introductory chemistry, 2 nd edition nivaldo tro chapter 9 electrons in atoms and the periodic table

Introductory ChemistryIntroductory Chemistry, 2, 2ndnd Edition EditionNivaldo TroNivaldo Tro

Chapter 9Electrons in Atoms

and thePeriodic Table

Tro's Introductory Chemistry, Chapter 9Tro's Introductory Chemistry, Chapter 9 22

Why do Blimps Float?Why do Blimps Float?

Because they are filled with a Because they are filled with a gas less dense than airgas less dense than airEarly blimps used Early blimps used hydrogenhydrogen gas; hydrogen’s flammability gas; hydrogen’s flammability led to the Hindenburg disasterled to the Hindenburg disasterBlimps now use Blimps now use heliumhelium, a , a nonflammable gas – in fact it nonflammable gas – in fact it doesn’t undergo any chemical doesn’t undergo any chemical reactionsreactionsThis chapter investigates This chapter investigates models of the atom we use to models of the atom we use to explain the differences in the explain the differences in the properties of the elementsproperties of the elements


Electromagnetic RadiationElectromagnetic Radiation

Light is one of the forms of Light is one of the forms of energyenergy

Light is one type of a more Light is one type of a more general form of energy general form of energy called called electromagnetic electromagnetic radiationradiation

Electromagnetic radiation Electromagnetic radiation travels in wavestravels in waves


Characteristics of a WaveCharacteristics of a Wave

Wavelength = distance from peak to peakWavelength = distance from peak to peakAmplitude = height of the peakAmplitude = height of the peakFrequency = the number of wave peaks that Frequency = the number of wave peaks that pass in a given timepass in a given timeSpeed = rate the waves travel Speed = rate the waves travel


Particles of LightParticles of Light

Scientists in the early 20Scientists in the early 20thth century showed that century showed that electromagnetic radiation was composed of electromagnetic radiation was composed of particles we call particles we call photonsphotons

– Max Planck and Albert EinsteinMax Planck and Albert Einstein

– photons are particles of light energyphotons are particles of light energy

Each wavelength of light has photons that Each wavelength of light has photons that have a different amount of energyhave a different amount of energy

– the longer the wavelength, the lower the the longer the wavelength, the lower the energy of the photonsenergy of the photons


The Electromagnetic SpectrumThe Electromagnetic Spectrum

Light passed through a prism is separated into all its colors Light passed through a prism is separated into all its colors = = continuous spectrumcontinuous spectrum; colors blend into each other; colors blend into each other

Color of light is determined by its wavelengthColor of light is determined by its wavelength


Electromagnetic SpectrumElectromagnetic Spectrum

Visible light is a very small portion of the Visible light is a very small portion of the electromagnetic spectrumelectromagnetic spectrum


Light’s Relationship to MatterLight’s Relationship to Matter

Atoms can absorb energy, but Atoms can absorb energy, but they must eventually release itthey must eventually release it

When atoms emit energy, it is When atoms emit energy, it is released in the form of light = released in the form of light = emission spectrumemission spectrum

Atoms don’t absorb or emit all Atoms don’t absorb or emit all colors, only very specific colors, only very specific wavelengths; the spectrum of wavelengths; the spectrum of wavelengths can be used to wavelengths can be used to identify the elementidentify the element


Emission Spectrum or Emission Spectrum or Line SpectrumLine Spectrum


Line Line SpectraSpectra = specific wavelengths are = specific wavelengths are emittedemitted; characteristic of atoms; characteristic of atoms


The Bohr Model of the AtomThe Bohr Model of the Atom

Nuclear Model of atom does not explain how Nuclear Model of atom does not explain how atom can gain or lose energyatom can gain or lose energyNeils Bohr developed a model to explain how Neils Bohr developed a model to explain how structure of the atom changes when it structure of the atom changes when it undergoes energy transitionsundergoes energy transitionsBohr postulated that energy of the atom was Bohr postulated that energy of the atom was quantizedquantized, and that the amount of energy in the , and that the amount of energy in the atom was related to the electron’s position in atom was related to the electron’s position in the atomthe atom– quantizedquantized means that the atom could only have very means that the atom could only have very

specific amounts of energyspecific amounts of energy

1212

Bohr Model of Atom: Electron OrbitsBohr Model of Atom: Electron Orbits

In the Bohr Model, electrons travel in orbits In the Bohr Model, electrons travel in orbits or energy levels around the nucleusor energy levels around the nucleus

The farther the electron is from the nucleus The farther the electron is from the nucleus the more energy it hasthe more energy it has


The Bohr Model of the Atom:The Bohr Model of the Atom:Orbits and EnergyOrbits and Energy

