Chapter 09 Tro Rev 1

8/3/2019 Chapter 09 Tro Rev 1

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Tro's Introductory Chemistry, Chapter 9 2

Why do Blimps Float?

Because they are filled with agas less dense than air

Early blimps used hydrogen gas; hydrogen’s flammabilityled to the Hindenburg disaster

Blimps now use helium, anonflammable gas – in fact itdoesn’t undergo any chemicalreactions

This chapter investigatesmodels of the atom we use toexplain the differences in theproperties of the elements

http://wps.prenhall.com/wps/media/objects/169/173803/FormationofWater.html

http://wps.prenhall.com/wps/media/objects/169/173803/FormationofWater.html




Electromagnetic Radiation

Light is one of the forms ofenergy

Light is one type of a moregeneral form of energycalled electromagnetic radiation

Electromagnetic radiationtravels in waves




Characteristics of a Wave

Wavelength = distance from peak to peak

Amplitude = height of the peak

Frequency = the number of wave peaks thatpass in a given time

Speed = rate the waves travel




Particles of Light

Scientists in the early 20th century showedthat electromagnetic radiation was composedof particles we call photons

– Max Planck and Albert Einstein

– photons are particles of light energy

Each wavelength of light has photons thathave a different amount of energy

– the longer the wavelength, the lower theenergy of the photons




The Electromagnetic Spectrum

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

Color of light is determined by its wavelength






Light’s Relationship to Matter

Atoms can absorb energy, butthey must eventually release it

When atoms emit energy, it is

released in the form of light =emission spectrum

Atoms don’t absorb or emit all

colors, only very specific

wavelengths; the spectrum ofwavelengths can be used toidentify the element

http://wps.prenhall.com/wps/media/objects/166/170213/FlameTestsforMetals.html

http://wps.prenhall.com/wps/media/objects/166/170213/FlameTestsforMetals.html




Emission Spectrum or Line Spectrum




Line Spectra = specific wavelengths areemitted; characteristic of atoms

http://wps.prenhall.com/wps/media/objects/166/170213/LinePairinSodiumSpectrum.html

http://wps.prenhall.com/wps/media/objects/166/170213/LinePairinSodiumSpectrum.html




The Bohr Model of the Atom

Nuclear Model of atom does not explain howatom can gain or lose energy

Neils Bohr developed a model to explain howstructure of the atom changes when itundergoes energy transitions

Bohr postulated that energy of the atom wasquantized , and that the amount of energy in the

atom was related to the electron’s position inthe atom – quantized means that the atom could only have very

specific amounts of energy



12

Bohr Model of Atom: Electron Orbits

In the Bohr Model, electrons travel in orbitsor energy levels around the nucleus

The farther the electron is from the nucleusthe more energy it has




The Bohr Model of the Atom:Orbits and Energy

Each orbit (energy level) has aspecific amount of energy

Energy of each orbit issymbolized by n , with values of1, 2, 3 etc; the higher the valuethe farther it is from the

nucleus and the more energyan electron in that orbit has




The Bohr Model of the Atom:Energy Transitions

Electrons can move froma lower to a higher(farther from nucleus)

energy level by absorbingenergy

When the electron movesfrom a higher to a lower

(closer to nucleus)energy level, energy isemitted from the atom asa photon of light




The Bohr Model of the AtomGround and Excited States

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

Excited state – a higher energy state;electrons jump to higher energy levels byabsorbing energy

Atom is less stable in an excited state; it willrelease the extra energy to return to theground state




Electron Energy Levels:

Energy Level How many e fit? (2n2

)3rd 18 electrons 2 x 32

2nd 8 electrons 2 x 22

1st

2 electrons 2 x 12

Each energy level has a maximum # ofelectrons it can hold.

H has one electron; it is in the 1st

energy level.

H Bohr model




Bohr Model for AtomElectrons fill the Lowest energy levels first

C

Bohr Model for C with 6 electrons




The Bohr Model of the AtomSuccess and Failure

The Bohr Model very accuratelypredicts the spectrum of hydrogen

with its one electronIt is inadequate when applied to atomswith many electrons

A better theory was needed




The Quantum-Mechanical ModelOrbitals

Erwin Schrödinger used mathematics topredict probability of finding an electron at acertain location in the atom

Result is a map of regions in the atom thathave a particular probability for finding theelectron

Orbital = a region with a very high probabilityof finding the electron when it has aparticular amount of energy




The Quantum-Mechanical Model

Each principal energy level or shell has one ormore subshells

– # of subshells same as the principal quantum

number or shell The subshells are often represented as aletter

– s, p, d, f

Each kind of subshell has orbitals with aparticular shape




Shells & Subshells




Probability Maps & Orbital Shapes orbitals are spherical




Probability Maps & Orbital Shape

p orbitals




Subshells and Orbitals

The subshells of a principal shell haveslightly different energies

– the subshells in a shell of H all have the sameenergy, but for multielectron atoms the subshells

have different energies – s < p < d < f

Each subshell contains one or more orbitals

– s subshells have 1 orbital

– p subshells have 3 orbitals

– d subshells have 5 orbitals

– f subshells have 7 orbitals




The Quantum Mechanical ModelEnergy Transitions

As in Bohr Model, atoms gain or loseenergy as electron moves betweenorbitals in different energy shells and

subshells

The ground state of the electron is thelowest energy orbital it can occupy

Excited state = when an electron movesto a higher energy orbital




The Bohr Model vs.The Quantum Mechanical Model

Both the Bohr and QuantumMechanical models predict the

spectrum of hydrogen very accurately

Only the Quantum Mechanical modelpredicts the spectra of multielectron

atoms




Electron Configurations

Electron configuration = distribution ofelectrons into the various energy shellsand subshells in an atom in its groundstate

