Ch. 3: Chemical Foundations: Elements, Atoms, and Ions

1
Ch. 3 Chemical Foundations Elements, Atoms, and
Ions

• 3.1-3.3
• Atomic Theory and Structure

2
History - The Greeks

• Leucippus, _______ (460-371 B.C.), Epicurus
  (341-270 B.C.)
  
• Proposed first theory of matter called
  ___________
  
• 5 points to their atomic idea
• 1. All matter is composed of tiny particles
  called ________ (means indivisible), which are
  too small to be seen and cannot be split into
  smaller portions.

Democritus
3
History - The Greeks

• There is a void of ______________ between atoms.
• Atoms are completely ________.
• Atomos are __________ structures with no internal
  structure.
  
• Atoms are different in ..
• ___________
• ___________
• ___________

4
History

• Aristotle (384-322 B.C.)
• Atomists ideas were _________
• by Aristotle and others
• Because of this the atom
• faded into the background
• Others posed the idea of the atom over the years,
  but not many scholars gave it much thought
  

5
History

• Due to a series of complex circumstances, the
  Catholic Church accepted Aristotles position,
  and actually equated Atomists ideas with
  Godlessness
• For example, Democritus said there was no end to
  the universe, since it was not created by any
  outside power
  
• According to the Church __________________
  ________________________________________
  
• This lead to a long period where little
  advancement in atomic theory
  
• Next big dude _________________

6
History

• by 1700s, all chemists agreed
• on the existence of atoms
• that atoms combined to make compounds
• Still did not agree on whether elements combined
  in the same ratio when making a compound
  

7
Law of Conservation of Mass

• Antoine ______________ discovered
• mass is neither created or destroyed during
  regular chemical or physical changes

8
Law of Definite Proportions

• Joseph __________ discovered this (1797)
• any amount of a compound contains the same
  _________ in the same___________ by __________

No matter where the copper carbonate is used, it
still has the same composition
9
Law of Multiple Proportions

• applies when 2 or more elements combine to make
  more than one type of compound
  
• the mass ratios of the second element simplify to
  _____________________
  

14.0
30.0
16.0
14.0
16.0
16.0
46.0
10
Law of Multiple Proportions
11
What?!

• Water has 8 g of oxygen per g of hydrogen.
• Hydrogen peroxide has 16 g of oxygen per g of
  hydrogen.
  
• 16/8 2/1
• Small whole number ratios.

12
Laws Summary

• Conservation of Mass
• Law of Definite Proportions- compounds have a
  constant composition.
  
• They react in specific ratios by mass.
• Multiple Proportions- When two elements form more
  than one compound, the ratios of the masses of
  the second element that combine with one gram of
  the first can be reduced to small whole numbers.

13
John Dalton (1766-1844)Father of Chemical
Atomic Theory

• He was attempting to explain the Laws of
  Conservation of Mass, Definite Proportions and
  Multiple Proportions
  
• His atomic theory is based upon belief in the
  following statements (1805)
  
• All matter is made of _________ (back to the
  Greeks)
  
• Atoms of same element are __________ and have the
  same ______, _______, and physical and chemical
  properties

14
John Daltons Atomic Theory

• The properties of the atoms of one element are
  ___________ from those of another element (again,
  back to the Greeks).
  
• Atoms cant be _________, __________ or
  ____________ (explains work of Lavoisier and Law
  of Conversation of Mass).
  
• Atoms of different elements combine in
  __________________ to make compounds (explains
  work of Proust and Law of Definite Proportions).
  
• In chemical reactions, atoms can be __________,
  __________, and __________

15
Modern Atomic Theory

• Some parts of Daltons theory were wrong
• __________________________________________________
  ____________________
  
• __________________________________________________
  __________________________________________________
  _____
  
• Most important parts of atomic theory
• all matter is made of atoms
• atoms of different elements have different
  properties
  
• His model called _______________ Model

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Problems with Daltons Atomic Theory?

