1
Chapter 2
Atoms, Molecules, and Ions
2
Atoms and Atomic Structure• Dalton’s Atomic Theory - 1808
1. -Elements are composed of small, nondivisible particles called atoms
2. -Atoms of an element have identical properties and differ from those of other elements
3. -Atoms cannot be created, destroyed, or transformed into other atoms
4. -Compounds are formed when atoms of different elements combine in whole-number ratios
5. -Atom ratios are constant in a given compound6. -Chemical reactions rearrange and recombine
atoms but do not destroy them
3
Structure of the Atom
1. -atom is mostly empty space2. -consists of a very small, dense center called
the nucleus3. -nearly all of the atom’s mass is in the
nucleus4. -the nuclear diameter is 1/10,000 to
1/100,000 times less than the atom’s radius
4
Particle Mass (amu) Charge
Electron (e-) 0.00054858 -1
Proton (p,p+) 1.0073 +1
Neutron(n,n0) 1.0087 0
Structure of the Atom
• -Sir John Joseph Thompson and Ernest Rutherford established a model of the atom still in use today
• -Three fundamental particles make-up atoms:
5
6
Elements• substances that cannot be
decomposed into simpler substances via chemical reactions
• Elemental symbols-abbreviation representing each element on periodic table– -First letter capital, second letter lower
case– ie: C, Ca, Co
– CO is not an element (it’s a compound) because there are two capital letters
7
The Periodic Table
• 1869 - Mendeleev & Meyer– Discovered the periodic law
• -Organized based on related chemical reactivities, physical properties, other behaviors and trends
• -The properties of the elements are periodic functions of their atomic numbers (not atomic masses)
Law of Chemical Periodicity
8
The Periodic Table
• Groups or families– Vertical group of elements on periodic table– Similar chemical and physical properties
•Period
–Horizontal group of elements on periodic table
–Transitions from metals to nonmetals •Three regions
–Metals, nonmetals and metalloids
9
•Period– Horizontal group of elements on
the periodic table•-Transition from metals to nonmetals
10
•Groups (families)– Vertical group of elements on the
periodic table•-similar chemical and physical
properties
11
•Metalloids• separate metals from nonmetals
• Metals are to the left of stair step– -Approximately 80% of the
elements
• Nonmetals are to the right of stair step– -Approximately 20% of the
elements
• Elements box on the stair step have properties between metals and nonmetals
12
The Periodic Table
• Chemical properties of metals
1. -Outer (valence) shells contain few electrons2. -Form cations by losing electrons3. -Form ionic compounds with nonmetals4. -Solid state characterized by metallic
bonding-Conductors of electricity and heat-Malleable: can be hammered-Ductile: drawn into wire-Typically solids (except mercury)
13
The Periodic Table
• Chemical properties of nonmetals
1. -Outer shells contain four or more electrons2. -Form anions by gaining electrons (- charge)3. -Form ionic compounds with metals and
covalent compounds with other nonmetals4. -Form covalently bound molecules; noble
gases are monatomic and have full electron shells
5. -Insulators meaning poor conductors6. -Typically gasses or solids (Br2 liquid I2 solid)
14
The Periodic Table:
• Periodic trends
PeriodicChart
More MetallicMoreMetallic
Periodic Table
Atomic number increase
Size decreases
Atomic number increase
Size increases
Form compounds with similar formulas
15
Metals • Group IA metals:
– Alkali metals- Li, Na, K, Rb, Cs, Fr– -solids, reactive, and never found in nature as free
elements– -chemical formula from top-to-bottom are the same
• Group IIA metals:– Alkaline earth metals- Be, Mg, Ca, Sr, Ba, Ra– -solids, reactive, and mostly found in nature as
compounds– -chemical formula from top-to-bottom are the same
16
Group IIIA: B, Al, Ga, In, Tl• -Aluminum (Al) most abundant metal in the earth’s
crust• -Boron (B) is the only nonmetal• -forms compounds of analogous chemical formulas
