Transcript Atoms, Molecules and Ions

Atoms, Molecules and Ions
Chapter 2
Foundations of Atomic Theory
• _________________________________________
– Mass is neither created nor destroyed. The total mass of
a compound must be the same as the total mass of
individual elements.
HgO  Hg + O
433.2 g
401.2g +
32g
Dalton’s Atomic Theory (1808)
1. Elements are composed of extremely small
particles called atoms. All atoms of a given
element are identical, having the same size,
mass and chemical properties. The atoms of
one element are different from the atoms of all
other elements.
2. Compounds are composed of atoms of more
than one element. The relative number of atoms
of each element in a given compound is always
the same.
3. Chemical reactions only involve the rearrangement
of atoms. Atoms are not created or destroyed in
chemical reactions.
JJ Thomson’s Cathode Ray Tube
Negatively Charged
Electrode
Positively Charged
Electrode
Cathode Ray Tube
• Scientists studied the flow of electric current in a
glass vacuum tube with electrodes at each end.
• The electrode is named by what type of particle it
attracts
– Cathode: Negative (-)
– Anode: Positive (+)
• When connected to electric current the remaining gas
glowed forming a ___________________________.
• The beam always originated at the _____________
electrode and toward the _____________electrode.
• 1897 JJ Thomson used magnets to deflect
the beam proving that particles had a
___________________________.
• Now with the knowledge of electrons,
and knowing the atom is neutral, there
must be a particle that is positive to
balance the negative charge.
• A small paddle wheel was placed inside
and it rolled toward the anode, providing
evidence that some _____________
MUST BE STRIKING THE WHEEL to
make it move.
Plum Pudding Model
Robert A. Millikan
• Performed the ____________________
• Determined the exact:
Measured Charge of e(1923 Nobel Prize in Physics)
e- charge = -1.60 x 10-19 C
e- mass = 9.10 x 10-28 g
Radioactivity
• Becquerel
– discovered _______________________
• uranium would expose photographic plates in the dark
– The properties of an element changed as it gave off
radiation
• Curie
– Discovered radium and polonium
The radioactive emissions of ___________,
___________ and __________rays were
identified.
(Uranium compound)
Ernest Rutherford’s Gold Foil
Experiment
• Set up Gold Foil with a detection sheet
around it.
• Set up radioactive source emitting alpha
particles.
• ____________________shot at gold foil.
Rutherford’s Gold Foil Experiment
Rutherford: It’s like shooting a cannon at a piece of tissue
paper and having it bounce back at you!
__________particles went through the gold foil
__________particles _____________back
Gold Foil Conclusions
1.
2.
3.
Rutherford’s Model of
the Atom
Goldstein and Wien - 1886
• Cathode Ray Tube with perforated cathode
• Discovered collection of positively charged
particles
**
Chadwick’s Experiment - 1932
• Found that alpha particles shot at
beryllium made a beam form
• The beam had the same mass of a proton
but was electrically neutral
**
Niels Bohr – 1913
• Developed a new diagram of the atom
• Electrons can only be at certain energies
• Electrons must gain a specific amount of
energy to move to a higher level, called a
quantum
**
Bohr’s Model of the Atom
SUBATOMIC PARTICLES
Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
A
X
Z
Isotopes:
1
1H
235
92
2
1H
U
(D)
238
92
3
1H
U
(T)
Do You Understand Isotopes?
How many protons, neutrons, and electrons are in 146
C?
How many protons, neutrons, and electrons are in 116
C?
Group
Period
Molecule: an aggregate of two or more atoms in a
definite arrangement held together by chemical bonds
H2
H2O
diatomic molecule:
polyatomic molecule:
NH3
CH4
An _______ is an atom, or group of atoms, that has
a net positive or negative charge.
cation –
Na
11 protons
11 electrons
Na+
11 protons
10 electrons
Cl-
17 protons
18 electrons
anion –
Cl
17 protons
17 electrons
monatomic ion:
polyatomic ion:
Do You Understand Ions?
+
27
3
How many protons and electrons are in 13 Al ?
2- ?
Se
How many protons and electrons are in 78
34
Relative Atomic Mass
• One atom is the standard – Carbon
• Mass of other elements are based off of the
standard
• Carbon: 6 p and 6 n = 12 amu
Atomic Mass Unit
• 1/12 mass of Carbon atom
• Periodic table lists weighted average atomic
masses of elements (like a GPA calculation)
Calculation AVERAGE Atomic Mass
75%
20%
??%
133Cs
132Cs
134Cs
Steps:
1. Percent to decimal
2. Multiply by mass
3. Add it up!