1. Chapter 2 Atoms, Molecules, and Ions
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Dalton's Postulates
Atoms of an element are not changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions.
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Dalton's Postulates
Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms.
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Subatomic Particles
Protons and electrons are the only particles that have a charge.
Protons and neutrons have essentially the same mass.
The mass of an electron is so small we ignore it.
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Symbols of Elements
Elements are symbolized by one or two letters.
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Symbols of Elements
All atoms of the same element have the same number of protons, which is called the atomic number, Z.
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Symbols of Elements
The mass of an atom in atomic mass units (amu) is the total number of protons and neutrons in the atom.
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Isotopes
Isotopes are atoms of the same element with different masses.
Isotopes have different numbers of neutrons.
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9. Key Points
The elements of The Periodic Table are classified into three groups – metals, nonmetals, and metalloids
Elements in a group have similar chemical properties
Elements in a in a period have different chemical properties

10. Metals, metalloids, and nonmetals.
Figure 2.11
Metals, metalloids, and nonmetals.
Cadmium
Copper
Lead
Chromium
Bismuth
Arsenic
Chlorine
Silicon
Antimony
Bromine
Sulfur
Iodine
Carbon
(graphite)
Boron
Tellurium

11. The modern periodic table.
Noble Gases
Alkali metals
Halogens
Alkaline earth metals
Transition Metals

12. The modern periodic table.
Figure 2.10
The modern periodic table. +1 +2 +3 NC -3 -2 -1 12

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Chemical Formulas
The subscript to the right of the symbol of an element tells the number of atoms of that element in one molecule of the compound.
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14. Diatomic Molecules
These seven elements occur naturally as molecules containing two atoms:
Hydrogen
Nitrogen
Oxygen
Fluorine
Chlorine
Bromine
Iodine
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15. Chemical Formulas Molecular Formula Empirical Formula
It only shows the exact number of atoms of each element in the smallest possible units of a substance
Ex. H2O, O2, N2
Empirical Formula
Tells us what elements are present and the simplest whole number ratio of their atoms
Not necessarily the actual number of atoms in a given molecule.
N2H4 molecular formula
NH2 empirical formula

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Ionic compounds (such as NaCl) are generally formed between metals and nonmetals.
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Chemical Formulas
Molecular (covalent or binary) compounds are composed of molecules and almost always contain only nonmetals.
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Ions
When atoms lose or gain electrons, they become ions.
Cations are positive and are formed by elements on the left side of the periodic chart (donate electrons to non- metals)
Anions are negative and are formed by elements on the right side of the periodic chart (gain electrons from metals)
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19. 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
2.5

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Writing Formulas
Because compounds are electrically neutral, one can determine the formula of a compound this way:
The charge on the cation becomes the subscript on the anion.
The charge on the anion becomes the subscript on the cation.
If these subscripts are not in the lowest whole-number ratio, divide them by the greatest common factor.
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21. Predicting Ionic Charge
The sum of the charges on the cation and the anion have to add up to zero, thus the compound is electronically neutral
Ex Al2O3
Predicting Ionic Charge
The number of electrons an atom loses or gains is related to its position on the periodic table.

22. Naming Ionic Compounds cont..
Certain Metals especially transition metals can form more than one type of cation
We use the Stock System to name them
Mn MnO (manganese (II) oxide)
Mn Mn2O3 (manganese (III) oxide)
Mn MnO2 (manganese (IV) oxide)

23. Naming Ionic Compounds cont..
Binary compounds: made from just 2 elements
Cation (electron donating number fixed) is named first and the name of the element stays the same
Cation (electron donating more than one) follow the mentioned above rules
Anion (electron accepting) is named second and you add -ide
Ex. Oxygen turns to Oxide
Ex Nitrogen turns to Nitride

24. Naming Binary Ionic Compounds
Sample Problem 2.5
Naming Binary Ionic Compounds
PROBLEM:
Name the ionic compound formed from the following pairs of elements:
(a) magnesium and nitrogen
(b) iodine and cadmium
(c) strontium and fluorine
(d) sulfur and cesium
SOLUTION:
(a) magnesium nitride
(b) cadmium iodide
(c) strontium fluoride
(d) cesium sulfide 24

