelength of 4.257 × 10-7 cm.
Prism analysis of the visible Prism analysis of the visible spectrum pspectrum produces all of the
colors in a continuous spectrum
Visible Light is a form a Visible Light is a form a electromagnetic radiation.electromagnetic radiation.
Between 400 nanometers to 700 nanometers
Refraction of White Light
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Types of electromagnetic radiation:The Electromagnetic Spectrum.
http://www.colorado.edu/physics/2000/waves_particles/index.html
The Photoelectric Effect
• Observed in the early 1900’s and explained light as a particle.
• Refers to the emission of electrons from a metal when light shines on the metal.– For a given metal, no electrons were
emitted if the light’s frequency was below a certain minimum.
Photoelectric Effect
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The Photoelectric Effect
• Max Planck proposed that a hot object does not emit electromagnetic energy continuously, but in packets called quanta.– Quanta is the minimum quantity of energy
that can be lost or gained by an atom.– Later Albert Einstein called these particles
photons.• A photon is a particle of electromagnetic
radiation having zero mass and carrying a quantum of energy.
E = h E = Energy, in units of Joules (kg·m2/s2)
h = Plank’s constant (6.626 x 10-34 J·s)
= frequency, in units of hertz (hz, sec-1)
Through experiment Plank determined that the energy (E ) of electromagnetic radiation is directly proportional to the frequency () of the radiation.
Quick Review
• Wavelength is inversely proportional to frequency.
• Frequency is directly proportional to Energy.
Long Wavelength
= Low Frequency
= Low ENERGY
Short Wavelength
= High Frequency
= High ENERGY
Wavelength TableWavelength Table
Practice Problem
Determine the energy in joules of a photon whose frequency is 3.55 × 1017 Hz.
The Hydrogen-Atom Line-The Hydrogen-Atom Line-Emission SpectrumEmission Spectrum
• When current is passed through gas at low pressure, the potential energy of some of the gas atoms increases. • Atoms increased from the ground state (the lowest energy state level of an atom) to an excited state (a state in which the atom has a higher potential energy than the ground state).
The Hydrogen-Atom Line-The Hydrogen-Atom Line-Emission SpectrumEmission Spectrum
• When an excited atom returns to its ground state, it gives off the energy it gained in the form of light.–Neon Signs.
…produces a line-emission spectrum
Prism analysis of the hydrogen spectrum…
…produces a line-emission spectrum
Prism analysis of the hydrogen spectrum…
Bohr Model of the Hydrogen Atom
http://www.colorado.edu/physics/2000/quantumzone/lines2.html
Pop Quiz1. Isotopes of the same element have the same
number of _________ and different numbers of ________.
2. If a wave has a long wavelength, how would you describe the frequency and energy?
3. How many protons, neutrons, and electrons does a neutral atom of Hydrogen-1 have?
4. Describe either Heisenberg Uncertainty Principle or Pauli Exclusion Principle.
The Bohr Model of the AtomThe Bohr Model of the Atom
Neils Bohr
I pictured electrons orbiting the nucleus much like planets orbiting the sun.But I was wrong! They’re more like bees around a hive.
WRONG!!!
Heisenberg Uncertainty Heisenberg Uncertainty PrinciplePrinciple
You can find out where the electron is, but not where it is going.OR…You can find out where the electron is going, but not where it is!
“One cannot simultaneously determine both the position and momentum of an electron.”
Werner Heisenberg
Quantum NumbersQuantum Numbers
Each electron in an atom has a unique set of 4 quantum numbers which describe it.
Principal quantum number Angular momentum quantum number Magnetic quantum number Spin quantum number
Pauli Exclusion PrinciplePauli Exclusion Principle
No two electrons in an atom can have the same four quantum numbers.
Wolfgang Pauli
Principal Quantum NumberPrincipal Quantum Number
Generally symbolized by n, it denotes the shell (energy level) in which the electron is located. Number of electrons that can fit in a shell:
2n2
Energy level 2 = 2(2)2 = 8 electrons
Angular Momentum Angular Momentum Quantum NumberQuantum Number
The angular momentum quantum
number, generally symbolized by l, denotes the orbital shape (subshell) in which the electron is located.
l Letter0 s1 p2 d3 f
Schrodinger Wave EquationSchrodinger Wave Equation
22
2 2
8dh EV
m dx
Equation for probabilityprobability of a single electron being found along a single axis (x-axis)
Erwin Schrodinger
http://www.colorado.edu/physics/2000/quantumzone/schroedinger.html
Orbital shapes are defined as the surface that contains 90% of the total electron probability.
