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Chapter 4. Arrangement of Electrons in Atoms. Light. A kind of electromagnetic radiation A form of energy that exhibits wavelike behavior as it travels through space. Electromagnetic Spectrum. Frequency. The number of wave peaks that occur in a given time period

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chapter 4

Chapter 4

Arrangement of Electrons in Atoms

Chemistry chapter 4

light
Light
  • A kind of electromagnetic radiation
    • A form of energy that exhibits wavelike behavior as it travels through space

Chemistry chapter 4

electromagnetic spectrum
Electromagnetic Spectrum

Chemistry chapter 4

frequency
Frequency
  • The number of wave peaks that occur in a given time period
  • Represented by the letter f or the greek letter nu (n).
  • One wave per second is 1 Hertz (Hz).

Chemistry chapter 4

wavelength
Wavelength
  • The distance between peaks
  • Measured in length units such as m or nm.
  • Represented by the letter l (lambda)

Chemistry chapter 4

frequency and wavelength
Frequency and wavelength

Chemistry chapter 4

the speed of light
The speed of light
  • c is the speed of light (and all electromagnetic waves)
    • It’s value is 3.0 x 108 m/s
  • Frequency and wavelength are related by the equation
    • c = lf

Chemistry chapter 4

photoelectric effect
Photoelectric effect
  • The emission of electrons from a metal when light shines on the metal
  • Only works when the light is above a certain frequency.

Chemistry chapter 4

planck s hypothesis
Planck’s Hypothesis
  • Quantum – the smallest amount of energy that can be lost or gained by an atom.
  • Quanta of radiant energy are called photons.
  • E=hf
  • h= 6.63 x 10-34 J∙s

Chemistry chapter 4

wave particle duality
Wave-Particle Duality
  • Introduced by Einstein in 1905
  • Light exhibits particle-like properties as well as wave-like ones.

Chemistry chapter 4

photon
Photon
  • Particle of electromagnetic radiation that has zero mass and carries a quantum of energy.

Chemistry chapter 4

photoelectric effect1
Photoelectric effect
  • Einstein explained
  • In order for an electron to be knocked loose, it must be struck by a single photon with a high enough energy.
  • This requires a high enough frequency.

Chemistry chapter 4

ground state
Ground State
  • The lowest energy state of an atom

Chemistry chapter 4

excited state
Excited State
  • A state in which an atom has a higher potential energy than its ground state.
  • When an atom returns to its ground state, it gives of the extra energy as EM radiation.

Chemistry chapter 4

continuous spectrum
Continuous spectrum
  • Continuous range of frequencies (colors)
  • Expected from classical theory

Chemistry chapter 4

line emission spectrum
Line-emission spectrum
  • Separated bands of light
  • Have different frequencies
  • Produced by passing light through a thin slit.
  • Different elements have different spectra.

Chemistry chapter 4

bohr model
Bohr model
  • Used quantum theory to explain line spectra.
  • Electrons only exist in specific energy states called orbitals.
  • Since the change in energy from one state to another is fixed, only certain frequencies are emitted.

Chemistry chapter 4

bohr model1
Bohr model
  • Successful for the hydrogen atom
  • Needs tweaking for other atoms

Chemistry chapter 4

de broglie hypothesis
De Broglie hypothesis
  • 1923
  • Louis De Broglie’s dissertation
  • Planck’s quantum theory implied that light, which had formerly been thought of as a wave, behaves as a particle.
  • De Broglie hypothesized that the reverse is true.

Chemistry chapter 4

interference
Interference
  • Occurs when waves overlap
  • Results in a reduction of energy in some areas and an increase of energy in others

Chemistry chapter 4

slide22

A two-slit light diffraction-interference pattern

A two-slit electron diffraction-interference pattern

Chemistry chapter 4

slide26
Chemistry chapter 4

An electron microscope

heisenberg
Heisenberg
  • Pointed out that it is impossible to know both the exact position and the exact momentum of an object at the same time.
  • By measuring one, we change the other.

