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2.1 Atoms and Their Structure

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2.1 Atoms and Their Structure Objective Relate historic experiments to the development of the modern model of the atom. Illustrate the modern model of the atom. – PowerPoint PPT presentation

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Date added: 29 July 2019
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Title: 2.1 Atoms and Their Structure


1
2.1 Atoms and Their Structure
  • Objective
  • Relate historic experiments to the development of
    the modern model of the atom.
  • Illustrate the modern model of the atom.
  • Interpret the information available in an element
    block of the periodic table.

2
Early Ideas About Matter
  • Our current model of the composition of matter is
    based on hundreds of years of work.
  • About 2500 years ago, the Greek philosophers
    thought about the nature of matter and its
    composition.
  • They proposed that matter was composed of four
    fundamental elements

3
And these were
  • Air
  • Water
  • Fire
  • Earth

4
Greek Philosophers
  • They also debated whether matter could be divided
    into smaller and smaller pieces endlessly or
    whether there was an ultimate smallest particle
    that could no longer be divided.
  • They were excellent observers, but they did not
    test their theories with experiments.

5
Democritus, 460-370 B.C.
  • Proposed that the world is made up a empty space
    and tiny particles called atoms.
  • He thought that atoms were the smallest particles
    of matter and that different types of atoms exist
    for every type of matter.
  • Atomic Theory- matter is made up of fundamental
    particles called atoms.

6
Antoine Lavoisier (1743-1794)
  • French chemist
  • In 1782 he made measurements of a chemical change
    in a sealed container.

7
Lavoisiers Conclusion
  • He observed that the mass of the reactants before
    the chemical reaction were equal to the mass of
    the products after the reaction.
  • In a sealed container 2.0 g of hydrogen gas
    reacted with 16.0 g of oxygen gas to produce 18.0
    g of water
  • Matter was neither created nor destroyed during a
    chemical reaction, but changed.
  • This became known as the law of conservation of
    matter

8
Law of Conservation of Mass
9
Joseph Proust
  • Joseph Proust, French chemist
  • September 26, 1754 July 5, 1826

10
Prousts Contribution
  • Observed that the composition of water is always
    11 hydrogen and 89 oxygen by mass. Regardless
    of its source
  • He observed many other compounds and observed
    that the elements that composed the compounds
    were always in a certain proportion by mass.
    This is referred to as law of definite
    proportions.

11
John Dalton
12
Daltons Atomic Theory
  • John Dalton (1766-1844), an English schoolteacher
    and chemist
  • Studied the experiments of Lavoisier, Proust, and
    many others.
  • Based on this he developed his atomic theory.

13
Daltons Atomic Theory
  1. All matter is made up of atoms.
  2. Atoms are indestructible and cannot be divided
    into smaller particles(Atoms are indivisible)
  3. All atoms of one element are exactly alike, but
    they are different from atoms of other elements.

14
Daltons Atomic Theory
  • This gave chemist a model of the particle nature
    of matter, but it also raised a lot of questions.
  • If all elements are made up of atoms then why are
    there so many different types of elements?
  • What makes one atom different from another?

15
Daltons Atomic Theory
  • Experiments performed late in the 19th century
    began to explain the properties and behavior of
    substances
  • This was done by the discovery of three smaller
    particles.
  • Protons, electrons and neutrons

16
Atomic Theory, Conservation of Matter and
Recycling
  • What happens to the stuff you throw away? What
    happens to the atoms?
  • As you have already learned matter is neither
    created nor destroyed, so what happens.

17
What happens?
  • When waste is incinerated or buried the atoms may
    combine with oxygen and other substances to form
    new compounds.
  • The atoms are recycled

18
Recycling
  • Recycling has become a part of life now.
  • Much of what you buy is either recycled or can be
    recycled.
  • We have found the advantage of recycling
    materials and therefore atoms. We mimic what
    nature does and conserve our natural resources.

19
Hypotheses
  • Hypothesis testable prediction to explain
    observations.
  • Hypotheses are based on observations.
  • They can be proven correct or incorrect by the
    experiments that are designed to test them.

20
Hypothesis
21
Theories
  • Theory- an explanation based on many observations
    and supported by the results of many experiments.
  • As scientists gather new information, a theory
    may be revised or replaced.

22
Theory
23
Laws
  • Scientific Law a fact of nature that is
    observed so often that it is accepted as the
    truth.
  • Examples
  • Sun rises in the east
  • A law can generally be used to make predictions
    but does not explain why something happens.
  • Theories explain laws.
  • One part of Daltons atomic theory explains why
    the law of conservation of matter is true.