• 1. matter is composed, indivisible particles
• _________________________________________________
  _______________________
  
• 2. all atoms of a particular element are
  identical
  
• __________________________________________________
  __________________________________________________
  ___________
  
• 3. different elements have different atoms
• _________

17
Problems with Daltons Atomic Theory?

• 4. atoms combine in certain whole-number ratios
• _________________________________________________
  _______________________
  
• 5. In a chemical reaction, atoms are merely
  rearranged to form new compounds they are not
  created, destroyed, or changed into atoms of any
  other elements.
• _________________________________________________
  __________________________________________________
  _________
  

18
J.J. Thomson

• J. J. Thomson- 1906
• used Cathode ray tubes
• Metals at one end of a tube produced a beam and a
  glow at other end of tube

19
Thomsons Experiment

-
Passing an electric current makes a beam appear
to move from the negative to the positive end.
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Thomsons Model

• Did experiments with cathode rays tubes
• Placed a cross in the middle of tube and a
  ____________ was produced
  
• Conclusion

21
Thomsons Model

• Placed a paddle-wheel in the middle of tube and
  the wheel _______________
  
• Conclusion

22
Thomsons Model

• Used various types of ________ and got same
  results
  
• Conclusion

23
Thomsons Experiment

-
By adding an electric field, he found that the
moving pieces were negative
24
Thomsons Model

• Performed his bending experiments and found
  that the particles always moved away from a
  negative charge and towards a positive charge
  
• Conclusion

25
Thomsons Model

• Found the _________.
• Couldnt find positive (for a while).
• Said the atom was like _______________ (he was
  English)
  
• A bunch of positive stuff, with the electrons
  able to be removed.

26
Robert Millikans Experiment
27
Millikans Experiment
X-rays
X-rays give some electrons a charge.
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Millikans Experiment
Some drops would hover
From the mass of the drop and the charge on
the plates, he calculated the mass of an electron
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Millikans Experiment
Real importance of his experiment is that he
discovered that electrons have little mass but
lots of charge!
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Radioactivity

• Discovered by accident
• Well do more later but for now
• Three types of radiation
• alpha (?) - helium nucleus (2 charge, large
  mass)
  
• beta (?) - high speed electron
• gamma (?) - high energy light

31
Rutherfords Experiment

• Classical Gold Foil Experiment
• Used uranium to produce _______ particles.
• Aimed alpha (__) particles at gold foil by
  drilling hole in lead block.
  
• Since the mass is evenly distributed in gold
  atoms alpha particles should go straight
  through.
  
• Used gold foil because it could be made a few
  atoms thin.

32
Florescent Screen
Lead block
Uranium
Gold Foil
33
What he expected
34
Because, he thought the mass was evenly
distributed in the atom and so ? particles should
all go straight through
35
What he got
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How he explained it

• Atom is mostly empty space
• Why?

37
How he explained it

• Small positive region at center (nucleus).
• Why?

38
How he explained it

• Nucleus is solid and dense and contains most of
  the mass.
  
• Why?

39
How he explained it
e-

• Electrons are in orbit circling the nucleus
• Why?

e-
e-
e-
40

• He also predicted the existence of a neutral
  particle
  
• Why?

e-
e-
e-
e-
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Whats Wrong with Rutherfords Model?

• According to laws of revolving bodies, the
  electrons should gradually _________ and fall
  into ____________ (sort of like satellites)
  
• The attraction of the negative electrons to the
  positive nucleus should ________ them into the
  nucleus
  
• The atom would _______________

42
Neils Bohr

• Student of Rutherfords
• His model was based on many experiments
  attempting to explain the spectral lines of
  hydrogen (more later)
  
• Came up with his model of the atom called the
  Bohr Model
  

43
Neils Bohr

• To explain various observations he developed his
  model of an atom based upon several assumptions.
  
• The center, or nucleus of the atom contained most
  of the atoms ________ and consisted of
  positively charged ____________.
  
• The electrons were found in _________, or
  _____________ around _______________
  
• Each energy level could hold a maximum number of
  electrons (______, where n energy level)
  
• The electrons in energy levels furthest from the
  nucleus had ________________.

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• The electrons went into the _______ energy level
  possible before they would go into a higher one.
  
• Electrons must be is a _______ energy level and
  not in between levels (like steps). He called
  this ___________ (specific quantity of
  energy).
• If electrons were in the lowest energy level
  possible, they ________________________. Called
  this the _______________.
  
• As outer energy levels filled in atoms, the
  electrons could not go into lower energy levels
  as they were already full.
  
• The energy levels are designated by n

45
Bohrs Model

• 1st energy level can hold _______ electrons.
• 2n2 2(1)2 2
• 2nd energy level can hold _______ electrons.
• 2n2 2(2)2 8
• 3rd energy level can hold _______ electrons.
• 2n2 2(3)2 18

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• If an atom is struck by energy (light,
  electricity, heat) the outer electrons may absorb
  this energy and move to a higher energy level
  
• It is now in the ___________________
• This is an ___________ state and so the electrons
  will __________ this energy and move back to
  the________________
  
• The energy is given off as electromagnetic
  radiation (EMR), some of which is in our visible
  spectrum (ROYGBIV)
  
• We see this energy as a color of light emitted
• Neon lights uses this