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Mr. Chimenti
Room 209

The number of digits in a measurement that are
definitely known plus one estimate
Ex. 13.5cm

2 known + 1 estimated=3 sig. figs.
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1.
2.
3.
4.
Zeros between nonzero numbers are significant
ex. 50.33 sig. figs.
Zeros in front of nonzero digits are insignificant
ex. .oo8233 sig. figs.
Zeros that are at the end of a number and also to
the right are significant ex. 2,000.006 sig. figs.
Zeros to the left of a deimal at the end of a number
are significant only if they are measured to the
smallest zero (insignificant zeros may be denoted
by placing a bar over the numbers)
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+ or –
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Takes place in columns, round the final answer to
the first column from the left with a sig. fig. for both
numbers.
Ex. On board
X or /

Final answer has the same # of sig. figs. As the
measurement with the least number of sig. figs.
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Quantities can only be
added or subtracted if
they have the same
dimensions (units)
Both sides of an
algebraic equation or
formula must have the
same final units or it is
invalid
Formulas whose
dimensions do not
agree are invalid
Abercrombie analyzed my
dimensions and decide to
pay me to not wear their
clothes!

Def.-study of the properties of chemicals and
the changes they can undergo
Chemical-def-any substance with a “definite
composition” (it’s always made of all the same stuff)
 Chemical reaction-anytime a substance or substances
change into one or more new substance(s)
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Solid-fixed volume and shape, particles are
held in a rigid structure, particles vibrate
Liquid-fixed volume but no fixed shape, take
shape of container, move about slowly
Gas-no fixed shape or volume, fill any
container that they occupy
Plasma-behaves like a gas whose particles have
broken apart and are charged
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Changes to a substance where it’s identity
remains the same

The arrangement, location or speed of the particles
may change
 Ex. Dissolving sugar, breaking a rock, ice melting,
Chuck Norris bumping into a boulder

Changes to a substance where it’s identity
changes
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Reactants-what is consumed by a chemical reaction
Products-what is created during a chemical reaction
Evidence of a chemical change
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Evolution of a gas
Formation of a precipitate
Release or absorbtion of energy
Color change
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Matter-anything that has mass and volume
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Volume-amount of space an object occupies
Mass-amount of matter an object has
Weight-force produced by gravity on an object
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Characteristic of a substance that
can be determined without
changing the nature of a substance
Density-the amount of matter per
unit volume

Density=mass/volume or d=m/v
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Atoms
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Smallest particles that exist of each element
Each atom of an element has the same number of
protons in its nucleus
Pure substances


All of the molecules are the same
2 types: elements and compunds

Pure substance whose atoms are all the same
type
Molecule-two or more atoms that are chemically
bonded together in a definite ratio
 Diatomic element-an element that exists in nature as
two atoms bonded together
 Allotrope-one of many different forms of an element

 Ex. Oxygen and ozone; graphite, coal and diamond
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Pure substances whose molecules are composed
of atoms of different elements in fixed ratios
Are represented by formulas
Molecular formula-symbols and subscripts are used to
represent elements and their ratios in each molecule of
a compound
 Structural formula-shows how the atoms are
connected in a molecule using symbols to represent
atoms and lines to represent chemical bonds
 Ball and stick model-shows 3-D representation of
molecules using different colored balls for atoms and
sticks for bonds
 Space filling model-uses balls of different size to
demonstrate the different sizes of atoms in the
molecules


Def.-sample of matter containing 2 or more
types of pure substances

Can be seperated by physical means
 2 main types: homogeneous and heterogeneous
 Homogeneous-same composition throughout
 Heterogeneous-different composition throughout

energy=the ability to do work (bring about a
change)
Physical change-altering physical properties of a
substance
 Chemical change-creating a new substance


During a physical or chemical change energy
can not be created or desroyed
Endothermic process-when energy is absorbed from
the environment to bring about a change (feels cold)
 Exothermic process-when energy is released to the
environment to bring about a change (feels hot)


Energy can exist in many forms (heat, electricty,
chemical bonds, motion, sound and light are some
examples)

Def-energy transferred between objects of
different temperatures
Temperature=measure of the average kinetic energy
of a substance (how fast molecules are moving)
 Kinetic energy=energy possessed in the form of
motion
 Heat and temperature are different

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1 kelvin is the same size as 1 degree celsius
The scale is simply moved 273 degrees up to
give us a better way of expressing the
temperature of a substance
Degrees Celsius+273= degrees Kelvin
Degrees Celsius=degrees Kelvin-273

