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The Structure of the Atom

Chapter 5Chemistry

Ch5 asgns. From book

• 5.1&2: 163/28,29,30,33-36• 5.4: 164/55,56,58,59,61,62• Quiz and Test #1 after 5.1,.2,.4.• 5.3: 163/42-48,50,51,69-75• Worksheets will also be assigned.• Test #2 after 5.3 is covered.

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It started a long time ago…Today460 – 370 BC

Democritus

Beginning of Atomism

You cannot divide something in half forever. The smallest piece of matter is called an atom.

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Today1808

DemocritusAtomism

460 – 370 BC

Dalton’s Postulates

4. Compounds are made from combining atoms in simple whole number ratios.

1. All elements are made of tiny indivisible particles called atoms.

2. All atoms of the same element are the same, but different from atoms of every

other element.

3. Chemical reactions rearrange atoms but do not create, destroy, or convert atoms from one element to another.

Over 2,000 years later John Dalton comes up with the first “modern” atomic theory.

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Another kind of light?Today1808 1870

DemocritusAtomism

460 – 370 BC

Dalton“Modern”

atomic theory

William Crookes invents a tube in which virtually all the gas has been removed.

Under high voltage, a ray was emitted from the cathode end of the tube.

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It started a long time ago…Today1808 1870 1897

DemocritusAtomism

460 – 370 BC

Dalton“Modern”

atomic theory

CrookesCathode rays

Cathode rays must be negative.

J.J. Thomson discovers the electron

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Today1808 1870 1897 1910

DemocritusAtomism

460 – 370 BC

Dalton“Modern”

atomic theory

CrookesCathode rays

ThomsonDiscovery

of the electron Ernest Rutherford discovers the nucleus

It started a long time ago…

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The size of the atom comes mostly from the space occupied

by the electrons

The mass of the atom comes mostly from the nucleus

Size and mass

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electronsprotons

neutrons

What happens when you change the number of protons?

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You obtain a different element!

6 protons in carbon

7 protons in nitrogen

8 protons in oxygen

The number of protons is also called the atomic number for that element.

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electronsprotons

neutrons

What happens when you change the number of electrons?

You get an ion – a charged particle.

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A neutral sodium atom

A positive sodium ion

Na

Na1+

The protons andelectrons cancel each other out

One proton is not neutralized by an electron, making this a +1 charged atom

One electron short

Balanced charges

11 protons

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A negative oxygen ion

O-2Two electrons are not neutralized by protons, making this a –2 charged atom

Two extra electrons

8 protons

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The electron cloud

Except for mass, virtually every property of atoms is determined by electrons, including size and chemical bonding

Electrons are very light and fast. They are not organized along orbits around the nucleus.

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electronsprotons

neutrons

What happens when you change the number of neutrons?

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Atomic number

Neutrons act as “glue.” They hold protons together in the nucleus.

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mass number: total number of protons and neutrons in a nucleus.

Mass number = 6 p + 6 n = 1212C

“carbon-12”

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Mass number

12 13 14

Name Carbon-12 Carbon-13Carbon-14

# protons 6 6 6# neutrons 6 7 8

isotopes: atoms or elements that have the same number of protons in the nucleus but different number of neutrons

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Number of neutrons for each of 100 lithium atoms randomly sampled from nature

It’s an AVERAGE mass!

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Isotope periodic table (first 4 rows)

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The periodic tableLi+

Na+

K+

Elements in the same column have similar chemical properties.

They tend to donate 1 electron.

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The periodic table

F–

Cl–

Br–

Elements in the same column have similar chemical properties.

They tend to accept 1 electron.

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Assignment:

5.1&2: 163/28,29,30,33-36and handout(s)

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Elements in the same column have similar chemical properties.

Electrons are responsible for these chemical properties.

Quantum theory explains how the

universe behaves on a very small scale.

Niels Bohr

A wave “particle”

We intuitively think of light as a waveand an electron as a particle

A wave “particle”

But light waves come in bundles of light (photons)and an electron behaves as a wave

frequency: the rate at which an oscillation repeats; one hertz (Hz) is a frequency of one oscillation per second.

wavelength: the distance (separation) between any two successive peaks (or valleys) of a wave.

