Chapter 4 Arrangement of Electrons in Atoms. New Atomic Model Rutherford model incomplete Early...

Chapter 4Chapter 4

Arrangement of Electrons in Atoms

New Atomic ModelNew Atomic Model

Rutherford model incomplete Early twentieth century-new

atomic model emerged Scientists noticed a relationship

between electrons and light

Rutherford model incomplete Early twentieth century-new

atomic model emerged Scientists noticed a relationship

between electrons and light

Properties of LightProperties of Light

Light behaves as a wave and a particle Wave description

Visible light is a kind of electromagnetic radiation

All forms of ER move at a speed of 3.0 X 108 m/s (vacuum)

Light behaves as a wave and a particle Wave description

Visible light is a kind of electromagnetic radiation

All forms of ER move at a speed of 3.0 X 108 m/s (vacuum)

B. EM SpectrumB. EM Spectrum

ENERGY

R O Y G. B I V

red orange yellow green blue indigo violet

WavesWaves

Wavelength (λ) is the distance between corresponding points on adjacent waves. Measured in distance (visible 400-700 nm)

Frequency (ν) is defined as the number of waves that pass a given point in a specific time, usually one second.

One wave per second or wave/second is called a Hertz (Hz)

Wavelength (λ) is the distance between corresponding points on adjacent waves. Measured in distance (visible 400-700 nm)

Frequency (ν) is defined as the number of waves that pass a given point in a specific time, usually one second.

One wave per second or wave/second is called a Hertz (Hz)

C=λν Frequency and wavelength are

inversely related The longer the wave the less go by

per second (if speed remains constant)

C=λν Frequency and wavelength are

inversely related The longer the wave the less go by

per second (if speed remains constant)

GIVEN:

ν = ?

λ = 434 nm = 4.34 10-7 m

c = 3.00 108 m/s

WORK:ν = c λ

ν = 3.00 108 m/s 4.34 10-7 m

ν = 6.91 1014 Hz

EX: Find the frequency of a photon with a wavelength of 434 nm.

The photoelectric effectThe photoelectric effect

Refers to the emission of electrons from a metal when light shines on the metal (see clip)

Max Planck was studying the emission of light by hot objects.

Theorized that the objects emit energy in small, specific packets called quanta.

Refers to the emission of electrons from a metal when light shines on the metal (see clip)

Max Planck was studying the emission of light by hot objects.

Theorized that the objects emit energy in small, specific packets called quanta.

Albert Einstein expanded on Planck’s theory

Proposed ER has a dual wave-particle nature

Exhibits wavelike properties and can be thought of as a stream of particles

Albert Einstein expanded on Planck’s theory

Proposed ER has a dual wave-particle nature

Exhibits wavelike properties and can be thought of as a stream of particles

Each particle of light carries a quantum of energy.

Einstein called them photons A photon is a particle of ER having

zero mass and carrying a quantum of energy.

Each particle of light carries a quantum of energy.

Einstein called them photons A photon is a particle of ER having

zero mass and carrying a quantum of energy.

Einstein explained photoelectric effect by stating ER is absorbed by matter in whole numbers of photons.

To shoot off an electron ER must have enough energy according to Planck’s equation.

Einstein explained photoelectric effect by stating ER is absorbed by matter in whole numbers of photons.

To shoot off an electron ER must have enough energy according to Planck’s equation.

Photoelectric effect

Photoelectric effectPhotoelectric effect

Photoelectric effect proved light behaves like a particle

Proved light’s dual nature

Photoelectric effect proved light behaves like a particle

Proved light’s dual nature

QuickTime™ and a decompressor

are needed to see this picture.

A quantum of energy is the minimum quantity of energy that can be lost or gained by an atom.

Planck proposed the following: E = hν Planck’s constant; h = 6.626 X 10-

34 J•s

A quantum of energy is the minimum quantity of energy that can be lost or gained by an atom.

Planck proposed the following: E = hν Planck’s constant; h = 6.626 X 10-

34 J•s

GIVEN:

E = ?ν = 4.57 1014 Hzh = 6.6262 10-34 J·s

E = hν

E=(6.626210-34J·s)(4.571014 Hz)

E = 3.03 10-19 J

EX: Find the energy of a red photon with a frequency of 4.57 1014 Hz.

