Download 24X + 24Y = 2904

Atoms – small “indivisible” particles that all
matter is made up of
Dalton’s First Atomic Theory:
•Elements are made up of small indivisible particles
called atoms
•Atoms of the same element are identical,
different elements are different
•Atoms are not created or destroyed in a chemical
reaction
•A compound always has the same relative numbers
and kinds of atoms
Models of the Atom
•Dalton (~1740) round, hard sphere; neutral,
“cue ball”
•Thomson (~1890) discovered the electron;
e- are part of the atom; there are both
positive and negative charges in the atom,
but it is still neutral. “grapes in Jello”
•Rutherford (~1905) small, dense, positive
charged nucleus; electrons outside the
nucleus “nucleus”
•Bohr – (~1910) electrons are in set orbits or
energy levels around the nucleus; the lower
energy levels are closer to the nucleus;
energy given off/absorbed when electrons
change orbits; only certain amounts of
energy can be gained or loss; “solar system”
Parts of the Atom
Name
Symbol
Charge
Mass
Location
proton
p
+1
1 amu
nucleus
neutron
n
0
1 amu
nucleus
electron
e-
-1
~ 0 amu
outside
nucleus
Atomic Number (AN) – number of protons in
an atom; determines the type of atom; for a
neutral atom it is also the number of
electrons
Mass Number (MN) – number of protons and
neutrons; determines the type of isotope
Isotope – two or more atoms of the same
element but with different numbers of
neutrons (same number of protons,
different numbers of neutrons)
Ion – atom/atoms with a net charge
Charge = p – e-
Mg-25
70
30Zn
AN
12
30
P
12
30
n
13
40
e-
12
30
MN
25
70
How many protons, neutrons and electrons?
p
n
e-
Mg-14
12
2
12
Zn-65
30
35
30
O-2-18
8
10
10
K+1-42
19
23
18
Se-2-79
34
45
36
Fe+3-60
26
34
23
Atomic Mass (atomic weight) – a weighted
average of the masses of all of the isotopes
of that element. It is not the same as the
mass number.
Chlorine: Cl-35 (75.00%)
Cl-37(25.00%)
(35.00)(0.7500) + (37.00)(0.2500) =
26.25
+
9.250
= 35.50 amu
Neon: Ne-20(90.92%), Ne-21(0.25%) and
Ne-22(8.83%)
20.17 amu
There are two isotopes of magnesium in a
container: Mg-24 and Mg-25. The mass of
121 atoms of magnesium is 2988 amu. How
many of each isotope are present?
•X = # Mg-24
Y = # Mg-25
•X + Y = 121
24X + 25Y = 2988
•24X + 25Y = 2988
24X + 24Y = 2904
Y = 84 (Mg-25)
X = 37 (Mg-24) (121 – 84)
A container has 10,000. carbon atoms have a mass of
120,110. amu. There are 2 carbon isotopes: C-12 and C-13.
How many of each isotope?
C-12 = 9890.
C-13 = 110.
The atomic weight of lithium is 6.072 amu. There are two
isotopes:Li-6 and Li-7. the mass of 151 atoms is 917 amu?
How many of each isotope?
Li-6 = 140.
Li-7 = 11
The mass of one nickel is 5.13 grams, the mass of one dime
is 2.73 grams, the mass of 1 envelope is 4.38 grams. Eight
coins are put into an envelope. The mass of the envelope
and coins is 38.22 grams. How many dimes and nickels are in
the envelope?
Dimes = 3
Nickels = 5
A container with a mass of 4.13 grams has a total of 25
dimes and quarters. The mass of a dime is 2.73 grams, and
a quarter is 7.26 grams. If the total mass of the container
and coins is 149.39 grams, how many dimes and how many
quarters are there?
D = # of dimes
Q = # quarters
D + Q = 25
2.73 D + 7.26 Q + 4.13 = 149.39
2.73 D + 7.26 Q = 145.26 (coins only)
2.73 D + 2.73 Q = 68.25
4.53 Q = 77.01
Q = 17 (quarters)
D = 8 (dimes 25 – 17)
Radioactivity – when the nucleus of an
atom is unstable causing it to decompose
into another nucleus
There are three types of radioactive
decay:
1. Alpha Decay – an alpha particle (α ) is produced which
is a helium nucleus, 42He+2
2. Beta Decay – an e- is kicked out of the nucleus (a
neutron breaks up into a proton and e-), 0-1e
3. Gamma Decay – energy is released from the nucleus,
but the nucleus itself does not change, but almost
always accompany alpha and beta decay
•Alpha Decay
230
90Th 
4
222
88Ra 
4
226 Ra
He
+
2
88
218 Rn
He
+
2
86
•Beta Decay
234
131
90Th 
53I 
0
0
234 Pa
e
+
-1
91
131 Xe
e
+
-1
54
•Gamma Decay
238
4 He +
U

92
2
234
90Th
+ energy
What are the products of Po-218 after it
undergoes alpha decay followed by a beta
decay, followed by beta decay followed by
alpha decay?
218
84Po 
214
0 e + 214 Bi
Pb

82
-1
83
214
83Bi 
0
214
84Po 
4
4
214 Pb
He
+
2
82
214 Po
e
+
-1
84
2He +
210
82Pb
Half-Life, t1/2, time required for one half of
the original sample of nuclei to decay.
•The half-life of Ra-223 is 12 days. If you
start with 100.0 grams of Ra-223, how
much will be left after 36 days?
100.0 g  50.00 g  25.00 g  12.50 g
•The half life of Ra-225 is 15 minutes. If
you have 10.0 grams now, how much did you
start with 60 minutes ago?
•10.0 g  20.0 g  40.0 g  80.0 g  160.g
Fission – when an atom splits into two or
more smaller atoms in a nuclear reaction.
1 n + 23592U 
energy
92
141 Ba + 3 n +
Kr
+
36
56
This is what takes place in a nuclear
reactor or an atomic bomb.
Fusion – when several smaller atoms
combine to make a larger atom
1 H
1
+ 21H 
3
2He
+ energy
This is how all of the elements were