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Tuesday September 11th, 2012
Today:
•Small Review
•Quiz
•Finish Chapter 2
•Chapter 3.1-3.4
•In Class Group Work
•Continue in Chapter 3
Frequency: CD
Classification of Matter
Matter is organized by its components: elements, compounds, and
mixtures.
A Comparison of Solids, Liquids,
and Gases
Chapter 2, Section 4
3
Summary of Chemical and Physical
Properties and Changes
Change of State:
Solid and Liquid
Liquid and Gas
Solid and Gas
5
Questions?
Quiz #2
Specific Heat
Specific heat
• is different for different substances.
• is the amount of heat that raises the temperature
of 1 g of a substance by 1 C.
• is represented by the equation,
where ΔT = the change in temperature.
• in the SI system, has units of J/g C.
• in the metric system, has units of cal/g C.
Calculating Specific Heat
What is the specific heat of a metal if 24.8 g
absorbs 65.7 cal of energy and the temperature
rises from 20.2 C to 24.5 C?
Given
24.8 g
65.7 cal
ΔT = 20.2 C to 24.5 C
Need
Heat Equation
Rearranging the specific heat expression gives the
heat equation:
The amount of heat lost or gained by a substance is
calculated from
• the mass of substance (g),
• the temperature change (T), or
• the specific heat of the substance (cal/g C) or
(J/g C).
Sample Calculation for using Specific
Heat
A hot-water bottle contains 750 g of water
at 65 C. If the water cools to body
temperature (37 C), how many calories of
heat could be transferred to sore muscles?
Given
Need
Calories of heat
transferred
Learning Check
How many kilojoules are needed to raise the
temperature of 325 g of water from 15.0 C to
77.0 C?
Calorimeters
A calorimeter
 is used to calculate the energy value of food.
 contains a reaction chamber and
thermometer in water.
 indicates the amount of heat lost by food by
observing the temperature increase of the
water.
Energy and Nutrition
On food labels, energy is shown as the
nutritional Calorie, written with a capital C.
In countries other than the United States,
energy is shown in kilojoules (kJ).
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Energy Values for 3 Food Types
The energy (caloric) values of food are the
kilojoules or kilocalories obtained from
burning 1 g of a carbohydrate, fat, or
protein.
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Food Nutrition Labels
On packaged foods, the
energy content is listed in
the Nutrition Facts label on
the package, usually in
terms of the number of
Calories for one serving.
Chapter 3 Atoms and Elements
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Elements
Elements are pure substances from which all other
things are built.
gold
carbon
aluminum
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Symbols of Elements
A symbol
 represents the name of an element.
 consists of 1 or 2 letters.
 starts with a capital letter.
Examples:
1-Letter Symbols
C carbon
N nitrogen
F fluorine
O oxygen
2-Letter Symbols
Co
cobalt
Ca
calcium
Al
aluminum
Mg
magnesium
Symbols of Common Elements
Symbols of some common elements:
S, sulfur
Al, aluminum
Au, gold
Ag, silver
Periodic Table
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21
Periods and Groups
On the periodic table,
 groups contain elements with similar properties and are
arranged in vertical columns ordered from left to right.
 periods are the horizontal rows of elements, and they are
counted from the top as Period 1 to
Period 7.
Periods and Groups
Group Numbers
Group numbers use
 numbers to identify the columns from left to right.
 the letter A for the representative elements (1A to 8A) and
the letter B for the transition elements.
The representative elements include the first
2 groups,
1A (1) and 2A (2), in addition to groups 3A (13), 4A (14), 5A
(15), 6A (16), 7A (17), and 8A (18).
Alkali Metals
Group 1A (1), the alkali metals, includes lithium sodium,
potassium, rubidium and cesium. The reactivity of these
elements increases from the top to bottom of the group.
Halogens
Group 7A (17), the
halogens, includes
fluorine, chlorine,
bromine, iodine, and
astatine. Fluorine and
chlorine are highly
reactive.
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Nobel Gases
Group 8A (18) is the nobel gases, which include helium (He),
neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Ra).
Nobel gas elements are unreactive and are seldom found in
combination with other elements.
Metals, Nonmetals, and Metalloids
The heavy zigzag line
separates metals and
nonmetals.
 Metals (blue) are located
to the left.
 Nonmetals (yellow) are
located to the right.
 Metalloids (green) are
located along the heavy
zigzag line between the
metals and nonmetals.
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Properties of Metals, Nonmetals, and
Metalloids
Metals are
 shiny and ductile.
 good conductors of heat and electricity.
Nonmetals are
 not especially shiny, ductile, or malleable.
 poor conductors of heat and electricity.
Metalloids are
 better conductors than nonmetals, but not as good as metals.
 used as semiconductors and insulators.
