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Chapter 3 Atomic Structure. You will explain why the model of the atom changed throughout history. Objective:. What is a model?. Models are used to help us understand things that cannot be seen directly

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what is a model
What is a model?
  • Models are used to help us understand things that cannot be seen directly
  • Models are used when something is too large, too small, or too dangerous to be studied directly.
examples of scientific models
Examples of Scientific Models

This model shows the alignment between the sun, moon, & earth. As it rotates, it shows the phases of the moon and how we measure a year.

This model is a mathematical representation of a sound wave. You cannot see sound, but you can see how it affects other objects with its vibrations.

examples of scientific models1
Examples of Scientific Models
  • What other examples can you think of?
  • Are there other models present in this room?
a good model
A good model…
  • Must be based on observations and indirect experimentation.
  • Must explain as many characteristics of the original object as possible.
  • Should be as simple as possible.
when do you change a model
When do you change a model?
  • All models have limitations —No model has ever been totally complete.
  • A model changes when observations of a new situation do not agree with the current model.
creating a model
Creating a Model
  • The “Think Tube”is also a model for something you cannot see directly.

?

THINK TUBE

creating a model1
Creating a Model
  • How many strings are on the inside?
  • Make your own model showing how

the “Think Tube” works.

atoms
Atoms
  • The atom has not changed over time, but our idea and model of the atom has.
definition of atom
Definition of Atom:
  • the smallest particle of an element that retains the chemical properties of that element.
democritus 400 bc
Democritus 400 BC

By convention there is color,By convention sweetness,By convention bitterness,But in reality there are atoms and space.   -Democritus (c. 400 BCE)

Convention means because we said so- doesn’t really exist

democritus 400 bc1
Democritus 400 BC
  • Democritus was smashing up sea shells one day and thought that you can break down the shell to tiny pieces, but it can not be completely destroyed.
slide14

Democritus 400 BC

  • Looked at sand on the beach. Cut sand in half and got fewer and fewer grains of sand.
  • What was the smallest piece?
  • He called it atomos =

greek word meaning cannot be cut

democritus 400 bc according to democritus atoms are
Democritus 400 BCAccording to Democritus atoms are:
  • Invisible
  • Indivisible
  • Solid
  • Eternal
  • Surrounded by an empty space

http://www.brl.ntt.co.jp/group/butsuden-g/img/redball.gif

democritus 400 bc continued
Democritus 400 BCcontinued:
  • Have an infinite number of possible
  • shapes.
  • Each type of atom had a different size.
democritus 400 bc atoms
Democritus 400 BCAtoms -

http://www.brl.ntt.co.jp/group/butsuden-g/img/redball.gif

slide19

Aristotle’s Idea 300 BC

  • All substances are made of 4 elements: Fire, Air, Earth, and Water
aristotle s idea 300 bc
Aristotle’s Idea 300 BC
  • There were also four qualities: dryness, hotness, coldness, and moistness.
  • Fire was dry and hot, while water was moist and cold, etc.
  • Each of these elements move naturally in a line to their "proper place," where it will be at rest.
aristotle 300 bc
Aristotle 300 BC
  • Water sits on top of the earth, he explained, because it is lighter, yet air floats above the water because it is lighter still—and fire, lightest of all, rises highest. Furthermore, he claimed that the planets beyond Earth were made up of a "fifth element," or quintessence, of which little could be known.
democritus vs aristotle
Democritus vs Aristotle
  • Ancient Greeks accepted Aristotle’s ideas and rejected Democritus.
  • What holds the particles together?
  • Democritus could not answer this question
  • Remained that way until the 17th century
slide24

Important Discoveries

  • Law of Conservation of Mass
  • Law of Definite Proportions
  • Law of Multiple Proportions
law of conservation of mass matter
Law of Conservation of Mass (Matter)
  • Lavosier measured the mass of chemicals before and after a chemical reaction and found that the weight did not change.
  • In a chemical reaction, matter is neither created nor destroyed.
law of definite proportions
Law of Definite Proportions
  • Also called Law of Constant Composition
  • Proposed by Joseph Proust
  • Elements always react and combine with one another in the same proportions.
law of definite proportions1
Law of Definite Proportions

A chemical compound is always composed of the same combination of atoms -

copper carbonate

CuCO3

http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH02/FG02_01.JPG

law of definite proportions2
Law of Definite Proportions
  • Water has the formula H2O. This means that water in the ocean, lakes, or in our sinks always contains 2 atoms of Hydrogen for every 1 atom of Oxygen. What percent of water is Hydrogen and what percent is Oxygen?

