Chapter 5Chapter 5Electrons in AtomsElectrons in Atoms

Mr. SamaniegoMr. Samaniego

Lawndale High SchoolLawndale High School

Summary of Atomic TheorySummary of Atomic TheoryYearYear EventEvent

400BC400BC Democritus Democritus proposes idea of proposes idea of atomatom

18081808 Dalton Dalton develops Atomic Theorydevelops Atomic Theory

18971897 Thomson Thomson uses cathode ray to uses cathode ray to discover electrondiscover electron

19161916 Millikan Millikan measures the mass of measures the mass of an ean e--

19191919 Rutherford Rutherford uses gold foil uses gold foil experiment to discover nucleusexperiment to discover nucleus

Structure Of An AtomStructure Of An Atom

So by this point, we know that protons and So by this point, we know that protons and neutrons are located in the nucleus and neutrons are located in the nucleus and electrons are around the outside of the electrons are around the outside of the nucleusnucleus

Section 5.1 – Models of the Section 5.1 – Models of the AtomAtom

Observed that a magnet deflected the straight paths

of the cathode rays

In 1897 J. J. Thomson discovered the In 1897 J. J. Thomson discovered the electronelectron

Atoms were known to be Atoms were known to be electrically electrically neutral which meant that there had to neutral which meant that there had to be some be some positively positively charged matter to charged matter to

balance the negative chargesbalance the negative charges

Ernest Rutherford’s Ernest Rutherford’s experiment experiment disproved disproved the plum pudding model the plum pudding model of the atom and of the atom and suggested that there was suggested that there was a a positively positively charged charged nucleus because most of nucleus because most of the alpha particles went the alpha particles went straight through the gold straight through the gold foilfoil

BUT, Rutherford’s atomic model could not explain the chemical properties of elements

The Bohr Model (Niels Bohr)The Bohr Model (Niels Bohr)

He noticed that light given He noticed that light given out when atoms were out when atoms were

heated always had heated always had specific amounts of specific amounts of

energyenergy, so , so Niels Bohr Niels Bohr proposed a model that proposed a model that

electrons in an atom must electrons in an atom must be orbiting the nucleus be orbiting the nucleus and can reside only in and can reside only in fixed fixed energy energy levelslevels

In 1913, Niels Bohr came up with a new In 1913, Niels Bohr came up with a new model model (Bohr was a student of (Bohr was a student of Rutherford)Rutherford)

Energy LevelsEnergy Levels

This is similar to steps of a This is similar to steps of a ladder ladder (can climb up the (can climb up the ladder, but cannot step in ladder, but cannot step in between the steps)between the steps)Quantum is the amount of Quantum is the amount of energy energy required to move an required to move an electron from one energy level electron from one energy level to another to another

Each of the electrons in Each of the electrons in Bohr’s model has a fixed Bohr’s model has a fixed amount of energy called amount of energy called energy levelsenergy levels

The further away from the The further away from the nucleusnucleus, the , the more energy the electron hasmore energy the electron has

While Rutherford’s model While Rutherford’s model described the described the path path the electron the electron moves, Erwin Schrodinger moves, Erwin Schrodinger solved solved mathematical mathematical equations to describe the equations to describe the behavior of electronbehavior of electron

The Quantum Mechanics The Quantum Mechanics Model (Erwin Schrodinger)Model (Erwin Schrodinger)

Similar to Bohr’s model, Schrodinger Similar to Bohr’s model, Schrodinger describes the energy of describes the energy of electrons electrons with with certain values but does not involve an certain values but does not involve an exact exact path path the electron takes around the electron takes around the nucleusthe nucleus

The Quantum Mechanics The Quantum Mechanics View of the Atom View of the Atom

(Schrodinger)(Schrodinger) The quantum The quantum

mechanical model mechanical model does not describe the does not describe the exact exact path path an an electron takes electron takes around the nucleus, around the nucleus, but determines the but determines the probabilityprobability of of finding an electron in finding an electron in a certain areaa certain area

Quantum Mechanical ModelQuantum Mechanical Model In this model, electrons move similar to a In this model, electrons move similar to a

rotating rotating propeller propeller bladeblade

You cannot tell its precise You cannot tell its precise location location at any at any instant because it’s a blurry region, but you instant because it’s a blurry region, but you have information regarding the have information regarding the probability probability of finding an electron within a certain volume of finding an electron within a certain volume of spaceof space Similar to a fuzzy cloud…the probability of Similar to a fuzzy cloud…the probability of finding an electron is finding an electron is higher higher where the cloud where the cloud is more denseis more dense

