Chapter 2: Atom, Molecules and Ions
1: The Observations That Led to an Atomic View
of Matter
2: The Observations That Led to the Nuclear Atom
Model
3: Dalton’s Atomic Theory and Today’s Version
4: Molecules and Ions
5. Elements: A First Look at the Periodic Table
6: Compounds: Introduction to Bonding
7: Compounds: Formulas and Names
Lecture 3:
Start Ch. 2.
Before Today’s Lecture:
Read syllabus, Appendix 1 & 2, & Ch. 1 & 2.
Initial Assessment on ALEKS, and start Obj. 1.
For Weds:
Get your Clicker and register its ID on Catalyst.
(same clicker may be used for all your courses).
Keep working toward Objective 1 on ALEKS, due
Friday 9 PM
Work extra problems from Ch. 1-2 (from my notes
on web and end of Chapter odd #s) on your own.
What calculator to buy / use?
You may use graphing calculators on exams and labs, but we
discourage it. You MAY NOT use any alpha (i.e., text)
memory on it during exams, or anything that we would
consider the electronic equivalent of a cheat sheet.
If you have anything with electronic communications or
internet of any type on it, you may NOT have it turned on or
even be outside your backpack during exams. This means, for
example, that you may NOT use calculators on cell phones,
etc.. during exams.
If you break any of the above rules, we will prosecute it as
ACADEMIC MISCONDUCT.
MY ADVICE: Buy a simple ~$10 calculator that has
exponents, logs, powers, etc., and get used to using it on HWs,
and use it on tests. It is faster to use for the type problems we
have on tests, and will be the only type calculator allowed in
some classes. Get good at using it! ADD TO SYLLABUS
Laws of Definite Proportions
Law of Definite ( or constant ) Proportions: No matter
what its source, a particular chemical
compound is composed of the same elements
in the same parts (fractions) by mass.
Law of Definite Proportions
Chemical analysis of a 9.07 g sample of calcium
phosphate shows that it contains 3.52 g of Ca.
How much Ca could be obtained from a 1.000 kg
sample?
Mass fraction Ca =
Mass Ca in 1.000 kg =
Law of Definite Proportions
Chemical analysis of a 9.07 g sample of calcium
phosphate shows that it contains 3.52 g of Ca.
How much Ca could be obtained from a 1.000 kg
sample?
Mass fraction Ca = 3.52 g Ca / (9.07 g total) = 0.388
(i.e., 38.8% Ca by mass in ANY sample of compound)
Mass Ca in 1.000 kg =
(1.000 kg total)x(0.388 kg Ca/ kg total) = 0.388 kg Ca
= 388 g Ca
Mass of Oxygen that Combines
with 1.00g of Carbon
Compound #1
1.33 g
Compound #2
2.66 g
Ratio = 2:1 exactly
Law of multiple proportions:
If elements A and B react to form two compounds, the different
masses of B that combine with a fixed mass of A can be
expressed as a ratio of small whole numbers (2:1 in this case).
Law of Multiple Proportions
The three smallest hydrocarbons:
• CH4
• C2H4
• C2H6
Atomic ratio and approximate mass ratio, C:H
• CH4
1:4
3:1
6:1
• C2H4 1:2
• C2H6 1:3
4:1
The C atom weighs ~12 times as much as the H atom.
Law of Multiple Proportions
If elements A and B react to form two compounds,
the different masses of B that combine with a fixed
mass of A can be expressed as a ratio of small whole
numbers.
Example: Mass ratios in NO and NO2
NO
NO2
: 46.68% Nitrogen and 53.32% Oxygen
: 30.45% Nitrogen and 69.55% Oxygen
If 100 g of NO: g O = 53.32 g
g N = 46.68 g
If NO2: 69.55 g
30.45 g
g O per g N = 1.142
2.284
2.284
2
=
= Twice as many g O per g N
1.142
1
in NO than in NO!!
2
2 H2 + 1 O2 → 2 H2O
Avogadro’s Hypothesis:
Equal volumes of different gases contain
the same numbers of “particles”
(i.e., molecules)
Dalton’s Atomic Theory (1808)
1. All matter consists of tiny particles called atoms.
2. Atoms of an element are identical in mass and other
properties and are different from atoms of any other
element.
