Chapter 5Chapter 5Electrons in AtomsElectrons in Atoms

Ms. WangMs. Wang

Lawndale High SchoolLawndale High School

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 electrically Atoms were known to be electrically neutral which meant that there had to neutral which meant that there had to

be some positively charged matter be some positively charged matter

to balance the negative chargesto balance the negative charges

Ernest Rutherford’s Ernest Rutherford’s experiment disproved the experiment disproved the plum pudding model of plum pudding model of the atom and suggested the atom and suggested that there was a that there was a positively charged positively charged nucleus because many of nucleus because many of the alpha particles hit the the alpha particles hit the thin gold foil and bounced thin gold foil and bounced backback

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

The Bohr ModelThe Bohr Model

He noticed that light He noticed that light given out when given out when

atoms were heated atoms were heated always had specific always had specific amounts of energy, amounts of energy, so he proposed that so he proposed that electrons in an atom electrons in an atom must be orbiting the must be orbiting the

nucleus and can nucleus and can reside only in fixed reside only in fixed

energy levels. energy levels.

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

Energy LevelsEnergy Levels

Energy levels – fixed energy Energy levels – fixed energy that an electron can havethat an electron can have

This is similar to steps of a This is similar to steps of a ladderladder

Quantum – amount of energy Quantum – amount of energy required to move an electron required to move an electron from one energy level to from one energy level to another energy level (to be another energy level (to be quantized)quantized)

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

The quantum The quantum mechanical model mechanical model that scientist use that scientist use today does not today does not describe the exact describe the exact path an electron takes path an electron takes around the nucleus around the nucleus but more concerned but more concerned with the probability of with the probability of finding an electron in finding an electron in a certain place. a certain place.

Atomic OrbitalsAtomic Orbitals

Atomic Orbitals – a region of Atomic Orbitals – a region of space in which there is a high space in which there is a high probability of finding an electronprobability of finding an electron

Each energy sublevel corresponds Each energy sublevel corresponds to an orbital of different shape to an orbital of different shape describing where the electron is describing where the electron is likely to be foundlikely to be found

Labeling Electrons in AtomsLabeling Electrons in Atoms

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

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

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

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 e-Location of e-ProbabilityProbability Probable location Probable location

of Finding of Finding BeyonceBeyonce

Energy level Energy level (n)(n)

High High ProbabilityProbability

Hotel FloorHotel Floor

Sublevel (l)Sublevel (l) Higher Higher ProbabilityProbability

WingWing

Orbitals (m)Orbitals (m) Highest Highest probabilityprobability

RoomRoom

n= principal quantum n= principal quantum numbernumber

Used to describe the energy of the Used to describe the energy of the electron. The farther away from electron. The farther away from nucleus, the higher the energynucleus, the higher the energy

The n quantum number The n quantum number can have values = 1, 2, 3, can have values = 1, 2, 3, …. n …. n n = 1 can hold 2 electronsn = 1 can hold 2 electrons

n = 2 can hold 8 electronsn = 2 can hold 8 electrons

n = 3 can hold 18 electronsn = 3 can hold 18 electrons

n = 4 can hold 32 electronsn = 4 can hold 32 electrons

Draw the electron shell diagram for Draw the electron shell diagram for Beryllium. Be has 4 electronsBeryllium. Be has 4 electrons

Draw the electron shell diagram for Draw the electron shell diagram for Nitrogen. N has 7 electronsNitrogen. N has 7 electrons

Electrons

Be

N

Nucleus

Draw the electron shell Draw the electron shell diagrams for these elementsdiagrams for these elements

NickelNickel AluminumAluminum ArgonArgon CarbonCarbon CalciumCalcium

What does n represent? What does n represent?

