Microsoft PowerPoint - apchp2Kotz [Compatibility Mode]atom
discovered by the time of
Benjamin Franklin (late 1700’s)
Radioactivity
1898- Marie/Pierre Curie: Isolated
polonium and radium which
Suggested particles emitted through
which states that atoms are indivisible
α, β and γ radiation
Radiation Movie 1 Radiation Movie 2
Components of the Atom
1897 by discovery of “negatively
charged” cathode rays using Cathode
Ray Tube (Crookes tube)
electron.
charge to mass ratio (q/m) for the electron
Thomson developed the “plum pudding”
model of the atom
Experiment
(-1.602x10-19C)
hydrogen having the smallest mass).
Protons and the Nucleus
experiment
-Bombardment of nitrogen gas
particle)
1919- Proton officially proclaimed
The Neutron
alpha particles
3
Atomic Number and Atomic Mass Atomic Mass Unit (u or amu) = 1/12 the
mass of a C-12 isotope. (aka 1dalton (Da))
About the mass of a proton or neutron (1u =
1.661x10-24g)
Isotopes
number of protons), that differ in their
number of neutrons.
number of protons)
The mass number of an isotope is not the sum
of the masses of the individual particles due to
the mass defect
Equations:
given isotope / total number of atoms of all
isotopes of that element)x100%
abundance of isotope 1)(mass of isotope 1) +
…
a) Argon has three isotopes with 18, 20
and 22 neutrons, respectively. What are
the mass number and symbols of these
three isotopes?
are in the nuclei of each of these
isotopes? If the abundance of Ga-69 is
60.1%, what is the abundance of Ga-71?
Answers:
p 31 31
n 38 40
e 31 31
neon. Their percent abundances and atomic masses
are: neon-20, 90.51%, 19.99244u; neon-21, 0.27%,
20.99395u; neon-22, 9.22%, 21.99138u. Calculate
the weighted average atomic mass of neon.
2. The two naturally occurring isotopes of copper are
copper-63, mass 62.9298u, and copper-65, mass
64.9278u. What is the percent abundances of each
of the two isotopes? (The atomic mass of copper
listed on the periodic table is 63.546u)
Answers:
isotope.
NA (Avogadro’s number) = 6.022x1023 = 1
mole
5
1) Taken in amu’s (u) = atomic mass (mass
of 1 atom)
of 1 mole of atoms)
24.30Mg If you have 24.30g of Mg you have
6.022x1023 atoms of Mg or 1mole
Determining the molar mass of a
compound
elements that the compound contains.
(multiply by MM) (divide by NA)
Grams Moles Basic Units (atoms, molecules, formula units, etc.)
(divide by MM) (multiply by NA)
Sample Problem
a) What is the mass, in grams, of 1.5 mol
of silicon?
represented by 454g? How many atoms?
c) What is the average mass (in grams) of
one sulfur atom?
42g42g42g42g
14.2mol14.2mol14.2mol14.2mol
6.022x1023atom)
= 5.325x105.325x105.325x105.325x10----23232323gggg
What is the volume (in cm3) of a piece of
gold that contains 2.6x1024 atoms? If the
piece of metal is a square with a
thickness of 0.10cm, what is the length (in
cm) of one side of the piece?
Answers:
Table based on mass instead of atomic number (prior to
understanding of atomic particles)
Trends allowed for prediction of elements that had not yet
been discovered.