Atomic OrbitalsAtomic Orbitals An Atomic Orbital is a region of An Atomic Orbital is a region of

space where there is a high space where there is a high probability probability of finding an electronof finding an electron

Each energy sublevel Each energy sublevel corresponds to an corresponds to an orbital of different orbital of different shape shape describing describing where the electron is where the electron is likely to be found (there likely to be found (there are 4 different types of are 4 different types of shapes)shapes)

Shapes of OrbitalsShapes of Orbitals

Shapes of OrbitalsShapes of Orbitals

Shapes of OrbitalsShapes of Orbitals

Each electron in an atom is assigned a set of four Each electron in an atom is assigned a set of four quantum quantum numbers. These help to determine the numbers. These help to determine the highest highest probability probability of finding the electrons.of finding the electrons.

Three of these numbers (n, l, m) give the Three of these numbers (n, l, m) give the location location of the electron of the electron

The fourth (s) describes the The fourth (s) describes the orientation orientation of an of an electron in an orbital. electron in an orbital.

Chapter 5.2 – Electron Chapter 5.2 – Electron Arrangement in AtomsArrangement in Atoms

Quantum letters can be thought of Quantum letters can be thought of like the numbers and letters on a like the numbers and letters on a

concert ticketconcert ticket

Labeling Electrons in AtomsLabeling Electrons in AtomsProbable Probable

Location of Location of electronelectron

ProbabilityProbability Probable location of Probable location of Finding Beyonce or Finding Beyonce or

TaylorTaylor

Energy level Energy level (n)(n)

High High ProbabilityProbability

Hotel NameHotel Name

Sublevel (l)Sublevel (l) Higher Higher ProbabilityProbability

Hotel Floor Hotel Floor NumberNumber

Orbital (m)Orbital (m) Highest Highest probabilityprobability

Hotel Room Hotel Room NumberNumber

Electron ConfigurationElectron Configuration

SublevelSublevel # of Orbitals # of Orbitals Available Available

# of Electrons # of Electrons AvailableAvailable

ss 11 22pp 33 66dd 55 1010

ff 77 1414

Electron ConfigurationsElectron Configurations

Filling order: 1s, 2s, 2p, 3s, 3p, 4s, Filling order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p5f, 6d, 7p Example He = 2 electronsExample He = 2 electrons

1s1s22

Example Li = 3 electrons Example Li = 3 electrons 1s1s222s2s11

Example B = 5 electronsExample B = 5 electrons 1s1s222s2s222p2p11

Practice Problems

Write electron configurations for the following atoms

1.1. LiLi 5. P5. P

2.2. NN 6. Si6. Si

3.3. BeBe 7. Mg7. Mg

4.4. CC 8. Al8. Al

Electron Configurations can be Electron Configurations can be written in terms of written in terms of noble noble

gasesgasesTo save space, configurations can be To save space, configurations can be

written in terms of noble gases written in terms of noble gases

Example 1: Ne = Example 1: Ne = 1s1s222s2s222p2p66

S = S = 1s1s222s2s222p2p663s3s223p3p44

OrOr S = [Ne] 3s S = [Ne] 3s223p3p44

Example 2: Ar = Example 2: Ar = 1s1s222s2s222p2p663s3s223p3p66

Mn = Mn = 1s1s222s2s222p2p663s3s223p3p664s4s223d3d55

Mn = [Ar] 4sMn = [Ar] 4s223d3d55

Reading the Periodic TableReading the Periodic Table

Locating Electrons in AtomsLocating Electrons in AtomsSo far we have discussed 3 quantum numbersSo far we have discussed 3 quantum numbers

n l

Number of electrons in sublevel

n= principal quantum level (principal energy n= principal quantum level (principal energy level)level) l= Sublevel l= Sublevel

m = magnetic quantum number (shape of m = magnetic quantum number (shape of orbitals)orbitals)

1s1s22

s = spins = spin When an electron moves, it When an electron moves, it

generates a magnetic field. generates a magnetic field. s describes the direction an electron s describes the direction an electron spinsspins They must spin in opposite directionsThey must spin in opposite directions

Spin= up downSpin= up down

There are two values of s: +1/2 and -There are two values of s: +1/2 and -1/21/2

Orbital DiagramsOrbital Diagrams

The electron The electron configuration gives configuration gives the number of the number of electrons in each electrons in each sublevel but does sublevel but does not show how the not show how the orbital of a sublevel orbital of a sublevel are occupied by the are occupied by the electrons electrons