25. Determining Formulas of Binary Ionic Compounds
Sample Problem 2.6
Determining Formulas of Binary Ionic Compounds
PROBLEM:
Write empirical formulas for the compounds named in Sample Problem 2.5.
SOLUTION:
(a) magnesium nitride
Mg2+ and N3-; three Mg2+(6+) and two N3-(6-); Mg3N2
(b) cadmium iodide
Cd2+ and I-; one Cd2+(2+) and two I-(2-); CdI2
(c) strontium fluoride
Sr2+ and F-; one Sr2+(2+) and two F-(2-); SrF2
(d) cesium sulfide
Cs+ and S2-; two Cs+(2+) and one S2- (2-); Cs2S 25

26. Naming Ionic Compounds cont..
Ternary Compounds: made up three elements
If cation (electron donating) has a fixed number of electrons to give the name will stay the same and it is named first
If the cation (electron donating) different number of electrons to give the name will stay the same but you will mention the number of electrons (roman numerals) that are being donating and it is still named first
If the anion (electron accepting) 1 element then you will add –ide
If the anion (electron accepting) more than one element refer to table 2.5 page 63, it is mentioned after the cation

27. Sample Problem 2.8
Determining Names and Formulas of Ionic Compounds Containing Polyatomic Ions
PROBLEM:
Give the systematic names or the formula or the formulas for the names of the following compounds:
(a) Fe(ClO4)2
(b) sodium sulfite
(c) Ba(OH)2 8H2O
SOLUTION:
(a) ClO4- is perchlorate; iron must have a 2+ charge. This is iron(II) perchlorate.
(b) The anion sulfite is SO32- therefore you need 2 sodiums per sulfite. The formula is Na2SO3.
(c) Hydroxide is OH- and barium is a 2+ ion. When water is included in the formula, we use the term “hydrate” and a prefix which indicates the number of waters. So it is barium hydroxide octahydrate. 27

28. Molecular Compounds They are usually composed of nonmetal elements
The chemical bond that forms between the elements is called “covalent bond”
Most of them are binary compounds
Named in the same manner as ionic compounds

29. Naming Molecular Compounds
The first name the element that is first in the formula, its name does not change
The second element in the formula is named second and –ide is added
HCl (hydrogen chloride)
HBr (hydrogen bromide)

30. Nomenclature of Binary Compounds
The less electronegative atom is usually listed first.
A prefix is used to denote the number of atoms of each element in the compound (mono- is not used on the first element listed, however) .
The ending on the more electronegative element is changed to -ide.
CO2: carbon dioxide
CCl4: carbon tetrachloride

31. Nomenclature of Binary Compounds
If the prefix ends with a or o and the name of the element begins with a vowel, the two successive vowels are often elided into one.
N2O5: dinitrogen pentoxide
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32. Patterns in Oxyanion Nomenclature
When there are two oxyanions involving the same element:
The one with fewer oxygens ends in -ite.
The one with more oxygens ends in -ate.
NO2− : nitrite; SO32− : sulfite
NO3− : nitrate; SO42− : sulfate
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33. Determining Names and Formulas of Binary Covalent Compounds
Sample Problem 2.11
Determining Names and Formulas of Binary Covalent Compounds
SOLUTION:
PROBLEM:
(a) What is the formula of carbon disulfide?
(b) What is the name of PCl5?
(c) Give the name and formula of the compound whose molecules each consist of two N atoms and four O atoms.
(a) Carbon is C, sulfide is sulfur S and di-means 2 - CS2.
(b) P is phosphorous, Cl is chloride, the prefix for 5 is penta-. Phosphorous pentachloride.
(c) N is nitrogen and is in a lower group number than O (oxygen). Therefore the formula is N2O4 - dinitrogen tetraoxide. 33

34. Acids
Acid: a substance that yields hydrogen ions (H +, equivalent to a proton) when dissolved in water
Formulas for acids contain one or more hydrogen as well as an anionic group
The name assigned to the compound depends on its physical state
Anions whose names end in “ide” form acids with a “hydro” prefix and an “ic” ending
HCl Hydrochloric acid

35. Naming Acids

36. Determining Names and Formulas of Anions and Acids
Sample Problem 2.10
Determining Names and Formulas of Anions and Acids
PROBLEM:
Name the following anions and give the names and formulas of the acids derived from them:
(a) Br -
(b) IO3 -
(c) CN -
(d) SO4 2-
(e) NO2 -
SOLUTION:
(a) The anion is bromide; the acid is hydrobromic acid, HBr.
(b) The anion is iodate; the acid is iodic acid, HIO3.
(c) The anion is cyanide; the acid is hydrocyanic acid, HCN.
(d) The anion is sulfate; the acid is sulfuric acid, H2SO4.
(e) The anion is nitrite; the acid is nitrous acid, HNO2. 36