Heat transfer can occur in 3 ways
Conduction-by molecules touching
 Convection-by the movement of heated molecules in
a fluid (liquid, gas or plasma)
 Radiation-movement of electromagnetic radiation


Atomic theory

Atoms are the building blocks of all matter
 Atoms are made of 3 main subatomic particles
 Protons-positive charge, mass=1amu
 Neutrons-no charge, mass=1amu
 Electrons-negative charge, mass=approx. 0 (barely large
enough to be detected)

2 samples of the same compound have the
same elements in exactly the same proportions

Ex. All water molecules have 2 hydrogen and 1
oxygen, all sulfur dioxide molecules have 1 sulfur
atom for every 2 oxygen atoms


Matter is not created or destroyed in a chemical
reaction
Mass of reactants=mass of products
1.
2.
3.
4.
5.
All matter is composed of atoms which can not
be created, subdivided or destroyed
Atoms of an element are identical in their
physical and chemical properties
Atoms of different elements have different
chemical and physical properties
Atoms of different elements combine in whole
number ratios to form compounds
Chemical reactions combine, separate or
rearrange atoms. ATOMS ARE NEVER
DESTROYED


Discovered using cathode rays (TV tubes) by JJ
Thompson
Cathode rays are made of electrons (which are
negatively charged)


Thompson deflected them with a magnet
Electrons have virtually no mass and negative
charge
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Earnest Rutherford fired positively charged
alpha particles at a piece of gold foil,
occasionally one would be deflected back at
him
He theorized that the deflection occurred
because of a dense positively charged nucleus
It is now known that the nucleus is composed
of protons and neutrons
Neutrons keep the positive charge of the
protons from repelling one another

Def.-the number of protons located in the
nucleus of an atom of a certain element
Is also the number of electrons in a neutrally charged
atom of a certain element
 Hydrogen atomic number =1
 Helium atomic number=2

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
Def-the total average number of protons and
neutrons in the nucleus of an atom
Mass number-atomic number=number of
neutrons

Def.-atoms of the same element with different
numbers of neutrons

May have slightly different physical and chemical
properies
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Chemical
Chemical reaction
Solid
Liquid
Gas
Molecules
Heat
Specific heat
Isotope
Plasma
Physical change
Chemical change
Matter
Volume
Homogeneous mixture
Conduction
protons
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Mass
Weight
Meter
Liter
Gram
Heterogeneous mixture
Convection
Neutron
Second
Density
Physical property
Chemical property
Atom
Energy
Radiation
electron
Element
Protons
Neutrons
Electrons
Atomic
mass
Atomic
number
He
2
2
2
4
2
N
7
8
7
15
7
V
23
29
23
52
23
Zn
30
34
30
64
30
Tc
43
56
43
99
43
Lu
71
105
71
176
71
Fr
87
137
87
224
87
Md
101
157
101
258
101
Gd
64
91
64
155
64
No
102
157
102
259
102
Sm
62
88
62
150
62
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Def.-how electrons are arranged around the
nucleus of an atom
Electrons orbit the nucleus in a cloud
Niels Bohr created a model of the atom that
confines electrons to energy levels
Each energy level is composed of one or more
orbital (these behave like clouds of electrons)
Electrons will remain as close to the nucleus of
an atom as possible unless they become
“excited” (this means that they have gained
energy and moved away from the nucleus)


When electrons become “excited” they move to a
higher energy level away from the nucleus
The electrons will return to their ground state closer
to the nucleus when the energy is emitted as light


Ground state-when an electron that is in the lowest possible
energy level
Excited state-when an electron has gained energy and
moved away from the nucleus
Q: how long would it take to spend a mole of $1 coins if
they were being spent at a rate of 1 billion per second?
Look at the “atomic masses” on the periodic table.
What do these represent?
 E.g. the atomic mass of C is 12 (atomic # is 6)
 We know there are 6 protons and 6 neutrons
 Protons and neutrons have roughly the same mass.
So, C weighs 12 u (atomic mass units).
 What is the actual mass of a C atom?
 Answer: approx. 2 x 10-23 grams (protons and
neutrons each weigh about 1.7 x10-24 grams)
Two problems
1. Atomic masses do not convert easily to grams
2. They can’t be weighed (they are too small)