Each orbit (energy level) has a Each orbit (energy level) has a specific amount of energyspecific amount of energy

Energy of each orbit is Energy of each orbit is symbolized by symbolized by nn, with values of , with values of 1, 2, 3 etc; the higher the value 1, 2, 3 etc; the higher the value the farther it is from the the farther it is from the nucleus and the more energy nucleus and the more energy an electron in that orbit hasan electron in that orbit has


The Bohr Model of the Atom:The Bohr Model of the Atom:Energy TransitionsEnergy Transitions

Electrons can move from Electrons can move from a lower to a higher a lower to a higher (farther from nucleus) (farther from nucleus) energy level by absorbing energy level by absorbing energy energy

When the electron moves When the electron moves from a higher to a lower from a higher to a lower (closer to nucleus) energy (closer to nucleus) energy level, energy is emitted level, energy is emitted from the atom as a from the atom as a photon of lightphoton of light


The Bohr Model of the AtomThe Bohr Model of the AtomGround and Excited StatesGround and Excited States

Ground stateGround state – atoms with their electrons in – atoms with their electrons in the lowest energy level possible; this lowest the lowest energy level possible; this lowest energy state is the most stable.energy state is the most stable.

Excited stateExcited state – a higher energy state; – a higher energy state; electrons jump to higher energy levels by electrons jump to higher energy levels by absorbing energyabsorbing energy

Atom is less stable in an excited state; it will Atom is less stable in an excited state; it will release the extra energy to return to the release the extra energy to return to the ground stateground state


Electron Energy Levels:Electron Energy Levels:

Energy LevelEnergy Level How many e fit? (2nHow many e fit? (2n22))33rdrd 18 electrons18 electrons 2 x 3 2 x 322

22ndnd 8 electrons8 electrons 2 x 2 2 x 222

11stst 2 electrons 2 electrons 2 x 1 2 x 122

Each energy level has a maximum # of Each energy level has a maximum # of electrons it can hold.electrons it can hold.

HH has one electron; it is in the 1 has one electron; it is in the 1stst energy level energy level..

HH Bohr modelBohr model


Bohr Model for AtomBohr Model for AtomElectrons fill the Lowest energy levels firstElectrons fill the Lowest energy levels first

CC

Bohr Model for C with 6 electronsBohr Model for C with 6 electrons


The Bohr Model of the AtomThe Bohr Model of the AtomSuccess and FailureSuccess and Failure

The Bohr Model very accurately The Bohr Model very accurately predicts the spectrum of hydrogen predicts the spectrum of hydrogen with its one electronwith its one electron

It is inadequate when applied to atoms It is inadequate when applied to atoms with many electronswith many electrons

A better theory was neededA better theory was needed


The Quantum-Mechanical ModelThe Quantum-Mechanical ModelOrbitalsOrbitals

Erwin SchrErwin Schrödinger used mathematics to ödinger used mathematics to predict predict probabilityprobability of finding an electron at a of finding an electron at a certain location in the atomcertain location in the atom

Result is a map of regions in the atom that Result is a map of regions in the atom that have a particular probability for finding the have a particular probability for finding the electronelectron

OrbitalOrbital = a region with a very high probability = a region with a very high probability of finding the electron when it has a of finding the electron when it has a particular amount of energyparticular amount of energy


The Quantum-Mechanical ModelThe Quantum-Mechanical Model

Each Each principal energy level or shellprincipal energy level or shell has one or has one or more more subshellssubshells– # of # of subshellssubshells same as the principal quantum same as the principal quantum

number or number or shellshell

The The subshellssubshells are often represented as a are often represented as a letterletter– s, p, d, fs, p, d, f

Each kind of subshell has Each kind of subshell has orbitalsorbitals with a with a particular shapeparticular shape


Shells & SubshellsShells & Subshells


Probability Maps & Orbital ShapeProbability Maps & Orbital Shapess orbitalsorbitals are sphericalare spherical


Probability Maps & Orbital ShapeProbability Maps & Orbital Shapepp orbitalsorbitals


Subshells and OrbitalsSubshells and Orbitals

The subshells of a principal shell have The subshells of a principal shell have slightly different energiesslightly different energies– the subshells in a shell of H all have the same the subshells in a shell of H all have the same

energy, but for multielectron atoms the subshells energy, but for multielectron atoms the subshells have different energieshave different energies

– ss < < pp < < dd < < ff

Each subshell contains one or more orbitalsEach subshell contains one or more orbitals– ss subshells have 1 orbital subshells have 1 orbital– pp subshells have 3 orbitals subshells have 3 orbitals– dd subshells have 5 orbitals subshells have 5 orbitals– f f subshells have 7 orbitalssubshells have 7 orbitals


