unit 4: atomic theory structure of the atom (& radioactivity)

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Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

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Page 1: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Unit 4: Atomic Theory

Structure of the Atom (& Radioactivity)

Page 2: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Early Atomic TheoriesModels of the Atom

Date scientist discovery________________ 100 BC Democritus/Greeks concept of the atom 1770 Antoine Lavosier Law of conservation of mass 1800 Joseph Proust Law of definite proportions 1803 John Dalton Law of multiple proportions Atomic Model I 1880 William Crookes Cathode Rays (electrons) 1885 Goldstein Canal Rays (protons) 1900 J.J. Thomson Plum Pudding Model

Electron Atomic Model II

1909 Ernest Rutherford nucleus of atom Atomic Model III 1913 Niels Bohr Planetary Model Atomic Model IV 1920- Schroedinger/Planck/ Modern or Wave Model Present DeBroglie/Einstein/etc. Atomic Model V

Page 3: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Early Atomic Theories Atomists and Democritus

Greeks approx. 2,500 years ago Matter was made up of atoms

“atomos” or “Indivisible” particles Seashell experiment—broken into

smaller & smaller pieces

Page 4: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Early Atomic Theories John Dalton

1766-1844; returned to theory of atoms Atoms are like billiard balls (solid spheres)

which can’t be broken down further 4 major postulates

1. All elements are composed of atoms2. Atoms of the same element are identical3. Atoms can physically mix or chemically

combine in simple whole number ratios4. Reactions occur when atoms separate, join,

or rearrange

Page 5: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Dalton’s Model of the Atom

No subatomic particles!

Page 6: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Early Atomic Theories

William Crookes Developed Crookes tube (a.k.a cathode

ray tube) in 1870’s First evidence for existence of electrons

because you could “see” electrons flow and confirm their existence.

Tube is precursor to today’s TV picture tubes

Page 7: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Building the Atom – The Electron J.J. Thomson

Discovered electron in 1897 Discovered positively charged particles

surrounded by electrons Found the ratio of the charge of an

electron to its mass to be 1/1837

Page 8: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Thomson’s Cathode Ray Tube Experiment J.J. Thomson

Video: Cathode Ray Tube Demo

Page 9: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Building the Atom – The Electron J.J. Thomson

Cathode ray tube experiments – advancement of Crookes tube

“plum-pudding model”

Page 10: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Thomson’s Model of the Atom (Plum Pudding Model)

Page 11: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Millikan’s Oil Drop Experiment Robert Millikan

Oil drop experiment Determined the charge and mass of an

electron

Video: Millikan's Oil Drop Experiment

Page 12: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Building the Atom – The Nucleus Ernest Rutherford

Discovered nucleus (dense core of atom) in 1911

Famous Gold foil experiment

Quote from E.R.’s Lab Notebook “It is about as incredible as if you had fired

a 15-inch shell at a piece of tissue paper and it came back and hit you.” -ER

Page 13: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Rutherford’s Gold Foil Experiment

Video Clip: Rutherford Gold Foil Experiment

Page 14: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Rutherford’s Model of the Atom

Page 15: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Building the Atom – The Neutron James Chadwick

Discovered the neutron (no charge, but same mass as proton)

Neutrons help disperse the strong repulsion of positive charges

Nucleus diameter = 10-5 nm Atom diameter = 10-1 nm If Nucleus = basketball -->

then Atom = 6 miles wide!

Page 16: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Building the Atom Niels Bohr

Improved on Rutherford’s work “Planetary model”- positive center is

surrounded by electrons in defined orbits circling the center

Page 17: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Bohr Model of the Atom (Planetary Model)

Page 18: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Bohr Model of the Atom Vocab. Energy level – the location where an

electron is found at a set distance from the nucleus dependent on the amount of energy it has

Ground state – the typical energy level where an electron is found; lowest energy

Excited state – an energy level higher than the ground state for an electron; temporary condition

Page 19: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Schrödinger Model (Quantum Mechanical Model) Quantum Mechanical Model

Erwin Schrödinger; Mathematical model Electron locations are based on probability Electrons are not particles, but waves!

Interactive Simulation: try it!

Defined: Orbital – region where an electron is likely to

be found 90% of the time

Page 20: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Schrödinger Model of the Atom(Quantum Mechanical Model)

Page 21: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Atomic TheoryAtom – the smallest particle of

matter that retains its properties. Smallest individual unit of an element

One atom of hydrogen is different from one atom of carbon.

