Download Atoms, Molecules and Ions

Atoms, Molecules and Ions
Chapter 3
Foundations of Atomic Theory
• Law of conservation of mass: Antoine Lavoisier
– 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 +
• Law of definite composition:
32g
Joseph Proust
– a chemical compound contains the same elements in
exactly the same proportions by mass regardless of the
size of the sample or source of the compound
Sugar: 42.1 % Carbon
51.4 % Oxygen
6.5 % Hydrogen
Whether you have a teaspoon or a truckload!
16 X
+
8Y
8 X2Y
• Law of multiple proportions:
John Dalton
– Applies to different compounds made from the
same elements
– The mass ratio for one of the elements that
combines with a fixed mass of the other element
can be expressed as a whole number ratio.
H2O
Water
2g H
16g O
H2O2
Peroxide
1:2 Ratio
2g H
32g O
2
Dalton’s Atomic Theory
(1808)
1. Elements are composed of extremely small
particles called atoms.
2. 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
3. Atoms cannot be subdivided, created or
destroyed
Dalton’s Atomic Theory
(1808) cont’d
4. Atoms of different elements combine in
simple whole-number ratios to form
chemical compounds.
5. Chemical reactions only involve the
rearrangement of atoms.
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.
• When connected to electric current the remaining gas
glowed forming a BEAM OF LIGHT.
• The beam always originated at the NEGATIVE
electrode and toward the POSITIVE electrode.
• 1897 JJ Thomson used magnets to deflect the beam
proving that particles had a NEGATIVE CHARGE.
JJ THOMSON DISCOVERED
A NEGATIVE PARTICLE
CALLED THE
ELECTRON!
CRT Video
Plum Pudding Model
Plum Pudding
OR
Chocolate Chip
Cookie
Robert A. Millikan
• Performed the Oil Drop Experiment
• Determined the exact charge of an
electron
Measured Charge of e(1923 Nobel Prize in Physics)
e- charge = -1.60 x 10-19 C
Thomson’s charge/mass of e- = -1.76 x 108 C/g
e- mass = 9.10 x 10-28 g
Oil Drop Experiment Video
Ernest Rutherford’s Gold Foil
Experiment
• Set up Gold Foil with a detection sheet
around it.
• Set up radioactive source emitting alpha
particles.
• ALPHA PARTICLES shot at gold foil.
• MOST particles went through the gold foil
• SOME particles BOUNCED back
Rutherford’s Gold Foil Experiment
Gold Foil Conclusions
1. The atom is made up of mostly
EMPTY SPACE
2. The center of the atom contains a
POSITIVE CHARGE
3. Rutherford called this positive
bundle of matter the NUCLEUS
Gold Foil Experiment Video
Rutherford’s Model of
the Atom
atomic radius ~ 100 pm = 1 x 10-10 m
nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m
Ob-scertainer
– You can’t see something, but you know
it’s there… you feel it moving… How is it
moving?
– Do your best to determine the movement
of the “particle” in your containers
Ob-scertainer Solutions
#1
#5
#2
#3
#4
#6
#7
#8
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
**DISCOVERED ENERGY LEVELS!!
Bohr’s Model of the Atom
Subatomic Particles (Table 2.1)
Mass
(g)
Particle
-
Charge
(Coulombs)
-28
-19
-1
1.67 x 10-24 +1.6 x 10-19
+1
Electron (e ) 9.1 x 10
Proton (p+)
Charge
(units)
Neutron (n) 1.67 x 10-24
-1.6 x 10
0
0
mass p = mass n = 1840 x mass e-
Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
Isotopes are atoms of the same element (X) with different
numbers of neutrons in their nuclei
Mass Number
A
ZX
Atomic Number
1
1H
235
92
2
1H
U
Element Symbol
(D)
238
92
3
1H
U
(T)
Do You Understand Isotopes?
How many protons, neutrons, and electrons are in 146
C?
6 protons, 8 (14 - 6) neutrons, 6 electrons
How many protons, neutrons, and electrons are in 116
6 protons, 5 (11 - 6) neutrons, 6 electrons
C?
Group
Period
A molecule is an aggregate of two or more atoms in a
definite arrangement held together by chemical bonds
H2
H2O
NH3
CH4
A diatomic molecule contains only two atoms
H2, N2, O2, Br2, HCl, CO
A polyatomic molecule contains more than two atoms
O3, H2O, NH3, CH4
An ion is an atom, or group of atoms, that has a net
positive or negative charge.
cation – ion with a positive charge
If a neutral atom loses one or more electrons
it becomes a cation.
Na
11 protons
11 electrons
Na+
11 protons
10 electrons
anion – ion with a negative charge
If a neutral atom gains one or more electrons
it becomes an anion.
Cl
17 protons
17 electrons
Cl-
17 protons
18 electrons
A monatomic ion contains only one atom
Na+, Cl-, Ca2+, O2-, Al3+, N3-
A polyatomic ion contains more than one atom
OH-, CN-, NH4+, NO3-
Do You Understand Ions?
+
27
3
How many protons and electrons are in 13 Al ?
13 protons, 10 (13 – 3) electrons
2- ?
Se
How many protons and electrons are in 78
34
34 protons, 36 (34 + 2) electrons
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%
5%
133Cs
132Cs
134Cs
Steps:
1. Percent to decimal
2. Multiply by mass
3. Add it up!