The Quantum Mechanical ModelThe Quantum Mechanical ModelEnergy TransitionsEnergy Transitions

As in Bohr Model, atoms gain or lose As in Bohr Model, atoms gain or lose energy as electron moves between energy as electron moves between orbitals in different energy shells and orbitals in different energy shells and subshellssubshells

The The ground stateground state of the electron is the of the electron is the lowest energy orbital it can occupylowest energy orbital it can occupy

Excited stateExcited state = when an electron moves = when an electron moves to a higher energy orbitalto a higher energy orbital


The Bohr Model vs.The Bohr Model vs.The Quantum Mechanical ModelThe Quantum Mechanical Model

Both the Bohr and Quantum Both the Bohr and Quantum Mechanical models predict the Mechanical models predict the spectrum of hydrogen very accuratelyspectrum of hydrogen very accurately

Only the Quantum Mechanical model Only the Quantum Mechanical model predicts the spectra of multielectron predicts the spectra of multielectron atomsatoms


Electron ConfigurationsElectron Configurations

Electron configurationElectron configuration = distribution of = distribution of electrons into the various energy shells electrons into the various energy shells and subshells in an atom in its ground and subshells in an atom in its ground statestate

Each energy shell and subshell has a Each energy shell and subshell has a maximum number of electrons it can maximum number of electrons it can holdhold

– s = 2s = 2, , pp = 6 = 6, , dd = 10 = 10, , ff = 14 = 14


Writing Writing Electron ConfigurationsElectron Configurations

We place electrons in the energy We place electrons in the energy shells and orbitals in order of shells and orbitals in order of energy, from low energy up: Aufbau energy, from low energy up: Aufbau Principle (order of filling of orbitals)Principle (order of filling of orbitals)

TheThe d d and and ff orbitals overlap into the orbitals overlap into the higher energy levelshigher energy levels


Ene

rgy

1s

7s

2s

2p

3s

3p3d

6s6p

6d

4s

4p4d

4f

5s

5p

5d5f

Relative Energy of Orbitals in the Quantum Mechanical Model


Order of Subshell FillingOrder of Subshell Fillingin Ground State Electron Configurationsin Ground State Electron Configurations

1s

2s 2p

3s 3p 3d

4s 4p 4d 4f

5s 5p 5d 5f

6s 6p 6d

7s

Start by drawing a diagramputting each energy shell ona row and listing the subshells, (s, p, d, f), for that shell in order of energy, (left-to-right)

next, draw arrows throughthe diagonals, looping back to the next diagonaleach time


Filling the Orbitals in a SubshellFilling the Orbitals in a Subshellwith Electronswith Electrons

Energy shells fill from lowest energy to highEnergy shells fill from lowest energy to high

Subshells fill from lowest energy to highSubshells fill from lowest energy to high– ss → → pp → → dd → → ff

A single orbital can hold a maximum of 2 A single orbital can hold a maximum of 2 electrons (Pauli’s exclusion principle); orbitals electrons (Pauli’s exclusion principle); orbitals that are in the same subshell have the same that are in the same subshell have the same energyenergy

When filling orbitals that have the same energy, When filling orbitals that have the same energy, place one electron in each before completing place one electron in each before completing pairs (Hund’s rule)pairs (Hund’s rule)


Electron Configuration of Atoms in Electron Configuration of Atoms in their Ground Statetheir Ground State

Electron configuration = order of filling with Electron configuration = order of filling with electrons; number of electrons in that subshell electrons; number of electrons in that subshell written as a superscriptwritten as a superscript

Kr = 36 electronsKr = 36 electrons = 1= 1ss2222ss2222pp6633ss2233pp6644ss2233dd101044pp66

Shorthand way: use the symbol of the previous Shorthand way: use the symbol of the previous noble gas in brackets to represent all the inner noble gas in brackets to represent all the inner electrons, then just write the last setelectrons, then just write the last set

Rb = 37 electronsRb = 37 electrons = 1= 1ss2222ss2222pp6633ss2233pp6644ss2233dd101044pp6655ss1 1 = = [Kr]5[Kr]5ss11


Electron ConfigurationsElectron Configurations

Nitrogen:Nitrogen: 1s 1s222s2s222p2p33

(atomic number = 7)(atomic number = 7)

energy levelenergy level orbitalorbital

how many electronsin that orbital


1.1. Determine the atomic number of the Determine the atomic number of the element from the Periodic Tableelement from the Periodic Table

– This gives the number of protons and This gives the number of protons and electrons in the atomelectrons in the atom

Mg, Z = 12, so Mg has 12 protons and 12 Mg, Z = 12, so Mg has 12 protons and 12 electronselectrons

Example – Write the Ground State Example – Write the Ground State Orbital Diagram and Electron Orbital Diagram and Electron Configuration of Magnesium. Configuration of Magnesium.