Each energy shell and subshell has amaximum number of electrons it canhold

– s = 2 , p = 6, d = 10, f = 14

http://wps.prenhall.com/wps/media/objects/166/170213/ElectronConfigurationsmov.html





Writing Electron Configurations

We place electrons in the energyshells and orbitals in order ofenergy, from low energy up: AufbauPrinciple (order of filling of orbitals)

The d and f orbitals overlap into the

higher energy levels






E n e r g y

1s

7s

2s

2p

3s

3p

3d

6s6p

6

d

4s

4p

4d4f

5s

5p

5d5f

Relative Energy of Orbitalsin the Quantum Mechanical Model




Order of Subshell Fillingin Ground State Electron Configurations

1s

2s 2 p

3s 3 p 3d

4s 4 p 4d 4 f

5s 5 p 5d 5 f

6s 6 p 6d

7s

Start by drawing a diagram

putting each energy shell on

a row and listing the subshells,

(s, p, d, f ), for that shell inorder of energy, (left-to-right)

next, draw arrows through

the diagonals, looping back

to the next diagonal

each time




Filling the Orbitals in a Subshellwith Electrons

Energy shells fill from lowest energy to high

Subshells fill from lowest energy to high

– s → p → d → f

A single orbital can hold a maximum of 2electrons (Pauli’s exclusion principle); orbitals

that are in the same subshell have the same

energyWhen filling orbitals that have the same energy,place one electron in each before completing

pairs (Hund’s rule)




Electron Configuration of Atomsin their Ground State

Electron configuration = order of filling withelectrons; number of electrons in that subshellwritten as a superscript

Kr = 36 electrons = 1s 22s 22p 63s 23p 64s 23d 104p 6 Shorthand way: use the symbol of the previousnoble gas in brackets to represent all the innerelectrons, then just write the last set

Rb = 37 electrons = 1s 22s 22p 63s 23p 64s 23d 104p 65s 1 =[Kr]5s 1




Electron Configurations

Nitrogen: 1s2

2s2

2p3

(atomic number = 7)

energy level orbital

how many electronsin that orbital




1. Determine the atomic number of the

element from the Periodic Table – This gives the number of protons and

electrons in the atom

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

Example – Write the Ground StateOrbital Diagram and Electron

Configuration of Magnesium.




2. Draw 9 boxes to represent the first 3

energy levels s and p orbitals

1s 2s 2p 3s 3p






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

• When pairing, put in opposite arrows

1s 2s 2p 3s 3p








4. Use the diagram to write the electronconfiguration

– Write the number of electrons in each setas a superscript next to the name of theorbital set

1s 22s 22p 63s 2 = [Ne]3s 2

1s 2s 2p 3s 3p




Valence Electrons

Valence electrons = electrons in all thesubshells with the highest principalenergy shell (outermost shell)

Core electrons = in lower energy shells

Valence electrons responsible for bothchemical and physical properties of

atoms.Valence electrons responsible forchemical reactions




Valence Electrons

Rb = 37 electrons =1s 22s 22p 63s 23p 64s 23d 104p 65s 1

The highest principal energy shell of Rb thatcontains electrons is the 5th, therefore Rb

has 1 valence electron and 36 core electrons

Kr = 36 electrons = 1s 22s 22p 63s 23p 64s 23d 104p 6

The highest principal energy shell of Kr that

contains electrons is the 4th

, therefore Kr has8 valence electrons and 28 core electrons




How many valence electronsdoes each atom have?

carbon: 1s

2

2s

2

2p

2

chlorine: 1s22s22p63s23p5




How many valence electrons

does each atom have?

carbon: 1s

2

2s

2

2p

2

= 4

chlorine: 1s22s22p63s23p5 = 7




Electron Configurations andthe Periodic Table




Electron Configurations fromthe Periodic Table

Elements in the same period (row) havevalence electrons in the same principalenergy shell

The number of valence electrons increasesby one as you progress across the period

Elements in the same group (column) have

the same number of valence electrons andthey are in the same kind of subshell




Electron Configuration & thePeriodic Table

Elements in the same column havesimilar chemical and physical

properties because their valence shell electron configuration is the same

The number of valence electrons for

the main group elements is the same as the group number

Th E l P f




The Explanatory Power ofthe Quantum-Mechanical Model

The properties of the elements arelargely determined by the number of

valence electrons they containSince elements in the same columnhave the same number of valence

electrons, they show similar properties

Th N bl G



The Noble GasElectron Configuration

The noble gases have 8 valenceelectrons

–

except for He, which has only 2 electronsNoble gases are especially unreactive

– He and Ne are practically inert

Reason noble gases are unreactive is

that the electron configuration of thenoble gases is especially stable

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Chapter 09 Tro Rev 1

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