Warm Up
9-4-15
1. Silicon (Si) has 14 protons how many
electrons are in Si?
2. What was the outcome of the gold foil
experiment?
3. Which subatomic particles are in the
nucleus?
4. Thompson is responsible for finding _____
Agenda
Homework
Go over Unit 1 Test
Notes Unit 2-3
Penny Alchemy lab
Element Poster and WS
Lab penny
Unit 1 Test
• According to the scientific method, the variable
that you change and manipulate is called
– Dependent variable
– Independent variable
• Which characteristics describes only a compound
but not a mixture?
– Two or more things are combined
– The element ratio is fixed
– Substances are combined and mixed
– Substances can separated by physical properties
Unit 1 Test
Unit 1 Test
• Water to steam is physical change because
H2O remain the same in both phases
• Baking soda and vinegar is a chemical change
because it creates CO2 gas which is a new
compound
• Object A = 47 g
• Object B = 31.2 g
Unit 2-3
Atomic Number and Mass Number
Average Atomic Mass
(always the bigger #)
Atomic Number and Mass Number
• The atomic number is the number assigned to a
specific element = # of proton
– Unique for each element
– Same atomic number = same element
Atomic Number and Mass Number
• Protons and neutrons account for most of the
mass of the atom.
 Masses of subatomic particles have units of
amu (atomic mass units) because they are too
small to use grams.
• 1 proton = 1 amu
• 1 neutron = 1 amu
• 1 electron = ~ .0005 amu (doesn’t account for
an atom’s mass)
• Mass number = # of protons + # of neutrons
Check in
1. Find the # of proton, electron and neutron
for Beryllium
Isotopes
• Isotopes are atoms of the same element that have
different numbers of neutrons.
 Because the number of neutrons is different, the
mass number will be different too.
– The number of protons stays the same!
Isotope Symbols
1. Chemists use a
special isotope
notation to
symbolize an
isotope.
2. Isotopes are referred to by their mass number
through hyphen notation
Examples: carbon-12 or chlorine-37
Average Atomic Mass and Mass Number
• The average atomic mass is the average of the mass
numbers of all the isotopes of that element.
• This picture shows that Molybdenum probably has more
isotopes with a mass number of 96, rather than 95,
because the average atomic mass is closer to 96.
Average Atomic Mass and Mass Number
What is the average mass of Lead? Based on the
given stable isotopes
Name of
Atom
Lead-204
Lead-206
Mass
Number
204
206
Abudance %
Lead-207
Lead-208
207
208
22.1
52.4
1.4
24.1
Isotope Symbols Check in
1. What is the mass of Gold?
2. How many electron, proton &
Neutron is in Gold?
3. Find the atomic # and mass for Lead-208
4. Find the atomic # and mass for Lead-205
Isotope Symbols Check-In
Write out the isotope symbols for:
– Chlorine-37
– Bromine-81
– Uranium-235
Penny Alchemy Lab
• Clean your pennies in vinegar about 30-60 secs.
• Place your pennies in the beaker with NaOH and
place the beaker on the hot plate
• DO NOT BOIL your NaOH solution (bad for lungs)
• Do not overlap your pennies
• Wait until your penny completely turned silver
before taking it out of your NaOH solution
Assignments
• Element Poster
• Lab penny
• Worksheet (front side of the poster)