3. Compounds result from the chemical combination of
a specific ratio of atoms of different elements.
4. Chemical reactions involve reorganization of the
atoms – changes in the way they are bonded. Atoms of
one element cannot be converted into atoms of another
element, and do not change during chemical reactions.
Next:
Structure of Atoms
electrons (-) in cloud around
nucleus = protons(+) + neutrons
Expts. which led to this picture.
(electron beams)
Fig.2.7
Deflection -> mass/charge
Fig.2.9
Millikan’s Expt.
1. Voltage across plates influenced speed, due to
charge of droplet.
2. Voltage to stop droplet, w/ laws of physics
→ amt. of charge on droplet.
3. RESULT: Different droplets had different
charges, but always a multiple of the same
number →
elementary charge on electron:
e = 1.602x10-19 coulombs (negative).
From cathode ray bending: mass/ charge ratio
Mass/charge ratio x e = mass of e-
Rutherford Experiment
• Alpha (i.e., subatomic) particles bombarding the
atom.
• Rationale - to study the internal structure of the
atom, and to know more about the mass
distribution in the atom!
• Bombarded a thin Gold foil with Alpha particles
from Radium.
Figs.2.11&12
Moving electron cloud
surrounding nucleus. It
is the main volume of __________________
the atom.
But almost all the
atom’s mass is in its
tiny nucleus!
(down to 10-15 m
for light elements)
1+
+
Notes: mass of e- tiny relative to p+, n.
p+, n have same mass (almost).
e-, p+ have same charge, opposite sign.
Atomic Definitions: Symbols, Isotopes, Numbers
X
Z
}
X=
Atomic symbol of the element, or element symbol
(found in the Period Table)
A
The Nuclear Symbol of the Atom, or Isotope
Z = The Atomic Number, the Number of Protons in the Nucleus
(All atoms of the same element have the same no. of protons.)
A = The Mass number; A = Z + N
N = The Number of Neutrons in the Nucleus N = A - Z
Isotopes = atoms of an element with the same number of protons,
but different numbers of Neutrons in the Nucleus
Figure 2.21: The periodic table
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CLICKER
There is a little LED light on the upper
left side of your clicker.
After you’ve sent your reply, the light
will turn green for a short time to signal
that your answer was received and stored.
Neutral ATOMS
If neutral, then # e-s = # p+s = atomic number.
Remember: #n s = A - # p+s
Numbers of each particle:
•
•
•
•
•
51 Cr
= p+ ( ), e- ( ),
n( )
239 Pu = p+( ), e-( ),
n( )
15 N = p+( ), e-( ), n( )
56 Fe = p+( ), e-( ),
n( )
235 U =p+( ), e-( ),
n( )
Figure 2.21: The periodic table
Copyright © Houghton Mifflin Company. All rights reserved.
Neutral ATOMS
If neutral, then # e-s = # p+s = atomic number.
Remember: #n s = A - # p+s
Numbers of each particle:
•
•
•
•
•
51 Cr
= p+ (24), e- (24 ),
n ( 27)
239 Pu = p+(94), e-(94),
n (145)
15 N = p+(7), e-(7), n(8)
56 Fe = p+(26), e-(26),
n (30)
235 U =p+(92), e-(92),
n (143)
Modern Reassessment of the Atomic Theory
1. All matter is composed of atoms. Although atoms are composed
of smaller particles (electrons, protons, and neutrons), the atom
is the smallest body that retains the unique identity of the element.
2. Atoms of one element cannot be converted into atoms of another
element in a chemical reaction. Elements can only be converted into
other elements in nuclear reactions in which protons are changed.
3. All atoms of an element have the same number of protons and
electrons, which determines the chemical behavior of the element.
Isotopes of an element differ in the number of neutrons, and thus
in mass number, but not in chemical behavior (much). A sample of
the element is treated as though its atoms have an average mass.
4. Compounds are formed by the chemical combination of two or more
elements in specific ratios, as originally stated by Dalton.
