Download Chapter 3 The Atom

Chapter 2
Atoms, Molecules, and
Ions
Honors Chemistry 1
“We are each so atomically numerous and
so vigorously recycled at death that a
significant number of our atoms – up to a
billion for each of us, probably once
belonged to Shakespeare. A billion more
each came from Buddha and Genghis
Khan and Beethoven and …”
Bill Bryson
Cont.
 Aristotle (Greek, 384322 B.C.) – did NOT
believe in atoms
 NO experimentation
history
 Democritus (Greek, 460-370 B.C.) –
basic particle of matter  atom
 NO experimentation
Cont.
 John Dalton (English,
1803) – Dalton’s
Atomic Theory
Dalton’s Atomic Theory
1. All matter composed of atoms
2. Atoms of given element identical (e.g.size,
mass) – atoms of diff. elements differ
3. Atoms can not be subdivided, created, or
destroyed
4. Atoms of diff. elements combine in simple
whole number ratios  cmpds.
5. Atoms combine, separate, or rearrange in
chem. reactions
 # 2, 3 now revised
History review
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Ancient cultures    present day
Philosophy < > Science
Role of experimentation
What is a theory
Conservation of mass
A
+

B
1 mass unit + 3 mass units 
AB

4 mass units 
A
+
1 mass unit +
AB
4 mass units
B
3 mass units
Law of multiple proportion
 If 2 or more diff. cmpds. are composed of the
same 2 elements, the masses of 2nd element
combined w/ a certain mass of the 1st element
can be expressed as ratios of sm. whole
numbers
 e.g. CO
12 g C + 16 g O
CO2
12 g C + 32 g O
16:32 = 1:2
Structure of the atom
 Atom – smallest particle
of an element that can
exist either alone or in
combination w/ other
atoms
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STM images
Discovery of the electron
(e )
 J.J. Thomson (1897)
Cathode ray tube (CRT)
 Thomson measured
chg./ mass ratio of
charged particles
CRT (cathode ray tube)
The cathode ray tube (CRT), invented by
German physicist Karl Ferdinand Braun in
1879, is an evacuated glass envelope
containing an electron gun (a source of
electrons) and a fluorescent screen,
usually with internal or external means to
accelerate and deflect the electrons.
When electrons strike the fluorescent
screen, light is emitted.
Thomson (CRT)
 Electrons have a neg. (-) chg
 Have a very small mass
 9.109 x 10-28 g =
(0.0000000000000000000000000009109 g)
Discovery of atomic
nucleus
 Rutherford, Geiger,
Marsden (1908,
1909)
 Used (+) charged
particle beam aimed
at metal foil
Gold foil experiment
Possible results:
Atoms have subatomic
particles, Ernest Rutherford.
 Students will be divided into two groups, atoms
and alpha particles.
 “Atoms” will line up with their arms
outstretched, touching only fingertips.
 “Alpha Particles” will first find a partner and
stand shoulder to shoulder.
 Groups of “alpha particles” will line up behind
one another.
 I will direct the “particles” to travel through the
“atoms.”
 Repeat with a second “layer” of atoms
Rutherford: the nucleus
 (+) chg.
 Dense central core of atom
 Contains nearly all mass of atom
Atomic nucleus
 2 types of particles:
 Protons, (+) chg,
mass= 1.673x10-24g
 Neutrons, neutral chg,
mass= 1.675x10-24g
Discovery of the neutron
 Chadwick, (1932),
England
 “Had the neutron been
isolated in the 1920s
(when work was started)
it is very likely the atomic
bomb would have been
developed in Europe,
undoubtedly by the
Germans” Bill Bryson
symbols
 Electron : e Proton : p+
 Neutron : no
Isotopes of hydrogen
 Protium: 1 p+, 1 e Deuterium: 1 p+, 1 e-, 1 n0
 Tritium: 1 p+, 1 e-, 2 n0 (radioactive)
Atomic number
 # of p+ in nucleus
Mass number
 # of p+ and n0 in nucleus
Isotopes
 Different forms of the same element with
different mass
 Same # p+
 Diff. # n0
