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```HW due Friday 9/15/06
• Ch. 2
– 8, 13, 30,33, 41, 43, 47, 50
• Ch. 3
– 6, 13, 19, 28, 40, 46, 59, 68, 76, 83
Working with numbers: examples
• Space shuttle
– traveling at 1400 nautical miles per hour
– was it going fast enough to escape Earth’s
gravity?
• Escape velocity > 10 km/s
Working with numbers: examples
• Density:
mass
density =
volume
m
d= V
• SI-derived unit is kg/m3
• Chunk of platinum metal:
– Density = 21.5 g/cm3
– Volume = 4.49 cm3
– Mass? (in SI units/simplified)
Three Temperature Scales
• Fahrenheit
– Absolute zero = -273.15°C
• Kelvin (K) (SI unit)
– Absolute zero = 0 K
K = 0C + 273.15
273 K = 0 0C
373 K = 100 0C
0F
= 9 x 0C + 32
5
32 0F = 0 0C
212 0F = 100 0C
1.7
Atoms, Molecules and Ions
Chapter 2
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Dalton’s Atomic Theory (1808)
1. Elements are composed of extremely small
particles called atoms.
2. All atoms of a given element are identical. The
atoms of one element are different from the
atoms of all other elements.
3. Compounds are composed of atoms of more
than one element, in specific ratios.
4. Chemical reactions only involve separation,
combination, or rearrangement of atoms. Atoms
are not created or destroyed in chemical
reactions
2
Law of multiple proportions:
Early argument for the existence of atoms
Dalton’s Atomic Theory (1808)
1. Elements are composed of extremely small
particles called atoms.
2. All atoms of a given element are identical. The
atoms of one element are different from the
atoms of all other elements.
3. Compounds are composed of atoms of more
than one element, in specific ratios.
4. Chemical reactions only involve separation,
combination, or rearrangement of atoms. Atoms
are not created or destroyed in chemical
reactions
16 X
+
8Y
8 X2Y
Law of conservation of mass
Atomic structure
• Late 1800s:
– Cathode ray tube experiment
– Charged particles deflected toward a positive
charge
– Negatively charged particles: electrons
J.J. Thomson, measured mass/charge of e(1906 Nobel Prize in Physics)
2.2
Atomic structure
• Early 1900s:
– Atom contain electrons (-) but are electrically
neutral
– Thomson’s ‘plum pudding’ model
2.2
Atomic structure
• Rutherford used a particles (protons) to
study the atom
– Hypothesis: plum pudding
– Prediction: positively charged particles will
pass easily through the diffuse plum pudding
(1908 Nobel Prize in Chemistry)
a particle velocity ~ 1.4 x 107 m/s
(~5% speed of light)
1. atoms positive charge is concentrated in the nucleus
2. proton (p) has opposite (+) charge of electron (-)
3. mass of p is 1840 x mass of e- (1.67 x 10-24 g)
2.2
Atomic structure
• Electrons (-) + Protons (+)
• Problem:
– Hydrogen: one proton
– Helium: two protons
– But, Helium has ~4x more mass than
Hydrogen
– No charge / mass ~ proton
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
“If the atom is the Houston Astrodome, then
the nucleus is a marble on the 50-yard line.”
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
14
in 6 C ?
6 protons, 8 (14 - 6) neutrons, 6 electrons
How many protons, neutrons, and electrons are
11
in 6 C ?
6 protons, 5 (11 - 6) neutrons, 6 electrons
The periodic table
The periodic table
Group 1A: alkali metals
Group 2A: alkaline earth metals
Group 7A: halogens
Group 8A: noble gases (rare gases)
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.
anion – ion with a negative charge
If a neutral atom gains one or more electrons
it becomes an anion.
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-
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