Download Isotopes and Shell Diagrams

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Isotopes
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An isotope of an element has the same atomic
number but different mass numbers because the
number of neutrons has changed.
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For example:
We can have Carbon-12 with 6 protons and 6
neutrons but...
| We can have Carbon-13 with 6 protons, 7
neutrons, and 6 electrons.
| We can also have Carbon-14 with 6 protons and 8
neutrons.
|
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Isotopes
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Since isotopes of an element have different
numbers of neutrons, they also have different mass
numbers and different atomic masses.
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Isotopes are chemically alike - same protons and
electrons.
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Isotopes: Symbolization
1. Use the chemical symbol with two additional
numbers to the left.
2. The mass number is a superscript.
3 The
3.
Th atomic
t i number
b iis a subscript.
b i t
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e.g. oxygen-18
8
O
atomic mass = 18; atomic number = 8
protons = 8; electrons = 8; neutrons = 10
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Try This
|
Write the isotopic symbols for the following and list
how many neutrons are in the atoms.
1. sulfur-32
2. silver-108
3. lead-207
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Similar Chemical Properties
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The reason for similar properties has do do with
electrons.
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We are able to predict the kinds of compounds that
metals and non-metals are able to form.
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Different elements have different numbers of
electrons.
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Niels Bohr (1885-1962)
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Student of Rutherford
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Proposed that electrons are arranged in a
concentric circular paths, or orbits, around the
nucleus
nucleus.
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Sometimes called the planetary model.
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Bohr-Rutherford Model
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Electrons in a particular path have a fixed energy.
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This means they do not lose energy and fall into
the nucleus.
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The Bohr model was different from the plum
pudding model because it displayed the electrons
going around the nucleus in an orbit and not in just
a big blob.
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The orbit that the electrons travel are displayed by
lines around the nucleus.
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Shells
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Shells are what electrons move around the nucleus
“on.”
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Electron Shells
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Electron Shell Patterns
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Period 1 elements have a single electron shell,
while Period 2 elements have two electron shells
and Period 3 elements have 3 electron shells.
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The first electron shell can hold two electrons while
the second and third shells can each hold eight
electrons.
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Elements in the same group have the same
number of electrons in their outermost shell.
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Predicting Chemical Reactivity
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Electron shell diagrams are useful because they
show the number of electrons in the outer shells.
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Knowing this is the key to understanding the
organization of the periodic table and the chemical
properties of elements.
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Elements in the same group have similar chemical
properties because they have the same number of
electrons in their outer shell.
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Drawing Bohr-Rutherford Model
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Steps
1. A circle is drawn to represent the nucleus of an
atom. Within this circle we write how many protons
and neutrons are in the atom
atom.
2. The next thing is to draw electron orbits around
the nucleus. The number of orbits depends on how
many electrons an atom has.
3. “Dots” drawn on the orbits represent electrons.
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