Chapter 2: Atoms, Molecules, and Ions
The Atomic Theory of Matter
Democritus (460-371 BC):
• matter consists of atoms
which are solid particles
(a-tomos = un-cuttable)
• Democritus' ideas were
ignored for the next 2000 years
Chapter 2: Atoms, Molecules, and Ions
The Atomic Theory of Matter
John Dalton (1766-1844):
•Elements are made of tiny
particles called atoms
• all atoms of one element are
identical
• atoms are not created nor
destroyed in chemical processes
• atoms of different elements
can combine to form compounds
Chapter 2: Atoms, Molecules, and Ions
The Atomic Theory of Matter
Dalton’s Atomic Theory explained..
… The Law of Constant Composition
[in one compound, number and kind of atoms is constant]
… The Law of Conservation of Mass
[total mass before reaction = total mass after reaction]
… The Law of Multiple Proportions
[If two elements form more than one compound, the ratios of the masses of
the second element which combine with a fixed mass of the first element
will be ratios of small whole numbers]
Chapter 2: Atoms, Molecules, and Ions
The Atomic Theory of Matter
The Law of Multiple Proportions:
12 g carbon + 16 g oxygen =>
CO
12 g carbon + 32 g oxygen =>
CO2
32 g : 16 g =
2:1
HW: 8
Chapter 2: Atoms, Molecules, and Ions
The Discovery of Atomic Structure
J.J. Thomson (1856-1940):
• discovered the electron
• atoms of all elements contain
electrons
• electron: negatively charged
particles of very small mass
Chapter 2: Atoms, Molecules, and Ions
The Discovery of Atomic Structure
Cathode Ray Tube
_
+
eHV
Determination of charge to mass ratio:
e-
charge
coulombs
= 1.76× 108
mass
g
Chapter 2: Atoms, Molecules, and Ions
The Discovery of Atomic Structure
J.J Thomson's original
Cathode Ray Tube
Chapter 2: Atoms, Molecules, and Ions
The Discovery of Atomic Structure
R. Millikan (1868-1953):
• measured electron charge
electron charge = 1.60× 10− 19 C
- 28
1.60× 10− 19 C
electron mass =
=
9.10×
10
g
8
1.76× 10 C / g
HW: 14a,b
Chapter 2: Atoms, Molecules, and Ions
The Discovery of Atomic Structure
Electrons are negatively charged but
atoms as a whole are neutral.
Rutherford's Model:
J.J. Thomson's Model:
“Plum Pudding Model”
+
"smeared-out" positive charge
Chapter 2: Atoms, Molecules, and Ions
The Discovery of Atomic Structure
Chapter 2: Atoms, Molecules, and Ions
The Discovery of Atomic Structure
Rutherford's Model:
+
Chapter 2: Atoms, Molecules, and Ions
The Discovery of Atomic Structure
Ernest Rutherford (1871-1937):
• Rutherford concluded that
(a) the atom has a positive charge
concentrated in the nucleus
(b) the electrons orbit around the
positive nucleus
(c) that the atom is mostly empty
space
Chapter 2: Atoms, Molecules, and Ions
HW: 12
The Discovery of Atomic Structure
More evidence for atomic substructure:
• some substances spontaneously break down into
smaller particles (radioactivity)
• a-particles (heavy, +2 charge)
• b-particles (small mass, -1 charge)
• g-rays (electromagnetic radiation => no mass, no charge)
Chapter 2: Atoms, Molecules, and Ions
The Modern View of Atomic Structure
The nucleus is structured:
PROTONS: positively charged (+1)
NEUTRONS: no charge
Chapter 2: Atoms, Molecules, and Ions
The Modern View of Atomic Structure
The mass of an atom is concentrated in its nucleus:
MASS
Charge
•proton:
1 atomic mass unit (1amu)
+1
•neutron:
1 amu
0
•electron:
negligible mass
(5.486 x 10-4 amu)
-1
1 amu = 1.66054 x 10-24 g
(1.6 x 10-19C)
Chapter 2: Atoms, Molecules, and Ions
The Modern View of Atomic Structure
Elements differ in their number of protons:
Hydrogen:
1 proton
1
1H
Helium:
2 protons
2 neutrons
Lithium:
3 protons
4 neutrons
He
Li
the mass number counts protons and neutrons
the atomic number counts the number of protons
Beryllium:
4 protons
5 neutrons
Be
Chapter 2: Atoms, Molecules, and Ions
The Modern View of Atomic Structure
How about the neutrons?