24
Review
  • What is the difference between a theory and a
    hypothesis?
  • What is the Law of Conservation of Mass?

25
The Discovery of Atomic Structure
  • Daltons atomic theory was almost true.
  • He assumed that atoms are the ultimate particles
    of matter and cant be broken up into smaller
    particles and that all atoms of the same element
    are identical.
  • His theory needed to be modified with the
    discovery of electrons, protons and neutrons.

26
The Electrons
  • In 1897, JJ Thomson a British physicist
    discovered that the solid ball of model was not
    accurate.
  • His experiments involved the use of a cathode
    ray.

27
Cathode Ray
  • Composed of a vacuum tube
  • At the end of the tube is a piece of metal called
    on electrode which is connected to a metal
    terminal on the outside of the tube.
  • The electrode becomes electrically charged when
    connected to a high voltage.
  • When the electrode is charged rays travel in the
    tube from the negative electrode(the cathode) to
    the positive electrode (the anode)

28
Cathode Ray
29
Cathode Ray
30
Thomsons Discovery
  • What he found that the ray would bend towards a
    positive charged plate and away from a negatively
    charged plate.
  • He concluded that the rays are composed of
    invisible negatively charged particles he called
    electrons
  • Electron negatively-charged particle

31
Early Atomic Model
  • The early atomic model was referred to as the
    plum pudding model you could more closely
    relate it to a chocolate chip cookie
  • Scientists believed that atoms were balls of
    positive charge with the negatively charged
    particles embedded in them.

32
Changes in the Atomic Model
Plum Pudding Model
Solid Ball Model
33
Ernest Rutherford
  • In 1909 he carried out the first of the
    experiments that would reveal an arrangement far
    different from the plum pudding model

34
Rutherfords Experiment
  • Gold Foil Experiment
  • He set up a lead-shielded box containing
    polonium, which emitted a positively charged beam
    of alpha particles.
  • When the beam struck a sheet of gold foil, most
    of the particles passed straight through the foil
  • However, some of the particles from the beam were
    deflected. Some were only slightly deflected and
    some bounced straight back.

35
Gold Foil Experiment
36
Gold Foil Experiment
37
The Nuclear Model of the Atom
  • Based on Rutherfords work the team devised a new
    model for the atom.
  • Because some of the particles bounced straight
    back they concluded that atoms must have a dense
    central core called the nucleus
  • Nucleus a small, dense, positively charged
    central core of an atom

38
Nuclear Model
39
Changes in the Atomic Model
Plum Pudding Model
Nuclear Model
Solid Ball Model
40
Atomic Model
  • It was hard for people to grasp that atoms
    contained a lot of empty space.
  • When they looked at a rock, it was very difficult
    to see how most of this object could be empty
    space.
  • If you were to enlarge an atom of hydrogen so the
    nucleus was the size of a golf ball, the electron
    would be a mile a way.
  • In one drop of water there is 6,500,000,000,000,00
    0,000,000 (6.5 sextillion) atoms

41
Atomic Numbers and Masses
  • The nucleus of an atom is composed of protons and
    neutrons. Electrons move in the space around the
    nucleus.
  • Atomic Number the number of protons in the
    nucleus of an atom.
  • Every element has a unique atomic number.
    Therefore, it is the number of protons that
    determines the identity of an element.

42
Atoms
  • Protons - positively charged subatomic
    particles.
  • Neutrons subatomic particle that does not have
    a charge, it is neutral
  • Atoms have no overall charge.
  • Therefore the number of protons and electrons
    must be equal.
  • If you elements atomic number is 2
  • 2 protons
  • 2 electrons

43
Mass Number
  • Mass number - the number of protons and neutrons
    in the nucleus of an atom.
  • Isotope atom of an element with a different
    number of neutrons and therefore a different mass
    number
  • Ne-20 neon 20(10 protons, 10 neutrons)
  • Ne-21 neon 21(10 protons, 11 neutrons)

44
Neon
45
Composition of Atoms
  • You can determine the composition of any element
    if you know the
  • Atomic number
  • Mass number

46
Atomic Mass
  • Since elements have different isotopes the atomic
    mass is the weighted average.
  • Located under the symbol on the periodic table.
  • You can use the atomic mass to determine the mass
    number of a element
  • You take the atomic mass rounded up

47
Determining Atomic Mass
62.930 X 0.6917 43.529 64.928 X 0.3083 20.017
43.529 20.017 63.546
48
Review
  • What information does the atomic number give us?
  • How do we determine the number of neutrons of any
    element?
  • Who discovered the electron?
  • What discovery did the Gold Foil Experiment led
    to?
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