Warm Up 9-4-151. 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 _____

HomeworkElement Poster and WSLab penny

AgendaGo over Unit 1 TestNotes Unit 2-3 Penny Alchemy lab

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 2-3Atomic 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 in1. 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 Symbols1. 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

Name of Atom

Mass Number

Abudance %

Lead-204 204 1.4Lead-206 206 24.1

Lead-207 207 22.1Lead-208 208 52.4

What is the average mass of Lead? Based on the given stable isotopes

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-2084. 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)