How many electrons can each n hold?How many electrons can each n hold?

l = sublevel l = sublevel Provides a code for the shape of orbitalsProvides a code for the shape of orbitals

ll letterletter

00 ss

11 pp

22 dd

33 f f

They are designated by letters They are designated by letters

• l =0, 1, 2, (n-1)l =0, 1, 2, (n-1)

Answer these questionsAnswer these questions

If n = 1 what does l =? Which letter If n = 1 what does l =? Which letter does that correspond to?does that correspond to?

If n = 2 what does l = Which letter If n = 2 what does l = Which letter does that correspond to?does that correspond to?

If n = 3 what does l =? Which letter If n = 3 what does l =? Which letter does that correspond to?does that correspond to?

• If n= 4 what does l =? Which letter If n= 4 what does l =? Which letter does the correspond to?does the correspond to?

Principal Energy Principal Energy

LevelLevelSublevels Available Sublevels Available

11 1s1s

22 2s2p2s2p

33 3s3p3d3s3p3d

44 4s4p4d4f4s4p4d4f

55 5s5p5d5f5g5s5p5d5f5g

66 6s6p6d6f6g6h6s6p6d6f6g6h

For principal energy level 3, there are 3 sublevelss < p< d <f in energy

m=magnetic quantum m=magnetic quantum numbernumber

Used to describe each orbital within Used to describe each orbital within a sublevela sublevel

SublevelSublevel Orbitals Available Orbitals Available

ss 1 = s1 = s

PP 3 = px, py, pz3 = px, py, pz

dd 5 = dxy, dxz, dyz, 5 = dxy, dxz, dyz, dxdx22 – y – y22, dz, dz22

Number or Number or electrons in the electrons in the sublevelsublevel

22

66

1010

http://chemviz.ncsa.uiuc.edu/images/l1s_sorb_200x218.gif

Section 5.2 – Electron Section 5.2 – Electron ConfigurationsConfigurations

Each orbital holds 2 electronsEach orbital holds 2 electrons Filling order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, Filling order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p

Example He = 2 electronsExample He = 2 electrons1s1s22

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 noble gaseswritten in terms of noble gases

To 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 of electron s describes the direction of electron spin around its axis. spin around its axis. 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 configuration gives the The electron configuration gives the number of electrons in each sublevel number of electrons in each sublevel but does not show how the orbitals of but does not show how the orbitals of a sublevel are occupied by the a sublevel are occupied by the electrons. electrons.

Orbital DiagramsOrbital Diagrams They are used to show how electrons They are used to show how electrons

are distributed within sublevels. are distributed within sublevels.

1s2p

2s

Each orbital is represented by a box Each orbital is represented by a box and each electron is represented by an and each electron is represented by an arrow. arrow. The direction of the spin is The direction of the spin is represented by the direction of the represented by the direction of the arrowarrowExample: 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

Aufbau PrincipleAufbau Principle Electrons must occupy the orbital Electrons must occupy the orbital

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

2p

2s1s

2p

2s1s

Pauli Exclusion PrinciplePauli Exclusion Principle An atomic orbital may describe at An atomic orbital may describe at

most two electronsmost two electrons The 2 electrons must have opposite The 2 electrons must have opposite

spinsspins Example: Oxygen 1sExample: Oxygen 1s222s2s222p2p44

2p

2s1s

2p

2s1s

Hund’s RuleHund’s Rule Orbitals of equal energy are each Orbitals of equal energy 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 absorb energy, electrons When atoms absorb energy, electrons move into higher energy levelsmove into higher energy levels

These electrons lose energy by These electrons lose energy by emitting light when they return to emitting light when they return to lower energy levelslower energy levels

Atomic Emission Spectrum – the Atomic Emission Spectrum – the discrete lines representing the discrete lines representing the frequencies of light emitted by an frequencies of light emitted by an elementelement

Atomic SpectraAtomic Spectra

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

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

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

HomeworkHomework

Chapter 5 Assessment Page 148Chapter 5 Assessment Page 148

#’s 22-24, 27, 29, 30-39, #’s 22-24, 27, 29, 30-39,

50-53, 57, 60, 68, 70-7250-53, 57, 60, 68, 70-72