Transcript What do you know about light?

Bohr-Rutherford Diagrams
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• In 1913, a Danish scientist named Neils Bohr
(1885 – 1962), explained why in the atom
electrons do not spiral into the nucleus.
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• Bohr’s model equated the nucleus of an atom
to the sun, and the electrons to the planets.
• The atoms positive nucleus exerts a strong
force of attraction on the negative electrons.
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• The electrons resist the attraction because they
are moving rapidly in fixed regions around the
nucleus.
• These regions are three dimensional and
sphere like, and are called electron shells.
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• The electrons orbit the nucleus in regions
called shells.
• Shells are areas that surround the nucleus like
layers around an onion.
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• Each shell is a certain distance away from the
nucleus.
• The first shell is closest to the nucleus; the second is
further away.
• Shells are often called orbitals or energy levels.
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• Each shell can hold a certain number of electrons and
no more.
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The first shell can hold 2 electrons
The second shell can hold 8 electrons
The third shell can hold 8 electrons
The fourth shell can hold 18 electrons
The First Shell
The Second Shell
You draw the third shell.
Remember, it has 8 electrons as well.
The Third Shell
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• The outer shell is called the valence shell.
• Electrons in the outer shell are therefore called
valence electrons.
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• Valence electrons are important because they
determine the element’s properties and how it
will react.
• It is only the valence electrons that are
involved in chemical reactions.
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• The valence electrons correspond to the atomic
number of an element.
Remember:
atomic number = # of electrons..
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• Ex: Lithium has an atomic number of 3, so it
would have 3 electrons:
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• The # of valence shells = the # of the period the
element is found in.
• The number of valence electrons (electrons in the
outer shell) = the # of the group the element is found
in.
How to Draw Bohr Diagrams
1.
Draw the nucleus as a solid circle.
2.
Put the number of protons (atomic number) in the
nucleus with the number of neutrons (mass number –
atomic number) under it.
3.
Place the number of electrons (same as protons) in orbits
around the nucleus by drawing circles around the
nucleus. In the second and the third shells, electrons
should be drawn in pairs when they number more than
four.
Ex: Carbon
Carbon: Period: 2, Group: 4
Bohr Diagram:
Complete Bohr Diagrams
for the First 20 elements of
the Periodic Table
Adding to your Periodic Table...
• Write the period number along the sides.
– Period 1 = Row 1
– Period 2 = Row 2
• Write the group number across the top.
– Group 1 = 1st column
– Group 2 = 2nd column
Lewis Dot Diagrams
Electron Dot Diagrams
• Electron dot diagrams (also called Lewis
Dot diagrams) are useful because they show
only the valence electrons, since these are
the important ones anyways.
• They include the element’s symbol and dots
to represent the valence electrons.
How to Draw Dot Diagrams
1. Write the element symbol..
2. Determine the number of valence
electrons the element has. Remember the
valence electrons = group number.
3. Place the number of valence electrons as
dots around the element symbol.
Electron Dot Diagrams
H
C
O
Ne
Draw Electron Dot Diagrams
for the First 20 Elements on
the Periodic Table
This will be to be handed in.