atomistructurenew.ppt

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Atomic Structure

(2)

What is a theory?

 a well-substantiated explanation of a well-substantiated explanation of

some aspect of the natural world; some aspect of the natural world;

 an organized system of accepted an organized system of accepted

knowledge that applies in a variety knowledge that applies in a variety

of circumstances to explain a of circumstances to explain a

specific set of phenomena; specific set of phenomena;

 "theories can incorporate facts and "theories can incorporate facts and

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"If I have seen

further it is

by standing

on the

shoulders of

Giants."

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Early Theories

Democritus: 4 B.C.: “atom”

Believed there were 4 elements:

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>All elements composed of tiny particles called atoms

>Atoms of same element are identical;

atoms of different elements are different

>Atoms of different elements can physically mix together or chemically combine to form compounds

>Chemical reactions cannot change atoms of one type of element to another

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Thomson: 1856-1940

>discovered electrons in 1897

>used a cathode ray tube

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Cathode Ray Tubes

 A cathode ray tube or CRT is a

specialized vacuum tube in which images are produced when an

electron beam strikes a phosphorescent surface.

 TVs, PCs, ATMs, video games, video cameras, and monitors all contain

cathode-ray tubes.

(8)

Rutherford: 1871-1937

>Gold Foil Experiment

>Discovered the nucleus

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Rutherford’s Gold Foil Experiment

Experiment

Shot positively charged alpha particles at

gold foil

Results

1) Most particles

passed through the foil

2) A few were

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Rutherford’s Gold Foil

Experiment

Conclusions

Conclusions

1)

1) small, dense, positively charged small, dense, positively charged

core (nucleus) core (nucleus)

2)

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Modern Theories

Bohr

Bohr  planetary model planetary model

 electrons arranged in concentric circular patterns  paths or orbits around nucleus (energy level)

Wave-Mechanical Model

Wave-Mechanical Model  Electron Cloud Electron Cloud Model

Model

 based on thebased on the ideas ideas that orbitals are the area of that orbitals are the area of

highest probability where an electron will be highest probability where an electron will be

found. found.

 Orbitals have a variety of shapes and names (s, p, Orbitals have a variety of shapes and names (s, p,

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Example: Wave Mechanical

Model

 ΨΨ22 (psi_(psi22) is a _{) is a}

calculation that calculation that can predict the can predict the

probability of probability of

finding an electron finding an electron

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Summary- Atomic

Models

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Thomson’s Plum Pudding

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Rutherford’s Nuclear

Model

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Bohr’s Planetary Model

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Wave-Mechanical Model

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Subatomic Particles

Name

Name SymbolSymbol ChargeCharge MassMass Proton

Proton (

(located in located in nucleus

nucleus 

nucleon) nucleon)

p

p++ +1₊₁ 1 amu _{1 amu}

Neutron Neutron

(

(located in located in nucleus

nucleus 

nucleon) nucleon)

n

n00 0₀ 1 amu_{1 amu}

Electron Electron

(

(located located outside the

outside the

nucleus in

orbitals

orbitals))

e

e-- -1_-1 1/1836 _1/1836

amu amu

**Note: amu = atomic mass unit

1 amu = 1/12th_{mass of a carbon-12}

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Atomic Number

 Equal to the number of protonsEqual to the number of protons

 Every element has its own atomic Every element has its own atomic

number number

 See Periodic TableSee Periodic Table

C

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Mass Number

 Equal to the sum of the protons and Equal to the sum of the protons and

the neutrons (whole number) the neutrons (whole number)

 Can be written as Can be written as carbon-12 carbon-12

C

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To find:

# of protons # of protons 

look up

look up atomic numberatomic number on Periodic on Periodic Table

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To find:

# of electrons # of electrons 

in a

in a neutral atomneutral atom, it is equal to the , it is equal to the number of protons

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To find:

# of neutrons # of neutrons 

if protons + neutrons = mass then, if protons + neutrons = mass then,

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Practice

Element Atomic # Mass # # of protons # of

neutrons # of electrons

Ca Mg Na He 20 12

40 20 20 20

11

24 12 12 ₁₂

2 4 11 12 11 23

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Ions

 Defined as Defined as “charged particles”“charged particles”

 Ions are formed when the Ions are formed when the

number of

number of electronselectrons changes. changes.

 If a (+) ion is formed, If a (+) ion is formed,

electrons are lost

electrons are lost (called (called cations).

cations).

