Chemistry Chapter 4 Chemistry Chapter 4 • Arrangement of Electrons in Arrangement of Electrons in Atoms Atoms The 1998 Nobel Prize in P hysics 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.
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Chemistry Chapter 4 Arrangement of Electrons in AtomsArrangement of Electrons in Atoms The 1998 Nobel Prize in Physics was awarded "for the discovery.
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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.
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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)
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Types of electromagnetic radiation:The Electromagnetic Spectrum.
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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.
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.