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Atoms and the Periodic Table
Chapter 17 page 506
Structure of the Atom
An atom is made up of smaller particles called
subatomic particles.
These are –
Protons – positive charge
Neutrons – no or neutral charge
Electrons – negative charge
Atom
Center is called the nucleus.
Nucleus contains the protons and neutrons.
Electrons fly in a cloud around the nucleus.
Atoms on the PT
The atomic number indicates the number of
protons in the nucleus.
Atomic mass indicates the average sum of the
protons and neutrons.
History of the Atomic Model
Democritus – 4th century BC philosopher
Suggested the world was made of
invisible units
He called them atoms.
Atom – Greek meaning unable to be
divided
Although his theory explained things, he
couldn’t provide any evidence.
John Dalton
In 1808 an English schoolteacher
came up with a theory that was
developed with a scientific basis.
Today, his theory is the foundation
of modern atomic theory.
Dalton’s Theory
Matter was made up of atoms that could not be
divided.
All atoms of a given element are exactly the
same.
Atoms of given elements could join to form
compounds.
Because he could provide scientific proof,
people believed him.
More Theories
In 1877 JJ Thomson theorized on particles
smaller than an atom. Electrons
In 1911 Ernest Rutherford theorized a nucleus in
an atom with a positive charge.
Niels Bohr
In 1913 this Danish scientist proposed a model
of the atom where electrons moved in definite
orbits around the nucleus.
Like planets around the sun.
Atomic Models
Today the atomic models is based on waves.
This means electrons do not travel in set paths
around the sun.
All we can tell is where an electron is most likely
to be found.
Today
Please take out:
–
–
–
–
periodic table,
Anatomy of an Atom Worksheet
Worksheet packet
Notebook.
Drawing an Atomic Model
First – number of protons is atomic number
Number of neutrons is atomic mass (rounded) atomic #
Electrons are also equal to atomic number
Electrons
First energy level holds 2 electrons.
Second orbital holds 8
Third holds 18, fourth 32,
Atomic Modeling
First place electrons equal to the number of
protons,
Now you must adjust according to the octet
rule.
All atoms want to have eight electrons or
complete orbitals in their highest energy level.
Add or take away electrons according to this
rule.
Atomic Model cont.
Now adjust the charge of the atom accordingly.
You’ll end with a positive # if you took away
electrons, negative if you added.
Try one.
Ne, atomic # 10 atomic mass of 20
Isotopes
Atoms of the same element having different
numbers of neutrons.
Sodium – It’s atomic mass is 22.98. So it can
have a mass of 22 or 23.
How many neutrons is in Sodium-23? Sodium22? Which one occurs more often?
Counting Atoms
During chemical reactions you
need to know how many
atoms are involved.
Remember, more than one
element bonded together is a
compound. – H2O
Counting Atoms cont.
O2 = two Oxygen atoms bonded together.
It’s now a molecule.
The 2 is called a subscript.
7H2O
The 7 is called a coefficient.
This means there are 7 water molecules, each
molecule having 2 Hydrogens and one Oxygen
Counting Atoms cont.
CO2 - How many Carbon atoms are present?
How many Oxygen atoms?
3SO4
How many Sulfer atoms?
How many Oxygen atoms?
How many protons?
Practice!
S(H20)2
S=1 H=4O=2
12H2SO4
8Na2(OH4)6
10C6H12O6(OH)12
3(Mg,Fe)7Si8O22(OH)2
Fukalite - 7Ca4Si2O6(CO3)(OH,F) 2
Periodic Acid – 12H5IO6