Do Now: Pass in homework to be peer
graded and returned
Objective: 4.3 Distinguishing Atoms
Home Work: Pg. 119 # 25 – 29, 32
1.
2.
3.
8.
9.
Indivisible and indestructible
By using experimental methods
Scanning Tunneling Microscope
Protons, Neutrons, and Electrons
A positively charges nucleus surrounded by electrons
which take up most of the volume
10. Proton + 1 , Neutron + 1, Electron – 1/1840
13. So many of the alpha particles went straight through
the gold foil.
14. Rutherford had a positively charged dense nucleus
that was tiny in comparison with the atom as a whole
while Thompson’s “plumpudding” model had
electrons that were stuck in the large positive area.
10/10/11
1) Indivisible and indestructible
4) All matter is composed of atoms. All atoms of the same
element are identical. Chemical change involves
rearrangement of atoms in whole number ratios
5) No.
6) 5 x 10-2 nm to 2 x 10-1 nm
8) Protons, neutrons, and electrons
9) A small, positively charged nucleus surrounded by
electrons, which take up most of the volume
10) protons, 1, +; neutrons, 1, none; electrons, ~0, -1
11)
4.3 Distinguishing Among Atoms
Atomic Number
• Elements are different because they contain
different numbers of protons.
Atomic Number =
Atomic Number
• Elements are different because they contain
different numbers of protons.
Atomic Number = the number of protons in
the nucleus of an atom of a
given element.
Mass Number
• Mass Number = The total number of protons
and neutrons in the nucleus
of an atom
Mass Number
• Mass Number = The total number of protons
and neutrons in the nucleus
of an atom
# of Neutrons = Mass Number - Atomic Number
Mass Number = # of protons + # of neutrons
Practice problem
• What is C.C. Carbon’s mass number?
I have 6 protons,
6 neutrons, and
6 electrons. Do I
look fat??!!?!?!
Mass Number= 6 protons + 6 neutrons = 12
*Never ask a lady about her atomic mass.
Isotopes
• Atoms with the same number of protons but
different numbers of neutrons are called
isotopes.
– Carbon-12 = 6 p+ and 6 no
– Carbon-13 = 6 p+ and 7 no
– Carbon-14 = 6 p+ and 8 no
– Same # of protons  all are still carbon.
We’re almost
identical!
Carbon-12
I’m
prettier!!!
Carbon-14
Isotopes
• Because isotopes of an element have different
numbers of neutrons, they also have different
mass numbers
– Mass number = # of protons + # of neutrons
We’re almost
identical!
Carbon-12
I’m
prettier!!!
Carbon-14
Atomic Mass
• An Atomic Mass Unit (amu)
is defined as 1/12th of the mass
of a Carbon-12 atom
• 1 amu ≈ mass of a proton or a neutron
Atomic Mass
• Why aren’t all the atomic masses on the
periodic table whole numbers?
– Because they are weighted averages of the mass
of isotopes of that element.
Example:
Element
Isotopes
% abundance
Average atomic
mass
Chlorine
Chlorine-35
76%
35.45
Chlorine-37
24%
Practice Problem!
• Calculate the atomic mass of bromine. The
two isotopes of bromine have mass numbers
and relative abundance of:
Br-79: 78.92 amu (50.69%)
Br-81: 80.92 amu (49.31%)
The Periodic Table
If there are around 117 elements why do you
think we organize them as in the Periodic Table
and don’t simply list them 1 -117?
The Periodic Table
Periods are the horizontal rows
Groups are the vertical columns
Friday, October 1
• Do Now – Current Events and Chemistry
• Objective – Chapter 4 Review
5.1 Models of the Atom
• Homework – Start Pg. 132 # 1-6 (Due Tuesday)