Chemistry SM-1131Week 5 Lesson 1

Dr. Jesse ReichAssistant Professor of Chemistry

Massachusetts Maritime AcademyFall 2008

Class Today• Test Wednesday• Poem• Movie• Review: Periodic Table, Isotopes and Atomic Mass• Atomic Mass• Review for the test

Quote

• Everything has to change, and that change has to start with me. -Utah Phillips

Just be careful because change will hurt. -D. Reich

Oil drop Movie

• http://chemistry.umeche.maine.edu/~amar/fall2004/Millikan.html

Skipping Ahead

• I’m skipping a lot of scientists and a lot of story

• We have a nucleus and it contains Protons and Neutrons

• Electrons are on the outside in set patterns

Nucleus Masses

• Protons have masses of 1.67262e-27kg• Neutrons have masses of 1.67493e-27kg• OK, talking about that mass is obnoxious. So

chemists came up with another scheme. They took an atom of Carbon, which has 6 neutrons and 6 protons, and they said 1/12 of that mass is now 1 amu.

• Protons by themselves have a mass of 1.0073 amu. Neutrons have a mass of 1.0087 amu.

Electrons

• Protons are over 1800 times larger than electrons. So, chemists say electrons have no mass.

• This is not exactly true, it’s more like they have negligible mass.

Charge

• Protons have a charge of +1• Electrons have a charge of -1• Neutrons have no charge at all.• Oppositely charged particles attract.• Similarly charged particles repel.• If an atom has an equal number of protons

and electrons the atom has no charge. For every extra proton it has +1 charge. For every extra electron it has -1 charge.

Periodic TableHydrogen is the element1 is the atomic number1.0079 is the atomic mass

Elements

• The number of protons is called the atomic number.

• If two elements have the same atomic number they are the same element. If two elements have different atomic numbers they are different.

The TableGroups/families are up and downRows/periods are left to right

The Table

Group 1. Alkali MetalsGroup 2. Alkaline Earth MetalsGroup 3-12 Transition MetalsGroup 17. HalogensGroup 18. Noble Gases

Main group 1,2 13-18H, C, N, O, P, S, Se are organic elements57-71 lanthanides89-103 actinidesB, Si, Ge, As, Sb, Te, Po are metaloids

Metals

• Shiny• Reflect• Malleable (bendable)• Ductile (can be drawn into strips)• Conduct electricity• LOSE ELECTRONS

Non-Metals

• Dull• Brittle• Don’t conduct• GAIN ELECTRONS(think graphite)

Metalloids

• Mixed Properties• Semiconductors• Some dull, some shiny• Etc.

Ions

• Any charged particle is called an ion.• # of Protons - # of Electrons = charge• If # of protons = # of electrons the charge is 0

and we call it neutral (not an ion)• If # of protons > # of electrons it has a positive

charge and we call it a cation.• If # of protons < # of electrons it has a positive

charge and we call it an anion.

Isotopes

• If two elements are the same they will have the same # of protons.

• If two atoms of the same element have different numbers of neutrons they are called Isotopes.

Ways to write Isotopes

• Two systems exist to write Isotopes.• Let’s take Chlorine for Example. There are two

major isotopes of chlorine. One where the atom has 17 protons and 18 neutrons and one where it has 17 protons and 20 neutrons.

• The easy way to write it is Cl-35 or Cl-37.• Or 35

17Cl, and 3717Cl.

• Top number = Mass # • Bottom = Atomic Number (# of protons)

Mass Number

• Simply put the mass is:• # of protons + # of neutrons = atomic number

Atomic Mass

• Atomic Mass is actually pretty complex.It’s an average mass of all the different isotopes.(%abundance * mass) + (%abundance*mass)

etc… = atomic mass

Neon

• Neon is made up to 3 isotopes• Ne-20 = 90.38%• Ne-21 =0.27%• Ne-22 = 9.25%• Atomic mass = 20.00*.9038 + 21.00*.0027 + 22.00*.0925 =

20.1677 = 20.17 amu = atomic massSo the masses on the periodic tables are average

masses of all the isotopes

Get Ready

• TEST WEDNESDAY!!!• 1: scientific method, vocab words• 2: sig fig, rounding, density• 3: Matter and Energy, chemical vs. physical,

temperature, heat capacity• 4: Atomic Theory, scientists, protons,

neutrons, electrons, periodic table, Ions, Isotopes, Atomic Mass, Atomic Number