Dismissed idea of the atom.

Early GreeksEarly Greeks Two schools of thought:

Matter is made of indestructible particles called “atomos”

Plato (428-348 BC)

Democritus (400 BC)

Both theories lacked Scientific Evidence so idea of atom was lost for 2000

years

2000 years of ALCHEMY2000 years of ALCHEMYAlchemy began as an Arab mixture of Egyptian arts of dyeing, painting, glass making, pyrotechnics, medical drugs, mining, and metallurgy with the theories of the Greeks (mostly Aristotle's) to explain changes in color and appearance of materials

Main goal was:

Philosopher’s stone

Transmutation

1700s1700sExperiments with air result in 1st balloon flights and further investigations of gases.

Joseph Priestley: Discovers oxygen and is able to isolate it from the air.

Antoine Lavoisier: Identifies the role oxygen plays in combustion.

Also discovers a natural law called:

Law of Conservation of Matter.

Early 1800sEarly 1800sJoseph Proust: Believed substances always combine in a definite way and in the same proportions.

Law of Definite Proportions

John Dalton: Showed that different substances with the same elements combined in ratios that were whole numbers.

Law of Multiple Proportions

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This indicated that matter exists as “ATOMS”. Atomic Theory

Dalton’s TheoryDalton’s TheoryExperimental evidence Scientific Laws

Law of Conservation on Matter You can’t create or destroy atoms.Law of Definite Proportions Same compounds are same ratio by mass.Law of Multiple Proportions

Different compounds with the same elements are whole number multiples of the atoms.

Experiments Scientific Laws Atomic Theory

(observations) (Patterns)(Explanations)

John Dalton realized that there must be an atom as Democritus first proposed.

Summary for Dalton’s Summary for Dalton’s Atomic TheoryAtomic Theory

Atoms are Tiny.

Atoms of the same element are the same.

Atoms of different elements are different.

Atoms can’t be divided, created or destroyed.

Atoms of different elements combine in simple whole-number ratios to form compounds.

Discovery of the ElectronDiscovery of the ElectronIn 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle.

Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.

Crookes Tube

Electrical Nature of MatterElectrical Nature of Matter

Opposite charges attract each other.

(+) (-)

Like charges repel each other.

(+) (+)

(-) (-)

Cathode Rays (electrons) Cathode Rays (electrons)

Observations:Cathode Ray Tube produces rays with constant charge to mass ratio.

Conclusions and Hypotheses:

Cathode rays (electrons) were found in all substances tested.

Cathode rays (electrons) were attracted to the positive plate every time.

Electrons are negatively charged.Neutral atoms are made up of equal amounts of (+) and (-) particles.

All substances have atoms that contain tiny particles called electrons.

The electron has a specific size and charge.

Thomson’s Atomic Model Thomson’s Atomic Model (1897)(1897)

Thomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model.

Rutherford’sRutherford’s“Gold Foil Experiment”“Gold Foil Experiment”

Alpha particles are helium nuclei, He2+

Particles were fired at a thin sheet of gold foil Particle hits on the detecting screen (film) are recorded

Radioactive source

(+)

Rutherford’s Findings (1911)Rutherford’s Findings (1911)

The atom is mostly empty space. The nucleus is dense. The nucleus is positively charged Electrons, e-, are moving large distances outside the nucleus.

Observations: Most of the alpha particles passed right through Some alpha particles were deflected slightly VERY FEW were greatly deflected“Like howitzer shells

bouncing off of tissue paper!”

Conclusions:

Rutherford’s Conclusion Rutherford’s Conclusion (1911)…(1911)…

Small, dense, positive nucleus.

Equal amounts of (-) electrons at large distances outside the nucleus.The neutron is not discovered until 1932

by James Chadwick (a student of Rutherford’s).

Neils Bohr’s Atomic model Neils Bohr’s Atomic model (1913)(1913)

Small, dense, positive nucleus.Equal amounts of (-) electrons at specific orbits around the nucleus.

This incorrect version of the atom is often used to represented atoms because it shows energy levels for electrons.

Current Atomic modelCurrent Atomic model

Small, dense, positive nucleus.

Equal amounts of (-) electrons occupy regions of space called “orbitals” in the electron cloud.

Atom

song

Explain the difference between mass number and average atomic mass.

Mass number refers to the total protons and neutrons in a specific isotope.

Atomic mass refers to all the isotopes masses averaged based on their relative abundance.

Also called “Average Atomic Mass” or “Atomic Weight”.

On the test you will have to:

Modern Atomic TheoryModern Atomic Theory

Atoms of the same element are chemically alike with a characteristic average mass which is unique to that element.

Atoms cannot be subdivided, created, or destroyed in ordinary chemical reactions. However, these changes CAN occur in nuclear reactions!

All matter is composed of atoms.

Atoms of any one element differ in properties from atoms of another element The exact path of electrons are unknown and e-’s are found in the electron cloud based on probability.

Atomic ScaleAtomic Scale Most of the mass of the atom is in the nucleus (protons and neutrons)

Electrons are found outside of the nucleus (the electron cloud)

Most of the volume of the atom is empty space

“q” is a particle called a “quark”Quarks:

About About QuarksQuarks…(particles that make up protons and neutrons)

Protons and neutrons are NOT fundamental particles.Protons are made of two “up” quarks and one “down” quark.Neutrons are made of one “up” quark and two “down” quarks.

Quarks are held togetherby “gluons”

Isotope Symbol

Atomic

number

Massnumber Protons Neutrons Electron

s

Cobalt-60

Iron-56

66 30

52 28

50 66

60

CoCobalt

27

58.93

Atomic #

Atomic mass(average)

FeIron

26

55.85

ZnZinc

30

65.39

27Co27

42Ca

20

56Fe

26

27 27-60-27= 3360

26 26 26-56 56-26= 30

42-20= 2220 2042 20-Calcium-42

Zinc-66

Chromium-52

30 30-

24 24-

66Zn

30

52Cr

24

66-30= 36

CrChromium

24

52.00

SnTin

50

118.71

Tin-116116

Sn50

50 50-50+66= 116

52-28= 24

Isotope Symbol

Atomic

number

Massnumber Protons Neutrons Electron

s

14 -12

130 -54

11 23

11 11

26

MgMagnesium

12

24.31

Atomic #

Atomic mass(average)

AsArsenic

33

74.92

XeXenon

54

131.29

12Mg12

130Xe

54

75As

33

1212+14=26

33 33 33-75 75-33= 42

130-54= 7654 54Xenon-130

Sodium-23 11-

11 11-

23Na

1123-11= 12

NaSodium

11

22.99

Magnesium-26

Arsenic-75

11

11+11=22Sodium-2222

Na11