2.2. Draw 9 boxes to represent the first 3 Draw 9 boxes to represent the first 3 energy levels energy levels ss andand pp orbitals orbitals

1s 2s 2p 3s 3p



3.3. Add one electron to each box in a set, Add one electron to each box in a set, then pair the electrons before going to then pair the electrons before going to the next set until you use all the the next set until you use all the electronselectrons

• When pairing, put in opposite arrowsWhen pairing, put in opposite arrows

1s 2s 2p 3s 3p




4.4. Use the diagram to write the electron Use the diagram to write the electron configurationconfiguration

– Write the number of electrons in each set Write the number of electrons in each set as a superscript next to the name of the as a superscript next to the name of the orbital set orbital set

11ss2222ss2222pp6633ss2 2 = [Ne]3= [Ne]3ss22

1s 2s 2p 3s 3p


Valence ElectronsValence Electrons

Valence electronsValence electrons = electrons in all the = electrons in all the subshells with the highest principal subshells with the highest principal energy shell (outermost shell)energy shell (outermost shell)

Core electronsCore electrons = = in lower energy shellsin lower energy shells

Valence electrons responsible for both Valence electrons responsible for both chemical and physical properties of chemical and physical properties of atoms.atoms.

Valence electronsValence electrons responsible for responsible for chemical reactionschemical reactions


Valence ElectronsValence Electrons

Rb = 37 electronsRb = 37 electrons = = 11ss2222ss2222pp6633ss2233pp6644ss2233dd101044pp6655ss11

The highest principal energy shell of Rb that The highest principal energy shell of Rb that contains electrons is the 5contains electrons is the 5thth, therefore Rb has , therefore Rb has 1 valence electron1 valence electron and and 36 core electrons36 core electrons

Kr = 36 electronsKr = 36 electrons = 1= 1ss2222ss2222pp6633ss2233pp6644ss2233dd101044pp66

The highest principal energy shell of Kr that The highest principal energy shell of Kr that contains electrons is the contains electrons is the 44thth, therefore Kr has , therefore Kr has 8 valence electrons8 valence electrons and and 28 core electrons28 core electrons


How many valence electrons How many valence electrons does each atom have?does each atom have?

carbon: 1scarbon: 1s222s2s222p2p22

chlorine: 1schlorine: 1s222s2s222p2p663s3s223p3p55


How many valence electrons How many valence electrons does each atom have?does each atom have?

carbon: 1scarbon: 1s222s2s222p2p22 = = 44

chlorine: 1schlorine: 1s222s2s222p2p663s3s223p3p55 = = 77


Electron Configurations andElectron Configurations andthe Periodic Tablethe Periodic Table


Electron Configurations fromElectron Configurations fromthe Periodic Tablethe Periodic Table

Elements in the same period (row) have Elements in the same period (row) have valence electrons in the same principal valence electrons in the same principal energy shellenergy shell

The number of valence electrons increases The number of valence electrons increases by one as you progress across the periodby one as you progress across the period

Elements in the same group (column) have Elements in the same group (column) have the same number of valence electrons and the same number of valence electrons and they are in the same kind of subshellthey are in the same kind of subshell


Electron Configuration & the Electron Configuration & the Periodic TablePeriodic Table

Elements in the same column have Elements in the same column have similar chemical and physical similar chemical and physical properties because their properties because their valence shellvalence shell electron configuration is the sameelectron configuration is the same

The The number of valence electronsnumber of valence electrons for for the main group elements is the the main group elements is the same same as the group numberas the group number


The Explanatory Power ofThe Explanatory Power ofthe Quantum-Mechanical Modelthe Quantum-Mechanical Model

The properties of the elements are The properties of the elements are largely determined by the number of largely determined by the number of valence electrons they containvalence electrons they contain

Since elements in the same column Since elements in the same column have the same number of valence have the same number of valence electrons, they show similar propertieselectrons, they show similar properties


The Noble Gas The Noble Gas Electron ConfigurationElectron Configuration

The noble gases have 8 valence The noble gases have 8 valence electronselectrons– except for He, which has only 2 electronsexcept for He, which has only 2 electrons

Noble gases are especially unreactiveNoble gases are especially unreactive– He and Ne are practically inertHe and Ne are practically inert

Reason noble gases are unreactive is Reason noble gases are unreactive is that the electron configuration of the that the electron configuration of the noble gases is especially stablenoble gases is especially stable

introductory chemistry, 2 nd edition nivaldo tro chapter 9 electrons in atoms and the periodic table

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