Chapter 3:
Elements, Compounds,
and the Periodic Table
Chemistry: The Molecular Nature
of Matter, 6E
Brady/Jespersen/Hyslop
Properties of Subatomic Particles
Nucleus (protons
+ neutrons)
 3 Kinds of subatomic
particles of principal
interest to Chemists
Electrons
Particle
Mass (g)
Electrical
Charge
Electron
9.109391028
1
Proton
1.672641024
+1
0
1 e
1
1
1 H, 1 p
Neutron
1.674951024
0
1
0n
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Chemistry: The Molecular Nature of Matter, 6E
Symbol
2
Atomic Notation
Atomic number (Z)
 Number of protons that atom has in nucleus
 Unique to each type of element
 Element is substance whose atoms all contain
identical number of protons
 Z = # protons
Isotopes
 Atoms of same element with different masses
 Same number of protons (11 p )
 Different number of neutrons (10n )
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Atomic Notation
Isotope Mass number (A)
 A = (# protons) + (# neutrons)
 A=Z+N
 For charge neutrality, number of electrons &
protons must be equal
Atomic Symbols
 Summarize information about subatomic particles
 Every isotope defined by 2 numbers Z & A
A
 Symbolized by X
Z
Ex. What is the atomic symbol for helium?
He has 2
Brady/Jespersen/Hyslop
e –,
2n&2
p+
Z = 2, A = 4
Chemistry: The Molecular Nature of Matter, 6E
4
2 He
4
Isotopes
 Most elements are mixtures of 2 or more stable
isotopes
 Each isotope has slightly different mass
 Chemically, isotopes have virtually identical chemical
properties
 Relative proportions of different isotopes are
essentially constant
 Isotopes distinguished by mass number (A):
Ex.
 3 isotopes of hydrogen (H)
 4 isotopes of iron (Fe)
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Chemistry: The Molecular Nature of Matter, 6E
5
Example:
What is the isotopic symbol for Uranium235?
 Number of protons (p+) = 92
= number of electrons in neutral atom
 Number of neutrons (1n) = 143
 Atomic number (Z) = 92
 Mass number (A) = 92 + 143 = 235
 Chemical symbol = U
 Summary for uranium-235: 235
92
U
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Chemistry: The Molecular Nature of Matter, 6E
6
Learning Check:
 Fill in the blanks:
symbol
neutrons
60Co
33
81Br
46
protons
27
electrons
27
35
35
29
29
65
29 Cu
36
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Chemistry: The Molecular Nature of Matter, 6E
7
Your Turn!
206
82
Pb has ___ protons, ___
An atom of
neutrons, and ___ electrons.
A. 82, 206, 124
B. 124, 206, 124
C. 124, 124, 124
D. 82, 124, 82
E. 82, 124, 124
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8
Carbon-12 Atomic Mass Scale
 Need uniform mass scale for atoms
Atomic mass units (symbol amu)
 Based on carbon:
 1 atom of carbon-12 = 12 amu (exactly)
 1 amu= 1/12 mass 1 atom of carbon-12 (exactly)
Why was 12C selected?
 Common
 Most abundant isotope of carbon
 All atomic masses of all other elements ~ whole
numbers
 Lightest element, H, has mass ~1 u
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Chemistry: The Molecular Nature of Matter, 6E
9
Calculating Atomic Mass
 Generally, elements are mixtures of isotopes
Ex. Hydrogen
Isotope
1H
2H
Mass
1.007825 amu
2.0140 amu
%Abundance
99.985
0.015
How do we define Atomic Mass?
 Average of masses of all stable isotopes of given
element
How do we calculate Average Atomic Mass?
 Weighted average.
 Use Isotopic Abundances & isotopic masses
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Chemistry: The Molecular Nature of Matter, 6E
10
Learning Check
 Calculate the average atomic mass of magnesium
which is a mixture of 3 isotopes:
78.99% of
24Mg
(atomic mass, 23.9850 amu),
10.00% of
25Mg
(atomic mass, 24.9858 amu),
11.01% of
26Mg
(atomic mass, 25.9826 amu).
0.7899 * 23.9850 amu = 18.946 amu 24Mg
0.1000 * 24.9858 amu = 2.4986 amu 25Mg
0.1101 * 25.9826 amu = 2.8607 amu 26Mg
Total mass of average atom =
24.3053 amu rounds up to 24.31 amu
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Chemistry: The Molecular Nature of Matter, 6E
11
Your Turn!