Subatomic particles – the component parts of an atom: proton, neutron, and electron

Page 22: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Atomic Theory Ion - atom with the same number of

protons but a different number of electrons i.e. an atom with a charge!

If the atom has a (+) charge it has more protons than electrons.

If the atom has a (-) charge it has more electrons than protons.

Page 23: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Subatomic ParticlesSubatomic

ParticleMass and

Abbreviation Charge Location Discoverer

Protonp+

Mass =1 amu+1 Nucleus ----

Neutron nMass =1 amu 0 Nucleus Chadwick

in 1932

Electrone-

Mass ≈ zero amu

-1

Electron cloud

(outside nucleus)

Thomson in 1897

Page 24: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Atomic SymbolsAtomic symbol – the letter or

letters that represent an element.

13

Al

26.981

Atomic number

Atom symbol

Atomic mass or weight

Page 25: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Atomic NumberAtomic number = the number of protons in the nucleus.

(same for every atom of that element)

13Al

26.981

Atomic number

Atom symbol

Atomic mass or weight

Page 26: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Mass Number

Mass Number = # protons + # neutrons

A Boron atom can have:5 p + 5 n = 10 amu

Named as boron-10

 Mass number

Atomic number

Page 27: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Calculations w/ Subatomic ParticlesAtomic number = # of protonsMass number = # of protons + # of

neutrons

(For a neutral atom): # of protons = # of electrons

(For a charged ion): Charge = #p+ - #e-

Page 28: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Isotope Notation Isotope (Isotopic Notation)

Mass #

Atomic #

Atomic Symbol

Z

AX

Example: Uranium-238

Page 29: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Example  

Page 30: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Example  

Page 31: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Sample ProblemWrite the atomic symbols for the following:

The isotope of carbon with a mass of 13

The nuclear symbol when A = 92 and the number of neutrons = 146.

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Page 32: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Isotopes Isotope – atoms of the same element with

different numbers of neutrons (different mass numbers) Example: Carbon-12 Carbon-14

Atomic mass – weighted average of the masses of all the isotopes of an element

Page 33: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Atomic Mass

The weighted average is the addition of the contributions from each isotope.

Isotopic Abundance is the percent or fraction of each isotope found in nature.

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Page 34: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Most Abundant Isotope

34

13

Al

26.981

Atomic number

Atom symbol

Atomic mass or weight

Usually can round atomic mass on the periodic table to nearest whole number

(but not always!!)

Page 35: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Example: Determine the average atomic mass of magnesium which has three isotopes with the following masses: 23.98 amu (78.6%), 24.98 amu (10.1%), 25.98 amu (11.3%).

1) Multiply the mass number of the isotope by the

decimal value of the percent for that isotope.

2) Add the relative masses of all of the isotopes to

get the atomic mass of the element.

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Page 36: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Example: Determine the average atomic mass of magnesium which has three isotopes with the following masses: 23.98 amu (78.6%), 24.98 amu (10.1%), 25.98 amu (11.3%).

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Page 37: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Now You Try!If 90% of the beryllium in the world has a mass number of 9 and only 10% has a mass number of 10, what is the atomic mass of beryllium?

Page 38: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Radioactivity - Vocabulary

Radioactivity - the spontaneous emission of radiation from a substance

Radiation - rays and/or particles emitted from radioactive material

Nuclear reactions - reactions involving changes in an atom’s nucleus

Page 39: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Radioactivity Radioactive isotopes are unstable

These isotopes decay over time by emitting particles and are transformed into other elements

Particles emitted: Alpha (α) particles: helium nuclei Beta (β) particles: High speed electrons Gamma (γ) rays: high energy light

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Page 40: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Types of Radiation – α particles

Alpha radiation - stream of high energy alpha particles Alpha particles consist of 2 protons and 2

neutrons and are identical to helium-4 nucleus.

Symbol: 4He 2+

2

Not much penetrating power, travel a few centimeters, stopped by paper, no health hazard

Page 41: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Types of Radiation – β particles

Beta radiation - High speed electrons To form beta radiation a neutron splits into

a proton and an electron The proton stays in nucleus and the

electron propels out at high speed.

Symbol: 0e- 0β

-1 -1

100 times more penetrating then alpha radiation, pass through clothing to damage skin

Page 42: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

Types of Radiation – Radiation

Gamma radiation Similar to X rays Doesn’t consist of particles (instead, high

energy light) Symbol:

0 0

Penetrates deeply into solid material, body tissue, stopped by Pb or concrete, dangerous

Page 43: Unit 4: Atomic Theory Structure of the Atom (& Radioactivity)

End of Unit 4!