An orbital is a region within an atom where there is a probability of finding an electron.
Magnetic Quantum NumberMagnetic Quantum Number
The magnetic quantum number, generally symbolized by m, denotes the orientation of the electron’s orbital with respect to the three axes in space.
s orbital shape
PP orbital shape orbital shape
d orbital shapes
Shape of f orbitalsShape of f orbitals
Assigning the NumbersAssigning the Numbers The three quantum numbers (n, l, and m) are integers. The principal quantum number (n) cannot be zero. n must be 1, 2, 3, etc. The angular momentum quantum number (l) can be any integer between 0 and n - 1. For n = 3, l can be either 0, 1, or 2. The magnetic quantum number (m) can be any integer between -l and +l. For l = 2, m can be either -2, -1, 0, +1, or +2.
Principle, angular momentum, and Principle, angular momentum, and magnetic quantum numbers: magnetic quantum numbers: nn, , ll, ,
and and mmll
Spin Quantum NumberSpin Quantum Number
Spin quantum number denotes the behavior (direction of spin) of an electron within a magnetic field.Possibilities for electron
spin: 1
2
1
2
1
2
1
2
Electron Configurations
• The arrangement of electrons in an atom.
• Since atoms of different elements have different numbers of electrons, a distinct electron configuration exists for the atoms of each element.
Electron Configurations
• Three Rules for adding electrons to orbitals:– Aufbau principle – an electron occupies the
lowest-energy orbital available.– Pauli exclusion principle – no two electrons
in the same atom can have the same set of four quantum numbers.
– Hund’s rule- One electron enters each orbital of equal energy until all orbitals contain one electron & all electrons in singly occupied orbitals must have the same spin.
Electron Configurations
• There are 3 ways to write electron configurations:–Orbital Notation
–Electron-Configuration Notation
–Nobel-Gas Notation
Aufbau principle
• an electron occupies the lowest-energy orbital available.
Orbital filling tableOrbital filling table
Pauli exclusion principle
• no two electrons in the same atom can have the same set of four quantum numbers
Orbital
Electronor
He
1s Whichorbital?
Orbital Notation
Electron-Configuration Notation
• Eliminates the lines and arrows.
• The number of e- in a sublevel is shown by adding a superscript to the sublevel designation.
• So for He…… He
1s
We rewrite He as 1s2 where 1 represents the energy level, s represents the orbital shape and 2 represents the number of electrons
1s2
Hund’s Rule
• One electron enters each orbital of equal energy until all orbitals contain one electron & all electrons in singly occupied orbitals must have the same spin.
N1s 2s 2p
Orbital Notation
Electron-Configuration Notation: 1s 2s 2p2 2 3
Practice
Si
Be
P
1s 2s 2p 3s 3p
1s 2s
1s 2s 2p 3s 3p
1s 3p2s 2p 3s
1s
2 2 26 2
2s2 2
1s 3p2s 3s2 2 26 3
2p
Practice
Kr1s 2s 2p 3s
4p
4s
3d
3p
1s 3p2s 3s2 2 26 6
2p 4s 3d 4p2 10 6
Irregular confirmations of Cr and CuIrregular confirmations of Cr and Cu
Chromium steals a 4s electron to half fill its 3d sublevel
Copper steals a 4s electron to FILL its 3d sublevel
1s 2s 2p 3s 4s
3d
3p
Cr
Cu1s 2s 2p 3s 4s
3d
3p
Pop Quiz
• Please write the orbital notation and electron configuration for Gold.
• Define the four quantum numbers and describe how to find the first three.
Nobel-Gas Notation
• Simplifies electron-configuration notation
• For example: P
1s 3p2s 3s2 2 26 3
2pP
Ne 1s 2s2 2 6
2p
[Ne] 3s23p3
