Chapter 3 atomic structure
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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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Chapter 3 Atomic Structure

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Chapter 3 atomic structure

Chapter 3Atomic Structure


Objective

You will explain why the model of the atom changed throughout history.

Objective:


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.


Chapter 3 atomic structure

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


Chapter 3 atomic structure

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


Chapter 3 atomic structure

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


Law of multiple proportions1

Law of Multiple Proportions


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


J j thompson s model

J.J. Thompson’s Model

_

_

+

+

_

+

+

_

_

+


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


Thomson s experiment1

Voltage source

Thomson’s Experiment

-

+


Chapter 3 atomic structure

Voltage source

Thomson’s Experiment

-

+


Chapter 3 atomic structure

Voltage source

Thomson’s Experiment

-

+


Chapter 3 atomic structure

Voltage source

Thomson’s Experiment

-

+


Chapter 3 atomic structure

Voltage source

Thomson’s Experiment

-

+


Chapter 3 atomic structure

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


Chapter 3 atomic structure

Voltage source

Thomson’s Experiment

+

-

  • By adding an electric field


Chapter 3 atomic structure

Voltage source

Thomson’s Experiment

+

-

  • By adding an electric field


Chapter 3 atomic structure

Voltage source

Thomson’s Experiment

+

-

  • By adding an electric field


Chapter 3 atomic structure

Voltage source

Thomson’s Experiment

+

-

  • By adding an electric field


Chapter 3 atomic structure

Voltage source

Thomson’s Experiment

+

-

  • By adding an electric field


Chapter 3 atomic structure

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).


Chapter 3 atomic structure

  • Made of 2 protons

  • and 2 neutrons.

  • Charge of +2, and a

  • mass of 4

  • Relatively slow and

  • heavy.


Chapter 3 atomic structure

  • Charge of minus 1

  • Mass is very small.

  • They are the same as

  • an electron.

  • They are fast, and light.


Chapter 3 atomic structure

  • 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.


Chapter 3 atomic structure

Fluorescent

Screen

Lead block

Uranium

Gold Foil

Here’s how it looked.


Chapter 3 atomic structure

What he expected


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.


Chapter 3 atomic structure

What was expected:


Chapter 3 atomic structure

What he got


Rutherford s gold foil results

Rutherford’s Gold Foil Results


What actually happened

+

What Actually Happened…

-

-

-

-

-

-


Chapter 3 atomic structure

+

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.

-

-

-

-

-

-


What actually happened1

What Actually Happened


Rutherford s atom a sea of electrons that surrounded a positively charged nucleus

Rutherford’s Atom:A sea of electrons that surrounded a positively charged nucleus.


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 atom1

Rutherford’s Atom

PROTONS

+


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.


Problems with rutherford s atom1

Problems with Rutherford’s Atom


2 years after rutherford neils bohr 1885 1962

2 years after Rutherford….Neils Bohr 1885 - 1962


Bohr model of the atom

Bohr Model of the Atom:


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!


James chadwick

James Chadwick


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)


Chadwicks atom

Chadwicks Atom


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.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


Chapter 3 atomic structure

Atoms are made up of three major parts:

PartFoundMass Charge

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

Protons Nucleus1.7x10-24g (1.0 AMU)+1

NeutronsNucleus 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


Chapter 3 atomic structure

  • APEMAN

    Atomic Number

    =Proton #

    =Electron #

    Mass #

    -Atomic Number

    = Neutron #


Chapter 3 atomic structure

Charge (if ion)

Mass Number

Symbol

Atomic Number


Atomic mass

Atomic Mass-

An isotopes contribution is determined by its relative abundance.


Chapter 3 atomic structure

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


Chapter 3 atomic structure

Hydrogen

H

1

1

Symbol

Atomic Mass

Atomic Number


Chapter 3 atomic structure

Hydrogen

Protons:

Electrons:

Neutrons:

H

1

1


Chapter 3 atomic structure

Hydrogen

Protons: 1

Electrons:

Neutrons:

H

1

1


Chapter 3 atomic structure

Hydrogen

Protons: 1

Electrons:1

Neutrons:

H

1

1


Chapter 3 atomic structure

Hydrogen

Protons: 1

Electrons:1

Neutrons:0

H

1

1


Chapter 3 atomic structure

Sodium

Protons:

Neutrons:

Electrons:

Na

23

11


Chapter 3 atomic structure

Sodium

Protons: 11

Neutrons:

Electrons:

Na

23

11


Chapter 3 atomic structure

Sodium

Protons: 11

Neutrons:

Electrons: 11

Na

23

11


Chapter 3 atomic structure

Sodium

Protons: 11

Neutrons:

Electrons: 11

12

Na

23

11

12


Chapter 3 atomic structure

Rhenium

75

Protons:

Neutrons:

Electrons:

Re

111

186

75

75

111


Chapter 3 atomic structure

Rhenium Isotope

75

Protons:

Neutrons:

Electrons:

Re

112

187

75

75

112


Chapter 3 atomic structure

Re-111


Chapter 3 atomic structure

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.


Chapter 3 atomic structure

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?"


Chapter 3 atomic structure

The sum of all the fractions of abundance

of each naturally occurring isotopes

should equal 1.00 or 100%.


Chapter 3 atomic structure

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

IsotopeAtomic Relative

Mass Abundance

Li-66.015 7.59

Li-77.01692.41


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 oxygen

What is the atomic mass of Oxygen?


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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