LECTURE: ATOMS, ISOTOPES, AND IONS
CHEMISTRY – MATERIALS
What is an atom?
Demo/discuss: cutting Al foil in half over and over and over again. How small can you go? Smallest piece that still is Al is
an atom.
Q students on what they already know about atoms. Review made up of electrons, protons, neutrons. Draw sketch.
Q to stu: Is atom smallest possible particle? NO! But is smallest particle that retains id of that element. Can distinguish
Al from other atoms. Can’t distinguish e- from different atoms.
Subatomic Particles
particle
symbol
charge
location in atom
+1
effective mass
(amu)
1
proton
p+
neutron
n
0
1
nucleus
electron
e-
-1
“0”
Not really 0, drop
of water in ocean
analogy
electron cloud
Nucleus:
nucleus
Electron Cloud:
center of atom
very small and very dense
grain of sand in center of football field
rest of atom outside of nucleus
very large and not dense, mostly empty space
constant e- mvmt “fills” space like fan blades
Atomic number:
= # protons in nucleus
determines type of atom: all O atoms have 8 p+, all atoms w/ 8 p+ are O
in neutral atom, # e- = #p+, but #e- does not detn id b/c it can change
Mass number:
= sum of p+ and n, since these are the particles with mass
essentially all mass of atom is in the nucleus, even though it is very small
What is an isotope?
atoms of the same type (same # p+) but with different numbers of neutrons
these atoms have same identity but different masses
ex stu might have heard of:
Hydrogen (H-1), Deuterium (H-2), and Tritium (H-3)
“heavy water” is D2O
U-238 most abundant, U-235 needed for nuke fuel
Isotope Symbols: Carbon: 12C
Hyphen Notation: Carbon-12
What is an ion?
13
C
Carbon-13
14
C
Carbon-14
Charged atom, due to loss or gain of electrons
# e- can change w/out changing atom id, thus atomic # = #p+ not #erecall e- small, mobile on outside, this is the part of the atom that interacts with other
atoms that it bumps into
Cation
+ ion
loss of e-
Anion
- ion
gain of eM. Showalter
Sept 2005
#p+ > #eusually metals
# p+ < #eusually nonmetals
Name
Symbol
Atomic
Number
Mass
Number
Number of
Protons
Number of
Neutrons
Number of
Electrons
1
Nitrogen atom
N
7
15
7
8
7
2
Calcium atom
Ca
20
42
20
22
20
3
Strontium atom
Sr
38
88
38
50
38
4
Silicon atom
Si
14
30
14
16
14
5
Barium atom
Ba
56
138
56
82
56
6
Silicon atom
Si
14
32
14
18
14
7
Magnesium ion
Mg+2
12
24
12
12
10
8
Oxygen ion
O-2
8
17
8
9
10
Which two rows contain isotopes of the same atom? Rows 4 and 6
Write isotope symbols and hyphen notation for these isotopes.
30
32
Si
Si
Silicon-30
Silicon-32
Which rows contain ions? 7,8
Cations? 7
Anions? 8
Note that magnesium ion and oxygen ion are isoelectronic – same number of eWhat neutral atom has same # e- as these ions? Neon
M. Showalter
Sept 2005