Hydrogen-Atom Line-Emission Spectrum

When an electrical current is passed through a gas at low pressure, the potential energy of some of the gas’s electrons increase.

The lowest energy state of an electron is called its ground state.

A state in which an electron has a higher potential energy that it has in its ground state is an excited state.

When an electrical current is passed through a gas at low pressure, the potential energy of some of the gas’s electrons increase.

The lowest energy state of an electron is called its ground state.

A state in which an electron has a higher potential energy that it has in its ground state is an excited state.

Current passed through hydrogen gas gives a characteristic pinkish glow.

When the light was placed in a prism, four characteristic colors emerged.

Called the Hydrogen-Atom Line Emission Spectrum

Current passed through hydrogen gas gives a characteristic pinkish glow.

When the light was placed in a prism, four characteristic colors emerged.

Called the Hydrogen-Atom Line Emission Spectrum

QuickTime™ and aTIFF (Uncompressed) decompressor

Hydrogen emission spectra

Puzzle of the Hydrogen Atom Spectrum

Niels Bohr theorized that electrons can circle the nucleus only in allowed paths called orbits.

Orbits can be compared to rungs on a ladder--> electrons can be in one orbit or another but not in between.

Niels Bohr theorized that electrons can circle the nucleus only in allowed paths called orbits.

Orbits can be compared to rungs on a ladder--> electrons can be in one orbit or another but not in between.

ExplanationExplanation

Electrons can move to a higher-energy orbit by gaining energy

This process is called absorption. When the electron falls back down

to a lower energy a photon of ER is emitted.

The process is called emission. The energy of each photon

corresponds to a specific frequency (E=hv)

Electrons can move to a higher-energy orbit by gaining energy

This process is called absorption. When the electron falls back down

to a lower energy a photon of ER is emitted.

The process is called emission. The energy of each photon

corresponds to a specific frequency (E=hv)

Explanation (cont’d)Explanation (cont’d)

Bohr related the possible energy-level changes to the lines in the hydrogen emission spectrum.

Energy-level changes are named after the scientists that discovered them

Bohr related the possible energy-level changes to the lines in the hydrogen emission spectrum.

Energy-level changes are named after the scientists that discovered them

Lyman seriesLyman series

Electron falls to the first energy level

Emits Ultraviolet radiation

Electron falls to the first energy level

Emits Ultraviolet radiation

Balmer seriesBalmer series

Electron falls to the second energy level

Emits visible light Discovered first (1885)

Electron falls to the second energy level

Emits visible light Discovered first (1885)

Paschen seriesPaschen series

Electron falls to the third energy level

Emits infrared radiation

Electron falls to the third energy level

Emits infrared radiation

Bohr’s model worked well for Hydrogen.

Didn’t work for any other element. Why?

Bohr’s model worked well for Hydrogen.

Didn’t work for any other element. Why?

Flame testsFlame tests

Flame tests are also used as a qualitative test for elements

When metals are heated the electrons enter the excited state, drop down to the ground state, and emit ER

Flame tests are also used as a qualitative test for elements

When metals are heated the electrons enter the excited state, drop down to the ground state, and emit ER

Lithium salts (ionic) give a red color

Sodium salts give a yellow color

Potassium salts give a lilac (purple) color

Lithium salts (ionic) give a red color

Sodium salts give a yellow color

Potassium salts give a lilac (purple) color

Copper salts - green

Strontium - crimson red

Barium - yellowish-green

Copper salts - green

Strontium - crimson red

Barium - yellowish-green

These are the chemicals that are used in fireworks to

give color.

Watch.

Quantum Model of the Atom

Bohr’s model didn’t make sense to scientists.

Why can electron’s only exist in certain energy levels?

Scientists began to think of electrons as waves

Bohr’s model didn’t make sense to scientists.

Why can electron’s only exist in certain energy levels?

Scientists began to think of electrons as waves

Electrons as wavesElectrons as waves

Light can exist as a wave and a particle

Why can’t electrons? 1924 Louis de Broglie suggested

electrons do behave as waves They follow the E=hv equation Electrons also show diffraction

pattern and interference patterns

Light can exist as a wave and a particle

Why can’t electrons? 1924 Louis de Broglie suggested

electrons do behave as waves They follow the E=hv equation Electrons also show diffraction

pattern and interference patterns

Electrons as wavesElectrons as waves

Diffraction refers to the bending of a wave as it passes by the edge of an object or through a small opening.

