Download BS5-Ch 2.

Ch 2. Elements, Compounds and
Chemical Reactions
REVIEW OF GENERAL
CONCEPTS
Adapted from
Brady & Senese, 5th Ed.
Chemical Laws
• The law of conservation of mass - in a chemical
reaction, the mass of the reactants (starting
materials) will equal the mass of resulting
products
 Implication: reactions involve the re-organization of
materials.
• The law of definite proportions- the ratio of
masses of each element is fixed for a given
compound
 Implication: Each atom has a fixed specific mass, thus
in unique combinations, the mass ratio is specific
2.1. Elements and atoms are described by Dalton’s atomic theory
2
Dalton’s Atomic Theory
•
•
Matter consists of tiny particles called atoms
Atoms are indestructible. In chemical reactions, the
atoms rearrange but they do not themselves break
apart
+
2.1. Elements and atoms are described by Dalton’s atomic theory
3
Dalton’s Atomic Theory (Cont.):
•
•
•
In any sample of a pure element, all the atoms
are identical in mass and other properties.
The atoms of different elements differ in mass
and other properties.
In a given compound the constituent atoms are
always present in the same fixed numerical
ratio.
NaCl has a 1:1 atom ratio on the atomic
level and larger
2.1. Elements and atoms are described by Dalton’s atomic theory
4
The Law Of Multiple Proportions
When two elements form more than one compound,
the different masses of one element that combine
with the same mass of the other element are in the
ratio of small whole numbers.
• cements the idea that atoms react as complete
(whole) particles.
• chemical formulas indicate whole numbers of
atoms- not fractions
2.1. Elements and atoms are described by Dalton’s atomic theory
5
Using The Law Of Multiple Proportions
sulfur
sulfur
dioxide
trioxide
Mass S
32.06 g
32.06 g
Mass O
32.00 g
48.00 g
Use these data to prove the law of
multiple proportions
2.1. Elements and atoms are described by Dalton’s atomic theory
6
Proof Of Atoms
• Since the early 1980’s, the Scanning Tunneling
Microscope (STM) has been used
• A surface can be scanned for topographical
information
• The image for all matter shows spherical regions of
matter-- atoms
2.1. Elements and atoms are described by Dalton’s atomic theory
7
Cathode Ray Tube (CRT)
A gas filled glass tube that has electrical charge
applied at both ends.
Such a tube glows with light and is the precursor of
the modern-day television screen.
2.2 Atoms are composed of subatomic particles
8
Discovery Of The Electron By JJ Thomson
• In 1897, Thomson placed a
magnet near CRT and noted
deflection of the beam
• Repeated experiment with an
electrical field and noted that
the discharge was deflected by
an electrical field toward the
(+) plate
• Announced discovery of (-)
particle, later named “electron”
by Stoney
2.2 Atoms are composed of subatomic particles
9
Determining The Charge On An e-: Millikan
2.2 Atoms are composed of subatomic particles
10
Rutherford’s Alpha Scattering Experiment
Most alpha rays passed right through the Au
A few were deflected off at an angle
1 in 8000 bounced back towards the alpha ray source
2.2 Atoms are composed of subatomic particles
11
Rutherford’s Nuclear Model of the Atom
• Since most of the alpha particles were not
deflected, most of the atom is empty space.
• Since some of the particles were deflected,
they encountered small particles of the
same charge.
• Since some particles were reflected, there
must be a small dense area.
2.2 Atoms are composed of subatomic particles
12
Discovery Of The Proton
• Discovered in 1918 in Ernest Rutherford’s lab
• Detected using a Mass Spectrometer
2.2 Atoms are composed of subatomic particles
13
Discovery Of The Neutron
• Chadwick determined that the nuclei of light
atoms could be caused to disintegrate by being
bombarded by alpha particles.