H: 2g/18g = 11% O: 16g/18g = 89%

law of multiple proportions
Law of Multiple Proportions
  • If two elements form more than one compound between them, then the ratios of the weights of the two atoms will be ratios that can be reduced to small whole numbers.

http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH02/FG02_02.JPG

john dalton 1766 1844
John Dalton 1766-1844
  • English school teacher and public lecturer by the age of 12.
  • As a Quaker, Dalton led a modest existence, although he received many honors later in life. In tribute, more than 40,000 people marched in his funeral procession.

http://www.unit5.org/christjs/John_Dalton.htm

john dalton s atomic theory
John Dalton’s Atomic Theory
  • Dalton’s Theory was a return to the ideas of Democritus
  • Dalton turned the idea into a scientific theory that could be tested
  • Not all of Daltons ideas are still true today. Some ideas were modified.
john dalton s atomic theory1
John Dalton’s Atomic Theory:
  • All matter is composed of atoms.
  • Atoms of a particular element have identical properties. Elements of a different element have different properties.
  • Atoms cannot be divided or destroyed.
  • Atoms combine to form compounds.
  • During a chemical reaction atoms are rearranged.
john dalton s atomic theory2
John Dalton’s Atomic Theory:
  • All matter is composed of atoms.
  • Atoms of a particular element have identical properties. Elements of a different element have different properties.
  • Atoms cannot be divided or destroyed.
  • Atoms combine to form compounds.
  • During a chemical reaction atoms are rearranged.
jj thomson 1856 1940
JJ Thomson 1856-1940

Excuse me... how can you discover a particle so small

that nobody has ever seen one?

http://www.aip.org/history/electron/jjsound.htm

discovery of the electron
Discovery of the Electron

JJ Thomson determined that:

  • Atom is a sphere of positive matter that holds electrons in it.
  • Also called the plum pudding model or the raisin dough model.
his experiment
His experiment

http://www.sciencemuseum.org.uk/on-line/electron/section2/shockwave2.asp

thomson s experiment

Voltage source

Thomson’s Experiment

-

+

Vacuum tube

Metal Disks

slide42

Voltage source

Thomson’s Experiment

-

+

slide43

Voltage source

Thomson’s Experiment

-

+

slide44

Voltage source

Thomson’s Experiment

-

+

slide45

Voltage source

Thomson’s Experiment

-

+

slide46

Voltage source

Thomson’s Experiment

-

+

j j thompson s cathode ray tube

Voltage source

J.J. Thompson’s Cathode Ray Tube
  • The cathode ray travels from the cathode to the anode when current was passed through the tube.

-

+

Cathode

Anode

slide48

Voltage source

Thomson’s Experiment

+

-

  • By adding an electric field
slide49

Voltage source

Thomson’s Experiment

+

-

  • By adding an electric field
slide50

Voltage source

Thomson’s Experiment

+

-

  • By adding an electric field
slide51

Voltage source

Thomson’s Experiment

+

-

  • By adding an electric field
slide52

Voltage source

Thomson’s Experiment

+

-

  • By adding an electric field
slide53

Voltage source

Thomson’s Experiment

+

-

  • By adding an electric field he found that the moving pieces were negative
maltese cross tube
Maltese Cross Tube
  • Using a Maltese cross as the anode, this produced a shadow that glowed at the end of the tube. This showed that the cathode rays traveled in straight lines.
paddle wheel discharge tube
Paddle Wheel Discharge Tube
  • A paddle wheel placed in the path of the cathode rays turned. This proved that the cathode rays contained mass, and that they might be made of particles.
thomson s plum pudding model
Thomson\'s “Plum Pudding Model"

http://www.broadeducation.com/htmlDemos/AbsorbChem/HistoryAtom/page.htmt

thomson s plum pudding model1
Thomson\'s “Plum Pudding Model"

Electrons are red.

