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Transcript
Atoms, Ions and
Molecules
Chapter 2
Dalton’s Atomic Theory (1808)
 All matter is composed of extremely small
particles called atoms
 Atoms of a given element are identical in size,
mass, and other properties; atoms of different
elements differ in size, mass, and other properties
John Dalton
 Atoms cannot be subdivided, created, or destroyed
 Atoms of different elements combine in simple whole-number ratios to
form chemical compounds
 In chemical reactions, atoms are combined, separated, or rearranged
Atomic Theory of Matter
 All matter is made of tiny indivisible
particles called atoms.
 This proposal has been verified
experimentally. Single atoms of a variety of
elements have been photographed with a
scanning transmission electron microscope.
Atomic Theory of Matter
2. Atoms of the same element are
identical and atoms of a different
element have different masses and
chemical properties.
 However you will learn that atoms of the
same element can have different masses.
Atomic Theory of Matter
 Atoms of different elements combine in
whole number ratios to form
compounds
 One molecule of water always consists of
two atoms of hydrogen and one atom of
oxygen.
Atomic Theory of Matter
4. Chemical reactions involve the
rearrangement of atoms. No new atoms
are created or destroyed.
 Modern research has altered this proposal.
Atoms are not indestructible and may lose
their identity when split during nuclear
reactions. However Dalton’s proposal
remains true, for chemical reactions.
Law of Multiple Proportions
Atoms of two or more elements may combine in
different ratios to produce more than one
compound.
Law of Constant Composition
A compound always contains two or more
elements combined in a definite
proportion by mass.
Law of Conservation of Mass
The total mass of materials present after a
chemical reaction is the same as the total
mass before the reaction
This is the basis for which postulate?
Parts of an Atom
J. J. Thomson - English physicist. 1897
Made a piece of equipment called a cathode
ray tube.

Determined the charge to mass ratio
It is a vacuum tube - all the air has been
pumped out.
Thomson’s Experiment
Voltage source
+
-
Vacuum tube
Metal Disks
Thomson Experiment
Voltage source
+
-
Passing
an electric current makes a beam
appear to move from the negative to the
positive end
Thomson’s Experiment
Voltage source
+
By
adding an electric field
Thomson’s Experiment
Voltage source
+
By
adding an electric field he found that
the moving pieces were negative
What Did Thomson
Demonstrate?
Cathode rays:
Travel in straight lines
Are negatively charged
Are deflected by electric and magnetic fields
Thomson’s Model
Found the electron
Said the atom was
like plum pudding
A bunch of positive
stuff, with the
electrons able to be
removed
Robert Millikan
American Scientist
Goal: Determine the charge on the
electron to determine its mass
Millikan’s Experiment
Atomizer
Oil droplets
+
-
Telescope
Oil
Millikan’s Experiment
X-rays
X-rays give some drops a charge.
Millikan’s Experiment
Some drops would hover
From the mass of the drop and the charge on
the plates, he calculated the mass of an electron
Radioactivity
Discovered by accident
French scientist Henri Bequerel
Studying pitchblende
Discovered that it spontaneously emits high energy
radiation
Three types



alpha- helium nucleus (+2 charge, large mass)
beta- high speed electron
gamma- high energy light
(Uranium compound)
2.2
Rutherford’s Experiment
Ernest Rutherford English physicist. (1910)
Believed in the plum pudding model of the
atom.
Used uranium to produce alpha particles.
Rutherford’s Experiment
Aimed alpha particles at gold foil by drilling
hole in lead block.
Since the mass is evenly distributed in gold
atoms alpha particles should go straight
through.
Used gold foil because it could be made
atoms thin.
Rutherford’s Experiment
When the alpha particles hit a florescent
screen, it glows.
Rutherford’s Experiment
Lead
block
Uranium
Florescent
Screen
Gold Foil
What he expected
Why ??
The alpha particles
would pass through
without changing
direction very much
The negative
charges were
spread out evenly.
Alone they were
not enough to stop
the alpha particles
What he got
How He Explained It
Atom is mostly empty
Small dense, positive
piece at center
Alpha particles are
deflected by it if they
get close enough
How He Explained It
+
Density and the Atom
Since most of the particles went through, it
was mostly empty.
Because the pieces turned so much, the
positive pieces were heavy.
Small volume, big mass, big density
This small dense positive area is the nucleus
Discovery of the Neutron
9
4
Be
+
4
2
He
12
6
C
+
1
0
n
James Chadwick bombarded beryllium-9 with alpha particles,
carbon-12 atoms were formed, and neutrons were emitted.
Dorin, Demmin, Gabel, Chemistry The Study of Matter 3rd Edition, page 764
*Walter Boethe
Modern View
The atom is mostly
empty space
Two regions
Nucleus- protons and
neutrons
Electron cloud- region
where you might find an
electron
Structure of Atom
There are two regions:

