1. Atoms, Molecules and Ions
Chapter 2
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2. Dalton’s Atomic Theory
Law of Multiple Proportions

3. Law of Conservation of Mass

4. Dalton’s Atomic Theory (1808)
Elements are made of tiny particles called atoms.
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5. Dalton’s Atomic Theory (continued)
2. All atoms of a given element are identical.
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6. Dalton’s Atomic Theory (continued)
3. The atoms of a given element are different from those of any other element.
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7. Dalton’s Atomic Theory (continued)
Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative numbers and types of atoms.
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8. Dalton’s Atomic Theory (continued)
5. Atoms are indivisible in chemical processes. Atoms are not created or destroyed in chemical reactions. A chemical reaction simply changes the way the atoms are grouped together.
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9. Concept Check
Which of the following statements regarding Dalton’s atomic theory are still believed to be true?
Elements are made of tiny particles called atoms.
All atoms of a given element are identical.
A given compound always has the same relative
numbers and types of atoms.
IV. Atoms are indestructible.
Statements I and III are true. Statement II is not true (due to isotopes and ions). Statement IV is not true (due to nuclear chemistry).
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10. Electrons – found outside the nucleus; negatively charged
The atom contains:
Electrons – found outside the nucleus; negatively charged
Protons – found in the nucleus; positive charge equal in magnitude to the electron’s negative charge
Neutrons – found in the nucleus; no charge; virtually same mass as a proton
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11. QUESTION
The chemical properties of a particular element are largely determined by the number of __________ an atom of that element possesses.
protons
neutrons
electrons

12. ANSWER
Choice #3 is correct. The protons and neutrons are buried within the atom in the nucleus. The electrons occupy most of the volume of the atom and affect the ways in which atoms interact, or react, with each other.
Section 4.6: Introduction to the Modern Concept of Atomic Structure

13. X = the symbol of the element
Z = the atomic number (# of protons)
A = the mass number (# of protons and neutrons)

14. Atomic number, Mass number and Isotopes
Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
Isotopes are atoms of the same element (X) with different numbers of neutrons in their nuclei
Mass Number X A Z
Element Symbol
Atomic Number H 1
H (D) 2
H (T) 3 U
235 92
238

15. Isotopes – An Example C = the symbol for carbon
6 = the atomic number (6 protons)
14 = the mass number (6 protons and 8 neutrons)
C = the symbol for carbon
6 = the atomic number (6 protons)
12 = the mass number (6 protons and 6 neutrons)

16. QUESTION
Lead-210 is used in radioactive dating of sediment cores. The number of protons, electrons, and neutrons in an atom of lead-210 respectively is
variable
82, 82, 128
210, 82, 128
128, 128, 82

17. ANSWER
Choice #2 is correct. Lead has an atomic number of 82; hence every lead atom has 82 protons and electrons. To find the number of neutrons, we subtract the number of protons from the mass number (210), which yields 128 neutrons. Lead-210 has a characteristic common to radioactive isotopes: it is relatively rich in neutrons.
Section 4.7: Isotopes

18. QUESTION
A certain isotope X contains 23 protons and 28 neutrons. Determine the mass number of this isotope and identify the element.
51; vanadium (V)
51; antimony (Sb)
5; boron (B)
5; nickel (Ni)

19. ANSWER
Choice #1 is the correct answer. The mass number is 51. Mass Number = # protons + # neutrons. Mass Number = = 51. The element is vanadium. The number of protons determines the identity of the element.
Section 4.7: Isotopes

20. Most elements are metals and occur on the left side.
The nonmetals appear on the right side.
Metalloids are elements that have some metallic and some nonmetallic properties.

21. Periods – horizontal rows of elements
The Periodic Table
Metals vs. Nonmetals
Groups – elements in the same vertical columns; have similar chemical properties
Periods – horizontal rows of elements

22. The Modern Periodic Table
Alkali Earth Metal
Noble Gas
Halogen
Alkali Metal
Group
Period

23. H2
H2O
NH3
CH4
A molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical forces

24. cation – ion with a positive charge
An ion is an atom, or group of atoms, that has a net positive or negative charge.
cation – ion with a positive charge
If a neutral atom loses one or more electrons
it becomes a cation. Na
11 protons
11 electrons
Na+
11 protons
10 electrons
anion – ion with a negative charge
If a neutral atom gains one or more electrons
it becomes an anion.
Cl-
17 protons
18 electrons Cl
17 protons
17 electrons

25. Oxidation Numbers
Oxidation is the loss of electrons; Reduction is the gain of electrons
Oxidation and reduction go together. Whenever a substance loses electrons and another substance gains electrons
Oxidation Numbers are a system that we can use to keep track of electron transfers

