Transcript Chapter 5 - Angelfire

Chapter 5
Atomic Structure
&
the Periodic Table
Early Scientists
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As scientists of the eighteenth century studied
the nature of materials, several things became
clear:
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1. Most natural materials are mixtures of pure
substances.
2. Pure substances are either elements or
combinations of elements called compounds.
3. A given compound always contains the same
proportions of the elements - Law of Constant
Composition.
Early Models of the Atom
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John Dalton
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English teacher
1766-1844
Studied ratios of elements in chemical
reactions.
Formulated hypotheses and theories to explain
his observations and came up with Dalton’s
atomic theory.
Dalton’s Atomic Theory
 1.
All elements are composed of tiny
particles called _________________.
Dalton’s Atomic Theory
 2.
Atoms of the same element are
_________________.
Dalton’s Atomic Theory
 3.
The _________________ of a given
element are different from those of any
other element.
Dalton’s Atomic Theory
 4.
Atoms of one element can combine
with atoms of other elements to form
_________________. A given
compound always has the same
relative numbers and types of atoms.
Dalton’s Atomic Theory
 5.
Atoms are _________________ in
chemical processes.
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That is, atoms are not created or
destroyed in chemical reactions.
A chemical reaction simply changes the
way the atoms are grouped together.
Dalton’s Atomic Theory
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Dalton’s model explained important
observations such as the
_____________________________.
His model was not accepted at first,
however, he used his model to explain the
existence of certain types of substances.
 He predicted correctly the formation of
multiple compounds and his theory became
widely accepted.
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Atoms
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The smallest substance that cannot be
divided any further and still maintain the
_________________ of the substance.
Structure of an Atom
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J.J. (John Joseph) Thomson, physicist
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1890-1900
Showed that the atoms of any element can be
made to emit tiny negative particles - called
_________________.
Thompson knew that the entire atom was not
negatively charged so he concluded that the
atom must also contain positive particles that
balance the negative charge, giving the atom a
_________________charge.
J.J. Thomson
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J.J. Thomson was chosen to head
the Cavendish Laboratory in
Cambridge, England in 1884
when he was only 28 years old.
Thomson was known for his gift
in designing experiments, but he
was not mechanically inclined
and needed help to build the
apparatus needed to perform the
experiments.
J.J. Thomson
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In the 1890s, one of the most common ways to study
electricity was to build a glass tube with metal
electrodes in each end, one of which was coated with
zinc sulfide. When the air was pumped out of the
tube, called a _________________, and a battery
was hooked to wires connected to the electrodes, a
bright, glowing spot was observed in the zinc sulfide.
After ten years of trying to figure what caused the
glow, Thomson finally concluded it must be due to a
stream of negative particles that he called
_________________- we now call them
_________________.
J.J. Thomson
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By the time of Thomson’s discovery in 1897,
the Cavendish had become the most
distinguished laboratory in England.
However, despite the prominence of Thomson
and his laboratory, the suggestion that these
particles came from inside atoms
(_________________), was not received by
the scientific community - many physicists did
not even believe in the existence of atoms.
Structure of an Atom
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William Thomson (Lord Kelvin, no relation to
J.J. Thomson)
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He had the idea that the atom might be something
like a pudding with raisins randomly distributed
throughout.
He reasoned that the atom might be thought of as
a uniform pudding of positives charge with
enough negative electrons scattered within to
counterbalance that positive charge.
Structure of an Atom
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Ernest Rutherford
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1911
Learned physics in J.J. Thomson’s laboratory in
the late 1890s.
Main area of interest was the
_________________ (α particle) - positively
charged particles with a mass approximately
7500 times that of an electron.
Ernest Rutherford
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In studying the flight of the α particle through
air, Rutherford found that some of the α
particles were deflected by something in the air.
He designed an experiment that involved
directing α particles toward thin metal foil.
Surrounding the foil was a detector coated with
a substance that produced tiny flashes wherever
it was hit by an α particle. The results of the
experiment were very different from those he
anticipated.
Ernest Rutherford
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Although most of the particles passed straight
through the foil, some of the particles were
deflected at large angles and some were
reflected backwards. (He described this results
as comparable to shooting a gun at a piece of
paper and having the bullet bounce back!)
