Transcript 24X + 24Y = 2904

Atoms –
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
proton
neutron
electron
Symbol
Charge
Mass
Location
Atomic Number (AN) –
Mass Number (MN) –
Isotope –
Ion –
Charge = p – e-
Mg-25
AN
P
n
eMN
70
30Zn
How many protons, neutrons and electrons?
p
Mg-14
Zn-65
O-2-18
K+1-42
Se-2-79
Fe+3-60
n
e-
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%)
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-12.
How many of each isotope?
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?
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?
Frequency, f, number of waves per sec; s-1
Wavelength, wl, distance between
corresponding parts on consecutive waves;
cm
Speed of light, c, 3.00 E 10 cm/s
f = c/wl
wl = c/f
c = f x wl
Frequency and wavelength are inversely
related; as one goes up, the other goes
down
Energy of light is ___________related to
the ________ of the light, and
___________related to the___________.
As Frequency goes up, Energy goes up.
As Wavelength goes up, Energy goes down.
Energy has units of Joules, J.
E = hf
h = Planck’s constant = 6.626 E-34 J. s
What is the energy and wavelength of
radiation whose frequency is 6.775 E 18 s-1?
wl = c/f
E = hf =
1. What is the wavelength of light that has
a frequency of 2.27 E 17 s-1?
2.What is the frequency of light that has a
wavelength of 9.13 E-8 cm?
3. What is the wavelength of light with a
frequency of 4.27 E 18 s-1?
4.Radiation has an energy of 1.23 E -16 J.
What is the frequency and wavelength of
the radiation?
1. wavelength =
2. frequency =
3. wavelength =
4. frequency =
wavelength =
Quantum Model of the Atom
•nucleus : protons and neutrons
•Electrons are in orbitals (region of space
that has a high probability of finding an
electron)
•The different types of orbitals refer to
different types or shapes
•Electrons can only gain or lose certain
amounts of energy
•There are four main types of orbitals:
s, p, d, f
•You can not know the exact location or
speed of the electron
•There are very complicated calculations
that are done to give information about the
distribution of electrons in the atom. The
calculations give four quantum numbers:
n, l, m, s that is an “electronic
address” for the electrons.
Orbital Diagrams – a way of putting
electrons into a diagram that ranks the
orbitals from lowest to highest energy
1. Fill from the lowest to highest energy level
2. The number of orbitals (lines) depends on the type of
orbital- s : 1, p : 3, d : 5, f : 7
3. Electrons are shown as arrows pointing up or pointing
down
4. Each orbital can hold at most 2 electrons, one pointing up
and one pointing down
5. If you reach a point where 3 or more lines are at the
same energy, put one arrow pointing up on each line
before the second arrow is added pointing down.
Electron Configurations – a different way of
showing the electrons distributed in the
different orbitals
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 …
Energy Level
Type of orbital
Number of electrons
Writing electron configurations using the
Periodic Table
•Each period (row) counts as an energy level
•Four different sections on the periodic
table: s block (group 1, 2 and He); p block
(groups 13-18); d block (groups 3-12) f block
(two rows at the bottom)
•Each box or element represents an
electron
•d block is one energy level behind, the f
block is two energy levels behind
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

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 
•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 
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