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Chapters 4-5: The Atom. Chemistry. What is this a painting of?. Henri Matisse, THE BEES, 1948. Seurat, 1884. Cans Seurat, 2007 60x92" Depicts 106,000 aluminum cans, the number used in the US every thirty seconds. Pointillism. Ferris Bueller’s Day Off. The Atom.

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what is this a painting of
What is this a painting of?

Henri Matisse, THE BEES, 1948

the atom
The Atom
  • Indivisible particle of matter
  • The smallest part of an element sample
  • Atoms combine to form molecules & compounds

Al Foil

?

theories involving matter atoms

Democritus of Abdera,

100 Greek Drachma (1967)

This note is now obsolete.

Theories Involving Matter & Atoms
  • Democritus (400 BC)
    • “atomos” = indivisible
    • atoms are the smallest particles possible
    • there are different kinds of atoms
    • a very general theory
    • not supported by evidence
aristotle 384 322 bc
Aristotle (384-322 BC)
  • Matter is Continuous
  • “Hyle”: a continuous substance making up all matter
  • A philosophical theory
antoine lavoisier 1743 1794
Antoine Lavoisier(1743-1794)
  • Law of Conservation of Mass:
    • Matter cannot be created nor destroyed in a reaction
    • Mass Before = Mass After
  • Determined formula for water (H2O)
  • Established the Metric System
  • French Revolution: Killed in Guillotine
joseph proust 1754 1826
Joseph Proust(1754-1826)

Law of Definite Composition

  • Elements combine in definite ratios to form compounds

Ex:

Table salt always contained 1.5 times as much chlorine as sodium

Water always contained eight times as much oxygen as hydrogen

john dalton 1766 1844
John Dalton (1766-1844)
  • British
  • Quaker
  • School Teacher
  • Recorded daily weather and barometric pressure
  • Color blind (called “Daltonism”)
  • Child Prodigy
dalton used the work of lavoisier and proust to form
Dalton used the work of Lavoisier and Proust to form…

Dalton’s Atomic Theory (1807)

1) All matter is composed of atoms

2) Atoms of an element are alike

3) Each atom has its own weight

4) Atoms unite in definite ratios to form compounds

and…

dalton used the work of lavosier and proust to form
Dalton used the work of Lavosier and Proust to form…

i.e.

NO 1:1

NO2 1:2

NO3 1:3

Law of Multiple Proportions

Atoms may combine in more than one ratio when forming compounds

Different compounds with entirely different properties

which law is illustrated
Which Law is Illustrated?

Law of Definite Composition

____ a) Water is 89% oxygen by mass

____ b) 3.10 g Mg combine with 2.04 g of oxygen to form ___ g of magnesium oxide

____ c) H2O (water) & H2O2 (hydrogen peroxide)

Law of Conservation of Mass

5.14

Law of Multiple Proportions

parts of the atom subatomic particles
Parts of the atom subatomic particles

Electron (e-)

  • negative charge (-1)
  • discovered by JJ Thomson (1897)—Nobel Prize for Physics in 1906
  • smallest unit of electrical charge
  • mass = 1/1837 of a proton

J.J. Thomson

(1856-1940)

slide17

Ernest Rutherford

100 New Zealand Dollars

Proton (p+)

  • positive charge (+1)
  • discovered by Ernest Rutherford

(J.J. Thomson’s student at Cavendish Labs)

  • Mass = 1 amu (atomic mass unit)
  • Atomic Number = Z = p+
slide18

James Chadwick

(1891-1974)

Neutron (no)

  • discovered in 1932 by Chadwick

(a student of Rutherford)

  • Awarded Nobel Prize for Physics in 1935
  • no charge –neutral
  • Mass of neutron  mass of proton
nucleons
Nucleons
  • Particles in the nucleus: protons & neutrons
  • Atomic Mass = #protons + #neutrons
  • Mass # = Atomic Weight rounded to the nearest whole number
example

24

12

12

12

24

12

12

10

24

12

12

13

Example
try this for fluorine f

9

9

10

9

18.998

19

Try This for Fluorine (F)

Z = __________

#p+ = _________

#no = _________

#e- = __________

Atomic Weight = ________

Mass # = ________

isotopes
Isotopes

Atoms of the same element having different masses

same number of ________

different number of ________

protons

neutons

symbolizing

40

Atomic Mass

(#p+ + #no)

22

2+

Ne

Ca

10

20

Atomic Number (Z)

(#p+)

charge

Not always the same as the P. T. !!!