• In collision of alpha particles with Be, a free
neutron was created
• the presence of the neutron confirmed in 1932
2.2 Atoms are composed of subatomic particles
14
Subatomic Particles
Particle
Symbol
electron
proton
neutron
0
1
1
1
e or e
-
p or 11H 
1
0
n or n
0
Mass (u)
Location
Charge
5.48579903(10-4)
orbital
1-
1.007276470
nucleus
1+
1.008664904
nucleus
0
2.2 Atoms are composed of subatomic particles
15
Atomic Mass
• Dalton’s atomic theory states that atoms of an
element have a constant, characteristic atomic mass
or atomic weight measured in amu (u)
• Atomic masses are based on a standard mass, that of
an atom of C
• 1 atom of Carbon-12 = 12 u
• Thus 1 u = 1/12 the mass of a Carbon-12 atom
2.2 Atoms are composed of subatomic particles
16
Isotopes
• Most elements in nature are uniform mixtures of two
or more kinds of atoms with slightly different masses
• Atoms of the same element with different masses are
called isotopes
 For example: there are 3 isotopes of hydrogen and 4
isotopes of iron
• Chemically, isotopes have virtually identical
properties
2.2 Atoms are composed of subatomic particles
17
Atomic Notation
A
Z
Sy
• An element is a substance whose atoms all contain
the identical number of protons, called the atomic
number (Z)
• Isotopes are distinguished by mass number (A):
 Atomic number, Z = number of protons
 Mass number, A = (number of protons) + (number of
neutrons)
 Note that for atoms, A is greater than Z: the symbol is topheavy
• For charge neutrality, the number of electrons and
protons must be equal
2.2 Atoms are composed of subatomic particles
18
Example: uranium-235
Mass number, A (protons + neutrons)  235
Chemical Symbol

U
Atomic number, Z (number of protons)  92
This information can be summarized:
 Number of protons = 92 ( = number of electrons)
 Number of neutrons = 143
 Atomic number (Z) = 92
 Mass number (A) = 92 + 143 = 235
 Chemical symbol = U
2.2 Atoms are composed of subatomic particles
19
Learning Check:
Fill in the blanks:
symbol
neutrons
60Co
81Br
65
29
Cu
33
46
36
protons
27
35
29
2.2 Atoms are composed of subatomic particles
electrons
27
35
29
20
Your Turn!
How many neutrons are there in 52Fe?
A. 52
B. 55
C. 26
D. none of these
2.2 Atoms are composed of subatomic particles
21
Learning Check: Atomic Mass
Naturally occurring chlorine is a mixture of two
isotopes. In every sample of this element, 75.77% of
the atoms are chlorine-35 and 24.23% are chlorine37. The measured mass of chlorine-35 is 34.9689 u
and that of chlorine-37 is 36.9659 u. Calculate the
average atomic mass of chlorine.
(75.77×34.9689) + (24.23×36.9659) u
100
35.45 u
2.2 Atoms are composed of subatomic particles
22
Your Turn
There are 2 isotopes of element Z. The first is
56.5% in abundance and has a mass of 152.3 u. If
the atomic mass is 155.5 u, what is the mass of
the other isotope?
A. 156 u
B. 44.5 u
C. 157. u
D. not enough information given
E. none of these 153.7 u
2.2 Atoms are composed of subatomic particles
23
Periodic Table
1A
2A
1
H
arranged in numbered rows –
“periods”
columns called “groups” or
“families”
3
4
Li
Be
11
12
Na
Mg
3B
4B
5B
6B
7B
8B
8B
8B
1B
19
20
21
22
23
24
25
26
27
28
K
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
37
38
39
40
41
42
43
44
Rb
Sr
Y
Zr
Nb
Mo
Tc
55
56
57
72
73
74
Cs
Ba
La
Hf
Ta
87
88
89
104
Fr
Ra
Ac
3A
4A
5A
6A
7A
8A
2
He
5
6
7
8
9
10
B
C
N
O
F
Ne
13
14
15
16
17
18
2B
Al
Si
P
S
Cl
Ar
29
30
31
32
33
34
35
36
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Kr
45
46
47
48
49
50
51
52
53
54
Ru
Rh
Pd
Ag
Cd
In
Sn
Sb
Te
I
Xe
75
76
77
78
79
80
81
82
83
84
85
86
W
Re
Os
Ir
Pt
Au
Hg
Tl
Pb
Bi
Po
At
Rn
