Transcript Chapter 4 Presentation

Chemistry
Chapter 4: How Atoms Differ:
• Atomic number = # p+ AND e(assume neutral atom for charge).
• Rounded (whole number) mass
number = # p+ + # n0.
• Rounded average mass number –
Atomic number = #n0.
• Symbol notation (Element; mass
# and atomic #).
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Chemistry
Ions:
When atoms are NOT balanced for
charge they are called ions.
• Positive ion: Atom has lost
electrons. Called cations (symbol).
• Negative ion: Atom has gained
electrons. Called anions (symbol).
• Symbol system for ions.
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Chemistry
Isotopes:
When the number of neutrons is
different BUT the proton number is
the same…:
• Chemical behavior is the same.
• The more neutrons, the greater the
mass number (mass).
• Most elements found in nature are a
mixture of isotopes.
• Isotopes differ for their relative
abundance in nature (show as a %).
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Chemistry
Atomic and Mass # Review:
– The atomic number provides the
number of protons in the nucleus and
the number of electrons in a neutral
atom.
– The mass number tells us the
number of protons and neutrons in the
nucleus. The mass # minus the atomic
# provides the number of neutrons.
The mass # is different for isotopes of
the same element.
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Chemistry
Isotopes and Ions Review:
– Different isotopes of the same element
that are neutral for charge are different
for neutron # and mass #; they are the
same for electron # and
proton #.
– Ions of the same element are different
for electron # and charge ; they are the
same for atomic # and mass #.
– Cations have a positive charge because
electrons have left the atom. Anions have
a negative charge because electrons
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have entered into the atom.
Chemistry
Average Atomic Mass:
– Chemists used a standard of C-12 as
being 12 amu; 1 amu is 1/12 of C-12.
– Calculating average atomic mass
need number of naturally occurring
isotopes, their masses AND their
abundance (percentage of the total found
in the environment).
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Chemistry
Average Atomic Mass:
–Round I: Calculate the atomic mass
of element X and identify the element
from the periodic table using the
following data:
•
•
63X
(62.930 amu; 69.2% abundance).
65X (64.928 amu; 30.8%)
– Answer: 63.5 amu; Copper (Cu)
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Chemistry
Average Atomic Mass:
– Round II: Calculate the atomic
mass of element Y and identify the
element from the periodic table using
the following data:
•
•
•
•
54Y
(53.940 amu; 5.9% abundance).
56Y (55.935 amu; 91.72%)
57Y (56.935 amu; 2.1% abundance)
58Y (57.933 amu; 0.28% abundance).
– Answer: 55.844 amu; Iron (Fe)
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