Carbon Dating
Isotopes of hydrogen
Atomic #
Neutron # mass#
protium
1
0
1
deuterium
1
1
2
tritium
1
2
3
2 ways of writing isotopes
(examples)
 Carbon-12, uranium-235 ( the 12 & the
235 are the mass numbers, e.g. U-235
has 92 p+ and 143 n0)
 235 (235 is mass #, 92 is atomic #)
92
U
Relative atomic mass
 The mass of carbon-12 is exactly 12
atomic mass units (u)
 This is a defined standard
 The mass of all other atoms are
expressed relative to carbon-12
Mass # v. Atomic mass
Isotope
Mass #
Atomic mass
Oxygen-16
16
15.994
Copper-63
63
62.939
Avg. Atomic Mass (atomic
weight)
 Weighted avg. of atomic masses of
naturally occurring isotopes of an
element
e.g. : naturally occurring
Cu
 69.17% Cu-63 (atomic mass 62.939)
 30.83% Cu-65 (atomic mass 64.927)
 (0.6917)(62.939)+(0.3083)(64.927) =
63.546
Found on periodic table
The Periodic Table
5 minute history of
chemistry
Aristotle’s elements
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Air
Water
Fire
Earth
Alchemy
Alchemy symbols
Origin of modern element symbols
(examples)
 e.g. carbon, symbol C, from the Latin word
"carbo" meaning "charcoal"
 e.g. lead, symbol Pb, the origin of the symbol
Pb is the Latin word "plumbum"
 e.g. mercury, symbol Hg, the origin of the
symbol Hg is the Latin word "hydrargyrum"
meaning "liquid silver"
 e.g., Bismuth, symbol Bi, from the German
word "bisemutum"
History (cont.)
 Dmitri Mendeleev
 His first periodic table
published in 1869
Mendeleev’s periodic table
 Left empty spaces for elements not yet
discovered
 When these were later discovered they
‘fit’ almost perfectly
 e.g. scandium
Modifications continue………
Element symbols
 One or two letter symbols
 First letter uppercase, e.g. Fe, C
 Second letter (if present) lowercase, e.g.
Ca
Periodic table
 An arrangement of the elements in order
of their atomic numbers so that elements
with similar properties fall in the same
column
 Groups: vertical
 Periods: horizontal
Alkali metals (group 1)
 Extremely reactive
 Not found as free elements in nature
 e.g. potassium
Alkaline-Earth metals
(group 2)
 Reactive (not as reactive as grp 1)
 e.g. Mg, Ca
Transition elements
(groups 3-12)
 Metals, e.g. Cu, Ag, Fe
 Good conductors
 Less reactive that grps 1, 2
Halogens (group 17)
 Most reactive nonmetals, e.g. Br, I
 React w/ metals to form salts
 e.g. 2K + Cl2  2 KCl
Noble gases (grp 18)
 Non reactive
 e.g. Xe, Kr
Trends
 Electronegativity
 Ability to attract electrons
 Atomic radius
Sub level blocks
Monatomic ions
 Ion with a single atom
 e.g. Na+, Cl-
Polyatomic ions
 Ions w/ more than one atom
 e.g. SO42-, NO3-
Ionic Compounds
 Na+ + Cl-  NaCl
 Mg2+ + Cl- Cl-  MgCl2
 Al3+ Al3+ + O2- O2- O2-  ?
Naming Ionic Compounds
 NaCl
 Sodium Chloride
 Name of metallic ion first + root name of
nonmetal + ide
Metals that form more than
one ion use roman numerals
as part of the name
 e.g. copper I Cu+
copper II Cu2+
 e.g. Cu(NO3)2 – copper II nitrate
Polyatomic ions
 e.g. ammonium ion NH4+
 Al3+ & SO42 Al3+ Al3+ SO42- SO42- SO42 Al2(SO4)3 aluminum sulfate
Prefixes
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1 - mono
2 – di
3 – tri
4 – tetra
5 – penta
6 – hexa
7 – hepta
8 – octa
Molecular compounds
(examples)
 CCl4
carbon tetrachloride
 N 2O 3
dinitrogen trioxide
Acids
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Sulfuric H2SO4
Hydrochloric HCl
Nitric HNO3
Phosphoric H3PO4
Acetic HC2H3O2
Hydrofluoric HF
Carbonic H2CO3
Diatomic molecules
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ClIF H BrON
Cl2
I2
F2
H2
Br2
O2
N2
Formula mass, molar mass,
formula weight (F. W.)
 E.g. CaCl2
 1 Ca atom x 40.078u / Ca atom = 40.078u
2 Cl atoms x 35.453u / Cl atom = 70.906u
+ ________
formula mass CaCl2 =
110.984u