• an element is defined by the number of protons
• atoms of one element can exist in different 'versions' :
all atoms must still have the same number of protons
but they may have a different number of neutrons
Chapter 2: Atoms, Molecules, and Ions
The Modern View of Atomic Structure
Isotopes of an element:
same number of protons but different number of neutrons
1
1
H
Hydrogen
or Protium
H
1
3
Deuterium
Tritium
2
1
H
Chapter 2: Atoms, Molecules, and Ions
Average Atomic Mass = Atomic Weight
Average Mass = fraction of heavy x mass of heavy + fraction of light x mass of light
= 3/4 x 70amu + 1/4 x 30amu
75%
= 0.75 x 70amu + 0.25 x 30amu = 60amu
25%
Chapter 2: Atoms, Molecules, and Ions
Average Atomic Mass = Atomic Weight
Si naturally occurs in three isotopes:
92.2% of 28Si (27.98 amu)
4.7%of 29Si (28.98 amu)
3.1%of 30Si (29.97 amu)
what is the atomic weight of Si?
HW: 33a
Chapter 2: Atoms, Molecules, and Ions
Periodic Table
●
Elements are sorted according to atomic number
6
C
12.01
Atomic weight
Atomic Number
Chapter 2: Atoms, Molecules, and Ions
HW: 23
How can you tell how many electrons an element has?
Hydrogen:
1 proton
1
1H
Helium:
2 protons
2 neutrons
4
2 He
Lithium:
3 protons
4 neutrons
7
3 Li
Beryllium:
4 protons
5 neutrons
9
4 Be
Chapter 2: Atoms, Molecules, and Ions
Periodic Table
●
Elements with similar properties fall in vertical groups
●
A row in the periodic table is called a period
Chapter 2: Atoms, Molecules, and Ions
HW: 37
Periodic Table
●
Most elements are metals
VIII A
I A II A
Alkaline Earth Metals
III A IV A VA VI A VIIA
Transition metals
Alkali Metals
Halogens
Noble
Gases
Chapter 2: Atoms, Molecules, and Ions
Molecules and Molecular Compounds
●
Some elements exist as diatomic molecules at room temp.
H2
N2
O2
F2
Cl2
Br2
I2
Chapter 2: Atoms, Molecules, and Ions
Molecules and Molecular Compounds
The periodic table helps predict how elements combine
Empirical Formulas
Only gives relative number
of atoms in compound
●
Subscripts are smallest
whole-number ratios
●
Molecular Formulas
Show actual number and
types of atoms in a molecule
●
Chapter 2: Atoms, Molecules, and Ions
Empirical Formulas
Molecular Formulas
H2O2
Hydrogen peroxide
C4H10
Butane
C3H8
Propane
Chapter 2: Atoms, Molecules, and Ions
HW: 45
Drawing Molecules: methane
Space-filling model
Perspective
drawing
Structural formula
Ball-and-Stick model
Chapter 2: Atoms, Molecules, and Ions
Ions and Ionic Compounds
Ions are formed when a neutral atom
- gains electrons or
- loses electrons
e-
Li
Li
Cation
-
e-
Br
+
Br
Anion
Chapter 2: Atoms, Molecules, and Ions
Which Elements form Anions, which Cations?
●
●
Metals tend to form Cations
Nonmetals tend to form Anions
VIII A
I A II A
Alkaline Earth Metals
Alkali Metals
III A IV A VA VI A VIIA
Halogens
Noble
Gases
Chapter 2: Atoms, Molecules, and Ions
HW: 49,50
How can you tell how many electrons an element will gain/lose?