105
106
107
108
109
110
111
112
114
Rf
Db
Sg
Bh
Hs
Mt
Ds
Uuu
Uub
Uuq
58
59
60
61
62
63
64
65
66
67
68
69
70
71
Ce
Pr
Nd
Pm
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
90
91
92
93
94
95
96
97
98
99
100
101
102
103
Th
Pa
U
Np
Pu
Am
Cm
Bk
Cf
Es
Fm
Md
No
Lr
2.3. The periodic table is used to organize and correlate facts
24
Periodic Table
• Summarizes chemical and physical properties of the
elements
• Mendeleev first arranged atoms by increasing atomic
mass. Noted repeating (periodic) properties
• Modern table is arranged by increasing atomic
number (Moseley)
2.3. The periodic table is used to organize and correlate facts
25
Some Important Classifications:
• A groups = representative elements or main group
elements
I A = alkali metals
VII A = halogens
II A = alkaline earth metals
VIII = noble (also inert) gases
• B groups = transition elements
• Inner transition elements = elements 58 – 71 and 90
– 103
58 – 71 = lanthanide elements
90 – 103 = actinide elements
2.3. The periodic table is used to organize and correlate facts
26
The modern periodic table
2.3. The periodic table is used to organize and correlate facts
27
Metals, Nonmetals, And Metalloids
2.4. Elements can be metals, non-metals, or metalloids
28
Your turn!
Which of the following is correct?
A. Cu is a representative transition element
B. Na is an alkaline earth metal
C. Al is a semimetal in group IIIa
D. F is a representative halogen
E. None of these are correct
2.4. Elements can be metals, non-metals, or metalloids
29
Properties Of Metals
• reflect light (have metallic luster)
• Can be hammered or rolled into thin sheets (are
malleable) and can be drawn into wire (are ductile)
• Are solids at room temperature (except Hg)
• conduct electricity and heat
2.4. Elements can be metals, non-metals, or metalloids
30
Nonmetals And Metalloids
• Nonmetals





Lack the properties of metals
Tend to pulverize when struck with a hammer
Non-conductors of electricity and heat
Many are gases, a few solids, and one liquid (Br)
React with metals to form (ionic) compounds
• Metalloids
 Have properties between metals and nonmetals
2.4. Elements can be metals, non-metals, or metalloids
31
Chemical Formulas
• Are symbols used to describe other elements in a
compound
• elements and compounds
• Free elements are not combined with another
element in a compound. Examples: Fe (iron), Na
(sodium), and K (potassium)
 Many non-metals occur in groups of 2 (as diatomic
molecules)- H, O, N, F, Cl, I, Br
 Some elements occur as molecules: P4, S, S8, P10, O3 ,
etc…
2.5. Formulas and equations describe substances and their reactions
32
Chemical Formulas (Cont.)
• Specify the composition of a substance
• Fe2O3 is composed of the elements iron and oxygen
in a 2:3 ratio
• CO(NH2)2 expands to CON2H4, but parentheses
often group atoms to show the compound’s
structure
2.5. Formulas and equations describe substances and their reactions
33
Hydrates
• Hydrates are crystals that contain water
molecules, for example plaster: CaSO4 • 2H2O
 When all the water is removed (by heating), the solid
that remains is said to be anhydrous (without water)
CuSO4 •5H2O
2.5. Formulas and equations describe substances and their reactions
CuSO4
34
Learning Check:
Count The Atoms In A Chemical Formula
•
•
•
•
•
Na2CO3
(NH4)2SO4 •
Mg3(PO4)2 •
CuSO4•5H2O •
___Na,
___
1 C, ___
2
3 O
2
8
1 ____O
4
___N,
___H,
___S,
8
3
2 ____O
___Mg,
___P,
___Cu,
___S,
___H
1
1 ___O,
10
9
2.5. Formulas and equations describe substances and their reactions
35
Molecules Form When Nonmetallic Elements
Combine
• Molecules are neutral
particles made of 2 or more
atoms.