Figure 2.14 (P28) Isotopes of sodium
Definitions
• ELEMENT - A substance that cannot be separated
into simpler substances by chemical means
• COMPOUND - A substance composed of atoms
of two or more elements chemically united in
fixed proportions
• PERIODIC TABLE - “MENDELEEV TABLE” A tabular arrangement of the elements, vertical
groups or families of elements based upon their
chemical properties - actually combining ratios
with oxygen
Figure 2.15: Space-filling model of the
methane molecule
CH4
Figure 2.17 : Ball-and-stick model
CH4
Figure 2.18 : Sodium metal reacts with chlorine gas
to make an ionic compound: NaCl(solid)
Na(solid) + ½ Cl2(gas) → NaCl(solid)
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Forming an ionic bond:
Electron transfer from sodium to chlorine
Step 1:
Neutral sodium atom to sodium+ ion
Step 2:
Electron added to chlorine
(neutral chlorine to chloride- ion)
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Figure 2.19 (a): Arrangement of
sodium ions and chloride ions
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Figure 2.21: The periodic table
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Periodic Table: Focus on top, left and right 2 rows
H
Li Be
NaMg
K Ca Sc Ti
Rb Sr Y Zr
Cs Ba La Hf
Fr Ra Ac Rf
B C N
Al Si P
V Cr Mn Fe Co Ni Cu Zn Ga Ge As
NbMo Tc Ru Rh Pd Ag Cd In Sn Sb
Ta W Re Os Ir Pt Au Hg Tl Pb Bi
Du Sg Bo HaMe
O
S
Se
Te
Po
He
F Ne
Cl Ar
Br Kr
I Xe
At Rn
Ce Pr Nd PmSm Eu Gd Tb Dy Ho Er TmYb Lu
Th Pa U Np PuAmCmBk Cf Es FmMd No Lr
The Alkali Metals
The Halogens
The Alkaline
Earth Metals
The Noble Gases
Definitions
Chemical Bonds – The forces that hold atoms together in compounds
Covalent Bonds – The sharing of electrons in a chemical bond
Ions - Atom with its # of electrons ≠ # of protons (later- also groups of atoms too)
Ionic bonds – Attraction between positive and negative ions
Molecule – A group of atoms held together by ionic or covalent bonds
Compounds – Molecules, but also ionic or covalent solids.
Chemical Formula – A way to express the atomic composition of compounds where
1. symbols for the elements are used to
indicate the types of atoms present, and
2. subscripts are used to indicate the numbers of
atoms present (or their relative numbers, for the case of solids).
Chemical Compounds and Bonds
Chemical Bonds - The electrostatic forces that hold the
atoms of elements together in the compound.
Covalent Compounds - Electrons are shared between
atoms of different elements to form Covalent Cpds.
Ionic Compounds - Electrons are transferred from one
atom to another to form Ionic Cpds.
“Cation” - An atom that has lost electron(s) to form “ + ” ions.
May be 1 or more e-s. Common with metal elements.
“Anion” - An atom which has gained electron(s), to form “ - ”
ions. Common w/ nonmetal elements.
Later we’ll learn that group of atoms can also be anion or cation
Mono-atomic (monatomic) ions form binary ionic compounds.
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The Periodic Table of the Elements
Most Probable Oxidation State
0
+1
+3 +_4 - 3
H +2
Li Be
B C N
+1 + 2 Al Si P
Na Mg +3 +4 +5
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb
Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi
Fr Ra Ac Rf Db Sg Bh Hs Mt Ds
+3
+3
-2 -1
He
O F Ne
S Cl Ar
Se Br Kr
Te I Xe
Po At Rn
Ce Pr Nd PmSm Eu Gd Tb Dy Ho Er TmYb Lu
Th Pa U Np Pu AmCmBk Cf Es FmMd No Lr
The rest of Ch. 2:
Rules for Naming
Compounds
Rules for naming binary ionic compounds
(ionic compounds made from just 2 elements)
Always list cation (+) name first, anion (-) name second.