A naturally occurring element consists of two
isotopes. The data on the isotopes:
isotope #1
68.5257 amu
60.226%
isotope #2
70.9429 amu
39.774%
Calculate the average atomic mass of this element.
A.70.943 amu
0.60226 * 68.5257 u = 41.270 amu
B.69.487 amu
0.39774 * 70.9429 u = 28.217 amu
C.69.526 amu
D.69.981 amu
69.487 amu
E.69.734 amu
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Periodic Table
 Summarizes periodic properties of elements
Early Versions of Periodic Tables
 Arranged by increasing atomic mass
 Mendeleev (Russian) & Meyer (German) in 1869
 Noted repeating (periodic) properties
Modern Periodic Table
 Arranged by increasing atomic number (Z):
 Rows called periods
 Columns called groups or families
 Identified by numbers
 1 – 18 standard international
 1A – 8A longer columns & 1B – 8B shorter columns
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13
Modern Periodic Table
with group labels and chemical families identified
Actinides
Note: Placement of elements 58 – 71 and 90 – 103 saves space
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Representative/Main Group Elements
A groups—Longer columns
 Alkali Metals (1A = first group)
 Very reactive
 All Metals except for H
 Tend to form +1 ions
 React with oxygen
 Form compounds that dissolve in water
 Yield strongly caustic or alkaline solution (M2O)
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Representative/Main Group Elements
A groups—Longer columns
 Alkaline Earth Metals (2A = second group)
 Reactive
 Tend to form +2 ions
 Oxygen compounds are strongly alkaline (MO)
 Many are not water soluble
 Accumulate in ground
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16
Representative/Main Group Elements
A groups—Longer columns
 Halogens (7A)
 Reactive
 Form diatomic molecules in elemental state
 2 gases
 1 liquid
 2 solids
 Form –1 ions with alkali metals—salts
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Representative/Main Group Elements
A groups—Longer columns
 Noble Gases
 8A = last group on right
 Inert—very unreactive
 Only heavier elements of group react & then very
limited
 Don’t form charged ions
 Monatomic gases
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Transition Elements
B groups—shorter columns
 All are metals
 In center of table
 Begin in fourth row
 Tend to form ions with several different charges
Ex.
 Fe2+ and Fe3+
 Cu+ and Cu2+
 Mn2+, Mn3+, Mn4+, Mn5+, Mn6+, Mn7+
Note: Last 3 columns all have 8B designation
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Metals, Nonmetals, or Metalloids
 Elements break down into 3 broad categories
 Organized by regions of periodic table
Metals
 Left-hand side
 Sodium, lead, iron, gold
Nonmetals
 Upper right hand corner
 Oxygen, nitrogen, chlorine
Metalloids
 Diagonal line between metals & nonmetals
 Boron to astatine
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Chemistry: The Molecular Nature of Matter, 6E
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Metals, Nonmetals, or Metalloids
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Metals
 Most elements in periodic table
Properties
 Metallic luster
 Shine or reflect light
 Malleable
 Can be hammered or
rolled into thin sheets
 Ductile
 Can be drawn into wire
 Hardness
 Some hard – iron & chromium
 Some soft – sodium, lead, copper
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Properties of Metals
 Conduct heat & electricity
 Solids at Room Temperature
 Melting points (mp) > 25 °C
 Hg only liquid metal (mp = –39 °C)
 Tungsten (W)
(mp = 3400 °C)
 Highest known for metal
 Chemical reactivity
 Varies greatly
 Au, Pt
very unreactive
 Na, K
very reactive
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Chemistry: The Molecular Nature of Matter, 6E
23
Nonmetals
 17 elements
 Upper right hand corner of periodic table
 Exist mostly as compounds rather than as pure
elements
 Many are Gases
 Monatomic (Noble)
He, Ne, Ar, Kr, Xe, Rn
 Diatomic
H2, O2, N2, F2, Cl2
 Some are Solids: I2, Se8, S8, P4, C
 3 forms of Carbon (graphite, coal, diamond)
 One is liquid: Br2
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Properties of Nonmetals
 Brittle
 Pulverize when struck
 Insulators
 Non-conductors of
electricity and heat
 Chemical reactivity
 Some inert
 Noble gases
 Some reactive
 F2, O2, H2
 React with metals to form ionic compounds
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 8 Elements
Metalloids
 Located on diagonal line between metals &
nonmetals
 B, Si, Ge, As, Sb, Te, Po, At
Properties
 Between metals & nonmetals
 Metallic shine
 Brittle like nonmetal
 Semiconductors
 Conduct electricity
 But not as well as metals
 Silicon (Si) & germanium (Ge)
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Chemistry: The Molecular Nature of Matter, 6E
26
Your Turn!
Which of the following statements 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
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Chemistry: The Molecular Nature of Matter, 6E
27
Your Turn!
All of the following are characteristics of metals
except:
A.Malleable
B.Ductile
C.Lustrous
D.Good conductors of heat
E.Tend to gain electrons in chemical reactions
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Ions
Ions & Ionic Compounds
 Transfer of 1 or more electrons from 1 atom to
another
 Form electrically charged particles
Ionic compound
 Compound composed of ions
 Formed from metal & nonmetal
 Infinite array of alternating Na+ & Cl ions
Formula unit
 Smallest neutral unit of ionic compound
 Smallest whole-number ratio of ions
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29
Formation of Ionic Compounds
Metal + Non-metal  ionic compound
2Na(s) + Cl2(g)
 2NaCl(s)
Na + Cl
+
Na

+ Cl
NaCl(s)
e
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Cations
Ionic Compounds
 Positively charged ions
 Formed from metals
 Atoms lose electrons
Ex. Na has 11 e– & 11 p+
Na+ has 10 e– & 11 p+
Anions
 Negatively charged ions
 Formed from non-metals
 Atoms gain electrons
Ex. Cl has 17 e– & 17 p+
Brady/Jespersen/Hyslop
Cl– has 16 e– & 17 p+
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31
Experimental Evidence for Ions
Electrical conductivity requires charge movement
Ionic compounds:
 Do not conduct electricity in solid state
 Do conduct electricity in liquid & aqueous states
where ions are free to move
Molecular compounds:
 Do not conduct electricity in any state
 Molecules are comprised of uncharged particles
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Ions of Representative Elements
 Can use periodic table to predict ion charges
 When we use North American numbering of
groups: Cation positive charge = group #
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Rules For Writing Ionic Formulas
1. Cation given first in formula
2. Subscripts in formula must produce
electrically neutral formula unit
3. Subscripts must be smallest whole numbers
possible

Divide by 2 if all subscripts are even

May have to repeat several times
4. Charges on ions not included in finished
formula unit of substance

If no subscript, then 1 implied
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Determining Ionic Formulas
Ex. Formula of ionic compound formed when
magnesium reacts with oxygen
 Mg is group 2A
 Forms +2 ion or Mg2+
 O is group 6A
 Forms –2 ion or O2–
 To get electrically neutral particle need
 1:1 ratio of Mg2+ & O2–
 Formula: MgO
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Chemistry: The Molecular Nature of Matter, 6E
35
Determining Ionic Formulas
“Criss-cross” rule
 Make magnitude of charge on one ion into
subscript for other
 When doing this, make sure that subscripts are
reduced to lowest whole number.
Ex. What is the formula of ionic compound
formed between aluminum & oxygen ions?
Al3+ O2–
Al2O3
36
Brady/Jespersen/Hyslop
Chemistry: The Molecular Nature of Matter, 6E
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.P2O3
E.K2O2
Brady/Jespersen/Hyslop
Chemistry: The Molecular Nature of Matter, 6E
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.FeS3
D.Fe2S3
E.Fe4S6
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Chemistry: The Molecular Nature of Matter, 6E
Cations of Transition Metals
Transition metals
 Center (shorter) region of periodic table
 Much less reactive than group 1A & 2A
 Still transfer electrons to nonmetals to form ionic
compounds
 # of electrons transferred less clear
 Form more than 1 positive ion
 Can form more than 1
compound with same non-metal
Ex. Fe + Cl
FeCl2 & FeCl3
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39
Cations of Post-transition Metals
Post-transition metals
 9 metals Ga, In, Sn, Tl, Pb, Bi, Uut, Uuq, Uub
 After transition metals & before metalloids
 2 very important ones – tin (Sn) & lead (Pb)
 Both have 2 possible oxidation states
 Both form 2 compounds with same nonmetal
Ex. Ionic compounds of tin & oxygen are
 SnO & SnO2
 Bismuth
 Only has +3 charge
 Bi3+
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Chemistry: The Molecular Nature of Matter, 6E
40
Ions of Some Transition Metals &
Post-transition Metals
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Compounds with Polyatomic Ions
Binary compounds
 Compounds formed from 2 different elements
Polyatomic ions
 Ions composed of 2 or more atoms linked by
molecular bonds
 If ions are negative, they have too many electrons
 If ions are positive, they have too few electrons
 Formulas for ionic compounds containing
polyatomic ions
 Follow same rules as ionic compounds
 Polyatomic ions are expressed in parentheses
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Chemistry: The Molecular Nature of Matter, 6E
42
Table 3.4 Polyatomic Ions
(Alternate Name in
parentheses)
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Chemistry: The Molecular Nature of Matter, 6E
43
Learning Check
Ex. What is the formula of the ionic compound
formed between ammonium and phosphate
ions?