• Many molecular compounds
contain hydrogen:
Group
Period IVA
VA
VIA
2
CH4
NH3
H2O
3
SiH4
PH3
H2S
4
GeH4 AsH3
H2Se
5
SbH3
H2Te
VIIA
HF
HCl
HBr
HI
Noble
Gas
Ne
Ar
Kr
Xe
2.6 Molecular compounds contain neutral particles called molecules
36
Ionic Compounds
• Positively charged ions are called cations
• Negatively charged ions are called anions
• subscripts in the formula always specify the
smallest whole-number ratio of the ions
needed to make a neutral combination
(formula unit)
2 Fe3+
3 O2-
Fe2O 3
2.7 Ionic compounds are composed of charged particles called ions
37
What About Ions?
•
•
•
•
Number of p+ = number of e- if neutral
Number of p+ < number of e- if negative
Number of p+ > number of e- if positive
The number of p+ never changes when ions form
How does Ca form Ca2+? Ca loses 2 electrons
How is N3- formed?
N gains 3 electrons
2.7 Ionic compounds are composed of charged particles called ions
38
Learning Check:
Fill in the blanks:
Symbol
neutrons
60Co3+
33
81Br-
Cu 2
65
29
46
36
protons
electrons
27
24
35
36
29
27
2.7 Ionic compounds are composed of charged particles called ions
39
The Charges On Many Representative Elements Can
Be Predicted
• Noble gases are especially stable
• Main group elements will often gain or lose
electrons to have the same number of electrons as
the nearest noble gas
• Metals form cations by losing electrons
 What is the expected charge on:
Ca? 2+
Na? +
• Nonmetals form anions by gaining electrons
 What is the expected charge on:
N? 3O? 2-
2.7 Ionic compounds are composed of charged particles called ions
40
Rules For Writing Formulas Of Ionic
Compounds
•
•
•
•
The cation is given first in the formula
The subscripts in the formula must produce an
electrically neutral formula unit
The subscripts should be the set of smallest whole
numbers possible
The charges on the ions are not included in the
finished formula of the substance
2.8 The formulas of many ionic compounds can be predicted
41
Ionic Compounds Are Neutral
• The positive charge
must balance the
negative charge
• We could use trial and
error to find the least
common charge
+
-
+
-
2.8 The formulas of many ionic compounds can be predicted
+
-
42
Determining The Formula Of An Ionic
Compound
• Practically, we can often accomplish this by making the charge
magnitude (not the charge) of one ion into the subscript for the
other. (The “Criss-cross” rule)
• If you choose this approach, make sure that the subscripts are
reduced to the lowest whole number.
Al3+ O2Al2O3
Al3+ O2MgO
Mg2+ O2Mg2+ O2+ (PO )3+
3(NH
)
(NH4)3PO4
NH4 PO4
4
4
2.8 The formulas of many ionic compounds can be predicted
43
Your Turn!
Which of the following is the correct formula for the
formula unit composed of potassium and oxygen
ions?
A. KO
B. KO2
C. K2O
D. none of these
Your Turn!
Which of the following is the correct formula for the
formula unit composed of Fe3+ and sulfide ions?
A. FeS
B. Fe3S2
C. Fe2S3
D. none of these
Transition And Post-transition Metals Usually Have
Multiple Charges
Transition Metals
Chromium
Cr2+, Cr3+
Manganese
Mn2+, Mn3+
Iron
Fe2+, Fe3+
Cobalt
Co2+, Co3+
Nickel
Ni2+
Copper Cu+, Cu2+
Post-transition Metals
Tin
Sn2+, Sn4+
Bismuth
Bi3+
Zinc Zn2+
Silver Ag+
Cadmium Cd2+
Gold Au+, Au3+
Mercury Hg22+, Hg2+
Lead
Pb2+, Pb4+
2.8 The formulas of many ionic compounds can be predicted
46
Some Polyatomic Ions
(Ions With Two Or More Atoms):
NH4+
Ammonium ion
CO32-
carbonate ion
OH-
hydroxide ion
H3O+
hydronium ion
NO2-
nitrite ion
SO32-
sulfite ion
NO3-
nitrate ion
SO42-
sulfate ion
ClO2-
chlorite ion
CrO42-
chromate ion
ClO3-
chlorate ion
Cr2O72- dichromate ion
PO43-
phosphate ion
2.8 The formulas of many ionic compounds can be predicted
47
The Stock System Of Naming Ionic Compounds
• Cations:
 If the metal forms only one positive ion, the cation
name is the English name for the metal
 If the metal forms more than one positive ion, the
cation name is the English name followed, without a
space, by the numerical value of the charge written as
a Roman numeral in parentheses
• Anions:
 monatomic anions are named by adding the “–ide”
suffix to the stem name for the element
 polyatomic ions use the names in Table 2.5
2.9 Molecular and ionic comounds are named following a system
48
Naming Binary Molecules
The first element in the formula is identified by its
English name, the second by appending the
suffix –ide to its stem
Chemical
Symbol
O
N
P
Cl
I
Name as
Stem
First Element
oxoxygen
nitrnitrogen
phosph- phosphorus
chlorchlorine
iodiodine
Name as
Second Element
oxide
nitride
phosphide
chloride
iodide
2.9 Molecular and ionic comounds are named following a system
49
Naming Binary Covalent Molecules
• Format:
number prefix + 1st element name number prefix + stem_ide for 2nd element.
