Chemistry Ch 4 Chemistry Ch 4

Arrangement of Electrons in Arrangement of Electrons in AtomsAtoms

Rutherford’s ModelRutherford’s Model

Gold Foil ExperimentGold Foil ExperimentDiscovered the nucleusDiscovered the nucleusDid not explain where the electrons were Did not explain where the electrons were

in an atomin an atomWhy were they not attracted to the protons Why were they not attracted to the protons

in the nucleus?in the nucleus?

Background InfoBackground Info

Electromagnetic Radiation are types of Electromagnetic Radiation are types of energy. energy.

We describe these as waves. Only a We describe these as waves. Only a portion of these waves are visible to us portion of these waves are visible to us (the visible light waves).(the visible light waves).

Each type of wave has different wave Each type of wave has different wave characteristics: frequency, wavelength, characteristics: frequency, wavelength, and the amount of energy it contains.and the amount of energy it contains.

Relationship between light and Relationship between light and electronselectrons

The electromagnetic spectrum includes all The electromagnetic spectrum includes all types of electromagnetic radiation that types of electromagnetic radiation that behaves as waves. behaves as waves.

Light can behave as a wave (as in the Light can behave as a wave (as in the spectrum) and as a particle of matter like a spectrum) and as a particle of matter like a marble.marble.

Speed of all electromagnetic radiation is 3.0 Speed of all electromagnetic radiation is 3.0 X 10X 108 8 m/s.m/s.

The Electromagnetic SpectrumThe Electromagnetic Spectrum

Wave CharacteristicsWave Characteristics

Wavelength (Wavelength (λλ)) -the distance between two -the distance between two points on a wave (measured in nm)points on a wave (measured in nm)

Frequency (v) –the number of waves that Frequency (v) –the number of waves that pass in a given point in one secondpass in a given point in one second

The speed of light (c) – is a constantThe speed of light (c) – is a constantC= C= λλ v v Wavelength and Frequency are inverse of Wavelength and Frequency are inverse of

each other (opposite).each other (opposite).

Converting Wavelength UnitsConverting Wavelength Units

Wavelength is measured in nm.Wavelength is measured in nm.Speed is measured in m/s.Speed is measured in m/s.They must both have the same unit so we They must both have the same unit so we

must convert nm to m to use it in the must convert nm to m to use it in the equation.equation.

You broke your big toe!  The x ray they take of  toe uses You broke your big toe!  The x ray they take of  toe uses waves that have a length waves that have a length      4.0 X 10     4.0 X 10-7-7m. ( 1 meter = 1 X 10m. ( 1 meter = 1 X 1099 nm) nm)

What is the wavelength in nm? What is the wavelength in nm? ((= 400 nm)= 400 nm)

Frequency and Wavelength Frequency and Wavelength ProblemsProblems

Calculate Calculate for a for a = 700 nm. = 700 nm. (Red 700nm(Red 700nm

            4.3 x 104.3 x 1014 14 /s    or  4.3 x 10/s    or  4.3 x 1014 14 Hz)Hz)

A purple light has a frequency of 7.42 x A purple light has a frequency of 7.42 x 10101414 Hz.   Hz.      What is its wavelength in nm?    What is its wavelength in nm?

= 404 nm)= 404 nm)

Lets look at a video to see what we are Lets look at a video to see what we are going to be learning and what the going to be learning and what the scientists were investigating…scientists were investigating…

Video of electron behavior as waves and particles

Photoelectric EffectPhotoelectric Effect

Experiments by Einstein and others in the Experiments by Einstein and others in the 1900s tried to explain the interactions 1900s tried to explain the interactions between light and matter that were not between light and matter that were not explained with the wave theoryexplained with the wave theory

Their research led them to discover the Their research led them to discover the dual wave particle nature. How dual wave particle nature. How electromagnetic radiation behaves as electromagnetic radiation behaves as waves and as particles. waves and as particles.

The evidence for this was the The evidence for this was the Photoelectric Effect experiment, which Photoelectric Effect experiment, which explained how light, that is usually thought explained how light, that is usually thought of as a wave, can also behave like a of as a wave, can also behave like a particle of matter. particle of matter.

Lois de Broglie wondered if electrons Lois de Broglie wondered if electrons (matter), normally thought of as a particle, (matter), normally thought of as a particle, maybe have some wave properties too.maybe have some wave properties too.

Photo of Photoelectric EffectPhoto of Photoelectric Effect

The wave theory predicted that light of any The wave theory predicted that light of any frequency could supply enough energy to frequency could supply enough energy to eject an electron from its position.eject an electron from its position.