26. Oxidation Numbers Oxidation numbers always refer to single atoms
The oxidation number of an uncombined element is always 0
O2, H2, Ne Zn
The oxidation number of Hydrogen is usually +1 Hydrides are an exception They are -1
HCl, H2SO4
The oxidation number of Oxygen is usually -2 Peroxides are an exception They are –1 In OF2 oxygen is a +2
H2O, NO2, et
Oxidation numbers of monatomic ions follow the charge of the ion
O2-, Zn2+
The sum of oxidation numbers is zero for a neutral compound. It is the charge on a polyatomic ion
LiMnO4
SO42-

27. Practice Assigning Oxidation Numbers
NO2
N2O5
HClO3
HNO3
Ca(NO3)2
KMnO4

28. Practice Assigning Oxidation Numbers
Fe(OH)3
K2Cr2O7
CO32-
CN-
K3Fe(CN)6

29. Practice Assigning Oxidation Numbers
NO2
N= +4, O = -2
N2O5
N = +5, O = -2
HClO3
H=+1, Cl=+5, O = -2
HNO3
H=+1, N = +5, O = -2
Ca(NO3)2
Ca=+2, N =+5, O= -2
KMnO4
K=+1, Mn=+7, O= -2

30. Practice Assigning Oxidation Numbers
Fe(OH)3
Fe =+3, O=-2, H=+1
K2Cr2O7
K=+1, Cr=+6, O=-2
CO32-
C=+4, O =-2
CN-
C=+4, N=-5
K3Fe(CN)6
K=+1, Fe=+3, C=+4, N=-5

31. Ion Charges and the Periodic Table
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32. An ion with a 3+ charge contains 23 electrons. Which ion is it?
Exercise
An ion with a 3+ charge contains 23 electrons. Which ion is it?
a) Fe3+
b) V3+
c) Ca3+
d) Sc3+
The 3+ charge on the ion means that the ion has lost 3 electrons, therefore the number of protons is 26 (23+3). The ion is Fe3+.
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33. A certain ion X+ contains 54 electrons and 78 neutrons.
Exercise
A certain ion X+ contains 54 electrons and 78 neutrons.
What is the mass number of this ion?
133
The mass number is 133. The plus charge in X+ means that the ion has lost an electron, therefore the number of protons is 55 (54+1). The ion is Cs+ with a mass number of 133 (55+78).
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34. A monatomic ion contains only one atom
Na+, Cl-, Ca2+, O2-, Al3+, N3-
A polyatomic ion contains more than one atom
OH-, CN-, NH4+, NO3-

35. Common Ions Shown on the Periodic Table

36. How many protons and electrons are in ? Al27 13 3+
13 protons, 10 (13 – 3) electrons
How many protons and electrons are in ? Se 78 34 2-
34 protons, 36 (34 + 2) electrons

37. Calculating atomic mass (weighted average)
Turn each percentage into a decimal number.
Multiply each mass by its matching decimal number.
Add them.

38. Problem 1 – Atomic mass bromine
Bromine has two isotopes with the first having a mass of amu and occupying 50.69% and the second isotope having a mass of amu and occupying 49.31%. What is the average atomic mass of bromine? (78.91 amu) (80.91 amu) = amu = g/mol

39. Problem 2 – Atomic mass
Verify the atomic mass of chlorine using this data for its two isotopes: chlorine-35 = amu; percent abundance = 75.77% chlorine-37 = amu percent abundance = 24.23% (34.96 amu) (36.96 amu) = amu = g/mol

40. Formulas and Models

41. A molecular formula shows the exact number of atoms of each element in the smallest unit of a substance
An empirical formula shows the simplest
whole-number ratio of the atoms in a substance
H2O
molecular
empirical
H2O
C6H12O6
CH2O O3 O
N2H4
NH2

42. The ionic compound NaCl
ionic compounds consist of a combination of cations and an anions
The formula is usually the same as the empirical formula
The sum of the charges on the cation(s) and anion(s) in each formula unit must equal zero
The ionic compound NaCl

43. The most reactive metals (green) and the most reactive nonmetals (blue) combine to form ionic compounds.

44. Formula of Ionic Compounds
2 x +3 = +6
3 x -2 = -6
Al2O3
Al3+
O2-
1 x +2 = +2
2 x -1 = -2
CaBr2
Ca2+
Br-
1 x +2 = +2
1 x -2 = -2
Na2CO3
Na+
CO32-

