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Models of the Atom
a Historical Perspective
Early Models of the Atom
• Throughout time, scientists have
developed ideas about atoms.
• The ideas have become more accurate
over time.
• For each scientist, you need to list their
major contributions, or what made their
model different from those that came
before.
Early Greek Theories
•400 B.C. - All matter is made of
indivisible particles called “atoms”.
Democritus
•Greek word “atomos” means not able
to be divided.
•Atom: the smallest unit of an element
that maintains the properties of an
element
John Dalton
• 1800 - Dalton proposed a modern atomic model
based on experimentation not on pure reason.
• All matter is made of atoms, atoms are small
particles, that cannot be created, divided, or
destroyed.
• Atoms of an element are identical.
• Each element has different atoms.
• Atoms of different elements combine in constant
ratios to form compounds.
Adding Electrons to the Model
JJ Thomson (1897)
•Atoms contain negatively charged
particles called electrons.
•Thought that the rest of the atom
must be positive.
•Called the “Plum Pudding” model.
(desert of choice at the time)
•Electrons: negatively charged
particles in an atom
Ernest Rutherford (1909)
Zinc sulfide screen
Thin gold foil
Lead block
Radioactive
substance path of invisible
-particles
• Did an experiment in which he shot
alpha particles at gold foil.
• Found that an atom is mostly empty
space.
• Found the dense, positively charged
central region of the atom, called the
nucleus. Nucleus in made up of protons
and neutrons.
Relative size of the Atom
(Page 548)
1) Dalton’s “Billiard ball” model (1800-1900)
Atoms are solid and indivisible.
2) Thompson “Plum pudding” model (1900)
Negative electrons in a positive framework.
3) The Rutherford model (around 1910)
Atoms are mostly empty space.
Negative electrons orbit a positive nucleus.
Bohr’s Model (1913)
• Electrons are in specific paths called
energy levels.
•Electrons can move from one energy
level to another.
•The farther from the nucleus, the more
energy the electrons have.
Presently
• Electrons do not travel in
definite paths, electrons
path cannot be predicted.
• Electron cloud:
Region around the
nucleus of an atom where
electrons are likely to be
found.
Parts of an Atom
• There are 3 types of subatomic particles.
• Protons: positive charge, found in nucleus
• Neutrons: no charge, found in nucleus
• Electrons: negative charge, found in electron clouds
• Atomic mass unit:
a unit of mass that describes the mass of an atom
amu = .00000000000000000000000017 g
• Proton: 1 amu
• Neutron: 1 amu
• Electron: 0 amu (1800 electrons to equal mass of 1 proton)
Subatomic Particle Chart
Particle
Location
Charge Mass
Proton
Nucleus
+1
1 amu
Neutron Nucleus
0
1 amu
Electron Outside nucleus,
in energy levels
-1
0
Atomic Number and Mass Number
• Atomic Number:
The number of protons
in an atom, also, the
number of electrons.
• Example:
lithium atomic number 3
will have 3 protons and
3 electrons
Mass number:
total number of protons
and neutrons
• Example:
lithium mass number 7
means 7 is the total
number of protons and
neutrons (3 protons
and 4 neutrons)
Atomic
#
Mass #
p+
n0
e–
Ca
20
40
20
20
20
Ar
18
40
18
22
18
Br
35
80
35
45
35
Energy Level Capacity Chart
Energy Level
1
Maximum Number of
Electrons
2
2
8
3
18
4
32
Bohr - Rutherford diagrams
• Putting all this together, we get B-R diagrams
• To draw them you must know the # of protons,
neutrons, and electrons.
• Draw protons (p+), (n0) in circle (i.e. “nucleus”)
• Draw electrons around in shells
He
Li
Li shorthand
p+
2
2 n0
p+
3
4 n0
3 p+
4 n0
2e– 1e–
Draw Be, B, Al and shorthand diagrams for O, Na
Be
B
Al
4 p+
5 n°
O
5 p+
6 n°
13 p+
14 n°
Na
8 p+ 2e– 6e–
8 n°
11 p+ 2e– 8e– 1e–
12 n°
Isotopes
•Atoms of the same element that have different
numbers of neutrons are called isotopes.
•Due to isotopes, mass #s are not round #s.
•H(1.00794) is made up of multiple hydrogens.
6Li
7Li
3 p+
3 n0
2e– 1e–
3 p+
4 n0
2e– 1e–
For more lessons, visit
www.chalkbored.com
Periodic Table
• Dmitri Medeleev
• Discovered a pattern to the
elements in 1869.
• He wrote the names and
properties of elements on cards,
once he arranged the elements by
atomic mass he realized a
pattern.
• Periodic:
describes something that occurs or
repeats at regualr intervals
Using the Periodic Table
“Groups and Periods”
• Groups are Vertical
Columns
• Elements in same group
have similar chemical
properties
• Elements in same group
have same number of
electrons in outer energy
level
• Ex: Lithium, group one,
one electron in outer
energy level
• Periods are horizontal rows
• Elements in same period
have different chemical
properties.