However, no electrons were emitted if a However, no electrons were emitted if a light’s frequency was below a certain light’s frequency was below a certain minimum, regardless of how long the light minimum, regardless of how long the light was shone.was shone.

Max Planck suggested that an object Max Planck suggested that an object emits energy in small, specific amounts, emits energy in small, specific amounts, called quanta.called quanta.

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

E= hvE= hvh = Planck’s constant 6.626 X 10h = Planck’s constant 6.626 X 10-34 -34 JsJs

Photons are the “particles of light” that Photons are the “particles of light” that carry a certain amount of energy.carry a certain amount of energy.

The energy of a photon depends on the The energy of a photon depends on the frequency of the wave.frequency of the wave.

In order for an electron to be ejected from In order for an electron to be ejected from a metal surface, the electron must be a metal surface, the electron must be struck by a single photon with the struck by a single photon with the minimum energy required to knock the minimum energy required to knock the electron lose. (supports the particle theory)electron lose. (supports the particle theory)

Because E = hv, the minimum energy Because E = hv, the minimum energy needed corresponds to the frequencyneeded corresponds to the frequency

Energy ProblemEnergy Problem

What is the energy of a photon whose What is the energy of a photon whose frequency is 3.0 X 10frequency is 3.0 X 101212 Hz? Hz?

E = hvE = hv

Where Where h= 6.626 x 10h= 6.626 x 10-34-34 J/Hz          J/Hz         

          

E =[6.626 x 3.0] E =[6.626 x 3.0] 10 (-34+12)10 (-34+12) J J

1.99 X 101.99 X 10-21-21 J J

An observation was that different metals An observation was that different metals required different amounts of energy or required different amounts of energy or frequencies to exhibit the photoelectric frequencies to exhibit the photoelectric effect. (different metals are different effect. (different metals are different elements with different numbers of elements with different numbers of electrons)electrons)

So what did all this mean for where the So what did all this mean for where the electrons were in an atom?electrons were in an atom?

It was concluded that electrons exist in It was concluded that electrons exist in specific energy levels in an atom:specific energy levels in an atom:

Ground state = lowest energy state of an Ground state = lowest energy state of an atomatom

Excited state = the highest energy stateExcited state = the highest energy stateWhen atoms are excited by energy (heat), When atoms are excited by energy (heat),

they emit energy in the form of light.they emit energy in the form of light.

Classical theory predicted that atoms would Classical theory predicted that atoms would be excited by whatever amount of energy be excited by whatever amount of energy that was added to them. (there would be a that was added to them. (there would be a continuous spectrum of frequencies given continuous spectrum of frequencies given off-like a prism)off-like a prism)

However, when current was passed through However, when current was passed through Hydrogen gas, a series of very specific Hydrogen gas, a series of very specific frequencies were emitted and only certain frequencies were emitted and only certain colors were seen (line emission spectrum)colors were seen (line emission spectrum)

Hydrogen Line Emission Hydrogen Line Emission SpectrumSpectrum

This suggested that the electrons of an This suggested that the electrons of an atom exist in very specific energy states.atom exist in very specific energy states.

So, Bohr put all this information together in So, Bohr put all this information together in his model of an atom.his model of an atom.

Bohr ModelBohr Model

Orbits-electrons can only circle the Orbits-electrons can only circle the nucleus in allowed pathsnucleus in allowed paths

Each orbit has a fixed amount of energyEach orbit has a fixed amount of energyClosest to the nucleus has the least Closest to the nucleus has the least

amount of energy (ground)amount of energy (ground)Farther from the nucleus has more energy Farther from the nucleus has more energy

(excited)(excited)

Or in other words,Or in other words,

When an excited electron returns to its When an excited electron returns to its ground state, it gives off the energy (a ground state, it gives off the energy (a photon) in the form of electromagnetic photon) in the form of electromagnetic radiation (sometimes visible light).radiation (sometimes visible light).

From E2 to E1, the electron will gain or From E2 to E1, the electron will gain or lose energy?lose energy?

From E1 to E5, the electron will gain or From E1 to E5, the electron will gain or lose energy?lose energy?

Why do different atoms emit Why do different atoms emit different light?different light?

Each atom is unique and contains its own Each atom is unique and contains its own unique electron structure in the different unique electron structure in the different energy levels. energy levels.

How does the emission of light How does the emission of light relate to the electron structure?relate to the electron structure?

