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College Prep Chemistry
 Atoms: the
smallest particle of an
element that retains the properties of that
element.
• (Greek: atomos = indivisible)
 Democritus
(Greek teacher in the 4th
century)
• First suggested that atoms existed
1700’s
– chemists were able to
relate changes to individual atoms
Average atom size:
• Mass = 1 x 10 –23 g
• Diameter = 1 x 10-8 cm
How small is that?100,000,000
copper atoms in a row would = 1 cm
in length!
1. All
elements are composed of
tiny indivisible particles called
atoms.
2. Atoms of the same element are
identical. The atoms of any one
element are different from those
of any other element.
 3.
Atoms of different elements can
combine with one another in simple
whole number ratios to form compounds.
• H2O
 4.
C12H22O11
NOT H2.5O¾
Chemical reactions occur when atoms
are separated, joined or rearranged.
Atoms of one element are not changed
into atoms of another!
 5.
Atoms can not be infinitely
subdivided.
 100,000,000
copper atoms in a row would
= 1 cm in length!
 Most
of Dalton’s Atomic Theory is
accepted
 One revision includes that idea that
atoms are indivisible….
 There
are 3 parts to an atom….
 1. electrons
 2. protons
 3. neutrons
 Negatively
charged subatomic particles
 J.J. Thomson discovered in 1897
• Passed a electric current through gases called a
“Cathode Ray”
• Opposites attract and the electrons were attracted to
the positive ends and lights up!
 How
televisions work!
 Positively
charged particles
 1,840 times heavier then an electron
 Subatomic
particles with no charge
 Discovered by Sir James Chadwick
 Mass is nearly the same as a proton
Approx.
Particle Symbol Relative Relative Actual
Charge
Mass
Mass (g)
(amu)
Electron
e11/1840 9.11x10-28
Proton
p+
1+
1
1.62x10-24
neutron
no
0
1
1.62x10-24
 Discovered
by Ernest Rutherford (1911)
 Gold Foil Experiment
 The
alpha particles were positively
charged - Like things repel
 Therefore – there must be a densely,
positively charged center
 Nucleus
– has a positive
center
- with an electron cloud
 Niehls
Bohr
 Atom has a nucleus but electrons
orbit in definite energy levels
 Atomic
Number - the number of protons
in the nucleus of an atom of an element
 Atoms are electrically neutral
• Tells how many electrons there are also!
 Periodic Table
• #1 – Hydrogen:
has 1 p+ and 1 e• #6 – Carbon:
has 6 p+ and 6 e-
 Mass
Number – total number of protons
and neutrons in a nucleus
#
of neutrons = mass #
- atomic #
= (# p+ + # no) - (# p+)
 Beryllium
–9
 The number “9” is the mass number
 # of p+?
# of no?
# of e-?
#
of protons = atomic number
#
of electrons = # of protons
#
neutrons = Mass # - Atomic #
(in a
neutral atom)
 Atoms
electron)
with a charge (results from gain/loss of
 If
an atom GAINS an electron =
ANION
• Negative charge
• Ex: Cl-
 If
an atom LOSES an electron =
CATION
• Positive charge
• Ex: Ca2+
 Definition
– atoms that have the same
number of protons but different numbers
of neutrons
 Different types of the same element
 Ex) Carbon – has 3 isotopes
• 1) Carbon – 12
• 2) Carbon – 13
• 3) Carbon – 14
• Differ by # of no
 All
have the same # of p+
• If not, it would be a different element
• All have 6 protons
 1)
Carbon – 12
• Has 6 neutrons
 2)
Carbon – 13
• Has 7 neutrons
 3)
Carbon – 14
• Has 8 neutrons
 Hydrogen-1: 1
p+ and 0 no
• Relative abundance = 99.985 %
• Commonly called normal “hydrogen”
 Hydrogen-2: 1
p+ and 1 no
• Relative abundance = 0.015%
• Commonly called heavy hydrogen or “deuterium”
 Hydrogen-3: 1
p+ and 2 no
• Relative abundance = ~0.00%
• Commonly called “tritium”
 Definition
– weighted average mass of
the atoms in a naturally occurring sample
of the element
 Carbon-12
= 98.89 % abundant
 Carbon-13 = 1.11% abundant
 Carbon-14 = ~0.0000001% abundant
 Formula:
 Atomic
= relative mass relative mass
mass
abund. x # + abund. x # +

Repeats for however many isotopes exist for
that element….
Sample
Problem:
Chlorine has 2 isotopes:
chlorine-35 which is 75.77%
abundant and chlorine-37
which is 24.33% abundant.
What is the atomic mass of
chlorine?
 35 Cl = 75.77% abundant
 37 Cl = 24.33% abundant
 Atomic
mass =
= (35 amu x 0.7577) + (37 amu x 0.2433)
= (26.5195 amu) + (9.0021 amu)
= 35.5 amu
 Compare
to value on Periodic Table =
35.45 amu which rounds to 35.5 amu
Dmitri
Mendeleev (1834-1907)
– first person to organize the
elements in a chart
Organized about 70 elements by
increasing atomic mass
Left blank spaces for elements
which were not discovered yet
Henry
Moseley (1913) – rearranged
Mendeleev’s periodic table to the
current configuration
Arranged by increasing atomic
number instead!
Also grouped elements by their
properties
What
is the mass of potassium
and argon?
#19 Potassium = 39.01 amu
#18 Argon = 39.95 amu
If Mendeleev’s Periodic Table
was our arrangement, the gas
Argon would be lined up with the
metals!
Arrangement:
• Groups/Families = columns
• Periods = rows
Periodic
Law: when the elements are
arranged in order of increasing
atomic number, there is a periodic
repetition of their physical and
chemical properties
Line
of Demarcation: jagged “stairs”
which separate the left and right
side
Metals = left and below the line of
demarcation
Nonmetals = right and above the
line of demarcation
Metalloids = elements along the line
Metals
•
•
•
•
•
•
Conduct electricity & heat
Malleable
Strong
High melting and freezing points
Mostly solids
Have Luster
Nonmetals
•
•
•
•
•
Insulators – do not conduct well
Brittle
Low melting and freezing points
Contain gases and liquids
Are dull
Metalloids
– have properties of both
metals and nonmetals
• Ex) Silicon
• -semi-conductor
• -brittle
Group
1 = Alkali Metals
• Violently react with water
• http://video.google.com/videoplay?docid=-
2134266654801392897
Group
•
•
•
•
•
•
•
•
2 = Alkali Earth Metals
Very common in the earth’s surface
Ex)
Beryllium
Magnesium
Calcium
Strontium
Barium
Radium
Group
3-12 = Transition Metals
• Most of the common metals
Lanthanide
& Actinide Series = Inner
Transition Metals
Group
13-16: Either metals,
metalloids, or nonmetal
• Depends on their side of the line
Group
17: Halogens
• Highly reactive
 Fluorine
 Chlorine
 Bromine
 Iodine
 Group
18: Noble Gases
• All gases
• Do not react or combine with any other
element
 Page: 129
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#33, 36, 38-43, 45-46, 48-49, 53,