NOBLE GASES
Na
Nb
X2
Nc
X1
X4
Nd
X3 Ne
Nf
Metals tend to form Cations
● Nonmetals tend to form Anions
●
Atoms tend to gain/lose the number of electrons needed
to achieve the electron configuration of the closest noble gas
●
Chapter 2: Atoms, Molecules, and Ions
Cations and Anions can combine to from Ionic Compounds
Li
Li
+
Cation
e-
Br
Br
Anion
Chapter 2: Atoms, Molecules, and Ions
Cations and Anions can combine to from Ionic Compounds
Ionic Crystal – not a discrete molecule
Chapter 2: Atoms, Molecules, and Ions
Empirical Formulas for Ionic Compounds:
(A) determine charge of ions formed
(B) add ions so that compound is neutral overall
Al, O =>
Na, O =>
Na2O
Al2O3
Chapter 2: Atoms, Molecules, and Ions
Li, Br =>
Mg, Cl =>
LiBr
MgCl2
HW: 51,53
Chapter 2: Atoms, Molecules, and Ions
Empirical Formulas for Ionic Compounds:
Al
3+
Mg
Ca
O
2-
2+
Cl 1
2+
2-
O
-
Al2O3
MgCl2
CaO
Chapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds: cations come first
(Ia) Monoatomic Cations:
●
Metal cations keep the name of the element:
Na+ sodium ion
Li+
Lithium ion
Zn2+ Zinc ion
If a metal can form different kinds of cations (transition metals),
the charge is indicated by a Roman Numeral:
●
Fe2+
Fe3+
Co2+
Iron(II) ion
Iron(III) ion
Cobalt(II) ion
Chapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds
(Ib) Cations formed from Nonmetals:
●
end in -ium:
NH4+ ammonium ion
H3O+ Hydronium ion
Chapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds
(IIa) Monoatomic and Simple Polyatomic Anions
●
Are derived from the element name by replacing the ending with -ide
N3-
Nitride ion
OH-
Hydroxide ion
O2-
Oxide ion
CN-
Cyanide ion
Chapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds
(IIb) Oxyanions (polyatomic anions containing oxygen)
●
●
●
●
The most common oxyanion of an element ends in -ate
One more oxygen: per-.....-ate
One fewer oxygen: -ite
Two fewer oxygen: hypo-.....-ite
Perchlorate
ClO3-
Chlorate
Chlorite
Hypochlorite
ClO4-
ClO2ClO-
Chapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds
(IIb) Oxyanions (polyatomic anions containing oxygen)
●
●
●
●
The most common oxyanion of an element ends in -ate
One more oxygen: per-.....-ate
One fewer oxygen: -ite
Two fewer oxygen: hypo-.....-ite
SO52-, S2O82- ]
[ Persulfate
SO42-
Sulfate
SO32-
Sulfite
Hyposulfite
SO22-
Chapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds
Common Oxyanions:
Carbonate
CO32-
Nitrate
NO3Phosphate
PO43-
Sulfate
SO42-
Chlorate
ClO3Bromate
BrO3Iodate
IO3-
Chapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds
Chapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds
HCO3-
You must know these!
Hydrogen carbonate ion
or Bicarbonate ion
Chapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds: chemical formula → name
Identify the ions
Cation
Anion
monoatomic or
Group 1A, 2A, 3A metal?
simple polyatomic
anion?
Transition metal ?
Element name
-ide
Nonmetal ion?
e.g. Ammonium
Element name
and charge in
Roman numerals
oxyanion?
per
...
...
...
hypo ...
ate
ate
ite
ite
Chapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds: chemical formula → name
MgSO4
FeCl3
NaClO
NH4OH
HW: 60,96
Chapter 2: Atoms, Molecules, and Ions
Naming Ionic Compounds: name → chemical formula
Fe(II) chloride
Magnesium hydroxide
Potassium cyanide
Sodium sulfite
HW: 61
Chapter 2: Atoms, Molecules, and Ions
Naming Molecular Compounds
ClO2
does not dissociate into ions!
Metal cations + Nonmetal anions
=>
Nonmetal cations + Nonmetal anions
(e.g. NH4+)
=>
Nonmetal + Nonmetal
=>
ionic compounds
ionic compounds
molecular compounds
Before you start naming, determine what kind of compound you have!
Chapter 2: Atoms, Molecules, and Ions
Naming Binary Molecular Compounds
ClO2
●
Chlorine dioxide
Name of the element farther to the left in the P.T. comes first
- except oxygen, which is usually named last
●
If both element are from the same group, the heavier one is named first
●
The second element is given an -ide ending
●
Greek prefixes indicate number of atoms of each element involved
[mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona- , deca-]
[mono-prefix is never used with 1st element]
Chapter 2: Atoms, Molecules, and Ions
Naming Compounds
NiO
1) Ionic or molecular?
2 a) Ionic: what are the ions?
b) molecular: how many atoms?
SO
KMnO4
BF3