Orbital DiagramsOrbital Diagrams Used to show how Used to show how electronselectrons are are

distributed within sublevelsdistributed within sublevels

1s2p

2s

Each orbital is Each orbital is representedrepresented by a box by a box and each electron is represented by an and each electron is represented by an arrow arrow Notice that each box is drawn Notice that each box is drawn higherhigher than the last set because it has more than the last set because it has more energyenergyExample: Boron 1sExample: Boron 1s222s2s222p2p11

Orbital DiagramsOrbital DiagramsSteps to writing orbital diagrams:ex F (Z=9)Steps to writing orbital diagrams:ex F (Z=9)

1.1. Write the electron configurationWrite the electron configuration

1s1s222s2s222p2p55

2. Construct an orbital filling diagram using 2. Construct an orbital filling diagram using boxes for each orbital boxes for each orbital

3. Use arrows to represent the electrons in 3. Use arrows to represent the electrons in each orbital. each orbital.

2p

2s1s

1s2p

2s

Rule #1 - Aufbau PrincipleRule #1 - Aufbau Principle Electrons must Electrons must occupy occupy the orbital the orbital

with the lowest energy firstwith the lowest energy first Example: Oxygen 1sExample: Oxygen 1s222s2s222p2p44

2p

2s1s

2p

2s1s

Rule #2 - Pauli Exclusion Rule #2 - Pauli Exclusion PrinciplePrinciple

Orbitals can only have Orbitals can only have two two electrons electrons maxmax

The 2 electrons must have opposite The 2 electrons must have opposite spinsspins

Example: Oxygen 1sExample: Oxygen 1s222s2s222p2p44

2p

2s1s

2p

2s1s

Rule #3 - Hund’s RuleRule #3 - Hund’s Rule Orbitals of equal Orbitals of equal energy energy are each are each

occupied by one electron before any occupied by one electron before any pairing occurspairing occurs

Example: Oxygen 1sExample: Oxygen 1s222s2s222p2p44

2p

2s1s

2p

2s1s

Draw orbital diagrams for Draw orbital diagrams for these elementsthese elements

1.1. LiLi 5. P5. P

2.2. NN 6. Si6. Si

3.3. BeBe 7. Mg7. Mg

4.4. CC 8. Al8. Al

Section 5.3 - Atomic SpectraSection 5.3 - Atomic Spectra When atoms When atoms absorb absorb energy, energy,

electrons move into electrons move into higher higher energy energy levels (excited state)levels (excited state)

When these When these electrons electrons return to their return to their lower energy levels, they lose lower energy levels, they lose energy energy by emitting lightby emitting light Atomic Emission Spectrum – the Atomic Emission Spectrum – the

discrete discrete lines lines representing the representing the frequencies frequencies of light emitted by an of light emitted by an elementelement

Calculating Wavelength of Calculating Wavelength of LightLight

c = c =

c = speed of light (3 x 10c = speed of light (3 x 108 8

m/sm/s22))

= wavelength (called = wavelength (called lambda)lambda)

= frequency (called nu)= frequency (called nu)

PracticePractice

1. Calculate the wavelength of a yellow light 1. Calculate the wavelength of a yellow light if the frequency is 5.10 x 10if the frequency is 5.10 x 101414 sec sec-1 -1 or Hz.or Hz.

Answer = 5.88 x 10Answer = 5.88 x 10-7-7mm

2. What is the wavelength of 1.50 x 102. What is the wavelength of 1.50 x 101313 secsec-1-1??

Answer = 2.00 x 10Answer = 2.00 x 10-5-5mm

3. What frequency is radiation with a 3. What frequency is radiation with a wavelength of 5.00 x 10wavelength of 5.00 x 10-8-8m?m?

Answer = 6.00 x 10Answer = 6.00 x 101515 sec sec-1-1 or Hertz or Hertz

Atomic SpectraAtomic Spectra

Each Each discrete discrete line in an emission line in an emission spectrum spectrum corresponds to one exact corresponds to one exact frequency frequency of light emitted by the atomof light emitted by the atom

Ground State – lowest Ground State – lowest possible possible energy of the energy of the electron electron in the Bohr in the Bohr modelmodel

The The light light emitted by an electron emitted by an electron moving from higher to a lower moving from higher to a lower energy energy level has a frequency level has a frequency directly proportional to the energy directly proportional to the energy change change of the electronof the electron

HomeworkHomework

Chapter 5 Assessment Page 148Chapter 5 Assessment Page 148

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