Negative electrons

Are embedded in a

Blue positive atom.

http://molaire1.club.fr/e_histoire.html

j j thompson s model1
J.J. Thompson’s Model
  • Cathode rays are beams of negatively-charged particles called electrons.
  • All atoms contain electrons.
  • Atoms also contain an equal and opposite positive charge.
ernest rutherford 1871 1937
Ernest Rutherford 1871-1937
  • "All science is either physics or stamp collecting."

http://www.pbs.org/wgbh/aso/databank/entries/bpruth.html

ernest rutherford s model
Ernest Rutherford’s Model
  • He became a student of a teacher named Professor J J Thomson at Cambridge University in England
ernest rutherford s model1
Ernest Rutherford’s Model
  • Rutherford studied how gold atoms interacted with radioactivity.
radioactivity
Radioactivity
  • Radioactivity is the

processes by which

unstable atomsemit

subatomic particles

(radiation).

slide63

Made of 2 protons

  • and 2 neutrons.
  • Charge of +2, and a
  • mass of 4
  • Relatively slow and
  • heavy.
slide64

Charge of minus 1

  • Mass is very small.
  • They are the same as
  • an electron.
  • They are fast, and light.
slide65

Gamma rays are

  • waves, not particles.
  • They have no mass
  • and no charge.
penetrating power
Penetrating Power
  • Alpha particles are easy to stop, gamma rays are hard to stop.
slide67

Fluorescent

Screen

Lead block

Uranium

Gold Foil

Here’s how it looked.

rutherford expected
Rutherford Expected:
  • The alpha particles to pass through without changing direction.
  • Because…?
  • …the positive charges were thought to be spread out evenly. Alone they were not enough to stop the large alpha particles.
slide75

+

How he explained it:

  • Atom is mostly empty.
  • It has a small
  • dense, positive piece

at center.

  • Alpha particles are deflected by

the nucleus if they

get close enough.

-

-

-

-

-

-

ernest rutherford s results

+

Ernest Rutherford’s Results:
  • Atom is mostly empty space.
  • Suggests that an atom has a nucleus that holds most of

the mass of the

atom.

-

-

-

-

-

-

rutherford s atom
Rutherford’s Atom
  • His model of the atom was similar to the solar system. Like planets, electrons orbited a central, sun-like nucleus.

http://www.broadeducation.com/htmlDemos/AbsorbChem/HistoryAtom/page.htmt

rutherford s atom2
Rutherford’s Atom

1. Most of the mass of an atom must be located in a small volume at the center of the atom (the nucleus).

2. The nucleus is made of positively charged particles called protons.

3. The electrons move in a large volume which is mostly empty space.

problems with rutherford s atom
Problems with Rutherford’s Atom
  • According to "classical" theory the electrons should lose energy by radiating electromagnetic radiation, as they are accelerated electric charges.
  • They should spiral into the nucleus.
bohr model of the atom1
Bohr Model of the Atom:
  • Electrons are a particular distance from the nucleus
  • The energy of each electron is not the same
  • Electrons close to center = low Energy
  • Electrons farther away = high Energy
neils bohr s model
Neils Bohr’s Model
  • There are 2 electrons in the lowest energy level, 8 electrons in the second energy level, and 18 in the third…

…this is the model of the atom we will use!

chadwick
Chadwick
  • In 1932, Chadwick proved the existence of neutrons - elementary particles devoid of any electrical charge.
  • Located in the nucleus

(Rutherford also put out the idea that there could be a particle with mass but no charge)

chadwick s atom modern atom
Chadwick’s Atom Modern Atom

1. Most of the atom\'s volume is occupied by electrons.

2. The number and arrangement of electrons in an atom determine its chemical properties.

chadwick s atom
Chadwick’s Atom

3. The identity of an element is determined by the number of protons in the nucleus.

4. Different isotopes of elements exist and differ only in the number of neutrons and hence the mass of the atom.

modern atom
Modern Atom
  • Electrons
  • Protons
  • Neutrons
alpha beta particles
Alpha & Beta particles

http://wps.prenhall.com/esm_brown_chemistry_9/0,4647,169289-,00.html

electrons
Electrons
  •  Electrons are tiny particles which behave like clouds
  • Electrons carry something called a negative electric charge.
  • Electrons are responsible for the chemistry of the atom.
electrons http education jlab org atomtour listofparticles html
Electronshttp://education.jlab.org/atomtour/listofparticles.htmlElectronshttp://education.jlab.org/atomtour/listofparticles.html
atoms1
Atoms