Monatomic anion’s name = first part of element name plus “-ide”
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Give the Name and Chemical Formulas of the
Compounds formed from the following pairs
of Elements
a) Sodium and Oxygen
b) Zinc and Chlorine
c) Calcium and Fluorine
d) Strontium and Nitrogen
e) Hydrogen and Iodine
f) Scandium and Sulfur
Na2O
Sodium Oxide
Give the Name and Chemical Formulas of the
Compounds formed from the following pairs
of Elements
a) Sodium and Oxygen
Na2O
Sodium Oxide
b) Zinc and Chlorine
ZnCl2
Zinc Chloride
c) Calcium and Fluorine
CaF2
Calcium Fluoride
d) Strontium and Nitrogen
Sr3N2
Strontium Nitride
e) Hydrogen and Iodine
HI
Hydrogen Iodide
f) Scandium and Sulfur
Sc2S3
Scandium Sulfide
(metals that have >1 possible oxidation states)
Demos:
cations with
multiple
oxidation
states:
NOTE: “oxidation state” means the charge on the ion, e.g., +3 for Fe(III), -1 for ClCopyright © Houghton Mifflin Company. All rights reserved.
V5+ yellow
V4+ blue;
Mn ions
Rules for naming binary ionic compounds
Always list cation (+) name first, anion (-) name second.
Monatomic anion’s name = first part of element name + “-ide”
If the ion is not listed in
the Type II table, assume
it’s Type I on HW.
Copyright © Houghton Mifflin Company. All rights reserved.
Determining Names and Formulas of Ionic Compounds
of Elements That Form More Than One Ion.
Give the systematic names for the formulas or the formulas
for the names of the following compounds.
a) Iron III Sulfide - Fe is +3, and S is -2 therefore the compound is:
Fe2S3
b) CoF2 -
c) Stannic Oxide -
d) NiCl3 -
Determining Names and Formulas of Ionic Compounds
of Elements That Form More Than One Ion.
Give the systematic names for the formulas or the formulas
for the names of the following compounds.
a) Iron III Sulfide - Fe is +3, and S is -2 therefore the compound is:
Fe2S3
b) CoF2 - the anion is Fluoride (F -1) and there are two F -1, the
cation is Cobalt and it must be Co+2 therefore the compound is:
Cobalt (II) Fluoride
c) Stannic Oxide - Stannic is the common name for Tin (IV), Sn+4, the
Oxide ion is O-2, therefore the formula of the compound is:
SnO2
d) NiCl3 - The anion is chloride (Cl-1), there are three anions, so the
Nickel cation is Ni+3, therefore the name of the compound is:
Nickel (III) Chloride
The Periodic Table of the Elements
Most Probable Oxidation State
0
+1
+3 +_4 - 3
H +2
Li Be
B C N
+1 + 2 Al Si P
Na Mg +3 +4 +5
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb
Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi
Fr Ra Ac Rf Db Sg Bh Hs Mt Ds
+3
+3
-2 -1
He
O F Ne
S Cl Ar
Se Br Kr
Te I Xe
Po At Rn
Ce Pr Nd PmSm Eu Gd Tb Dy Ho Er TmYb Lu
Th Pa U Np Pu AmCmBk Cf Es FmMd No Lr
The rest of Ch. 2:
Rules for Naming
Compounds
(continued)
The Periodic Table of the Elements
Most Probable Oxidation State
0
+1
+3 +_4 - 3
H +2
Li Be
B C N
+1 + 2 Al Si P
Na Mg +3 +4 +5
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb
Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi
Fr Ra Ac Rf Db Sg Bh Hs Mt Ds
+3
+3
-2 -1
He
O F Ne
S Cl Ar
Se Br Kr
Te I Xe
Po At Rn
Ce Pr Nd PmSm Eu Gd Tb Dy Ho Er TmYb Lu
Th Pa U Np Pu AmCmBk Cf Es FmMd No Lr
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The
polyatomic
ion
Naming Compounds containing Polyatomic Ions
(Same as before, just use these new ion names.)
• KNO2
Potassium Nitrite
• Mg(NO3)2 Magnesium Nitrate
• LiClO4 Lithium Perchlorate
• NaClO3 Sodium Chlorate
• RbClO2 Rubidium Chlorite
• CsClO Cesium Hypochlorite
BaSO3 Barium Sulfite
Na2SO4 Sodium Sulfate
Naming Compounds containing Polyatomic Ions
(Self test)
• Calcium Nitrate
Ammonium Sulfite
• Strontium Sulfate
Lithium Nitrite
• Potassium Hypochlorite
• Rubidium Chlorate
• Ammonium Chlorite
• Sodium Perchlorate
Naming Compounds containing Polyatomic Ions
(Self test- answers.)