Group IVA: C, Si, Ge, Sn, Pb -most variation in their properties -Carbon (C) is the “element of life”
CO2 carbonate-limestone, coral, shellsfossil fuels-coal, petroleum, natural gas
-Silicon (Si) is found as gemstones, glass, and sand -Lead (Pb) was used as water pipes, paint, and in
gasoline -form compounds of analogous chemical formulas
Metals
17
Allotropes
• elements (nonmetals) that exist in several different and distinct forms each having its own properties
18
Group VA: N, P, As, Sb, Bi
• Nitrogen (N) • -makes up ~75% of the earth’s atmosphere • -used to make fertilizer (NH3)• -found in biological systems in proteins and
DNA
• Phosphorous (P)• -has several allotropes most common are
white and red phosphorus • -white ignites spontaneously in air and used
to make phosphoric acid• -red phosphorus is used in striking strips of
matchbooks• -form similar types of chemical compounds
19
•Group VIA: nonmetals– Chalcogens– O, S, Se, Te
-Oxygen (O) is the power source of life on earth by combining with other substances, and has allotropes-Sulfur (S) (and even Selenium, Se) is fowl smelling, and S appears as allotropes-these elements are considered poisonous, but essential for human diets-Some variations is chemistries, but form analogous formulas
20
•Group VIIA nonmetals– halogens– F, Cl, Br, I
-All exist in the form of diatomic molecules-At room temperature, Fluorine (F) and Chlorine (Cl) are gases where Bromine (Br) is a liquid and Iodine (I) is a solid-Some of the most reactive of all elements they react with metals and nonmetals to form compounds
21
•Group VIIIA nonmetals– noble, inert or rare gases– He, Ne, Ar, Kr, Xe, Rn
-least reactive elements and for a long time considered unreactive-all are gases and none are abundant on earth-He is the second most abundant element in the universe
22
Transition Metals• Most are found as compounds in
nature – -Ag, Au, Pt are less reactive and can be
found as pure substances– -These elements are commercially
useful as building materials, in paints, catalytic converters, coins, batteries, and fireworks
– -Play important roles in biological processes
– -Bottom two rows of the periodic table are used in television picture tubes, atomic fuel, smoke detectors
23
24
Atomic Number (Z)
the number of protons in the nucleus•-numbered consecutively on the periodic
table
• atomic number determines the element:•-elements differ from one another by the
number of protons in the nucleus •-the number of electrons in a neutral atom
(no charge) is equal to the atomic number•-negatively charged species have more
electrons•-positively charged species have less
electrons
25
Mass Number (A)
• sum of the number of protons and neutrons– Z = atomic number (number of protons) – N = number of neutrons– A = Z + N
• One common symbolism used to show mass and proton numbers is: AuCa, C, example for E 197
794820
126
AZ
?Cu, N, 188
63?
14?
26
Mass Number (A)•How many protons and neutrons are in
the following?
U
U
O
O
23692
23892
188
168
23216
8235
24020
2311
S
Br
Ca
Na
27
Mass Number (A)
Give the number of protons, neutrons and electrons and the correct element symbol:
?
?
?
157
20079
2412
28
Isotopes• Atoms of the same element but with different
numbers of neutrons (or same atomic number, but different mass numbers)
Isotopes have different masses and mass number(A) values but are the same element
• Example: hydrogen isotopes or protium is the most common hydrogen isotope
• -one proton and no neutrons or deuterium (D) is the second most abundant hydrogen isotope
• -one proton and one neutron or tritium (T) is a radioactive hydrogen isotope
• -one proton and two neutrons
H
H
H
31
21
11
29
Atomic Weights
• How do we know what the values of these atomic weights are?
30
Atomic Weight
• the weighted average of the masses of the elements stable isotopes
• Example: Naturally occurring Cu consists of 2 isotopes. It is 69.1% 63Cu with a mass of 62.9 amu, and 30.9% 65Cu, which has a mass of 64.9 amu. Calculate the atomic weight of Cu to one decimal place.