Interference occurs when waves overlap. It results in a reduction of in energy in some areas.

Diffraction refers to the bending of a wave as it passes by the edge of an object or through a small opening.

Interference occurs when waves overlap. It results in a reduction of in energy in some areas.

Heisenberg Uncertainty Principle

States that it is impossible to determine simultaneously both the position and velocity of an electron or any other particle.

Because photons have about the same energy as electron, any attempt to locate the electron with a photon knocks the electron off course.

States that it is impossible to determine simultaneously both the position and velocity of an electron or any other particle.

Because photons have about the same energy as electron, any attempt to locate the electron with a photon knocks the electron off course.

Schrodinger’s Wave Equation

1926 Austrian physicist Erwin Scrödinger used Heisenberg’s principle to develop a mathematical equation to explain electron behavior.

Quantum theoryQuantum theory

Heisenberg and Schrödinger’s work paved laid foundation for modern quantum theory.

Quantum theory describes mathematically the wave properties of electrons and other very small particles.

Heisenberg and Schrödinger’s work paved laid foundation for modern quantum theory.

Quantum theory describes mathematically the wave properties of electrons and other very small particles.

Atomic Orbitals and Quantum NumbersAtomic Orbitals and Quantum Numbers

Scientists use Quantum numbers to specify the properties of atomic orbitals and the properties of electrons in orbitals.

The first three quantum numbers indicate the main energy level, the shape, and the orientation of an orbital.

The fourth, the spin quantum number, describes the state of the electron in the orbital.

Scientists use Quantum numbers to specify the properties of atomic orbitals and the properties of electrons in orbitals.

The first three quantum numbers indicate the main energy level, the shape, and the orientation of an orbital.

The fourth, the spin quantum number, describes the state of the electron in the orbital.

Principal quantum numberPrincipal quantum number

Symbolized by n Indicates the main energy level

occupied by the electron. Whole numbers The lower the n value the closer to

the nuclues Ex/ n=1 n=2 n=3

Symbolized by n Indicates the main energy level

occupied by the electron. Whole numbers The lower the n value the closer to

the nuclues Ex/ n=1 n=2 n=3

Angular Momentum Quantum Number

Symbolized by l Orbitals of different shapes exist-

known as sublevels The angular momentum quantum

number indicates the shape

Symbolized by l Orbitals of different shapes exist-

known as sublevels The angular momentum quantum

number indicates the shape

Indicates the shape 4 shapes --> s, p, d, f l = 0 indicates s shape l = 1 indicates p shape l = 2 indicates d shape l = 3 indicates?

s shape is spherical, it is the only sublevel possible in the first energy level (n=1)

p sublevel is in a “dumbbell” shape

Available in the 2nd energy level (n=2)

p sublevel is in a “dumbbell” shape

Available in the 2nd energy level (n=2)

d orbital available in the 3rd energy level

Shape more complex

d orbital available in the 3rd energy level

Shape more complex

f shape available in 4th energy level

Magnetic Quantum Number

Atomic orbitals can have the same shape but different orientations around the nucleus.

Magnetic quantum number- symbolized by m, indicates the orientation of an orbital around the nucleus in the xyz axis.

Atomic orbitals can have the same shape but different orientations around the nucleus.

Magnetic quantum number- symbolized by m, indicates the orientation of an orbital around the nucleus in the xyz axis.

s orbitals are spherical it can only have one orientation

p orbitals can have three orientations along the xyz axis.

d orbitals can have five different orientations

f can have 7 different orientations

s orbitals are spherical it can only have one orientation

p orbitals can have three orientations along the xyz axis.

d orbitals can have five different orientations

f can have 7 different orientations

Different orientations can occur simultaneously

A single orbital can hold a maximum of two electrons

Different orientations can occur simultaneously

A single orbital can hold a maximum of two electrons

Shape # orbitals max electrons first found

s 1 2 n=1

p 3 6 n=2

d 5 10 n=3

f 7 14 n=4

Spin Quantum NumberSpin Quantum Number

An electron in an orbital behaves like a planet spinning on an axis.

Can either spin one way or the other

Given two possible values (+1/2 or -1/2)

Symbolized by arrows or by ms

An electron in an orbital behaves like a planet spinning on an axis.

