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Atomic Structure
Brought to you by those crazy
teachers in ...
Science II
The Basic Analogy
Atom
Molecule
Element
Compound
ElementCannot be broken down into another substance
Is made up of only one type of atom
Molecules & Compounds
Properties of the
Elements
Properties of the
Compound
Hydrogen?
Water?
Oxygen?
Analogy: It’s like putting two lego blocks together and getting
a Cow! (but there are reasons why this happens)
So…What’s in an Atom?
Particle
Location
Charge
Mass
Proton
Nucleus
+1
1 amu
Neutron
Nucleus
0
1 amu
Electron
Orbitals
-1
0 amu
AnATOMy of An ATOM
Electron
Nucleus with
Protons &
Neutrons
Some Typical Atoms
Hydrogen
1e-
1P+
Carbon
6e-
6P+
6N
Rules for Atoms
• The Net Charge for any atom should
equal … 0
• This means that there should be the
same number of Protons and
Electrons!
• The number of PROTONS defines the
element (This is the Atomic Number)
More About Atoms
• The MASS NUMBER of an atom is the
sum of the number of PROTONS and
the number of NEUTRONS.
What happens if...
• An atom gains or loses electrons?
– you get an ION…a charged particle
• An atom gains or loses neutrons?
– you get an ISOTOPE…a heavier or lighter
form of the same substance
• An atom gains or loses protons?
– you get a different element (happens in nuclear
fission or fusion)
Atomic Mass (not Mass Number)
• Definition: the weighted average of all of
the isotopes of an element.
• What’s a weighted average?
– Take carbon for example. You’ll notice that the
atomic mass is very close to 12. There are heavier
forms of carbon, but they occur much less frequently
than Carbon 12. If you take the average based on
how frequently they occur, the relative amount of
Carbon 12 brings the average close to 12.
A Little History...
• Democritus
– Greek Thinker (I hope so!)
– Atoms are the basic unit which cannot be cut
• Dalton
– 1809 - Basic table and symbols
• Thompson
-
- -- - --- --
– 1890s - A positively charged GOO, with little
negative charges floating around in it!
More History (Yippeeee!)
Ernie’s (Rutherford) Big Adventure
Thin Sheet of Gold
Atoms
Rutherford’s Conclusion
• Atoms are made of
mostly EMPTY SPACE!
– Actually, the ratio of the size
of the nucleus to the diameter
of the orbits of electrons can
be compared with placing a
marble in the middle of a
football stadium!
Constructing Atoms…
• An atom has an atomic number of
“6”, and a mass number of “14”.
– Sketch the Atom
• Use the 2-8-8…rule for electron orbitals
– Identify the Element (Periodic Table)
– Is the atom the most common form for the
element?
• An atom has an atomic number of
“14”. Sketch its most common form!
Patterns in the periodic table...
• Sketch the most common form of the
first 18 elements (poster size if you
prefer).
• Make a list of any patterns that
become obvious to you as you look
at the structure of your atoms.
• Note: Look carefully at the
relationship between elements in the
same column…or row!
Periodic Table
H
H
He
He
Li
Li Be
Be B
B C
C N
N O
O FF Ne
Ne
Mg
Na
Na Mg Al
Al Si
Si PP SS Cl
Cl Ar
Ar
Periods
Group...
• Within a Group or Family
– Same number of electrons in outer level
– React similarly
– Are likely to form similar Ions
• Moving Down a Group
– Add one electron shell each time
– Elements on the left (Group 1) get more
reactive as you go down a column.
– Elements on the right (Group 7) get less
reactive as you go down a column.
Periods...
• Elements in the same period…
– Have the same number of energy levels
• As you go across a period…
–
–
–
–
Atomic number increases by “1”
One electron is added to the outer shell each time
Change in reactivity
Form different types of Ions
Who gains? Who loses?
• In your “Pictorial Periodic Table”,
which atoms do you think are most
likely to lose electrons?
• Which are most likely to gain
electrons?
• Make some predictions about the
following…
Ca, H, Cl, Al, F, Na, K