• Calcium Nitrate Ca(NO3)2
• Strontium Sulfate SrSO4
• Potassium Hypochlorite KClO
• Rubidium Chlorate
RbClO3
• Ammonium Chlorite NH4ClO2
• Sodium Perchlorate NaClO4
Ammonium Sulfite
Lithium Nitrite
(NH4)2SO3
LiNO2
Naming binary covalent compounds:
1. The element further left in the periodic table goes
first, named as if it were the cation.
2. Second element is named as if it were the anion.
3. Use prefixes to say how many atoms of each
element are present, EXCEPT never use
“mono-” on first element.
EXAMPLES:
N2O dinitrogen monoxide
NO nitrogen monoxide
N2O4 dinitrogen tetroxide
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Determining Names and Formulas of Binary
Covalent Compounds
Problem: What are the name or chemical formulas of the following
chemical compounds:
a) Carbon dioxide b) PCl3 c) Give the name and chemical formula
of the compound formed from two P atoms and five O atoms.
Solution:
a) Carbon dioxide
b) PCl3
c) The compound formed from two P atoms and five O atoms
Determining Names and Formulas of Binary
Covalent Compounds
Problem: What are the name or Chemical formulas of the following
Chemical compounds:
a) Carbon dioxide b) PCl3 c) Give the name and chemical formula
of the compound formed from two P atoms and five O atoms.
Solution:
a) Carbon dioxide The prefix “di-” means “two.” The formula is CO2
b) PCl3 P is the symbol for phosphorous; there are three chlorine
atoms which require the prefix “tri-.” The name of the compound is:
phosphorous trichloride
c) The compound formed from two P atoms and five O atoms
P comes first in the name (left of O in Periodic Table).
The compound is: diphosphorous pentaoxide
Figure 2.21: Flowchart for naming binary
compounds (ionic or covalent)
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Figure 2.22: Flowchart for overall strategy
for naming chemical compounds
2.21
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SOLIDS:
Ways to make a pure solid compounds:
• Ionic compounds
• Covalent solids (e.g., silicon carbide, boron nitride)
• Molecular solids:
Density of soda demo
Sucrose, commonly known as table sugar.
About 150,000,000 tonnes are produced annually.
H
C
O
Acids
Many common anions, when combined with H+ as the
cation(s), make a very reactive compound called an acid,
which dissociates in water to give the two separate ions
both dissolved in water.
Examples (demo):
H2O +P4O10 → H3PO4(aq) → H+(aq) + H2PO4-(aq)
phosphoric acid
HCl → H+(aq) + Cl-(aq)
hydrochloric acid
H2SO4 → 2 H+(aq) + SO42-(aq)
sulfuric acid
Litmus paper – indicates if it’s an acidic solution
pH = quantitative measure of H+ concentration in water
Figure 2.23: Flowchart for naming acids
Acids = Molecules which dissociate when dissolved in water to give H+(aq)
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Copyright © Houghton Mifflin Company. All rights reserved.
Determining Names and Formulas of
Anions and Acids
Problem: Name the following anions and give the names and
a) I -
Answer:
a) I b) ClO3c) SO3-2
d) NO3e) CN -
formulas of the acid solutions derived from them:
b) ClO3c) SO3-2 d) NO3e) CN RULE: -ite = -ous
&
-ate = -ic
Determining Names and Formulas of
Anions and Acids
Problem: Name the following anions and give the names and
a) I -
formulas of the acid solutions derived from them:
b) ClO3c) SO3-2 d) NO3e) CN -
Answer:
a) The anion is Iodide; and the acid is Hydroiodic acid, HI
b) The anion is Chlorate; and the acid is Chloric acid, HClO3
c) The anion is Sulfite; and the acid is Sulfurous acid, H2SO3
d) The anion is Nitrate; and the acid is Nitric acid, HNO3
e) The anion is Cyanide; and the acid is Hydrocyanic acid, HCN