1. Chapter 2 Atoms, Molecules, and Ions
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2. Contents and Concepts Atomic Theory and Atomic Structure
The key concept in chemistry is that all matter is composed of very small particles called atoms. We will look at atomic theory, discuss atomic structure, and finally describe the periodic table, which organizes the elements.
Atomic Theory of Matter
The Structure of the Atom
Nuclear Structure; Isotopes
Atomic Masses
Periodic Table of the Elements
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3. Chemical Substances: Formulas and Names
We explore how atoms combine in various ways to
yield the millions of known substances.
6. Chemical Formulas; Molecules and Ionic Substances
7. Organic Compounds
8. Naming Simple compounds
Chemical Reactions: Equations
9. Writing Chemical Equations
10. Balancing Chemical Equations
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4. Learning Objectives Atomic Theory and Atomic Structure
1. Atomic Theory of Matter
List the postulates of the atomic theory.
Define element, compound, and chemical reaction in the context of these postulates.
Recognize the atomic symbols of the elements.
Explain the significance of the law of multiple proportions.
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5. 2. The Structure of the Atom
Describe Thomson’s experiment in which he discovered the electron.
Describe Rutherford’s experiment that led to the nuclear model of the atom.
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6. 3. Nuclear Structure; Isotopes
Name and describe the nuclear particles making up the nucleus of the atom.
Define atomic number, mass number, and nuclide.
Write the nuclide symbol for a given nucleus.
Define and provide examples of isotopes of an element.
Write the nuclide symbol of an element.
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7. Define atomic mass unit and atomic mass.
4. Atomic Masses
Define atomic mass unit and atomic mass.
Describe how a mass spectrometer can be used to determine the fractional abundance of the isotopes of an element.
Determine the atomic mass of an element from the isotopic masses and fractional abundance.
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8. 5. Periodic Table of the Elements
Identify periods and groups on the periodic table.
Find the main-group and transition elements on the periodic table.
c. Locate the alkali metal and halogen groups on the periodic table.
d. Recognize the portions of the periodic table that contain the metals, nonmetals, and metalloids (semimetals).
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9. Chemical Substances: Formulas and Names
6. Chemical Formulas; Molecular and Ionic Substances
Determine when the chemical formula of a compound represents a molecule.
Determine whether a chemical formula is also a molecular formula.
Define ion, cation, and anion.
d. Classify a compound as ionic or molecular.
e. Define and provide examples for the term formula unit.
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10. f. Specify the charge on all substances, whether ionic and molecular.
g. Write an ionic formula, given the ions.
7. Organic Compounds
List the attributes of molecular substances that make them organic compounds.
Explain what makes a molecule a hydrocarbon.
Recognize some functional groups of organic molecules.
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11. 8. Naming Simple Compounds Recognize ionic compounds.
Learn the rules for predicting the charges of monatomic ions in ionic compounds.
Apply the rules for naming monatomic ions.
Learn the names and charges of common polyatomic ions.
Name an ionic compound from its formula.
Write the formula of binary compound from its name.
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12. g. Determine the order of elements in a binary (molecular) compound.
h. Learn the rules for naming binary molecular compounds.
Name a binary compound from its formula.
Write the formula of a binary compound from its name.
Name a binary molecular compound from its molecular model.
Recognize molecular compounds that are acids.
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13. m. Determine whether an acid is an oxoacid.
n. Learn the approach for naming binary acids and oxoacids.
o. Write the name and formula of an anion from the acid.
p. Recognize compounds that are hydrates.
q. Learn the rules for naming hydrates.
Name a hydrate from its formula.
Write the formula of a hydrate from its name.
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14. Chemical Reactions: Equations 9. Writing Chemical Equations
Identify reactants and products in a chemical equation.
Write chemical equations using appropriate phase labels, symbols of reaction conditions, and the presence of a catalyst.
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15. 10. Balancing Chemical Equations
Determine if a chemical reaction is balanced.
Master the technique for balancing chemical equations.
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16. Postulates of Dalton’s Atomic Theory
All matter is composed of indivisible atoms. An atom is an extremely small particle of matter that retains its identity during chemical reactions.
An element is a type of matter composed of only one kind of atom.