Symbolizing
try this

6

6

6

6

6

8

6

6

12

14

Try This:

C

C

which is the most common isotope for neon
Which is the most common isotope for Neon?

Ne-22 or Ne-21 or Ne-20

How do you know?

Average Atomic Weight for Ne is 20.2 g/mol

slide26
Why are atomic masses not whole numbers?

Atomic masses are averages of the isotopes present

think about it
Think About It!
  • An atoms weight comes from the protons and neutrons. The electrons are so tiny they don’t matter for weight!
  • Like a sumo wrestler weighing in with ten lady bugs on his shoulder. (the electrons are like the lady bugs, they don’t change his mass very much).
a practical use for isotopes and mass differences
A practical use for Isotopes and Mass Differences
  • To build an atom bomb scientists needed pure U-235, a tiny fraction of natural uranium samples.
  • Separated using mass differences.
isotope review heavy water
Isotope ReviewHeavy Water
  • Isotopes of hydrogen:
    • Hydrogen
    • Deuterium
    • Tritium

Deuterium Water = D2O and a molecular weight of 20 g/mol

remember john dalton s atom
Remember John Dalton’s Atom
  • Dalton thought of atoms as indivisible spheres
  • His proof for this was the Law of Definite Composition (water is H2O not H1.5O)
  • He of course was wrong…
  • Atoms can be split into parts
  • nop+ and e-
models of the atom thomson model
Models of the Atom—Thomson Model

electrons

J.J. Thomson

sphere of positive charge

  • Discovered the existence of the electron (1897)
  • Proved Dalton’s idea that the atom was indivisible was wrong
  • Thought electrons were imbedded in the atom
  • Called the Plum Pudding Model
rutherford model
Rutherford Model
  • Gold Foil Experiment (1911)
  • The atom has a dense nucleus
  • The atom is made of mostly empty space

click picture for video

turn down volume

major shortcomings of rutherford s model
Major Shortcomings of Rutherford’s Model:
  • Electrons cannot orbit the nucleus;

they would lose energy and the atom would collapse

bohr model
Bohr Model
  • e-s move at different levels around the nucleus

n = 4

n = 3

n = 2

n = 1

Niels Bohr

1885-1962

Click picture for video

(after Lab 16 demo)

bohr model of the atom

Continuous Spectrum

ROY G BIV

Bright-Line Spectrum

Bohr Model of the Atom
  • Energy (heat or electricity) causes e-s to move to higher level/excited states
  • When e-s move back, energy is released in packets called

QUANTA

shortcomings of bohr
Shortcomings of Bohr
  • Only worked for the Hydrogen atom

500 Danish Kroner

quantum theory modern model of the atom
Quantum Theory—Modern Model of the Atom
  • Cannot be visualized
  • A mathematical description of atom
  • Energy is transferred in units (quanta)
  • Electron position described by probability and quanta (packets) of energy
energy levels of the atom

n = 4

n = 3

n = 2

n = 1

Energy Levels of the Atom

Levels

  • Principal Quantum Number (n)
  • Also called: shell, quantum, energy level
  • Horizontal Rows on the diagram on the back of your PT

n = 1 is ground state

(lowest energy level)

n > 1 is an excited state

slide40

n = 2

n = 3

n = 4

n = 1

maximum e s per energy level 2n 2
Maximum #e-s per energy level = 2n2

2(1)2 = 2

2(2)2 = 8

2(3)2 = 18

2(4)2 = 32

slide42

n = 2

n = 3

n = 4

n = 1

2

32

18

8

sublevels l
Sublevels (l)
  • Shape of the probability region of the e-
  • Each energy level has n sublevels
  • Circles on the diagram on the back of your PT