 If a (-) ion is formed, If a (-) ion is formed, electrons electrons

are gained

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Examples

 CaCa2+2+

A Ca

A Ca atomatom has has 20 20 protons and

protons and 2020 electrons.

electrons.

A Ca

A Ca2+2+ ion has _{ion has}lost two _{lost two}

electrons

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Examples

 ClCl-

-A Cl

A Cl atom atom has has 1717 protons and protons and 1717 electrons.

electrons. A Cl

A Cl-- ion_ion has _hasgained one electron_{gained one electron} to _to

have

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Practice

Elemen Elemen t t Atomi Atomi c #

c # Mass Mass

#

# p

p nn ee

Zn Zn

Fe Fe3+3+

F F

I I-

-Li Li++

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Isotopes

 Definition: Atoms that have the same Definition: Atoms that have the same

atomic number (same # of protons) atomic number (same # of protons)

but a different mass number but a different mass number

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Isotopic Symbols

 Must write isotopic symbol to show Must write isotopic symbol to show

mass mass

 2 Isotopes will have the same atomic 2 Isotopes will have the same atomic

# (bottom) and a different mass # # (bottom) and a different mass #

(top) (top)

X

Mass #

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Write the isotopic symbol

for:

 Carbon-14 (write a symbol for a Carbon-14 (write a symbol for a

different isotope of carbon) different isotope of carbon)

C

14

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for:

 Oxygen-17Oxygen-17 (write a symbol for a (write a symbol for a

O

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Write the isotopic symbol

for:

 Chlorine-37Chlorine-37 (write a symbol for a (write a symbol for a

Cl

37

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3 Common Isotopes of

Hydrogen

Name

Name SymbolSymbol #p#p #e#e ## n n Mass Mass Protium Protium

H

1

1 11 00 11

Deuteriu Deuteriu m m

H

1

1 11 11 22

Tritium

H

1

1 11 22 33

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Why is atomic mass

not

a

whole number?

 The atomic mass on the periodic The atomic mass on the periodic

table is a

table is a weighted averageweighted average of the _{of the}

isotopes

isotopes of the elements. of the elements.

 The The weighted atomic massweighted atomic mass takes takes

into account the

into account the relative relative abundances

abundances of all the naturally of all the naturally occurring isotopes.

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How do you calculate a

weighted average?

 To calculate the weighted average you To calculate the weighted average you convert each percentage to a decimal by convert each percentage to a decimal by

moving it 2 places left. Multiply the moving it 2 places left. Multiply the

decimal by the mass for each isotope and decimal by the mass for each isotope and

add them all up. add them all up.

 Or you can multiply the percent Or you can multiply the percent

abundance (without moving the decimal) abundance (without moving the decimal)

by the mass for each isotope add them all by the mass for each isotope add them all

(38)

Example of a general

weighted average

 Your grade in chemistry Your grade in chemistry

 70% exams 8570% exams 85

 10% quizzes 10010% quizzes 100

 10% labs 9510% labs 95

 10% HW/CW 8010% HW/CW 80

(0.70)85 + (0.10)100 + (0.10)95

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Example 1:

 Determine weighted atomic massDetermine weighted atomic mass

 Boron-10 19.78% 10.013 amuBoron-10 19.78% 10.013 amu

 Boron-11 80.22% 11.009 amuBoron-11 80.22% 11.009 amu

(0.1978) 10.013 +

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Example 2

 Determine weighted atomic massDetermine weighted atomic mass

 Potassium-39 93.12% 38.964 amuPotassium-39 93.12% 38.964 amu

 Potassium-41 6.88% 40.962 amuPotassium-41 6.88% 40.962 amu

(0.9312) 38.964 +

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Do Now

1.

1. How many total electrons does an AlHow many total electrons does an Al+3+3 ion have? ion have?

2.

2. If a neutral atom has 10 neutrons and 8 electrons If a neutral atom has 10 neutrons and 8 electrons

how many protons does it have?

3.

3. How does an atom of Lithium-7 differ from an atom How does an atom of Lithium-7 differ from an atom

of Beryllium-9

4.

4. Compare a NaCompare a Na+1+1 ion to a Na atom? ion to a Na atom?

5.

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Bohr models

How do electrons “orbit” the nucleus?