The higher the frequency, the higher the energy

Electrons Light

On the scale of atoms

Planck’s constant (h) is used to calculate the energy and wavelength of electrons and photons

4.136x10-3 eV or

or 4.136x10-3 eV

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l = h = √ 2mE

l = 6.626x10-34Js √2(9.109x10-31kg)(6.636x10-20J

l = 1.906 x 10-9 m

Light travels as bundles called photons

1 electron volt (eV) = 1.602 x 10–19 J.

A very small unit of energy

Energy of a photon

Wavelength and frequency are related

1 Hertz, Hz = 1 cycle = 1 = s-1

sec sec

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What is the frequency of a yellow light with wavelength 580 nm? 1 nm = 10-9 m

c = fl --> f = cl

f = 3 x 10 8 m 580 x 10-9 ms

f = 5.2 x 1014 Hz

The wavelength of red laser light is 652 nm. What is its frequency, n? How much energy, E, does a photon of this light have in electron volts?

Asked: Frequency and energyGiven:

Relationships:

Solve:

Answer:

Since 1 Hz = 1/s, the frequency is 4.6 x 1014 Hz and the energy is 1.9 eV.

9652 10 ml

,c E hln n

8 14

9

15 14

3 10 / 4.6 10652 10

4.136 10 4.6 10 .91 /

c m sc thereforem

e

s

E h e VV s s

ln nl

n

1 nm = 10-9 m

Wave addition

The sum of two waves can give a “bigger”

wave.

The sum of two waves can be

zero!

Wave addition

Imagine a wave (wave 1) inside a box…

Wave 1 bounces off the wall and creates wave 2.

Could the waves cancel out each other?

Wave 1

Wave 2

Wave that “survives”

Wave addition

Perfect “fit” Poor

“fit”

Allo

wed

Not

allo

wed

The wavelength of the electron must be a “multiple” of the “size” of the atom.

Only certain wavelengths are allowed…

… and wavelength is related to energy.

The Bohr model

Only certain energy levels are allowed

Energy is quantized!

Different quantum states can have the same

wavelength

The Bohr model

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orbital: group of quantum states that have similar spatial shapes, labeled s, p, d, and f.

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Today1808 1870 1897 1910 1925

DemocritusAtomism

460 – 370 BC

Dalton“Modern”

atomic theory

CrookesCathode rays

ThomsonDiscovery

of the electron

RutherfordDiscovery of the nucleus

Wolfgang Pauli Quantum rule on electron structure

Pauli exclusion principle: two electrons in the same atom may never be in the same quantum state.

A look at history

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Quantum states can have the same energy level

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One electron per quantum state

Fill lower-energy levels first

Lithium’s 3rd electron has to go into the 2nd energy level

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Electrons settle into the lowest unfilled quantum states

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1st row

Full energy level

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2nd row

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Orbitals

s

Principle quantum number

1

Energy levelsQuantum states

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Orbitals

s

s p

Principle quantum number

1

2

Energy levelsQuantum states

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Orbitals

s

s

s

p

p

Principle quantum number

1

2

3

Energy levelsQuantum states

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Orbitals

s

s

s

s

p

p

pd

Principle quantum number

1

2

3

4

Energy levelsQuantum states

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Orbitals

s

s

s

s

s

p

p

p

p

d

d

Principle quantum number

1

2

3

4

5

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Orbitals

s

s

s

s

s

s

p

p

p

p

p

d

d

d

Principle quantum number

1

2

3

4

5

6

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Orbital

s

Principle quantum number

1

Energy levels

Quantum states

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Note how the 3p orbital gets filled before 3d

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Write the electron configuration for silicon.14 protons

There is a net charge of zero, so silicon has 14 electrons.

The chart shows that 12 electrons fill up to 3s2.

The remaining 2 electrons go to a 3p orbital.

The electron configuration for silicon is:

1s22s22p63s23p2.

Electron Arrangement

Another link for reviewhttp://www.mrcoulter.com/LECTURES/28Elec-config.pdf

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Assignment: 5.4: 164/55,56,58,59,61,62And handout(s)

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CHAPTER 5

The Structure of the Atom

5.4 Light and Spectroscopy

Light is a form of electromagnetic energy that comes from electrons in atoms

The human eye can only detect a certain range of that energy: the visible spectrum.

White light from a lamp or the sun is not truly white!

Analyzing starlight with a prism(one of the first spectrometers)

Visible light is only a small range in the electromagnetic spectrum

We are surrounded by electromagnetic energy

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prism

electron

all possible energy levels

Light from an incandescent light bulb:

prism

electron

fixed energy levels

Light from pure hydrogen:

Hydrogen atoms can only absorb and emit light of very specific energies.