Rutherford knew that if the plum pudding
model of the atom was correct, the massive α
particles would crash through the thin foil like
cannonballs through paper.
Ernest Rutherford
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Rutherford concluded that the plum pudding model
for the atom could not be correct.
The large deflections of the α particles could be
caused only by a center of concentrated
_________________ charge that would repel the
positively charged α particles.
Most of the α particles passed directly through the
foil because the atom is mostly
_________________.
Ernest Rutherford
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The deflected particles were those that had a “close
encounter” with the positive center of the atom, and
the few reflected α particles were those that scored a
“direct hit” on the positive center.
These results could be explained only in terms of a
nuclear atom - an atom with a dense center of
_________________ (the nucleus) around which
tiny electrons moved in a space that was empty.
He concluded that the nucleus must have a
_________________ charge to balance the
_________________ charge of the electrons and
that it must be small and dense.
Ernest Rutherford
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By 1919, Rutherford concluded that the nucleus of an
atom contained what he called
_________________ (has the same magnitude of
charge as the electron, but its charge is positive)
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_________________ have a 1+ charge and the
_________________ a charge of 1-
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1932, he and a coworker (James Chadwick) were
able to show that most nuclei also contain a neutral
particle that they named the _________________
(which has no charge)
Modern Concept of Atomic Structure
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The simplest view of the atom is that it consists of a
tiny nucleus that is about 10-13 cm in diameter.
Electrons move about the nucleus at an average
distance of about 10-8 cm from it.
Nucleus contains _________________, which
have a positive charge equal in magnitude to the
_________________ negative charge, and
_________________, which have almost the
same mass as a proton but no charge.
Modern Concept of Atomic Structure
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Mass and charge of the electron (e-), proton
(p+), and neutron (N)
The mass and charge of the electron, proton, and neutron.
Particle
Relative Mass*
Relative Charge
Electron
1
1Proton
1836
1+
Neutron
1839
None
*The electron is assigned a mass of 1 for comparison
Modern Concept of Atomic Structure
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If all atoms are composed of these same
components, why do different atoms have
different chemical properties?
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The answer lies in the number and arrangement of the
_________________.
The number of e- a given atom greatly affects the way
it can interact with other _________________.
As a result, atoms of different elements, which have
different numbers of electrons, show different
_________________ behavior.
Distinguishing Between Atoms
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_________________ and
_________________ are equal in an atom of an
element (_________________).
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The atomic number of an element is the number of
_________________ in the nucleus of an atom
of that element. (If the p+ and e- are the same,
then the atomic number will also identify the
number of e-)
Distinguishing Between Atoms
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The sum of the number of _________________
and the number of _________________ in a
given nucleus is called the atom’s
_________________.
Isotopes
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atoms with the same number of
_________________ but different numbers of
_________________.
Elements on the periodic table are the most common
_________________ of those substances.
Distinguishing Between Atoms
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Isotopes
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Because they have different numbers of
neutrons, their mass numbers will be different.
Neon - 20
Neon - 21
Neon - 22
All of these are isotopes of neon.
Distinguishing Between Atoms
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Isotopes
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3 known isotopes of hydrogen
 hydrogen
-1
 hydrogen - 2
 hydrogen - 3
[hydrogen]
[deuterium]
[tritium]
Isotopic Symbols
X = the symbol of the element
 A = the mass number
 Z = the atomic number
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1H
1
2H
1
3H
1
Hydrogen
Deuterium
Tritium
A
Z
X
Atomic Masses
Because atoms are so tiny, the normal units
of mass - the gram and the kilogram - are
much too large to be convenient.
 Mass of a single carbon atom is 1.00 x 10-23
grams.
 When describing the mass of an atom,
scientists have defined a much smaller unit
of mass called the __________________________________.
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Atomic Masses
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In terms of grams:
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1 amu = atomic weight of a substance
expressed in grams
1 carbon atom = 12.01 amu = 12.01 grams
1 aluminum atom = 26.98 amu = 26.98 grams
Periodic Table of Elements
Shows all the known elements and gives a
lot of information about each element.
 Invaluable in chemistry!
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