Can either spin one way or the other

Given two possible values (+1/2 or -1/2)

Symbolized by arrows or by ms

Spin Quantum NumberSpin Quantum Number

Electron ConfigurationsElectron Configurations

The arrangement of an atom’s electrons is known as its electron configuration.

Electron ConfigurationsElectron Configurations

Electrons are added one by one according to three rules: Aufbau principle Pauli Exclusion principle Hund’s Rule

Aufbau principleAufbau principle

An electron occupies the lowest energy orbital that can receive it.

1s fills first, it can hold 2 electrons 2s fills second, also holds 2 2p fills third, holds 6 3s 3p 4s ? 3d ?

An electron occupies the lowest energy orbital that can receive it.

1s fills first, it can hold 2 electrons 2s fills second, also holds 2 2p fills third, holds 6 3s 3p 4s ? 3d ?

Aufbau principleAufbau principle

Why does the 4s come before the 3d?

Aufbau PrincipleAufbau Principle

The 4s energy level is lower than the 3d

Think of it as the 4s shape is closer than the 3d shape

There is a pattern

The 4s energy level is lower than the 3d

Think of it as the 4s shape is closer than the 3d shape

There is a pattern

Pauli Exclusion PrinciplePauli Exclusion Principle

Electrons occupying the same orbital must have opposite spin states

Hund’s RuleHund’s Rule

Electrons in equal energy orbitals don’t pair up unless they have to

Representing Electron Configurations

Three ways to represent electron configurations Orbital Notation Electron Configuration Notation Noble Gas Notation

Orbital NotationOrbital Notation

Electrons are symbolized by arrows

Orbitals are symbolized by __

Electrons are symbolized by arrows

Orbitals are symbolized by __

Name the element.

Electron Configuration Notation

Number of electrons are shown by adding a superscript the the sublevel Ex/ Hydrogen has how many

electrons? 1s1

Ex 2/ Carbon’s electron configuration?

1s22s22p2

Number of electrons are shown by adding a superscript the the sublevel Ex/ Hydrogen has how many

electrons? 1s1

Ex 2/ Carbon’s electron configuration?

1s22s22p2

How to use periodic table for electron configurationsHow to use periodic table for electron configurations Find the element on the periodic

table Know how the sublevels apply to

the periodic table Write all sublevels you “pass”

going left to right

Find the element on the periodic table

Know how the sublevels apply to the periodic table

Write all sublevels you “pass” going left to right

d1 d10

Noble gas notationNoble gas notation

Shortcut to writing electron configurations

Find the noble gas that comes before the element

Put that noble gas in brackets Start from there

Shortcut to writing electron configurations

Find the noble gas that comes before the element

Put that noble gas in brackets Start from there

Noble Gas ConfigurationNoble Gas Configuration

Example: Chlorine has 17 electrons 1s22s22p63s23p5

Find the noble gas before it, put it in brackets

[Ne]3s23p5

[Ne] replaces the 1s22s22p6

Example: Chlorine has 17 electrons 1s22s22p63s23p5

Find the noble gas before it, put it in brackets

[Ne]3s23p5

[Ne] replaces the 1s22s22p6

Noble Gas ConfigurationNoble Gas Configuration

Iodine has 53 electrons! Written as [Kr]4d105s25p5

ExceptionsExceptions

There are many exceptions to the electron configuration pattern

All are found in the transition metal region of the periodic table

Ex Chromium 24 electrons Should be [Ar]3d44s2

Actually [Ar]3d54s1

There are many exceptions to the electron configuration pattern

All are found in the transition metal region of the periodic table

Ex Chromium 24 electrons Should be [Ar]3d44s2

Actually [Ar]3d54s1

ExceptionsExceptions

All elements in Copper’s Family should end in d9s2

Actually end in d10s1

Copper is [Ar]3d104s1

All elements in Copper’s Family should end in d9s2

Actually end in d10s1

Copper is [Ar]3d104s1

Why?Why?

We don’t know Best explanation is two half filled

orbitals is more stable than one completely filled one

And one completely filled d orbital is more stable than a half filled s

We don’t know Best explanation is two half filled

orbitals is more stable than one completely filled one

And one completely filled d orbital is more stable than a half filled s

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