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Science-10
E.Brennan
Atomic Structure
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

is a counting number
equals the number of protons
is the identity of the element (all atoms of a given element have the same # of
protons)
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
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is a counting number
equals sum of protons + neutrons
(is not equal to 2 x protons since protons and neutrons do not always come in identical
numbers)
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
is a calculated (think ‘decimal points’) number
approximately equal to sum of protons + neutrons (which make up essentially the mass)
1.
Within atoms of the same element, the number of ________________will never vary
from one atom to the next.
2. Within atoms of the same element, the number of ________________will vary from
one atom to the next. These various form of the element are called
___________________.
3. All the isotopes of a particular element have the same ___________________ but
they have different _____________________________.
4. ______ elements exist naturally as a mix of isotopes, so the________ number we use is
just a way of indicating which isotope we mean.
5. The _______________________ is actually a weighted average of all naturally
occurring isotopes (taking into account how frequently each is found).
6. In a neutral atom the number of ____________ equals the number of ___________.
7. If the atom is charged it is because it gained or lost one or more ________________.
Example: charge of 2+ is the result of ________________________, while charge
of 3- is the result of ______________________.
8. Charged atoms have mass that is _________________________ than their neutral
counterparts.
Science-10
E.Brennan
All atoms in chart are neutral.
Symbol
1
Name
Atomic
Number
Atomic
Mass
Neutrons
B
2
11
4
Isotopic
Symbol
39
88.9
39
29
35
Pb
208
7
103
8
9
Mass
Number
23
31
5
Electrons
6
3
6
Protons
70
89
Mo
54
10
12
6
C
11
14
6
C
12
10
5
B
So, what’s up with all these isotopes anyway?
In nature elements are not made up of atoms that are all exactly the same!
Some will be heavier than others, even though they are still the same type of atom.
C-12 and C-14 are both Carbon, with all the usual Carbon properties, but the C-14 has two more neutrons,
and is heavier.
Both Carbons exist in nature, but in different abundances. They are not 50/50 or else we would average the
two weights and report a calculated Atomic Mass in the periodic table of 13. Because the reported Atomic
Mass is very very close to 12, we know that almost all of the Carbon found in nature is C-12, with a teeny bit
of C-14.
Look up Chlorine in the periodic table. In nature it consists of Cl-35 and Cl-37. Since its Atomic Mass is
reported to be 35.45 we can conclude which isotope occurs the most (...........right?)
(You will look at the math behind these calculations in Chem11.)