- Atomic diameter ~ 1 to 5x10-8 cm

- Are about 10,000,000 in 1 mm

- An H atom weighs 1.67x10-24 g

  • Note: (6.02x1023) x (1.67x10-24 g) = 1.00 g
  • 6.02x1023 = Avogadro’s Number
slide98
Atoms are made up of three major parts:

Part Found Mass Charge

Electrons Outside 9.1x10-28g (small) -1

Protons Nucleus 1.7x10-24g (1.0 AMU) +1

Neutrons Nucleus 1.7x10-24g (1.0 AMU) 0

atomic structure
Atomic Structure

1) Neutral atoms contain equal number of electrons and protons.

atomic structure1
Atomic Structure

2) Atoms can loose or gain electrons to become charged = ions

atomic structure2
Atomic Structure

3) Number protons determines the identity of the atom or ion.

Atomic Number

atomic structure3
Atomic Structure

4) Mass Number =

# Protons + # Neutrons

slide103
APEMAN

Atomic Number

=Proton #

=Electron #

Mass #

-Atomic Number

= Neutron #

slide104

Charge (if ion)

Mass Number

Symbol

Atomic Number

atomic mass
Atomic Mass-

An isotopes contribution is determined by its relative abundance.

slide106

133

55

EXAMPLE

How many protons, neutrons and electrons are found in an atom of

Cs

Atomic number = protons and electrons

There are 55 protons and 55 electrons

Mass number = sum of protons and neutrons

133 – 55 = 78

There are 78 neutrons

slide107

Hydrogen

H

1

1

Symbol

Atomic Mass

Atomic Number

slide108

Hydrogen

Protons:

Electrons:

Neutrons:

H

1

1

slide109

Hydrogen

Protons: 1

Electrons:

Neutrons:

H

1

1

slide110

Hydrogen

Protons: 1

Electrons:1

Neutrons:

H

1

1

slide111

Hydrogen

Protons: 1

Electrons:1

Neutrons:0

H

1

1

slide112

Sodium

Protons:

Neutrons:

Electrons:

Na

23

11

slide113

Sodium

Protons: 11

Neutrons:

Electrons:

Na

23

11

slide114

Sodium

Protons: 11

Neutrons:

Electrons: 11

Na

23

11

slide115

Sodium

Protons: 11

Neutrons:

Electrons: 11

12

Na

23

11

12

slide116

Rhenium

75

Protons:

Neutrons:

Electrons:

Re

111

186

75

75

111

slide117

Rhenium Isotope

75

Protons:

Neutrons:

Electrons:

Re

112

187

75

75

112

slide119

C-12

C

12

6

isotopes
Isotopes
  • Atoms of a given element with differing numbers of neutrons are called isotopes.
isotopes1
Isotopes
  • An atom is still the same element if it is missing an electron. The same goes for isotopes. They are still the same element. They are just a little different from every other atom of the same element.
atomic weight
Atomic Weight-

An isotopes contribution is determined by its relative abundance.

slide123
Atomic numbers are whole numbers

Mass numbers are whole numbers

The atomic mass is not a whole number.

calculating atomic mass
Calculating Atomic Mass

atomic mass =

(% abundance of isotope 1)(mass of isotope 1) +

(% abundance of isotope 2)(mass of isotope 2) +

(% abundance of isotope 3)(mass of isotope3) +...

calculating atomic mass1
Calculating Atomic Mass

Answer the following questions:

"How many naturally occurring isotopes does carbon have?"

"What is the abundance of each of the isotopes?"

slide126

The sum of all the fractions of abundance

of each naturally occurring isotopes

should equal 1.00 or 100%.

slide127
atomic mass of carbon =

(0.9893)(12.000 amu)

+(0.0107)(13.00 amu)

= 11.868 amu + 0.1391 amu

= 12.0107 amu

what is the atomic mass of lithium
What is the atomic mass of Lithium

Isotope Atomic Relative

Mass Abundance

Li-6 6.015 7.59

Li-7 7.016 92.41

what is the atomic mass of lithium1
What is the atomic mass of Lithium

0.0759*6.015 =

+ 0.9241* 7.016 =

0.4565

6.4828

6.9393

what is the atomic mass of oxygen1
What is the atomic mass of Oxygen

0.99757*16 =

+ 0.00038*17=

+ 0.00205*18=

15.96112

0.00646

+0.0369

16.00448

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