n = 1

1 sublevel

s

n = 2

2 sublevels

s, p

n = 3

3 sublevels

s, p, d

n = 4

4sublevels

s, p, d, f

slide44

n = 2

n = 3

n = 4

n = 1

2

32

18

8

s

s, p

s, p, d

s, p, d, f

slide45
s –

p –

orbitals m

# orbitals in that energy level = n2

Orbitals (m)

The s, p, d, f circles on the diagram on the back of your PT

  • Orientation of the sublevel
  • Maximum of 2 e-s per orbital
    • s sublevels contain 1 orientation
    • p sublevels contain 3 orientations
    • d sublevels contain 5 orientations
    • f sublevels contain 7 orientations

s sublevel

p sublevel

f sublevel

d sublevel

slide47
Spin
  • 2 e-s in the same orbital have opposite spin

(opposite North and South Poles)

  • Discovered in 1928
  • The lines you draw in the circles on the diagram
electron configurations
Electron Configurations

3 Simple Rules

  • Electrons fill lowest energy level first
  • Maximum number of 2 e- per orbital
  • Orbitals half-fill before they fill

(Each orbital gets one before an orbital can get seconds)

NOT

si 14 e

6p

5d

4f

6s

5p

4d

5s

4p

3d

4s

3p

3s

2p

2s

1s

Si = 14 e-

1s2

2s2

2p6

3s2

3p2

br 35 e

6p

5d

4f

6s

5p

4d

5s

4p

3d

4s

3p

3s

2p

2s

1s

Br = 35 e-

1s2

4p5

2s2

2p6

3s2

3p6

4s2

3d10

slide51
NOW!
  • Get the table on Assignment #4 done before you leave!!!
dot diagrams
Dot Diagrams
  • Symbolize

(s and p orbitals only)

  • Why?

outer shell electrons

Those are the electrons involved in bonding and chemical reactions

left right top bottom
LEFTRIGHTTOPBOTTOM

X

Draw the dot diagram for the following:

Mg

Mg 1s22s22p63s2

N

N 1s22s22p3

In

In 1s22s22p63s23p64s23d104p65s24d105p1

lab 20

Highest s and p ONLY

Lab 20

nitrogen(7)

1s22s22p3

N

s

p

average atomic mass atomic weight
Average Atomic Mass (Atomic Weight)
  • An average of an element’s isotopes
  • The number seen on the periodic table
how to calculate average atomic weight
How to Calculate Average Atomic Weight

Na is made up of:

95.6% Na-23 and 4.4% Na-22

{ (0.956) (23) + (0.044) (22) }

=

=

(21.988 + 0.968)

22.956 23.0 g/mol

try this59
Try This

Calculate the average atomic mass of Cu:

69.17% Cu-63 and 30.83% Cu-65

{ (0.6917) (63) + (0.3083) (65) } =

43.5771 + 20.0395 =

63.6166 = 63.6 g/mol

carbon dating
Carbon Dating
  • All living things contain carbon
  • There are 2 isotopes of carbon:

C-12 (stable) and C-14 (unstable)

slide61

Age 0 Age 5700 yrs Age 11,400 yrs Age 17,100 yrs

  • In living things, the ratio of C-12 : C-14 is constant
  • After an organism dies, C-14 is converted to N-14 so the ratio changes
  • Half-life of C-14, t1/2 = 5700 years
  • Every 5700 yrs, half of the C-14 is converted to N-14
  • By studying the ratio of fossils, ancient artifacts, etc. scientists can determine the age of objects
lab 19 explanation
Lab 19 Explanation

Nitrogen ~ 78%

Oxygen ~ 21%

CO2 ~ 0.3%

Height of Water = the space the oxygen gas used to take up before it became a solid