Chemistry chapter 4

measuring position
Measuring position
  • If we measure the position of an object by hitting it with a photon of energy, the collision with the photon changes its momentum.

Chemistry chapter 4

measuring momentum
Measuring momentum
  • If we measure an objects momentum by observing its collision with another object, we have altered its position.

Chemistry chapter 4

schr dinger
Schrödinger
  • Heisenberg treated the electron as a particle.
  • Schrödinger treated it as a wave
  • Formulated a difficult wave equation with solutions called wave functions

Chemistry chapter 4

quantum theory
Quantum theory
  • Describes mathematically the wave properties of electrons and other very small particles

Chemistry chapter 4

probability
Probability
  • Wave functions only give the probability of finding an electron at a given place
  • Electrons don’t travel in neat orbits
  • “God doesn’t play dice” - Einstein

Chemistry chapter 4

orbital
Orbital
  • A 3D region around the nucleus that indicates the probable location of an electron

Chemistry chapter 4

discuss
Discuss
  • What is quantum theory?
  • What radical new idea did de Broglie introduce?
  • What is interference?

Chemistry chapter 4

slide36
Omaha zip codes
  • 681 -

Chemistry chapter 4

four quantum numbers
Four quantum numbers
  • Specify the properties of atomic orbitals and the properties of electrons in orbitals
  • Each electron in an atom has a unique set of quantum numbers

Chemistry chapter 4

principal quantum number n
Principal quantum number, n
  • Indicates the main energy level occupied by the electron
  • Start numbering with 1 at the level closest to the nucleus.

Chemistry chapter 4

electrons in a given level
Electrons in a given level
  • The greatest number of electrons that can be in a given level is calculated by the formula 2n2.
  • So, in the first level there can be 2 ∙ 12 = 2 electrons.

Chemistry chapter 4

the angular momentum quantum number l
The angular momentum quantum number, l
  • Indicates the shape of the orbital
  • Allowed values: 0, 1, 2, … n – 1

Chemistry chapter 4

s orbital
s orbital
  • When l = 0
  • spherical

Chemistry chapter 4

p orbital
p orbital
  • When l = 1
  • Dumbbell shaped

Chemistry chapter 4

d orbital
d orbital
  • When l = 2
  • More complex

Chemistry chapter 4

f orbital
f orbital
  • When l = 3
  • Too complex for this class

Chemistry chapter 4

sublevels
Sublevels
  • Each orbital is designated by the principal quantum number and the orbital letter.
  • Examples:
    • 1s
    • 2p
    • 4f

Chemistry chapter 4

magnetic quantum number m
Magnetic quantum number, m
  • Indicates the orientation of an orbital around the nucleus
  • Allowed values: -l to l

Chemistry chapter 4

s orbital1
s orbital
  • Each s sublevel only has one s orbital
  • m = 0

Chemistry chapter 4

p orbitals
p orbitals
  • Each p sublevel has 3 different p orbitals
  • m = -1, m = 0, m = 1

Chemistry chapter 4

d orbitals
d orbitals
  • There are 5 different d orbitals in each d sublevel
  • m = -2, m = -1, m = 0, m = 1, m = 2

Chemistry chapter 4

spin quantum number
Spin quantum number
  • Has only two values, + ½ and – ½
  • Indicate the two fundamental spin states of an electron
  • Spin up or spin down

Chemistry chapter 4

discussion
Discussion
  • Study table 4-2 on page 104
  • Answer the section review questions on that page.

Chemistry chapter 4

electron configuration
Electron configuration
  • The arrangement of electrons in an atom
  • Each element has its own unique one.

Chemistry chapter 4

ground state configuration
Ground-state configuration
  • Has the lowest energy
  • All systems in nature tend to be in lowest energy state.
  • We can determine the ground-state configuration with rules

Chemistry chapter 4

aufbau principle
Aufbau principle
  • An electron occupies the lowest-energy orbital that can receive it.
  • For the order, see page 105 or the chart on the wall.
  • 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p

Chemistry chapter 4

orbital filling diagram
Orbital filling diagram
  • This diagram is on your objectives sheet.

Chemistry chapter 4

pauli exclusion principle
Pauli exclusion principle
  • No two electrons in the same atom have the same set of four quantum numbers.
  • The principal, angular momentum and magnetic quantum numbers specify the orbital.
  • The spin number specifies the electron.
  • Each orbital can hold two electrons.

Chemistry chapter 4

hund s rule
Hund’s rule
  • Orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron.
  • All single electrons must have the same spin.

Chemistry chapter 4

orbital notation
Orbital notation
  • An unoccupied orbital is represented by a line, ___, with the orbital’s name written under the line.
  • An orbital containing an electron is written as ↑ .
  • An orbital containing two electrons is written as ↑↓ .

Chemistry chapter 4

electron configuration notation
Electron-configuration notation
  • Uses superscripts instead of arrows.
  • The superscript 1 indicates 1 electron in the sublevel.
  • The superscript 2 indicates 2 electrons in the sublevel.

Chemistry chapter 4

hydrogen

1s

Hydrogen
  • One electron.

H

Configuration: 1s1

Chemistry chapter 4

helium

1s

Helium
  • Two electrons.

He

1s2

Chemistry chapter 4

lithium

1s

2s

Lithium
  • Three electrons.

Li

1s22s1

Chemistry chapter 4

carbon

2s

1s

2p

Carbon
  • Six electrons.

C

1s22s22p2

Chemistry chapter 4

oxygen

1s

2s

2p

Oxygen
  • Eight electrons.

O

1s22s22p4

Chemistry chapter 4

discuss1
Discuss
  • What is an atom’s electron configuration?
  • What three principles guide the electron configuration of an atom?

Chemistry chapter 4

discuss2
Discuss
  • The electron configuration of fluorine is 1s22s22p5. How many electrons does fluorine have? What is its atomic number?
  • Write the electron configuration of sulfur, which has an atomic number of 16.

Chemistry chapter 4

highest occupied level
Highest occupied level
  • The highest n level that contains an electron.

Chemistry chapter 4

inner shell electrons
Inner-shell electrons
  • Aren’t in the highest occupied level

Chemistry chapter 4

octet
octet
  • The 8 electrons (or electron spaces) in the highest occupied level.
  • The s and p orbitals.
  • If they are all occupied, then the octet is full.

Chemistry chapter 4

noble gases
Noble Gases
  • Group 18 elements
  • Have a full octet

Chemistry chapter 4

noble gas notation
Noble Gas notation
  • Shorthand for electron-configuration.
  • Start with the noble gas from the period above, then add on.
  • Example: magnesium
    • 1s22s22p63s2
    • [Ne]3s2

Chemistry chapter 4

you try
You try
  • Write the electron configuration and noble gas notations for titanium
  • 1s22s22p63s23p63d24s2
  • [Ar] 3d24s2
  • Notice that we write the 3d sublevel before the 4s, even though the 4s fills first

Chemistry chapter 4

you try1
You try
  • Write the electron configuration and noble gas notations for copper
  • 1s22s22p63s23p63d104s1
  • [Ar]3d104s1

Chemistry chapter 4

exceptions to the rules
Exceptions to the rules
  • An electron will leave the 4s orbital to create a half-filled or a filled 3d sublevel.
  • This configuration is more stable.
  • Chromium [Ar]3d54s1

Chemistry chapter 4

exceptions to the rules1
Exceptions to the rules
  • Sometimes an electron will leave the 5s sublevel to go to the 4d sublevel. This makes the atom more stable.
  • There isn’t a pattern like the 4s to 3d switch.

Chemistry chapter 4

discuss3
Discuss
  • Write the noble-gas notation for aluminum.
    • [Ne]3s23p1
  • How many outer-shell electrons does an atom of aluminum have?
    • 3
  • How many unpaired electrons does an atom of aluminum contain?
    • 1

Chemistry chapter 4

extra credit
Extra Credit
  • Write a paragraph explaining how you can use the periodic table to determine the order in which orbitals are filled. Your explanation should include references to group and period numbers. Worth up to 10 extra credit points.

Chemistry chapter 4