Remember: only some energy levels are

allowed.

Why does the atom absorb only specific (discrete) energies?

Matter and light

Energy levels

Photon(energy)

Energy levels

Energy of the photon matches a gap between

levels

Energy (light) is absorbed.

Energy of the photon does not match a gap between

levels

Energy (light) passes through the atom.

Matter and light

Energy levelsPhoton(energy)

Energy of the photon matches a gap between

levels

Energy (light) is absorbed.

another photon is emitted

specific color(wavelength)

Matter and light

Each type of atom has a different electron structure.Each element has unique energy levels like a fingerprint.

Spectrum cards

How to read the spectrum

cards

Combinations of elements contain spectral lines from both.

Spectrum cards

Photon emitted

Photon absorbed

Energy levels

Photon(energy)

Energy of the photon matches a gap between

levels

Reemission of light has two steps:

Visible light is only a small range of the electromagnetic spectrum.

Each type of atom has a different electron structure.Each element has unique energy levels like a fingerprint.

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Assignment:

5.3: 163/42-48,50,51,71-75and handout(s)

Quantum Numbers

• Quantum numbers specify the properties of atomic orbitals and the properties of electrons in orbitals. This is also known as probable location of electrons about the nucleus of an atom.

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Principal Quantum Number, n

Indicates the main energy level occupied by an electron(n=1,2,3,…7)

http://library.thinkquest.org/C006669/82

Angular momentum quantum number has 4 basic shapes

• The values and shapes are • l = 0 s shape• l = 1 p• l = 2 d• l = 3 f

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Angular Momentum Quantum Number, l

• s shape

sparknotes.com84

p shape

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d shaped orbitals

Courtesy of bluelight.ru86

f orbitals

f orbitals are very complex and you will not be responsible for drawing them. The site below has more informtion.

http://www.d.umn.edu/~pkiprof/ChemWebV2/AOs/ao4.html

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Spin quantum number, s, has only two possible values

• Has only two possible values: +1/2, -1/2.

• See table 2 on page 110 to get a better idea of the number of orbitals and electrons per energy level.

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Electron Configurations

I. Rules Governing Electron ConfigurationsII. Orbital NotationIII. Electron-Configuration Nottion

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Rules Governing Electron Configurations

I. Aufbrau Principle – an electron occupies the lowest-energy orbital that can receive it.

Source: https://chemistry.twu.edu/tutorial/AufbauSum.html

This is really a thought process in which we think about building up an atom from the one that preceeds it in atomic number, by adding a proton and neutrons to the nucleus and one electron to the appropriate atomic orbital.

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II. Pauli Exclusion Principle – no two electrons in the same atom can have the same set of four quantum numbers.

Rules Governing Electron Configurations, cont.

The box at left shows the different spin states of two electrons in the same orbital. This drawing is the electron configuration of a helium atom’s 1 s orbital.

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Rules Governing Electron Configurations, cont.

III. Hund’s Rule – orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron, and all electrons in singly occupied orbitals must have the same spin state.

en.citizendium.org

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Source: chem.wisc.edu

Periodic Table: Orbitals

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Orbital Notation

Source: naturalphilosophers.org

Pair of electrons in an orbital

Unpaired electron

Orbital name

What element is this showing?Fluorine

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Sample problems

Write the electron configuration notation for Silicon and Scandium (use the Aufbrau diagram)Si has 14 electrons2 in 1s 2 in 2s6 in 2p 2 in 3s 2 in 3p written as:1s2 2s2 2p6 3s2 3p2

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Scandium Electron Configuration Notation

Sc has 21 electrons

1s2 2s2 2p6 3s2 3p6 4s2 3d1

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Scandium Notations

Electron Configuration Notation1s2 2s2 2p6 3s2 3p6 4s2 3d1

Orbital Notation__ __ __ __ __ __ __ __ __ __ __ __ __ __ _1s 2s 2p 3s 3p 4s 3d

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Notations,cont.Noble gas notation – back up to the last noble gas prior to the element

and add orbitals:[Ar]4s23d1

Dot notation - shows only the outer shell electrons for an element’s atom (maximum number of e’s in an outer shell is 8) for Sc: 4s2 for F: 2s22p5 for Ne: 2s22p6

.. . . Sc : : F : : Ne : . . .

Other info: atoms are more stable when they have a half-filled or completely

filled outer shell

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