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17. A compound is a type of matter composed of atoms of two or more elements chemically combined in fixed proportions.
A chemical reaction involves the rearrangement of the atoms present in the reacting substances to give new chemical combinations present in the substances formed by the reaction.
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18. The first letter must be UPPERCASE.
Atomic Symbol
A one- or two-letter notation used to represent an atom corresponding to a particular element.
The first letter must be UPPERCASE.
The second letter, when present, must be lowercase.
Symbols come from the element name; several names come from Latin.
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19. Law of Multiple Proportions
When two elements form more than one compound, the masses of one element in these compounds for a fixed mass of the other element are in small, whole-number ratios.
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20. The ratio of oxygen in CO2 to CO:
As an example, compare the mass of oxygen in the two oxygen compounds of carbon:
Carbon monoxide 12 g C 16 g O
Carbon dioxide 12 g C 32 g O
The ratio of oxygen in CO2 to CO:
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21. Like Dalton, today’s chemists model atoms using spheres
Like Dalton, today’s chemists model atoms using spheres. Modern models are often drawn using computer programs and use different colors to represent atoms of different elements. Which of these models depicts CO2?
A B C D E
E is CO2
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22. The atom is composed of two parts:
Structure of the Atom
The atom is composed of two parts:
Nucleus
Central core
Positively charged
Contains most of the atom’s mass
Electrons
Very light
Negatively charged
Exist in the region around the nucleus
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23. Discovery of the Electron
J. J. Thomson used an apparatus similar to the one shown on the next slide, a cathode ray tube.
He discovered that the particles that make up the cathode ray are negative and are part of all matter. This finding is illustrated on the following slides.
As a result, Thomson concluded that atoms are not indivisible, as Dalton had postulated.
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24. Cathode Ray Tube
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25. Cathode rays are attracted to the positive end of the magnet and repelled by the negative end.
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26. Thomson’s experiments allowed him to calculate the ratio of the electron’s mass to its charge.
Robert Millikan calculated the charge on the electron. He determined the charge on various drops of oil and found the smallest increment in charge—that is, the charge on the electron. This is illustrated on the next slide.
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28. Nuclear Model of the Atom
Experiments done in Ernest Rutherford’s laboratory used positively charged alpha particles to bombard very thin gold (and other metals) foil.
Most alpha particles passed through the foil, but a few were scattered at large angles, sometimes almost straight backward.
Based on these findings, Rutherford proposed that 99.95% of the atom’s mass is in the positively charged nucleus.
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31. The number of protons in an atom is called the atomic number, Z.
A nuclear particle having a positive charge equal to that of the electron and a mass more than 1800 times that of the electron.
The number of protons in an atom is called the atomic number, Z.
An element is a substance whose atoms have the same number of protons and thus the same atomic number, Z.
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32. Neutron
A nuclear particle having a mass almost equal to that of the proton but no electrical charge
The mass number, A, is the total number of protons and neutrons in the nucleus.
Isotopes are atoms whose nuclei have the same atomic number (number of protons) but different numbers of neutrons (mass number).
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33. Nuclide
An atom characterized by a certain atomic number, Z, and mass number, A.
Nuclide symbol
Examples:
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34. The element is potassium, K.
Write the nuclide symbol for the atom that has 19 protons and 20 neutrons.
Atomic number: Z = 19
The element is potassium, K.
Mass number: A = = 39
The nuclide symbol is
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35. Equal to exactly one-twelfth the mass of a carbon-12 atom
Atomic Mass
The average atomic mass for the naturally occurring element expressed in atomic mass units (amu).
Atomic Mass Unit
Equal to exactly one-twelfth the mass of a carbon-12 atom
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36. Percentage Abundance Mass (amu)
An element has four naturally occurring isotopes. The mass and percentage of each isotope are as follows:
Percentage Abundance
Mass (amu)
1.48
23.6
22.6
52.3
What is the atomic weight and name of the element?
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37. Fractional Abundance Mass (amu) Mass From Isotope
To find the portion of the atomic weight due to each isotope, multiply the fraction by the mass of the isotope. The atomic weight is the sum of these products.
Fractional Abundance
Mass (amu)
Mass From Isotope
0.0148
0.236
0.226
0.523
The atomic weight is 207 amu; the element is lead.
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38. Periodic Table of the Elements
A tabular arrangement of elements in rows and columns, highlighting the regular repetition of properties of the elements.
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39. A period consists of the elements in one horizontal row.
A group consists of the elements in one vertical column.
Groups are numbered using two systems:
IUPAC Numbers 1 through 18
Older system Roman numerals I–VIII and the letters A and B
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40. An element that does not exhibit the characteristics of a metal
A substance or mixture that has a characteristic luster or shine and is generally a good conductor of heat and electricity.
Nonmetal
An element that does not exhibit the characteristics of a metal
Metalloid
An element having characteristics of both metals and nonmetals
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41. Chemical Formula
A notation that uses atomic symbols with numerical subscripts to convey the relative proportions of atoms of the different elements in the substance.
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42. Molecule
A definite group of atoms that are chemically bonded together (tightly connected by attractive forces).
Molecular Formula
A formula giving the exact number of different atoms of an element in a molecule.
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43. The small molecules that are linked together to form a polymer.
A very large molecule that is made up of a number of smaller molecules repeatedly linked together.
Monomers
The small molecules that are linked together to form a polymer.
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44. An ion is an electrically charged particle obtained from an atom or chemically bonded group of atoms by adding or removing one or more electrons.
A cation is a positively charged ion formed by losing one or more electrons. A cation is named by its element name followed by the word ion. For example, Na+ is the sodium ion, etc. Under the definition of anion add the following: An anion is named by changing the last part of the element name to –ide followed by the word ion. For example, F- is the fluoride ion, O2- is the oxide ion, N3- is the nitride ion, etc.
An anion is a negatively charged ion formed by gaining one or more electrons.
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45. An ionic compound is composed of cations and anions.
Ions are arranged in a repeating three-dimensional pattern, forming a crystal.
The formula of an ionic compound gives the smallest possible integer number of ions in the substance (without writing charges) so that the combination is electrically neutral.
The formula gives the formula unit of the compounds. A formula unit is not a molecule!
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46. What is formula of the ionic compound of Mg2+ and N3-?
The common multiple of the charges is 6, so we need three Mg2+ and two N3-. The resulting formula is
Mg3N2
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47. What is the formula of the ionic compound of Ca2+ and PO43-?
The common multiple of the charges is 6, so we need three Ca2+ and two PO43-. The resulting formula is
Ca3(PO4)2
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48. Hydrocarbons contain only carbon and hydrogen.
Organic Compounds
An important class of molecular substances; they contain carbon combined with other elements – notably hydrogen, oxygen, and nitrogen.
Hydrocarbons contain only carbon and hydrogen.
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49. Examples Name of Group Functional Group
A functional group is a reactive portion of a molecule that undergoes predictable reactions.
Examples
Name of Group
Functional Group
Methyl alcohol
Alcohol
Dimethyl ether
Ether
Acetic acid
Carboxylic acid
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50. Chemical nomenclature is the systematic naming of chemical compounds.
Compounds that are not organic are called inorganic compounds.
Carbon monoxide, carbon dioxide, carbonates, and cyanides are also classified as inorganic compounds.
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51. Naming Inorganic Compounds
The cation is always named first with the name of the cation without the word ion.
The anion is named second with the name of the anion without the word ion.
Examples:
Cation Anion Name
Na+ Br- Sodium bromide
Mg2- O2- Magnesium oxide
Al3+ Cl- Aluminum chloride
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52. Ions formed from a single atom.
Monatomic ions
Ions formed from a single atom.
Common monatomic ions are listed on the next slide by group and by period.
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53. Common Monatomic Ions of the Main-Group Elements6 5 4 3 2 1
VIIA
VIA VA
IVA
IIIA
IIA IA
Period H-
Li+
Be2+
N3-
O2- F-
Na+
Mg2+
Al3+
S2-
Cl- K+
Ca2+
Ga3+
Se2-
Br-
Rb+
Sr2+
In3+
Sn2+
Te2- I-
Cs+
Ba2+
Tl3+, Tl+
Pb2+
Bi3+
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54. Rules for Predicting the Charge on a Monatomic Ion
1. Most main-group metals have one monatomic ions with a charge equal to the group number.
Al, in Group IIIA(3), has one ion, Al3+.
Sr, in Group IIA(2), has one ion, Sr2+.
K, in Group IA(1), has one ion, K+.
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55. Pb in Group IVA(14) has two ions: Pb2+ and Pb4+
2. Some main-group metals with high atomic number have more than one cation. One cation will have the charge of the group number minus 2; the second cation will have a charge equal to the group number
Pb in Group IVA(14) has two ions:
Pb2+ and Pb4+
Tl in Group IIIA(13) has two ions:
Tl+ and Tl3+
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56. Zn and Cd form only the +2 ion. Ag forms only the +1 ion.
3. Most transition metals form more than one cation, of which one is +2.
Zn and Cd form only the +2 ion.
Ag forms only the +1 ion.
4. Nonmetal main-group elements form one monatomic anion with a charge equal to the group number minus 8.
F in Group VIIA(17) forms the F- ion.
S in Group VIA(16) forms the S2- ion.
N in Group VA(15) forms the N3- ion.
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57. Naming Monatomic Ions
Monatomic cations are named after the element if the element forms only one cation.
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58. If more than one cation forms:
In the Stock system, the charge is written using a Roman numeral and is enclosed in parentheses.
Cu2+ is copper(II).
Cu+ is copper(I).
In an older system, the suffix –ic (for the higher-charged cation) or –ous for the lower-charged cation) is added to the element’s stem.
Cu2+ is cupric.
Cu+ is cuprous.
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59. Fe3+ is iron(III) or ferric ion. Fe2+ is iron(II) or ferrous ion.
Hg2+ is mercury(II) or mercuric ion.
The second ion mercury forms is diatomic:
Hg22+ is mercury(I) or mercurous ion.
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60. Cr3+ is chromium(III) or chromic ion.
Cr2+ is chromium(II) or chromous ion.
Mn2+ is manganese(II) or manganous ion.
Co2+ is cobalt(II) or cobaltous ion.
Zinc forms only Zn2+, so it is called zinc ion.
Cadmium forms only Cd2+, so it is called cadmium ion.
Silver forms only Ag+, so it is called silver ion.
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61. Table 2.5 lists common polyatomic ions.
An ion consisting of two or more atoms chemically bonded together and carrying an electrical charge.
Table 2.5 lists common polyatomic ions.
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62. mercury(I) or mercurous Hg22+ ammonium NH4+
Cations
mercury(I) or mercurous Hg22+
ammonium NH4+
Anions
peroxide O2-
hydroxide OH-
cyanide CN-
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63. monohydrogen phosphate HPO42- dihydrogen phosphate H2PO4-
phosphate PO43-
monohydrogen phosphate HPO42-
dihydrogen phosphate H2PO4-
carbonate CO32-
hydrogen carbonate (bicarbonate) HCO3-
sulfate SO42-
hydrogen sulfate (bisulfate) HSO4-
sulfite SO32-
hydrogen sulfite (bisulfite) HSO3-
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64. acetate C2H3O2- oxalate C2O42- chromate CrO42- dichromate Cr2O72-
permanganate MnO4-
nitrate NO3-
nitrite NO2-
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65. hypochlorite ClO- chlorite ClO2- chlorate ClO3- perchlorate ClO4-
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66. What are the names of the following ionic compounds? BaO Cr2(SO4)3
BaO is barium oxide.
Cr2(SO4)3 is chromium(III) sulfate or chromic sulfate.
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67. What are the chemical formulas for the following ionic compounds?
potassium carbonate
manganese(II) sulfate
The ions K+ and CO32- form K2CO3
The ions Mn2+ and SO42- form MnSO4
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68. Binary Molecular Compounds A compound composed of only two elements.
Binary compound of a metal and a nonmetal are generally named using ionic rules.
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69. Naming Binary Molecular Compounds
We usually name the elements in the order given in the formula.
Name the first element using the element name.
Name the second element using the element root + -ide suffix.
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70. N2O4 dinitrogen tetroxide (“a” is dropped)
Add a prefix to each name to indicate the number of atoms of that element. The prefix mono- is used only when needed to distinguish two compounds of the same two elements.
The final vowel of the prefix is often dropped when followed by an element name that begins with a vowel. Oxygen is the most common example.
N2O4 dinitrogen tetroxide (“a” is dropped)
NO nitrogen monoxide (only one “o”)
(also called nitric oxide)
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71. Prefixes (Greek) One (1) mono- Two (2) di- Three (3) tri-
Four (4) tetra-
Five (5) penta-
Six (6) hexa-
Seven (7) hepta-
Eight (8) octa-
Nine (9) nona-
Ten (10) deca-
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72. H2S hydrogen sulfide (the “di” is omitted) H2O water NH3 ammonia
Some compounds have common names that differ from their systematic names:
H2S hydrogen sulfide (the “di” is omitted)
H2O water
NH3 ammonia
Common names need to be memorized.
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73. Acids and Corresponding Anions
Oxoacids contain hydrogen, oxygen, and a third central atom.
To name an acid from its anion name:
Change an –ate suffix to –ic.
Change an –ite suffix to –ous.
Add the word “acid.””
For example:
HNO3 nitric acid
H2SO4 sulfuric acid
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74. Oxoacid Oxoanion carbonate ion CO32- carbonic acid H2CO3 nitrite ion
NO2-
nitrous acid
HNO2
nitrate ion
NO3-
nitric acid
HNO3
phosphate ion
PO43-
phosphoric acid
H3PO4
sulfite ion
SO32-
sulfurous acid
H2SO3
sulfate ion
SO42-
sulfuric acid
H2SO4
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75. Oxoacid Oxoanion hypochlorite ion ClO- hypochlorous acid HClO
chlorate ion
ClO3-
chloric acid
HClO3
perchloric acid
HClO4
perchlorate ion
ClO4-
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76. What are the names of the following compounds? OF2 S4N4 BCl3
OF2 is oxygen difluoride
S4N4 is tetrasulfur tetranitride
BCl3 is boron trichloride
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77. What are the formulas for the following binary molecular compounds?
carbon disulfide
nitrogen tribromide
dinitrogen tetrafluoride
The formula for carbon disulfide is CS2.
The formula for nitrogen tribromide is NBr3.
The formula for dinitrogen tetrafluoride is N2F4.
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78. Bromine has an oxoacid, HBrO2, bromous acid (compare to HClO2, chlorous acid). What are the name and formula of the corresponding anion?
The anion corresponding to HBrO2 is bromite, BrO2-.
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79. A compound that contains water molecules weakly bound in the crystals.
Hydrate
A compound that contains water molecules weakly bound in the crystals.
The formula of a hydrate is written with a dot before the water molecule(s) included.
For example:
CuSO45H2O
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80. copper(II) sulfate pentahydrate.
Hydrates are named using the anhydrous (without water) compound name followed by the prefix for the number of water molecules included and the word “hydrate.”
For example:
CuSO45H2O is named
copper(II) sulfate pentahydrate.
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81. A compound whose common name is green vitriol has the chemical formula FeSO47H2O. What is the chemical name of this compound?
FeSO47H2O is iron(II) sulfate heptahydrate.
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82. Calcium chloride hexahydrate is used to melt snow on roads
Calcium chloride hexahydrate is used to melt snow on roads. What is the chemical formula of the compound?
The chemical formula for calcium chloride hexahydrate is CaCl26H2O.
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83. For example: 2Na + Cl2  2NaCl
A chemical equation is the symbolic representation of a chemical reaction in terms of chemical formulas.
For example: 2Na + Cl2  2NaCl
Reactants are the starting materials; they are written on the left of the equation.
Products are the materials at the end of the reaction; they are written on the right of the equation.
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84. This is called balancing the equation.
Because a reaction must accurately describe the chemical reaction, it must be consistent with the law of conservation of mass.
When this is not the case, after correct formulas are written for each reactant and product, the coefficients are adjusted so that the same number of each atom is present in both the reactants and the products.
This is called balancing the equation.
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85. First, we determine the correct formula for each compound.
For example, the reaction of sodium with chlorine produced sodium chloride.
First, we determine the correct formula for each compound.
Sodium is Na.
Chlorine is Cl2.