Dalton’s Atomic Theory
Dalton theorized that Atoms
 are tiny particles of matter too
small to see,
 are able to combine with
other atoms to make
compounds, and
 are similar to each other for
each element and different
from atoms of other elements.
A chemical reaction is the
rearrangement of atoms.
Images of nickel atoms
are produced when nickel is magnified
millions of times by a scanning
tunneling microscope (STM). This
instrument generates an image of
the atomic structure.
Subatomic Particles
Atoms contain subatomic
particles such as
 Protons, which have a
positive (+) charge;
 electrons, which have a
negative (–) charge; and
 neutrons, which have no
charge.
Experiments show that like
charges repel and unlike
charges attract.
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Rutherford’s Gold-Foil Experiment
In Rutherford’s gold-foil experiment, positively
charged particles were aimed at atoms of gold and
 most went straight through the atoms, but
 some were deflected only occasionally.
Conclusion:
There must be a small, dense, positively charged
nucleus in the atom that deflects positive particles
that come close.
Rutherford’s Gold-Foil Experiment
(a) Positive particles are aimed at a piece of gold foil. (b) Particles that come
close to the atomic nuclei of gold are deflected from their straight path.
Structure of the Atom
An atom consists of
 a nucleus that
contains protons
and neutrons, and
 electrons in a large,
empty space around
the nucleus.
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34
Atomic Mass Scale
On the atomic mass scale for subatomic particles,
1 atomic mass unit (amu) is defined as 1/12 of the mass
of the carbon-12 atom. Therefore,
 a proton has a mass of about 1 (1.007) amu.
 a neutron has a mass of about 1 (1.008) amu.
 an electron has a very small mass, 0.00055 amu.
Atomic Number
The atomic number
 is specific for each element.
 is the same for all atoms of an element.
 is equal to the number of protons in an atom.
 appears above the symbol of an element in the periodic table.
Atomic Number
Symbol
11
Na
Atomic Number and Protons
Each element has a unique atomic number equal to the
number of protons:
 Hydrogen has atomic number 1; every H atom has one
proton.
 Carbon has atomic number 6; every C atom has six protons.
 Copper has atomic number 29; every Cu atom has 29
protons.
Learning Check
State the number of protons in each of the following:
1. A nitrogen atom
A. 5 protons
B. 7 protons
C. 14 protons
2. A sulfur atom
A. 32 protons
3. A barium atom
A. 137 protons
B. 16 protons
B. 81 protons
C. 6 protons
C. 56 protons
Solution
State the number of protons in each of the following:
1. A nitrogen atom
B. 7 protons
2. A sulfur atom
B. 16 protons
3. A barium atom
C. 56 protons
Number of Electrons in an Atom
All atoms of an element are electrically neutral; they
have
 a net charge of zero.
 an equal number of protons and electrons.
Number of protons = Number of electrons
Example:
Aluminum atoms have 13 protons and 13 electrons; the
net charge is zero.
Mass Number
The mass number represents the number of subatomic particles
in the nucleus, which is equal to the sum of the
number of protons + number of neutrons.
Since protons and neutrons account for the majority of mass in
an atom, we call this the mass number.
Atomic Models
Learning Check
An atom of zinc has a mass number of 65.
1. How many protons are in a zinc atom?
A. 30
B. 35
C. 65
2. How many neutrons are in a zinc atom?
A. 30
B. 35
C. 65
Learning Check
An atom has 14 protons and 20 neutrons.
1. What is its atomic number?
A. 14
B. 20
C. 34
2. What is its mass number?
A. 14
B. 20
C. 34
3. What is this element?
A. Si
B. Ca
C. Ar
Isotopes
Isotopes
 are atoms of the same element that have different mass
numbers.
 have the same number of protons but different numbers
of neutrons.
 can be distinguished by atomic symbols.
Isotopes and Mass and Atomic Symbols
Since each isotope of an element has a different
number of neutrons, each isotope’s mass number will
be different. We write these as atomic symbols:
 Mass numbers are in the upper left corner.
 Atomic numbers are in the lower left corner.
Example: An atom of sodium with atomic number 11
and a mass number 23 has the following atomic
symbol:
23
mass number
atomic number
11
Na
Atomic Symbols
For an atom, the atomic symbol gives the number of
 protons (p+),
 neutrons (n), and
 electrons (e–).
16
8
O
8 p+
8n
8 e–
31
15
P
15 p+
16 n
15 e–
65
30
Zn
30 p+
35 n
30 e–
Learning Check
Naturally occurring carbon consists of three isotopes:
C-12, C-13, and C-14. State the number of protons,
neutrons, and electrons in each of the following.
Protons
______
13
6
______
Neutrons
______
______
______
Electrons
______
______
______
12
6
C
C
14
6
______
C
Group Assignment
#2
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