The nucleus: with protons and neutrons
Almost all the mass

Electron cloud- Most of the volume of an
atom
The region where the electron can be found
Size of Atom
Atoms are small.
Measured in picometers, 10-12 meters
Hydrogen atom, 32 pm radius
Size of Atom
Nucleus tiny compared to atom
IF the atom was the size of a stadium,
the nucleus would be the size of a
marble.
Radius of the nucleus near 10-15m.
Density near 1014 g/cm3
Subatomic Particles
ATOM
ATOM
NUCLEUS
NUCLEUS
ELECTRONS
ELECTRONS
PROTONS
PROTONS
NEUTRONS
NEUTRONS
POSITIVE
Positive
CHARGE
Charge
NEUTRAL
Neutral
CHARGE
Charge
NEGATIVE
CHARGE
Negative Charge
equal in a
Most of the atom’s mass.
neutral atom
QUARKS
Subatomic particles
Name
Symbol
Relative
Charge mass
Actual
mass (g)
Electron
e-
-1
1/1840
9.11 x 10-28
Proton
p+
+1
1
1.67 x 10-24
Neutron
no
0
1
1.67 x 10-24
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)
Symbols
Find the
number of protons
number of
neutrons
number of
electrons
Atomic number
Mass Number
19
9
F
Symbols
 Find
the
–number of protons
–number of neutrons
–number of electrons
–Atomic number
–Mass Number
80
35
Br
Symbols
if an element has an atomic number of 34
and a mass number of 78 what is the
number of protons
number of neutrons
number of electrons
Complete symbol
Atomic Mass
How heavy is an atom of oxygen?
There are different kinds of oxygen atoms.
More concerned with average atomic mass.
Based on abundance of each element in
nature.
Don’t use grams because the numbers
would be too small
Measuring Atomic Mass
Unit is the Atomic Mass Unit (amu)
One twelfth the mass of a carbon-12
atom.
Each isotope has its own atomic mass
we need the average from percent
abundance.
Calculating averages
You have five rocks, four with a mass of 50
g, and one with a mass of 60 g. What is the
average mass of the rocks?
Total mass =
4 x 50 + 1 x 60 = 260 g
Average mass = 4 x 50 + 1 x 60 = 260 g
5
5
Calculating averages
Average mass = 4 x 50 + 1 x 60 = 260 g
5
5
5
Average mass = .8 x 50 + .2 x 60
80% of the rocks were 50 grams
20% of the rocks were 60 grams
Average = % as decimal x mass +
% as decimal x mass +
% as decimal x mass +
Atomic Mass
Calculate the atomic mass of copper if
copper has two isotopes. 69.1% has a mass
of 62.93 amu and the rest has a mass of
64.93 amu.
Atomic Mass
Magnesium has three isotopes. 78.99%
magnesium 24 with a mass of 23.9850 amu,
10.00% magnesium 25 with a mass of 24.9858
amu, and the rest magnesium 25 with a mass of
25.9826 amu. What is the atomic mass of
magnesium?
If not told otherwise, the mass of the isotope is the
mass number in amu
The Periodic Table
Noble Gas
Halogen
Group
Alkali Metal
Alkali Earth Metal
Period
2.4
Atoms and ions
Atoms are electrically neutral.
Same number of protons and electrons.
Ions are atoms, or groups of atoms, with
a charge.
Atoms and Ions
Different numbers of protons and
electrons.
Only electrons can move.
Gain or lose electrons.
Anion
A negative ion.
Has gained electrons.
Non metals can gain electrons.
Charge is written as a super script on
the right.
-1
F
-2
O
Has gained one electron
Has gained two electrons
Cations
Positive ions.
 Formed by losing electrons.
 More protons than electrons.
 Metals form cations.

+1
Has lost one electron
K
+2
Has lost two electrons
Ca
Two Types of Compounds
Molecular compounds


Made of molecules.
Made by joining nonmetal atoms together
into molecules.
Two Types of Compounds
Ionic Compounds





Made of cations and anions.
Metals and nonmetals.
The electrons lost by the cation are gained
by the anion.
The cation and anions surround each
other.
Smallest piece is a FORMULA UNIT.
Two Types of Compounds
Smallest
piece
Types of
elements
State
Melting
Point
Ionic
Molecular
Formula Unit
Molecule
Metal and
Nonmetal
Nonmetals
solid
Solid, liquid
or gas
High >300ºC
Low <300ºC
Chemical Formulas
Shows the kind and number of atoms in
the smallest piece of a substance.
Molecular formula- number and kinds of
atoms in a molecule.
CO2
Charges on ions
For most of the Group A elements, the
Periodic Table can tell what kind of ion
they will form from their location.
Elements in the same group have
similar properties.
Including the charge when they are
ions.
+1
+2
+3
-3 -2 -1
Naming ions
We will use the systematic way.
Cation- if the charge is always the same
(Group A) just write the name of the metal.
Transition metals can have more than one
type of charge.

Indicate the charge with roman numerals in
parenthesis.
Name these
Na+1
Ca+2
Al+3
Fe+3
Fe+2
Pb+2
Li+1
Write Formulas for these
Potassium ion
Magnesium ion
Copper (II) ion
Chromium (VI) ion
Barium ion
Mercury (II) ion
Naming Anions
Anions are always the same.
Change the element ending to – ide
F-1 Fluoride
Name these
Cl-1
N-3
Br-1
O-2
Write these
Sulfide ion
iodide ion
phosphide ion
Strontium ion
Polyatomic ions
Groups of atoms that stay together and
have a charge.
You must memorize these (table 2.5).