Since each atom is unique in its electron Since each atom is unique in its electron structure with differing levels of energy, structure with differing levels of energy, the transitions between those levels will be the transitions between those levels will be unique to each atom. unique to each atom.

Electrons are in certain energy levels. Electrons are in certain energy levels. When electrons give off light, they emit When electrons give off light, they emit energy, and move to a lower level closer energy, and move to a lower level closer to the nucleus. to the nucleus.

Balmer Series Balmer Series

Emission SpectrumEmission Spectrum

Some electron transitions result in Some electron transitions result in energies and wavelengths within the energies and wavelengths within the visible light spectrum so we can see them visible light spectrum so we can see them (400-750 nm).(400-750 nm).

However, there are many transitions that However, there are many transitions that we cannot see (radio waves, x-rays, we cannot see (radio waves, x-rays, gamma rays)gamma rays)

de Broglie concluded that since an de Broglie concluded that since an electron is so small but its speed is so electron is so small but its speed is so great, it could orbit a nucleus millions of great, it could orbit a nucleus millions of times in 1 second! (He used algebraic times in 1 second! (He used algebraic methods and the equations of Einstein, methods and the equations of Einstein, Planck, and the speed of a wave to figure)Planck, and the speed of a wave to figure)

So, how could we possibly know where an So, how could we possibly know where an electron is in an atom?electron is in an atom?

Schrödinger suggested that since Schrödinger suggested that since electrons can be thought of like waves, electrons can be thought of like waves, they may be like standing waves outside they may be like standing waves outside the nucleus.the nucleus.

Only a certain number of waves can exist Only a certain number of waves can exist between the nucleus and a certain point. between the nucleus and a certain point.

This fits with Bohr’s idea of energy levels This fits with Bohr’s idea of energy levels in an atom. in an atom.

Ch. 4-2 The Quantum ModelCh. 4-2 The Quantum Model

Light can behave as waves and particlesLight can behave as waves and particles Louis De Broglie investigated that Louis De Broglie investigated that

electrons also behave like waves electrons also behave like waves because:because:

1.1. They are confined to a specific frequencyThey are confined to a specific frequency2.2. Diffraction-bending of a wave as it Diffraction-bending of a wave as it

passes by somethingpasses by something3.3. Interference-waves overlappingInterference-waves overlappingFig. 4-10Fig. 4-10

Heisenberg Uncertainty PrincipleHeisenberg Uncertainty Principle

Heisenberg: It is impossible to Heisenberg: It is impossible to simultaneously determine the location and simultaneously determine the location and velocity of an electron or particlevelocity of an electron or particle

Schrodinger’s theory (that there can only Schrodinger’s theory (that there can only be so many wavelengths of energy in a be so many wavelengths of energy in a certain level) led to the development of the certain level) led to the development of the quantum theoryquantum theory

Quantum theory-describes the wave Quantum theory-describes the wave patterns of electrons mathematicallypatterns of electrons mathematically

As a result of the Schrodinger equation As a result of the Schrodinger equation and Heisenberg’s Principle, the location of and Heisenberg’s Principle, the location of an electron is only its an electron is only its probable probable location location around a nucleusaround a nucleus

Orbital-3D region around the nucleus that Orbital-3D region around the nucleus that describes its describes its probable probable locationlocation

Fig. 4-11Fig. 4-11

Quantum NumbersQuantum Numbers

Specify the properties of atomic orbitals Specify the properties of atomic orbitals and properties of electrons in orbitalsand properties of electrons in orbitals

There are 4 quantum numbers for each There are 4 quantum numbers for each electron: electron:

1.1. Principle Quantum NumberPrinciple Quantum Number

2.2. Angular Momentum Quantum NumberAngular Momentum Quantum Number

3.3. Magnetic Quantum NumberMagnetic Quantum Number

4.4. Spin Quantum NumberSpin Quantum Number

NO two electrons have the same 4 NO two electrons have the same 4 quantum numbersquantum numbers

Similar to a zip code-no 2 cities have the Similar to a zip code-no 2 cities have the same zip codesame zip code

1.1. Principal Quantum Number (n)-indicates the main energy level of Principal Quantum Number (n)-indicates the main energy level of the electronthe electron

Ex: n= 1, 2, 3…..Ex: n= 1, 2, 3…..Also indicates how many sublevels there may be for a main energy Also indicates how many sublevels there may be for a main energy

levellevel

2.2. Angular Momentum Quantum Number (l)-indicates the shape of Angular Momentum Quantum Number (l)-indicates the shape of the sublevel or oribitalthe sublevel or oribital