• Greek prefixes
mono- = 1 (omitted on 1st atom)
di=2
tri=3
tetra- = 4
penta- = 5
hexaheptaoctanonadeca-
2.9 Molecular and ionic comounds are named following a system
=6
=7
= 8
= 9
= 10
50
Learning Check: Name The Following
• PF5
= •phosphorus pentafluoride
• HCl = •hydrogen chloride
• N2O5 = •dinitrogen tetraoxide
or dinitrogen tetroxide
2.9 Molecular and ionic comounds are named following a system
51
Your Turn!
Which is the correct formula for nitrogen
triiodide?
A. N3I
B. NI3
C. NIO3
D. N(IO3)3
E. none of the above
Your Turn!
Which is the correct name for P4O10?
A. phosphorus decoxide
B. tetraphosphorous decoxide
C. tetraphosphorus decoxide
D. tetraphosphorus oxide
E. none of these
2.9 Molecular and ionic comounds are named following a system
54
Learning Check: Name The Following
•
•
•
•
•
•
Na2O
K2O
NH4ClO3
Mg(C2H3O2)2
Cr2O3
ZnBr2
•sodium oxide
•potassium oxide
•ammonium chlorate
•magnesium acetate
•chromium(III) oxide
•zinc bromide
2.9 Molecular and ionic comounds are named following a system
55
Learning Check: Determine The Formula
• calcium hydroxide
 Ca(OH)2
• mercury(I) nitride
 (Hg2)3N2
• ammonium phosphate
 (NH4)3PO4
2.9 Molecular and ionic comounds are named following a system
56
Your Turn!
Which is the correct name for Cu2S?
A. copper sulfide
B. copper(II) sulfide
C. copper(I) sulfide
D. none of these
Your Turn!
Which is the correct formula for ammonium sulfite?
A.
B.
C.
D.
NH4SO4
(NH4)2S
NH4S
none of these
(NH4)2SO3
Overview: Molecules vs. Formula Units
• electrically neutral, discrete particles called
molecules
• Neutral groups of charged particles called
formula units
59
Summary of Properties
Hardness and brittleness
 Molecular compounds tend to be soft and easily crushed
because the attractions between molecules are weak and
molecules can slide past each other
 Ionic compounds are hard and brittle because of the strong
attractions and repulsions between ions
60
Melting Points
To melt the a solid, there must be sufficient kinetic
energy to overcome the attractions between particles
 Molecular compounds have weak attractions between
particles and so tend to have low melting points
 Many molecular compounds are gases at room
temperature
 Ionic compounds tend to have strong attractions so they
have high melting points
 Nearly all ionic compounds are solids at room
temperature
61
Electrical Conductivity
• Requires the movement of electrical
charge
• Ionic compounds:
 Do not conduct electricity in the solid
state
 Do conduct electricity in the liquid and
aqueous states-the ions are free to move
• Molecular compounds:
 Do not conduct electricity in any state
 Molecules are comprised of uncharged
particles
62
Your Turn!
Which of the following is likely true of NO2?
A. it conducts electricity well
B. It has a low melting point
C. It is likely a solid in its pure form
D. None of these