Ch.13 Structure of an Atom

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Ch.13 Structure of an Atom
Atomic Number of Protons ()
atomic weight - The atomic weight of an atom is a
measure of how much mass an atom has. It is
calculated by adding the number of protons and
neutrons together.
http//ippex.pppl.gov/interactive/matter/atoms.htm
l
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Atomic masses are not listed as whole numbers on
the periodic table because atoms can come in
forms with different amounts of neutrons.
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• Atoms are the building blocks of matter. Matter
  is neither created or destroyed, simple recycled.
• An atom is the smallest unit of a substance that
  still has all the properties of that substance.
• Atoms have 3 Functional Parts
• Protons
• Neutrons
• Electrons
• Protons have a positive () charge, Neutrons have
  no charge (0), and electrons have a negative
  charge (-).

Summary
Particle Relative Mass Relative
Charge Proton
1
1 Neutron
1
0 Electron
1 1840
-1
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7 million atoms joined together in a straight
line would be about 1mm long.
The nucleus contains protons and neutrons.
http//www.schoolchem.com/xa1.htm
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Electrons
All atoms have electrons. For any atom, the
number of protons is the same as the number of
electrons.
------? of Protons of electrons
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If an atom loses or gains electrons, it is called
an ion.
Each proton has an electrical charge of 1.
Each electron
has a charge of -1.
The neutron has no charge (it is neutral).

Because an atom has the same number of protons
and electrons, the overall charge is zero (it is
neutral).
Summary
Particle Relative Mass Relative
Charge Proton
1
1 Neutron
1
0 Electron
1 1840
-1
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Electron Shells (energy levels)
Electrons are arranged in shells (shown as
circles around the nucleus).
The maximum number of electrons in each shell,
going from the
middle to the outside, are 2,
8, 18, 32.
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Atoms with full shells are STABLE.
These atoms do not react with other atoms.
These atoms belong to a group called The Noble
Gases.
If the outer shell of an atom has less than its
maximum number of electrons or is not full,
then it
will not be stable.
These atoms will react with other
atoms.
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Atomic Number
Atomic number - The number of protons in the
nucleus.
tells you what the element is (Periodic Table)
never changes
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Atomic Weight or Mass Number
Atomic Weight or mass number - number of protons
plus the number of neutrons.
Atomic weight of protons of neutrons
The mass number of any atom will be a whole
number.
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Sodium has 11 protons and 12 neutrons, the mass
number is 23.
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Isotopes Isotopes - Atoms of the same element
that have different numbers of neutrons. For
example, Chlorine (atomic number 17) may have 18
or 20 neutrons. The mass number will be either
35 or 37. Isotopes of the
same element will have the same chemical
properties, because the number of protons and
electrons will be the same.
35
37
Cl
Cl
or
17
17
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Relative Atomic Mass (RAM)
In a naturally occurring sample of Chlorine,
75 of the atoms will
have a mass number of 35,
35
Cl
17
25 will have a mass number of 37.
37
Cl
17
The average mass number for the sample will be
(75 x 35) (25 x 37) 35.5
RAM
The you see on the periodic table!
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Carbon - 14
Carbon - 12
1
1
2
3
2
Carbon 12 7 atoms
weight 7 X 12 amu
84 amu
5
4
Carbon 14 2 atoms
28 amu
weight 2 X 14 amu
84 amu
28 amu
Total 112 amu
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7
112 amu 9 atoms 12.444
Atomic Mass 12.444
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180 atoms of Carbon - 12
Each weighs 12 amu
180 atoms X 12 amu 2160 amu
1 atom of Carbon - 14
Each weighs 14 amu
1 atoms X 14 amu 14 amu
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Average Mass or Atomic Mass of Element 1
_______ Name of Element 1 _________________
2160
12.011
180
12
Carbon
14
1
14

2174
181
6
Carbon - 12
6
6
Carbon - 14
6
8
6
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• Atomic Nucleus
• Protons and neutrons only are found in the
  nucleus/center of an atom.
• It is tightly bound together and contains the
  majority of the atoms mass.

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• Atomic Number of Protons ()
• Ex 6C (Carbon), 8O (Oxygen), 16S (Sulfur)
• Atoms can have differing numbers of neutrons and
  electrons while still retaining the original
  characteristic properties of that atom.
• ISOTOPE 2 or more atoms whose nuclei contain
  the same number of protons, but a different of
  neutrons.
• However, if an atom gains or loses a proton, in
  essence, it changes its atomic number and becomes
  an entirely new atom with new characteristics

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• In 1909, Rutherford was bombarding a thin gold
  foil with alpha particles when he noticed that
  although almost all of them went through the
  gold, one in eight thousand would "bounce" (i.e.,
  scatter) back. The amazed Rutherford commented
  that it was "as if you fired a 15-inch naval
  shell at a piece of tissue paper and the shell
  came right back and hit you."
• From this simple observation, Rutherford
  concluded that the atom's mass must be
  concentrated in a small positively-charged
  nucleus while the electrons inhabit the farthest
  reaches of the atom.
• Pg.318

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• atomic weight - The atomic weight of an atom is a
  measure of how much mass an atom has.
• It is calculated by adding the number of protons
  and neutrons together.
• Ex Carbon has 6 p and 6 n0 612C
• Atomic masses are not listed as whole numbers on
  the periodic table because atoms can come in
  forms with different amounts of neutrons.
• The atomic weight reported for any particular
  element is an average weight of all the known
  forms of that element.

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The Electron

• A charged particle, with a negative charge.
• Electrons Protons
• Electrons surround the nucleus in orbits.
• The mass of an electron is very, very slight,
  only about 9.1 10-31 kg.

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Electron

• A Danish physicist, Niels Bohr, was very
  interested in Rutherfords work, especially in
  the arrangement of the negatively charged
  electrons in the space surrounding the nucleus.
• Electrons have fixed orbits (fixed energy
  levels). Almost like satellites orbiting Earth.

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Bohrs Electron Orbits/Shells

• Electrons orbit the nucleus with different
  energies. An e- boosted from a lower energy
  inner orbit to a higher energy outer orbit is
  said to be excited.
• When an electron jumps from an outer orbit to an
  inner orbit, the atom emits a spark of light
  called a photon.
• When an electron is boosted from an inner orbit
  to an outer one, the atom absorbs light.

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Electron Orbit Shapes

• Just understand that electron orbits are not
  2-dimensionally shaped. They differ by shape and
  size. Pg.328

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Bohrs Planetary Model of the Atom 2orbit2

• K Inner orbit hold up to 2 e-
• L 2nd orbit holds up to 8 e-
• M 3rd orbit holds up to 18 e-
• N 4th orbit holds up to 32 e-

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• Understand how and why electrons are arranged.
• Energy/orbits, e- in each

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• Borh could thus represent the electron
  arrangements of any of the elements.
• ELEMENT One of about 110 distinct natural or
  man-made types of matter which, singly or in
  combination, compose all materials of the
  universe an atom is the smallest representative
  unit of an element

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Elements

• A Russian named Mendeleev was recognized as the
  Father of the Periodic Table.
• The Periodic Table is an organized view of all
  the known elements.
• It is based with vertical columns call GROUPS and
  horizontal rows called PERIODS.

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• The Periodic Table.

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The Periodic Table

• Group I
• Alkali metals Li, Na, K,
• Group II
• Alkaline Earth metals Be, Mg, Ca,...
• Transition Metals

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5 6
440
11
5
6
5
Boron
40
10
100
5
10
5
5
10.8
540
50
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• Group VII
• Halogens F, Cl, Br, I,
• Group VIII
• Noble Gases He, Ne, Ar, Kr.