Each principal energy level …

 is a fixed distance from the nucleus

 can hold a specific number of electrons

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

The greater the distance from the

nucleus…the greater the energy of

the electrons in it.

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Energy levels or shells

energy level number of

1 2

2 8

3 18

4 32

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Bohr models: examples

P+

n0 2

8 e-nucleus---

# protons And neutrons

-energy levels

and total number of electrons

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TRY THESE

12 p+ 12 n0 Mg

2 8 2

e-Electron configuration (bottom left corner on PT): Mg 2-8-2

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H Na

H 1 Na 2-8-1

F C

F 2-7 C 2-4

1p+

1

e-11 p+ 12 n0

2 e-

812 7

2 4

e-answers

answers

9 p+ 10 n0

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Lewis Dot Diagrams

Valence shell: outer most shell of an atom that contains electrons

Valence electrons: electrons that occupy the valence shell (last number in electron configuration)

Electron dot diagrams or Lewis dot diagrams:

show only the valence shell of the atom

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TRY THESE

O F C

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Ions

For ions:

For ions: remember that ions have gained remember that ions have gained or lost electrons.

or lost electrons.

Use periodic table to find charge of ion Use periodic table to find charge of ion

(see table) (see table)

For dot diagrams of Ions For dot diagrams of Ions

(+)ions

(+)ions  indicate charge no dots around _{indicate charge no dots around} the symbol

the symbol (-)ions

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Dot Diagrams for Ions

Ca



Ca

+2

Cl

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Ground State vs. Excited

State

 When all electrons in an atom occupy the When all electrons in an atom occupy the lowest available orbitals, it is said to be lowest available orbitals, it is said to be

in the

in the ground stateground state..

 When electron(s) absorb energy, they When electron(s) absorb energy, they have the ability to

have the ability to jump to higher energy jump to higher energy levels

levels. .

 The The excited stateexcited state is when electrons have is when electrons have absorbed energy and no longer occupy absorbed energy and no longer occupy

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Possible Excited States

Na (ground state)

Na (possible excited

state)

Na (another possible

excited state)

Na (another possible

excited state)

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Absorption

 When an electron “jumps” to a When an electron “jumps” to a

higher energy level it

higher energy level it absorbs absorbs energy

energy..

 The excited state is a The excited state is a temporary temporary

state.

state. Excited State (i.e. energy level 2)

Ground State (i.e. Energy level 1)

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e-Emission

Emission

 The electron then The electron then falls falls back down to the back down to the ground state,

ground state, emitting energyemitting energy. .

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 This This radiant energyradiant energy has a characteristic has a characteristic color

color and and wavelengthwavelength that can be that can be determined.

determined.

 Every electron transition produces a Every electron transition produces a specific wavelength of light and all specific wavelength of light and all

transitions for an element blend together. transitions for an element blend together.  This light can be This light can be separated separated through a through a

prism

prism into its various wavelength into its various wavelength components.

components.

 Every element has its own unique Every element has its own unique bright bright line spectrum

line spectrum that can be used to help that can be used to help identify the presence of that element. identify the presence of that element.

 Ex: elements in a star, forensic analysis, Ex: elements in a star, forensic analysis, flame tests, spectroscopy

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Light and Atomic Spectra

(bright line spectra)

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Sunlight and prisms

 Sunlight produces Sunlight produces a continuous

a continuous

range of

wavelengths and

frequencies

frequencies that that can be separated

can be separated

into all the colors

of the

of the rainbowrainbow..

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

Atomic emission spectra

produce

narrow lines of color

called bright line spectra

.



Each line corresponds to an

exact

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Experiments – Flame

Tests

 Flame Tests – Flame Tests – demonstrates the demonstrates the

emission spectrum of a

substance.

 Completed by heating elements Completed by heating elements

to high temperatures so they

may enter excited state.

 Characteristic color will be Characteristic color will be

emitted as

emitted as excited electrons excited electrons return to ground state.

return to ground state.

 Used to determine Used to determine metal ion metal ion

presence

presence in unknown in unknown substance.

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Experiments –

Spectroscopy

 Spectroscopy – Spectroscopy – used to used to view the bright line

view the bright line

spectra for given gases.

 Completed by viewing a Completed by viewing a gas tube through which

gas tube through which

an electric current is

passed.

 Use an instrument Use an instrument called a

called a spectroscopespectroscope, , contains a prism to

contains a prism to

separate emitted light

into line spectra.

ss

vacuum tube