31
Atomic Mass• weighted average of the masses of
an elements stable isotopes as listed on the periodic table– For example: hydrogen (H) = 1.008
amu– calcium (Ca) = 40.078
amu
32
Moleculessmallest unit of a pure substance that can be
divided and still retain the composition and chemical properties of the substance
Examples of molecules:– H2
– O2
– S8
– H2O
– CH4
– C2H6O
Molecular formulas: describe the composition of substances, but provide no structural information
33
Classes of Substances:
monatomic elementsHe, Au, Na
diatomic elements (binary molecules)O2, H2, Cl2, F2, I2, N2,Br2
complex elementsO3, S4, P8
Compounds (molecules)H2O, C12H22O11
34
Molecular (Chemical) Formulas
Compound Contains HCl H2O
NH3
C3H8
35
Chemical bondsAttractive forces that hold atoms together in
compounds Chemical bond types:
1. Ionic bonding: resulting from electrostatic attractions between ions -formed by the transfer of one or more electrons from one atom to
another -attraction of cations for anions typically form solids -most often formed by interactions between metals and
nonmetals
2. Covalent bonding: results from sharing one or more electron pairs between two atoms - typically formed by interactions between nonmetals and
nonmetals
36
Ionic CompoundsAn ion is an atom or a group of atoms
possessing a net electrical charge
positive (+) ions or cationsThese atoms have lost 1 or more electronsMetals lose electrons to form cations (monoatomic
cations)Consider Group IA and IIA metals
negative (-) ions or anionsThese atoms have gained 1 or more electrons.Nonmetals gain electrons to form anions
(monoatomic anions)Consider the nonmetals-groups IVA through VIIA
37
Ionic Compounds
• Coulomb’s Law: dictates the strength of ionic bonds – it is an inverse square law
ions ofcenter between distance d
ionson charge of magnitude q
ionsbetween attraction of force F
where
d
qqkF
2
=
38
Ionic CompoundsCations:
Na+, Ca2+, Al3+ (monoatomic cations)NH4
+ (polyatomic cation)
Anions:F-, O2-, N3- (monoatomic anions)SO4
2-, PO43-, HCO3
- (polyatomic anions)
Transition metals forming cationsNo pattern exists for determining the chargeMany metals form several different ions (charge
states)
H and noble gases are special cases
39
Ionic Formulas
Formulas of ionic compounds are determined by the charges of the ions
-total charge of the cations must equal the total charge of the anions
-The compound must be neutral
NaCl sodium chloride (Na1+ & Cl1-)KOH potassium hydroxide (K1+ & OH1-)CaSO4 calcium sulfate (Ca2+ & SO4
2-)
Al(OH)3 aluminum hydroxide (Al3+ & OH1-)
40
Writing binary chemical formulasCharge becomes subscript. Then give the
subscript as lowest common denominator
??
??
??
23
2
2332
2222
33
22
1
OFe
ICu
ClK
NBaNBa
MgOOMgOMg
AlBrBrAl
CaFFCa
LiClClLi
41
Naming Ionic Compoundsmetal cation and a nonmetal anion
1. Name the cation2. Name the anion, nonmetal stem with –
ide ending
LiBr lithium bromide magnesium chloride
Li2S lithium sulfide
Al2O3 You do it!You do it!
42
Naming Ionic CompoundsLiBr lithium bromideMgCl2 magnesium chloride
Li2S lithium sulfide
Al2O3 aluminum oxide
Na3P
Mg3N2
Notice that binary ionic compounds with metals having one oxidation state
They do not use prefixes or Roman numerals!!!
43
Naming CationsMonoatomic cations
use the name of the metal plus the word “cation”
Examples: Al3+, Li+, Ca2+
Transition metals that have multiple charges:Two methods are used1. Older method: -add suffix “ic” to element’s Latin name for higher
oxidation state (higher positive charge) -add suffix “ous” to element’s Latin name for lower
oxidation state (lower positive charge)2. Modern method: use Roman numerals in parentheses to indicate
metal’s oxidation state
44
Naming Ionic Compounds
ionic compounds containing metals with more than one oxidation state (charge)
memorize them on your handout
Metals exhibiting multiple oxidation states are:1. most of the transition metals2. metals in groups IIIA (except Al), IVA, &
VA on the periodic table
45
Compound Old System Modern System
FeBr2 ferrous bromide iron(II) bromideferric bromide iron(III) bromide
SnO tin(II) oxideSnO2 tin(IV) oxide
CoCl2 cobaltous chloride
CoCl3 cobaltic chlorideplumbous sulfide lead(II) sulfideplumbic sulfide lead(IV) sulfide
Naming Ionic Compounds
46
Naming Ionic CompoundsThere are polyatomic ions that form binary
ionic compounds
1. OH- hydroxide2. CN- cyanide3. NH4
+ ammonium
KOH potassium hydroxidebarium hydroxide
Al(OH)3 aluminum hydroxide
Fe(OH)2 You do it!You do it!