Sodium chloride is NaCl.
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86. Second, we write the reaction. Na + Cl2  NaCl
Third, we check the number of each atom on each side of the equation.
This equation shows two Cl atoms on the reactant side and only one Cl atom on the product side. To balance the Cl atoms, we insert a coefficient of “2” before NaCl on the product side.
Na + Cl2  2NaCl
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87. The reaction is now balanced!
Na + Cl2  2NaCl
Now the Na are not balanced: there is one on the reactant side and there are two on the product side. To balance Na, we insert the coefficient “2” before Na on the reactant side.
2Na + Cl2  2NaCl
The reaction is now balanced!
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88. Balance the following equation: CS2 + O2  CO2 + SO2
Tally the number of each atom on each side:
C 1 on reactant side; 1 on product side
S 2 on reactant side; 1 on product side
O 2 on reactant side; 4 on product side
Begin by inserting the coefficient “2” before SO2 on the product side. We leave O2 until later because it is an element.
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89. C 1 on reactant side; 1 on product side
CS2 + O2  CO2 + 2SO2
Tally the atoms again:
C 1 on reactant side; 1 on product side
S 2 on reactant side; 2 on product side
O 2 on reactant side; 6 on product side
Insert a “3” before O2:
CS2 + 3O2  CO2 + 2SO2
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90. C 1 on reactant side; 1 on product side
CS2 + 3O2  CO2 + 2SO2
Tally the atoms again:
C 1 on reactant side; 1 on product side
S 2 on reactant side; 2 on product side
O 6 on reactant side; 6 on product side
The reaction is now balanced!
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91. Balance the following equation: NH3 + O2  NO + H2O
Tally the number of each atom on each side:
N 1 on reactant side; 1 on product side
H 3 on reactant side; 2 on product side
O 2 on reactant side; 2 on product side
Begin by inserting the coefficient “2” before NH3 on the reactant side and the coefficient “3” before H2O on the product side. We leave O2 until later because it is an element.
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92. N 2 on reactant side; 1 on product side
2NH3 + O2  NO + 3H2O
Tally the atoms again:
N 2 on reactant side; 1 on product side
H 6 on reactant side; 6 on product side
O 2 on reactant side; 4 on product side
To balance N, insert a “2” before NO:
2NH3 + O2  2NO + 3H2O
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93. N 2 on reactant side; 2 on product side
2NH3 + O2  2NO + 3H2O
Tally the atoms again:
N 2 on reactant side; 2 on product side
H 6 on reactant side; 6 on product side
O 2 on reactant side; 5 on product side
Since this gives us an odd number oxygens, we double the coefficients on NH3, NO, and H2O and to balance O, insert a “5” before O2.
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94. Tally the atoms again to double check: 4NH3 + 5O2  4NO + 6H2O
N 4 on reactant side; 4 on product side
H 12 on reactant side; 12 on product side
O 10 on reactant side; 10 on product side
The reaction is now balanced!
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95. Balance the following equation: C2H5OH + O2  CO2 + H2O
Tally the number of each atom on each side:
C 2 on reactant side; 1 on product side
H 6 on reactant side; 2 on product side
O 3 on reactant side; 3 on product side
Begin by balancing H. Insert the coefficient “3” before H2O on the product side. We leave O2 until later because it is an element.
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96. Tally the number of each atom on each side:
C2H5OH + O2  CO2 + 3H2O
Tally the number of each atom on each side:
C 2 on reactant side; 1 on product side
H 6 on reactant side; 6 on product side
O 3 on reactant side; 5 on product side
To balance C, insert a “2” before CO2.
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97. Tally the number of each atom on each side:
C2H5OH + O2  2CO2 + 3H2O
Tally the number of each atom on each side:
C 2 on reactant side; 2 on product side
H 6 on reactant side; 6 on product side
O 3 on reactant side; 7 on product side
To balance O, insert a “3” before O2.
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98. Tally the number of each atom on each side:
C2H5OH + 3O2  2CO2 + 3H2O
Tally the number of each atom on each side:
C 2 on reactant side; 2 on product side
H 6 on reactant side; 6 on product side
O 7 on reactant side; 7 on product side
The reaction is now balanced!
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