• Elements in same period
have different number of
electrons in outer energy
level.
• Elements in same period
have same number of
energy levels.
• Ex: lithium, period 2,
2 energy levels
Types of Elements
Metals
• 3 or fewer
electrons
in outer
energy
level
• Left side of
P.T.
Nonmetals
Metalloids
•5 or more
elements that
electrons in outer border the
energy level
zig-zag line
•Right side of P.T.
Similar element
13
Type of element
2
2
# of E.L.
E in outer e.l.
3
7
period
group
neutrons
electrons
protons
mass
atomic
Symbol
11
Ionic Compound Vocabulary
Compound- 2 or more elements chemically joined
Chemical Formula -combination of symbols and subscripts
that shows what elements and how many atoms of each
are in a compound, Example:
Ionic Compound- compound that contains ionic bonds
Ionic Bond- force of attraction between oppositely charged
ions
Ionic Compound Vocabulary
Octet Rule –chemical rule of thumb that states that atoms tend to
combine in such a way that they each have eight electrons in their
valence shells, giving them the same electronic configuration as a
noble gas
Valence Electron – an electron found in the outermost energy level
Ion- charged particle that results from a neutral atom gaining or
losing electrons
Polyatomic ion- 2 or more atoms that combine and act like one ion
A. Naming ionic compounds made of a metal
and nonmetal
M-N
1.
Name the metal
• NaCl
• Sodium chloride
2. Name the nonmetal, add –ide
ending
*never use prefixes
• Li2O
• Lithium oxide
Practice
1. KCl
2. Fe2O3
3. KF
4. MgO
5. BeS
6. NaI
7. HBr
8. Sr3N2
B. Naming Compounds with Polyatomic Ions
These compounds have 3 or
more elements, usually a
metal and a polyatomic
ion
• Li2 SO4
1. Name what comes first
usually metal
• NaOH
• Lithium sulfate
• Sodium hydroxide
2.
Name what comes
second usually PI
How do Ions form?
What is an ion?
• A charged particle that
results from a neutral
atom gaining or losing
electrons to become
stable.
Writing Balanced Formulas for
Ionic Compounds
1. Write the symbols
2. Pencil in the charges
3. If the charges=0, you are
finished
4. If the charges do not equal
zero, balance the charges
by crossing the charges to
the subscripts
5. Rewrite the formula, do
not write charges or
subscripts of 1.
• Sodium oxide
• Na O
• Na+1 O-2
• Na+1 O-2
• Na2O
Practice Problems
Strontium fluoride
Cesium carbonate
Sodium nitride
Magnesium oxide
Lithium phosphate
Beryllium chlorate
Calcium chloride
Potassium chromate
Aluminum sulfate
Aluminum oxide
Formula Writing
•
Write the correct formula for the following
Ionic compounds:
1.
2.
3.
4.
5.
Lithium sulfide
Magnesium oxide
Sodium phosphate
Aluminum oxide
Calcium chlorate
Calculating Formula Mass of Ionic
Compounds
• What is formula mass?
– The sum of the masses
of the ions in a formula
unit of an ionic
compound
Example
Al2O3
Al 2 x 27amu= 54amu
O 3 x 16amu= 48amu
Formula mass= 102amu
“Calculating formula mass, so easy, a Caveman could
do it!”
“That’s so
condescending!”
Covalent Compounds Vocabulary
• Covalent compound- a compound containing covalent bonds
• Covalent Bond- bond formed by a shared pair of electrons
How do covalent compounds form?
• Covalent compounds form when 2 or more
nonmetals share pairs of electrons to
become stable.
• Electron dot diagrams are used to show the
sharing of electrons.
Ne
He
Use an electron dot diagram to show how the
following covalent compounds form.
H 2O
H2
CH4
CO2
Ne
He
C. Naming Covalent Compounds
(N-N)
Prefix
Meaning
Rules
Di
2
1. Name left nonmetal, use
prefix if needed
Tri
3
Tetra
4
Penta
5
Hexa
6
Hepta
7
octa
8
2. Name right nonmetal, use
prefix if needed, add –ide
Example:
PBr3
Practice Problems
1. CF4
2. SCl6
3. N2O3
4. N3Br4
Writing Formulas for Covalent
Compounds
1. Diphosphorous pentoxide
2. Diselenium trisulfide
3. Nitrogen trioxide
4. Carbon oxide
5. Phosphorous tetrafluoride
6. Trinitrogen hexasulfide
8. Carbon dioxide
7. Silicon dioxide
10. Carbon tetrachloride
9. Nitrogen octabromide
Molecular Mass
“Yes, it’s me
again, and I
• The sum of the masses of the atoms in covalentcan do
compounds
molecular
• CF4
• C 1 x 12 = 12 amu
• F 4 x 19= 76 amu
» 88 amu
mass, big
deal!”