47
Naming Ionic Compounds
KOH potassium hydroxideBa(OH)2 barium hydroxide
Al(OH)3 aluminum hydroxide
Fe(OH)2 iron (II) hydroxide
iron (III) hydroxide
Ba(CN)2
ammonium sulfideNH4CN
48
Naming AnionsMonoatomic anions
use the name of the nonmetal plus the word “-ide” at the end
Examples: F-, Cl-, S2-
Polyatomic anionsSome guidelines for oxoanions (contain Oxygen)
• If only 2 similar formula type anions exist, the one containing the greater number of oxygen atoms have an “–ate” ending, and the smaller number of oxygen atoms have an “-ite” ending
NO3- NO2
-
SO42- SO3
2-
• If more than two exist, the one with the largest number of oxygen atoms have a prefix “per-” and an “-ate” ending, and the smallest number of oxygen atoms have a prefix “hypo-” and an “-ite” ending ClO4
- ClO3-
ClO2- ClO-
• Oxoanions containing H are named with the word hydrogen in front, if more than one H is contained in the oxoanion, then prefixes are used to indicate the number of hydrogen atoms HPO4
2- H2PO4-
49
Naming Ionic CompoundsOn Your Own
NaNO2 sodium nitritesodium nitrate
Na2SO3
sodium sulfateNa3PO4
MgSO4
Ca(NO3)2
BaCO3
potassium phosphate
50
Ionic Formulas
What is the name of K2SO3?Potassium sulfite
What is charge on sulfite ion?-2
What is the formula of ammonium sulfide?(NH4)2S
What is charge on ammonium ion?+1
What is the formula of aluminum sulfate?Al2(SO4)3
What is charge on both ions?+3 -2
51
Name or Write the formula: Formula Name1.Cu(OH)2 2.CuOH3.MgCl24.Li2O
5.Zn3N2
6. calcium bromide7. sodium hydroxide8. aluminum phosphide9. barium iodide10. magnesium cyanide
52
Name or Write the formula:
Formula Name1. iron(II) bromide2. iron(III) hydroxide3. copper(II) oxide4. lead(IV) cyanide
53
Commonly Found Ionic Compounds
54
Covalent Compounds
Covalent Bonds: Sharing of one or more electron pairs between atoms
Representation of the formation of a H2 molecule from 2 H atoms
55
Naming Molecular (Covalent) Compounds
molecular formulas for these compounds are generally written with increasing group number
– Use the first nonmetal’s name with the appropriate prefix di-, tri-, tetra-, etc (excluding mono-)
– Followed by the next nonmetal: use this nonmetal’s stem with “-ide” ending and the appropriate prefix mono-, di-, tri-, etc
Exception: hydrogen – write the word hydrogen– then the following nonmetal: use the nonmetal stem
with the “-ide” ending
56
Naming Nonmetals
Element StemBoron (B) borCarbon (C) carbSilicon (Si) silicNitrogen (N) nitrFluorine (F) fluorChlorine (Cl) chlor
57
Naming Nonmetals
Element StemBromine (Br) bromIodine (I) iodOxygen (O) oxSulfur (S) sulfSelenium (Se) selenPhosphorus (P) phosphHydrogen (H) hydr
58
Naming Molecular Compounds
59
Naming Covalent Compounds
Formula NameHF hydrogen fluoride(hydrofluoric acid)HCl hydrogen chloride (hydrochloric acid)HBr hydrogen bromide (hydrobromic acid)H2S You do it!You do it!
60
Names and Formulas
• What is the formula of nitric acid?
• What is the formula of sulfur trioxide?