 Ammonium = NH4+
 Phosphate = PO43–
(NH4)+ (PO4)3–
(NH4)3PO4
Ex. Between strontium ion and nitrate ion?
 Strontium = Sr2+
 Nitrate = NO32–
Sr2+ (NO3)–
Brady/Jespersen/Hyslop
Sr(NO3)2
Chemistry: The Molecular Nature of Matter, 6E
44
Learning Check: Name The
Following
 K2O
potassium oxide
 NH4ClO3
ammonium chlorate
 Mg(C2H3O2)2
magnesium acetate
 Cr2O3
chromium(III) oxide
 ZnBr2
zinc bromide
Brady/Jespersen/Hyslop
Chemistry: The Molecular Nature of Matter, 6E
45
Learning Check: Determine The
Formula
 Calcium hydroxide
 Ca(OH)2
 Manganese(II) bromide
 MnBr2
 Ammonium phosphate
 (NH4)3PO4
 Mercury(I) nitride
 (Hg2)3N2
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Chemistry: The Molecular Nature of Matter, 6E
46
Your Turn!
Which is the correct name for Cu2S?
A.
B.
C.
D.
E.
copper sulfide
copper(II) sulfide
copper(II) sulfate
copper(I) sulfide
copper(I) sulfite
Brady/Jespersen/Hyslop
Chemistry: The Molecular Nature of Matter, 6E
Your Turn!
Which is the correct formula for ammonium sulfite?
a) NH4SO3
b) (NH4)2SO3
c) (NH4)2SO4
d) NH4S
e) (NH4)2S
Brady/Jespersen/Hyslop
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Naming Hydrates
 Ionic compounds
 Crystals contain water molecules
 Fixed proportions relative to ionic substance
 Naming
 Name ionic compound
 Give number of water molecules in formula using
Greek prefixes
monoditritetrapentaBrady/Jespersen/Hyslop
=
=
=
=
=
1
2
3
4
5
hexaheptaoctanonadeca-
Chemistry: The Molecular Nature of Matter, 6E
=
=
=
=
=
6
7
8
9
10
49
Learning Check: Naming Hydrates
 CaSO4 · 2H2O
 calcium sulfate dihydrate
 CoCl2 · 6H2O
 cobalt(II) chloride hexahydrate
 FeI3 · 3H2O
 iron(III) iodide trihydrate
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50
Your Turn!
What is the correct formula for copper(II) sulfate
pentahydrate?
A.CuSO4 · 6H2O
B.CuSO3 · 5H2O
C.CoSO4 · 4H2O
D.CoSO3 · 5H2O
E.CuSO4 · 5H2O
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Learning Check: Name Each
Format:
 Number prefix + 1st element name
 Number prefix + stem + –ide for 2nd element
 AsF3
 HBr
=
=
arsenic trifluoride
 N2O4
 N2O5
 CO
=
=
=
dinitrogen tetroxide
 CO2
=
carbon dioxide
Brady/Jespersen/Hyslop
hydrogen bromide
dinitrogen pentoxide
carbon monoxide
Chemistry: The Molecular Nature of Matter, 6E
52
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
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Chemistry: The Molecular Nature of Matter, 6E
Your Turn!
Which is the correct name for P4O10?
A. phosphorus oxide
B. phosphorous decoxide
C. tetraphosphorus decoxide
D. tetraphosphorus oxide
E. decoxygen tetraphosphide
Brady/Jespersen/Hyslop
Chemistry: The Molecular Nature of Matter, 6E