46. a) Ti2+ b) Sc+ c) Ca2+ d) Cr2+ Concept Check
A compound contains an unknown ion X and has the formula XCl2. Ion X contains 20 electrons. What is the identity of X?
a) Ti2+
b) Sc+
c) Ca2+
d) Cr2+
The charge on the cation must be +2 since there are two Cl’s each with a –1 charge (giving an overall charge of –2 for the anion side). The cation can now be represented as X2+, containing 20 electrons. Therefore, 22 protons must be present to give a charge of +2 (+22p – 20e = +2). The element with 22 protons is titanium.
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47. QUESTION
A member of the alkaline earth metal family whose most stable ion contains 36 electrons forms a compound with bromine. What is the correct formula for this compound?
1. CaBr2
2. KrBr
3. RbBr
4. SrBr2

48. ANSWER
Choice #4 is the correct answer. An element in the alkaline earth metal family (Group 2) forms a +2 charge when forming a compound. Therefore two Br– ions will be required to give a net zero charge overall. 38 protons must be present to give a charge of +2 (+38p – 36e = +2). The element with 38 protons is strontium. The compound is therefore SrBr2.
Section 4.11: Compounds That Contain Ions

49. Chemical Nomenclature
Ionic Compounds
Often a metal + nonmetal
Anion (nonmetal), add “ide” to element name
BaCl2
barium chloride
K2O
potassium oxide
Mg(OH)2
magnesium hydroxide
KNO3
potassium nitrate

50. Transition metal ionic compounds
indicate charge on metal with Roman numerals
FeCl2
2 Cl- -2 so Fe is +2
iron(II) chloride
FeCl3
3 Cl- -3 so Fe is +3
iron(III) chloride
Cr2S3
3 S-2 -6 so Cr is +3 (6/2)
chromium(III) sulfide

51. QUESTION What is the name of the compound CrO2? 1. chromium oxide
2. chromium(II) oxide
3. chromium(IV) oxide
4. chromium dioxide

52. ANSWER
Choice #3 is the correct answer. Cr is the symbol for chromium. O is the symbol for oxygen, but take the first part of the element name (the root) and add –ide to get the name oxide. Since chromium can have more than one charge, a Roman numeral must be used to identify that charge. There are two oxygen ions each with a 2– charge, giving an overall charge of –4. Therefore, the charge on chromium must be +4.
Section 5.2: Naming Binary Compounds That Contain a Metal and a Nonmetal (Types I & II)

53. Molecular compounds Nonmetals or nonmetals + metalloids Common names
H2O, NH3, CH4,
Element furthest to the left in a period and closest to the bottom of a group on periodic table is placed first in formula
If more than one compound can be formed from the same elements, use prefixes to indicate number of each kind of atom
Last element name ends in ide

54. Molecular Compounds HI hydrogen iodide NF3 nitrogen trifluoride SO2
sulfur dioxide
N2Cl4
dinitrogen tetrachloride
NO2
nitrogen dioxide
N2O
dinitrogen monoxide

55. An acid can be defined as a substance that yields
hydrogen ions (H+) when dissolved in water.
For example: HCl gas and HCl in water
Pure substance, hydrogen chloride
Dissolved in water (H3O+ and Cl−),
hydrochloric acid

57. An oxoacid is an acid that contains hydrogen, oxygen, and another element.
HNO3
nitric acid
H2CO3
carbonic acid
H3PO4
phosphoric acid

58. What is the name of the compound KClO3? a) potassium chlorite
Exercise
What is the name of the compound KClO3?
a) potassium chlorite
b) potassium chlorate
c) potassium perchlorate
d) potassium carbonate
ClO3– is the polyatomic ion chlorate.
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59. Exercise
Examine the following table of formulas and names. Which of the compounds are named correctly?
a) I, II
b) I, III, IV
c) I, IV
d) I only
Formula
Name I
P2O5
Diphosphorus pentoxide II
ClO2
Chlorine oxide
III
PbI4
Lead iodide IV
CuSO4
Copper(I) sulfate
Only Formula I is named correctly. Formula II is chlorine dioxide. Formula III is lead(IV) iodide. Formula IV is copper(II) sulfate.
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60. A base can be defined as a substance that yields
hydroxide ions (OH-) when dissolved in water.
NaOH
sodium hydroxide
KOH
potassium hydroxide
Ba(OH)2
barium hydroxide

61. Hydrates are compounds that have a specific number of water molecules attached to them.
BaCl2•2H2O
barium chloride dihydrate
LiCl•H2O
lithium chloride monohydrate
MgSO4•7H2O
magnesium sulfate heptahydrate
Sr(NO3)2 •4H2O
strontium nitrate tetrahydrate
CuSO4•5H2O
CuSO4