61
Naming Covalent Compounds
Formula NameCO _________________ carbon dioxideSO3
oxygen difluorideP4O6
tetraphosphorus decoxide
62
Naming Covalent Compounds
Formula Modern NameN2O dinitrogen monoxide
NO nitrogen monoxideN2O3
NO2
dinitrogen tetroxide
dinitrogen pentoxide
63
64
Describing Compound Formulas
% composition = mass of an individual element in a compound divided by the total mass of the compound x 100
% comp = x 100
component mass
total mass
65
Percent Composition
What is the percent composition of H in C3H8?
66
Percent Composition
What is the percent composition of H in H2O?
Ans: 11.21%
67
Percent Composition
Calculate the percent composition of each component in Fe2(SO4)3 to 3 sig. fig.
On your own
27.9% Fe24.1% S48.0% OTotal = 100%
68
Empirical and Molecular Formulas
Empirical Formula: smallest whole-number ratio of atoms present in a
compound
Molecular Formula: actual numbers of atoms of each element present in a
molecule of the compound
We determine the empirical and molecular formulas of a compound from the percent composition
69
Empirical And Molecular Formulas
70
Empirical FormulasA compound contains 24.74% K, 34.76%
Mn, and 40.50% O by mass. What is its empirical formula?
Make the simplifying assumption that we have 100.0 g of compound
In 100.0 g of compound there are:24.74 g of K34.76 g of Mn40.50 g of O
71
Empirical Formulas
A sample of a compound contains 6.541g of Co and 2.368g of O. What is empirical formula for this compound?
You do it!You do it!
72
Molecular Formulas
A compound is found to contain 85.63% C and 14.37% H by mass. In another experiment its molar mass is found to be 56.1 g/mol. What is its molecular formula?
73
More Practice
What mass of ammonium phosphate, (NH4)3PO4, would contain 15.0 g of N?MW = 149.08626
g/mol
74
The Mole• an amount of a substance that
contains as many elemental entities as there are atoms in exactly 12.000g of carbon-12 isotope
– -This number is an amount of atoms, ions, or molecules that is large enough to see and easier to handle
– -A mole (mol) = some number of things• Just like a dozen = 12 things• One mole = 6.022 x 1023 things
– -Avogadro’s number (NA) = 6.022 x 1023
75
The Mole
• Molar mass: mass in grams that is equal to the atomic weight of the element (in grams)
• H has an atomic weight of 1.00794 g 1.00794 g of H atoms = 6.022 x 1023 H atoms (= 1
mol)
• Mg has an atomic weight of 24.3050 g 24.3050 g of Mg atoms = 6.022 x 1023 Mg atoms (= 1
mol)
76
The Mole
77
The Mole
78
The Mole
• Calculate the mass of a single Mg atom, in grams, to 3 significant figures.
79
The Mole
• Calculate the number of atoms in one-millionth of a gram of Mg to 3 significant figures.
80
The Mole
• How many atoms are contained in 1.67 moles of Mg?
81
The Mole
• How many moles of Mg atoms are present in 73.4 g of Mg?
YOU MUST KNOWHOW TO DO THESE PROBLEMS
82
Molecular WeightsAdd atomic weights of each atom
in the molecule
molar mass (molecular weight) of propane (C3H8):
amu 44.11 mass Molar
amu 8.08 amu 1.01 8H 8
amu 36.03amu 12.01 3C 3
83
Molecular Weights
molar mass of calcium nitrate, Ca(NO3)2:
84
Formula Weights, Molecular Weights, and Moles
One Mole of: ContainsCl2 = 70.90g 6.022 x 1023 Cl2 molecules
2(6.022 x 1023 ) Cl atoms= 1.204 x 1024 Cl atoms
C3H8 = 44.11 g 6.022 x 1023 C3H8 molecules
3 (6.022 x 1023 ) C atoms 8 (6.022 x 1023 ) H atoms
85
Formula Weights, Molecular Weights, and Moles
Calculate the number of C3H8 molecules in 74.6 g of propane:
86
Formula Weights, Molecular Weights, and Moles
Calculate the number of O atoms in 26.5 g of Li2CO3: