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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


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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
  • Due on test day

Chemistry chapter 4