S-sphereS-sphereP-dumbbell shapedP-dumbbell shapedD-3D shapeD-3D shapeF- Too complexF- Too complexPg. 102Pg. 102

3.3. Magnetic Quantum Number (m) –Magnetic Quantum Number (m) –orientation of an orbital around the orientation of an orbital around the nucleusnucleus

S-1S-1

P-3P-3

D-5D-5

F-7F-7

Each orbital can hold 2 electronsEach orbital can hold 2 electrons

So, total electrons for each S = 2 (1 X 2)So, total electrons for each S = 2 (1 X 2)

P = 6 (3 X 2)P = 6 (3 X 2)

D = 10 (5 X 2)D = 10 (5 X 2)

F = 14 (7 X 2)F = 14 (7 X 2)

How many electrons in each How many electrons in each energy level?energy level?

Use 2nUse 2n2 2 to figure out how many electrons to figure out how many electrons can be in each energy levelcan be in each energy level

Ex: for energy level 5, n=5Ex: for energy level 5, n=5

So 2 (5)So 2 (5)22 = 50 electrons = 50 electrons

4.4. Spin Quantum Number – indicates the Spin Quantum Number – indicates the direction the electron will spin in orbitdirection the electron will spin in orbit

* has only 2 possible values for the spin, * has only 2 possible values for the spin, either +1/2 or -1/2either +1/2 or -1/2

* The two electrons in each orbital have to * The two electrons in each orbital have to have opposite spinshave opposite spins

Ch. 4-3 Electron ConfigurationsCh. 4-3 Electron Configurations

The quantum model tells us more than the The quantum model tells us more than the Bohr model of the atom because it tells us Bohr model of the atom because it tells us where the electrons are locatedwhere the electrons are located

Electron configurations-the arrangement of Electron configurations-the arrangement of electrons in an atomelectrons in an atom

Aufbau principle-an electron occupies the Aufbau principle-an electron occupies the lowest-energy orbital that can receive itlowest-energy orbital that can receive it

Fig. 4-16Fig. 4-16

We always start at 1s and work up to 2s, 2p, We always start at 1s and work up to 2s, 2p, etc.etc.

Pauli exclusion principle-no two electrons Pauli exclusion principle-no two electrons in the same atom can have the same set in the same atom can have the same set of four quantum numbersof four quantum numbers

Ex: zip codeEx: zip code

Hund’s Rule-orbitals of equal energy are Hund’s Rule-orbitals of equal energy are each occupied by one electron before any each occupied by one electron before any orbital is occupied by a second electron. orbital is occupied by a second electron. All the first electrons must all have the All the first electrons must all have the same spinsame spin

Electron ConfigurationsElectron Configurations

Electrons fill orbitals (s, p, d, f) and energy Electrons fill orbitals (s, p, d, f) and energy levels (1, 2, 3…) in a certain order levels (1, 2, 3…) in a certain order according to energy:according to energy:

Remember, s orbitals can hold 2 electronsRemember, s orbitals can hold 2 electrons

p orbitals can hold 6 electronsp orbitals can hold 6 electrons

d orbitals can hold 10 electronsd orbitals can hold 10 electrons

f orbitals can hold 14 electronsf orbitals can hold 14 electrons

Electron ConfigurationsElectron Configurations

11. . Electron Configuration NotationElectron Configuration Notation

Ex: He- 1sEx: He- 1s22

Ex: Na-1sEx: Na-1s222s2s222p2p663s3s11

2. 2. Orbital NotationOrbital Notation

Ex: He-_Ex: He-_↑↓↑↓__

Ex: Na- (1s)_↑↓_ (2s)_↑↓_ (2p)_↑↓_ _↑↓_ _↑↓_ (3s) Ex: Na- (1s)_↑↓_ (2s)_↑↓_ (2p)_↑↓_ _↑↓_ _↑↓_ (3s) _↑__↑_

3. 3. Noble Gas ConfigurationNoble Gas Configuration

Ex: Li- [He] 2sEx: Li- [He] 2s11

Ex: Na-[Ne] 3sEx: Na-[Ne] 3s11

Practice Practice

Practice Configurations on pg. 114 and Practice Configurations on pg. 114 and 116116

Or Practice writing all 3 configurations for Or Practice writing all 3 configurations for Al, Cu, Ag, and CsAl, Cu, Ag, and Cs