Download Atom, Ion, Isotope Notes from 10/5 and 10/6

Atom and Ion Notes
8
O
15.999
Atomic Number
Element’s symbol
Atomic mass
Atomic number = number of protons in the nucleus
Mass number= protons + neutrons!
-the mass number is also the atomic mass rounded to the
closest whole number.
Unless told otherwise, we assume atoms are neutral (they
don’t have an overall charge). !
In this case the protons (+) = electrons (-)
Ions- atoms that have an overall charge. This
electrons
- or
happens when _____________enter
(__)
leave (__)
+ the atom. Only electrons can come
and go because the protons are held in the
nucleus by the _____________________
strong nuclear force.
O
2O
+
O
8 protons, 8 electrons
8 protons, 10 electrons!
(gained 2 electrons)
8 protons, 7 electrons!
(lost 1 electron)
ISOTOPE NOTES
element
Isotope: atoms of the same ________________
that have a
different number of _______________
in their
neutrons
nucleus
_______________.
Think of them as different forms of the
same element.
Carbon- 12
mass number
6 protons!
6 neutrons
Carbon -mass
13 number
6 protons!
7 neutrons
Carbon’s atomic mass is 12.011amu….WHY?
In a sample of 1,000 carbon atoms:!
989 have a mass of 12 amu!
11 has a mass of 13 amu
Scientists will find the average of all the masses of all of
the isotopes in a sample of the element.
989 x 12 = 11868
11 x 13 = + 143
12,011 amu
12,011 / 1,000 = 12.011 amu
The average of all the possible isotopes of carbon is
12.011. The most common isotope is carbon-12, but there
are some carbon-13, which brings the average up slightly
from 12.
The atomic mass is a decimal because it is an average of
all of the possible isotopes for that element. Atoms can’t
have “parts” of protons and neutrons, so that is why we
use the mass number when finding the number of protons
and neutrons.
Rounding the atomic mass to the nearest whole number is
a good estimation for finding the most common stable
isotope of an atom. HOWEVER, it is not a perfect method.
Look at Ag for example. It’s atomic mass is 107.87 amu,
which would round to 108 amu. This is actually NOT a
stable isotope of Ag (only 107 amu and 109 amu are). If
you really wanted to know the stable isotopes of an atom,
you’d have to look it up online. Since we don’t have that
ability all of the time, we are going to use the rounding
trick. I just want you to know that this isn’t always
accurate!