With these problems, why use atomic mass at all?
1. Masses give information about # of p+, n0, e–
2. It is useful to know relative mass
E.g. Q - What ratio is needed to make H2O?
A - 2:1 by atoms, but 2:16 by mass
 It is useful to associate atomic mass with a mass in
grams. It has been found that
1 g H, 12 g C, or 23 g Na have 6.02 x 1023 atoms
 6.02 x 1023 is a “mole” or “Avogadro’s number”
 “mol” is used in equations, “mole” is used in writing;
one gram = 1 g, one mole = 1 mol.
Q: how long would it take to spend a mole of $1
coins if they were being spent at a rate of 1 billion
per second?
A: $ 6.02 x 1023 / $1 000 000 000
= 6.02 x 1014 payments = 6.02 x 1014 seconds
6.02 x 1014 seconds / 60 = 1.003 x 1013 minutes
1.003 x 1013 minutes / 60 = 1.672 x 1011 hours
1.672 x 1011 hours / 24 = 6.968 x 109 days
6.968 x 109 days / 365.25 = 1.908 x 107 years
A: It would take 19 million years
Same
1 gram each
1 mol each
No, they have dif. No, molecules
volume?
densities.
have dif. sizes.
Yes, that’s what
No, molecules
mass?
grams are.
have dif. masses
No, they have dif.
Yes.
# of moles? molar masses
No, they have dif. Yes (6.02x1023
# of
in each)
molecules? molar masses
No, sugar has
# of atoms?
No
more (45:3 ratio)
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
The mass of one mole is called “molar mass”
E.g. 1 mol Li = 6.94 g Li
This is expressed as 6.94 g/mol
What are the following molar masses?
S 32.06 g/mol
SO2 64.06 g/mol
Cu3(BO3)2 308.27 g/mol
Calculate molar masses (to 2 decimal places)
CaCl2
Cu x 3 = 63.55 x 3 = 190.65
(NH4)2CO3 B x 2 = 10.81 x 2 = 21.62
O2
O x 6 = 16.00 x 6 = 96.00
308.27
Pb3(PO4)2
C6H12O6




The mass of one mole is called “molar mass”
E.g. 1 mol Li = 6.94 g Li
This is expressed as 6.94 g/mol
What are the following molar masses?
S 32.06 g/mol
SO264.06 g/mol
Cu3(BO3)2 308.27 g/mol
Calculate molar masses (to 2 decimal places)
CaCl2
110.98 g/mol (Cax1, Clx2)
(NH4)2CO3 96.11 g/mol (Nx2, Hx8, Cx1, Ox3)
O2
32.00 g/mol (Ox2)
Pb3(PO4)2 811.54 g/mol (Pbx3, Px2, Ox8)
C6H12O6 180.18 g/mol (Cx6, Hx12, Ox6)
If we are given the # of grams of a compound we can
determine the # of moles, & vise-versa
 In order to convert from one to the other you must first
calculate molar mass
g
g = mol x g/mol
mol g/mol
mol = g  g/mol
 This can be represented in an “equation triangle”

Formula
HCl
H2SO4
NaCl
Cu
g/mol
36.46
98.08
58.44
63.55
g
mol (n)
9.1
0.25
53.15 0.5419
207
3.55
1.27 0.0200
Equation
g= g/mol x mol
mol= g  g/mol
g= g/mol x mol
mol= g  g/mol
Consider NaCl (ionic) vs. H2O2 (covalent)
Na Cl Na Cl
Cl Na Cl Na
• Chemical formulas are either “simplest” (a.k.a.
“empirical”) or “molecular”. Ionic compounds
are always expressed as simplest formulas.
• Covalent compounds can either be molecular
formulas (I.e. H2O2) or simplest (e.g. HO)
Q - Write simplest formulas for propene (C3H6),
C2H2, glucose (C6H12O6), octane (C8H14)
Q - Identify these as simplest formula, molecular
formula, or both H2O, C4H10, CH, NaCl
For more lessons, visit
www.chalkbored.com
Q - Write simplest formulas for propene (C3H6),
C2H2, glucose (C6H12O6), octane (C8H14)
Q - Identify these as simplest formula, molecular
formula, or both H2O, C4H10, CH, NaCl
A - CH2 CH CH2O
C 4H 7
A - H2O is both simplest and molecular
C4H10 is molecular (C2H5 would be simplest)
CH is simplest (not molecular since CH can’t
form a molecule - recall Lewis diagrams)
NaCl is simplest (it’s ionic, thus it doesn’t
form molecules; it has no molecular formula)