Acetate C2H3O2-1

Nitrate NO3-1




Nitrite NO2-1
Hydroxide OH-1
Permanganate MnO4-1
Cyanide CN-1
Polyatomic ions
Sulfate SO4-2
Sulfite SO3-2
Carbonate CO3-2
Chromate CrO4-2
Dichromate
Cr2O7-2
Chlorate ClO3-
Phosphate PO4-3
Phosphite PO3-3
Hydronium H3O +
Perchlorate
ClO4Ammonium NH4+1
Chlorite ClO2 -
Polyatomic Ions
Hypochlorite ClOHydrogen carbonate ion HCO3Dihydrogen phosphate ion H2PO4-
Ions and Ionic
Compounds
Naming Binary Ionic Compounds
Binary Compounds - 2 elements.
Ionic - a cation and an anion.
To write the names just name the two
ions.
Easy with Representative elements.
Group A
NaCl = Na+ Cl- = sodium chloride
MgBr2 = Mg+2 Br- = magnesium bromide
Naming Binary Ionic Compounds
The problem comes with the transition
metals.
Need to figure out their charges.
The compound must be neutral.
same number of + and – charges.
Use the anion to determine the charge
on the positive ion.
Naming Binary Ionic Compounds
Write the name of CuO
Need the charge of Cu
O is -2
copper must be +2
Copper (II) chloride
Name CoCl3
Cl is -1 and there are three of them = -3
Co must be +3 Cobalt (III) chloride
Naming Binary Ionic
Compounds
Write the name of Cu2S.
Since S is -2, the Cu2 must be +2, so
each one is +1.
copper (I) sulfide
Fe2O3
Each O is -2
Fe must be = + 3
iron (III) oxide
Naming Binary Ionic Compounds
Write the names of the following:
KCl
Na3N
CrN
Na2Se
Ternary Ionic Compounds
Will have polyatomic ions
At least three elements
name the ions
NaNO3
CaSO4
CuSO3
(NH4)2O
Ternary Ionic Compounds
LiCN
Fe(OH)3
(NH4)2CO3
NiPO4
Writing Formulas
The charges have to add up to zero.
Get charges on pieces.
Cations from name of table.
Anions from table or polyatomic.
Balance the charges by adding
subscripts.
Put polyatomics in parenthesis.
Writing Formulas
Write the formula for calcium chloride.
Calcium is Ca+2
Chloride is Cl-1
Ca+2 Cl-1
CaCl2
Write the formulas for these
Lithium sulfide
tin (II) oxide
tin (IV) oxide
Magnesium fluoride
Copper (II) sulfate
Iron (III) phosphide
gallium nitrate
Iron (III) sulfide
Write the formulas for these
Ammonium chloride
ammonium sulfide
barium nitrate
Things to look for
If cations have (), the number is their
charge.

Transition metal
If anions end in -ide they are probably off
the periodic table (Monoatomic)
If anion ends in -ate or -ite it is
polyatomic
Molecular Compounds
Molecular compounds
made of just nonmetals
smallest piece is a molecule
can’t be held together because of
opposite charges
can’t use charges to figure out how many
of each atom
Easier
Ionic compounds use charges to determine how many
of each

Have to figure out charges

Have to figure out numbers
Molecular compounds name tells you the number of
atoms

Uses prefixes to tell you the number
Prefixes
1 mono2 di3 tri4 tetra5 penta6 hexa7 hepta8 octa-
Prefixes
9 nona10 decaOne exception is we don’t write mono- if
there is only one of the first element.
Name These
N2O
NO2
Cl2O7
CBr4
CO2
BaCl2
Write formulas for these
diphosphorus pentoxide
tetraiodide nonoxide
sulfur hexaflouride
nitrogen trioxide
Carbon tetrahydride
phosphorus trifluoride
aluminum chloride
Naming Acids
a little tricky so pay attention
Acids
Compounds that give off hydrogen ions
when dissolved in water
Must have H in them (somewhere)
will always be some H next to an anion
The anion determines the name.
Naming acids
If the anion attached to hydrogen ends in -ide, put the
prefix hydro- and change -ide to -ic acid
HCl - hydrogen ion and chloride ion
hydrochloric acid
H2S hydrogen ion and sulfide ion
hydrosulfuric acid
Naming Acids
If the anion has oxygen in it
it ends in -ate or -ite
change the suffix -ate to -ic acid
HNO3 Hydrogen and nitrate ions
Nitric acid
change the suffix -ite to -ous acid
HNO2 Hydrogen and nitrite ions
Nitrous acid
Name these
HF
H3P
H2SO4
H2SO3
HCN
H2CrO4
Writing Formulas
Hydrogen will always be first
name will tell you the anion
make the charges cancel out.
Starts with hydro- no oxygen, -ide
no hydro, -ate comes from -ic, -ite comes from -ous
Write formulas for these
hydroiodic acid
acetic acid
carbonic acid
phosphorous acid
hydrobromic acid