Chapter 6 Chemical Names and Formulas

Chapter 6Chemical Names and Formulas

Section 6.1Introduction to Chemical Bonding • OBJECTIVES: • Distinguish between ionic and molecular compounds.

Section 6.1Introduction to Chemical Bonding • OBJECTIVES: • Define cation and anion, and relate them to metal and nonmetal.

Molecules and Molecular Compounds • About 100 different elements • Millions of compounds from them • Naming is essential in chemistry • Noble gases, such as He and Ne • Isolated atoms- monatomic, they consist of single atoms

Molecules and Molecular Compounds • Molecule- smallest electrically neutral unit, still has properties of the substance • Made from only nonmetals • Can be from one element- O2 • Can make a compound- CO2

Molecules and Molecular Compounds • Properties of molecular compounds • Low melting and boiling points • Usually gas or liquid • Composed of two or more nonmetals • O2, O3, H2O

Systematic Naming • There are too many compounds to remember the names of them all. • Compound is made of two or more elements. • Put together atoms. • Name should tell us how many and what type of atoms.

Atoms and ions • Atoms are electrically neutral. • Same number of protons and electrons. • Ions are atoms, or groups of atoms, with a charge (positive or negative) • Different numbers of protons and electrons. • Only electrons can move. • Gain or lose electrons.

Anion • A negative ion. • Has gained electrons. • Nonmetals can gain electrons. • Charge is written as a superscript on the right. Has gained one electron (-ide is new ending= fluoride) F- O2- Gained two electrons (oxide)

Cations • Positive ions. • Formed by losing electrons. • More protons than electrons. • Metals can lose electrons Has lost one electron (no name change for positive ions) K+ Ca2+ Has lost two electrons

Ionic Compounds • Ionic compounds- from joining metal cations and nonmetal anions- they are electrically neutral • Usually solid crystals • Melt at high temperatures

Two Types of Compounds • Molecular compounds • Made of molecules. • Made by joining nonmetal atoms together into molecules.

Two Types of Compounds • Ionic Compounds • Made of cations and anions. • Metals and nonmetals. • The electrons lost by the cation are gained by the anion. • The cation and anions surround each other. • Smallest piece is a FORMULA UNIT.

Two Types of Compounds Ionic Molecular Smallest piece Formula Unit Molecule Types of elements Metal and Nonmetal Nonmetals Solid, liquid or gas State solid Melting Point High >300ºC Low <300ºC

Section 6.2Representing Chemical Compounds • OBJECTIVES: • Distinguish among chemical formulas, molecular formulas, and formula units.

Section 6.2Representing Chemical Compounds • OBJECTIVES: • Use experimental data to show that a compound obeys the law of definite proportions.

Chemical Formulas • Shows the kind and number of atoms in the smallest piece of a substance. • Molecular formula- number and kinds of atoms in a molecule. • CO2 • C6H12O6

Chemical Formulas • More than one atom? –use a subscript (H2O) • There are 7 diatomic elements • Hydrogen (H2), Nitrogen (N2), Oxygen (O2), Fluorine (F2), Chlorine (Cl2), Bromine (Br2), and Iodine (I2) • Remember: “Br I N Cl H O F”

Ionic Compounds • This formula represents not a molecule, but a formula unit • The smallest whole number ratio of atoms in an ionic compound. • Ions surround each other so you can’t say which is hooked to which. (p. 140)

Some Laws: • 1. Law of Definite Proportions- in a sample of a chemical compound, the masses of the elements are always in the same proportions. • H2O (water) and H2O2 (hydrogen peroxide)

Some Laws: • 2. Law of Multiple Proportions- Dalton stated that whenever two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers. • Figure 6.11, p. 141

Section 6.3Ionic Charges • OBJECTIVES: • Use the periodic table to determine the charge on an ion.

Section 6.3Ionic Charges • OBJECTIVES: • Define a polyatomic ion, and give the names and formulas of the most common polyatomic ions.

Charges on ions • For most of the Group A elements, the Periodic Table can tell what kind of ion they will form from their location; monatomic ions • Elements in the same group have similar properties. • Including the charge when they are ions.

1+ 2+ 3+ 3- 2- 1-

What about the others? • Groups 4A and 0 do not usually form ions (in fact, Group 0 rarely forms compounds!) • Many transition metals have more than one common ionic charge

Naming ions • Two methods if more than one charge is possible: • 1. Stock system – uses roman numerals in parenthesis to indicate the numerical value • 2. Classical method – uses root word with suffixes (-ous, -ic) • Does not give true value

Naming ions • We will use the Stock system. • Cation- if the charge is always the same (Group A) just write the name of the metal. • Transition metals can have more than one type of charge. • Indicate the charge with roman numerals in parenthesis (Table 6.3, p.144)

Name these • Na+ • Ca2+ • Al3+ • Fe3+ • Fe2+ • Pb2+ • Li+

Write Formulas for these • Potassium ion • Magnesium ion • Copper (II) ion • Chromium (VI) ion • Barium ion • Mercury (II) ion

Naming Anions • Anions are always the same charge • Change the element ending to – ide • F- Fluorine

Naming Anions • Anions are always the same charge • Change the element ending to – ide • F-Fluorin

Naming Anions • Anions are always the same charge • Change the element ending to – ide • F-Fluori

Naming Anions • Anions are always the same charge • Change the element ending to – ide • F- Fluor

Naming Anions • Anions are always the same charge • Change the element ending to – ide • F-Fluori

Naming Anions • Anions are always the same charge • Change the element ending to – ide • F-Fluorid

Naming Anions • Anions are always the same charge • Change the element ending to – ide • F- Fluoride

Name these • Cl- • N3- • Br- • O2- • Ga3+

Write these • Sulfide ion • iodide ion • phosphide ion • Strontium ion

Exceptions: • Some of the transition metals have only one ionic charge: • Do not use roman numerals for these: • Silver is always 1+ (Ag+) • Cadmium and Zinc are always 2+ (Cd2+ and Zn2+) • Note Fig. 6.13, p. 145

Polyatomic ions • Groups of atoms that stay together and have a charge. • Learn these - Table 6.4, p.147 • Acetate C2H3O2- • Nitrate NO3- • Nitrite NO2- • Hydroxide OH- and Cyanide CN- • Permanganate MnO4-

Sulfate SO42- Sulfite SO32- Carbonate CO32- Chromate CrO42- Dichromate Cr2O72- Phosphate PO43- PhosphitePO33- Ammonium NH4+ Polyatomic ions

Section 6.4Ionic Compounds • OBJECTIVES: • Apply the rules for naming and writing formulas for binary ionic compounds.

Section 6.4Ionic Compounds • OBJECTIVES: • Apply the rules for naming and writing formulas for ternary ionic compounds.

Naming Binary Ionic Compounds • Binary Compounds - 2 elements. • Ionic - a cation and an anion. • To write the names, just name the two ions. • Easy with Representative elements (which are Group A elements) • NaCl = Na+Cl- = sodium chloride • MgBr2 = Mg2+Br-= magnesium bromide

Naming Binary Ionic Compounds • The problem comes with the transition metals. • Need to figure out their charges. • The compound must be neutral. • same number of + and – charges. • Use the anion to determine the charge on the positive ion.

Naming Binary Ionic Compounds • Write the name of CuO • Need the charge of Cu • O is 2- • copper must be 2+ • Copper (II) oxide • Name CoCl3 • Cl is 1- and there are three of them = 3- • Co must be 3+ Cobalt (III) chloride

Naming Binary Ionic Compounds • Write the name of Cu2S. • Since S is 2-, the Cu2 must be 2+, so each one is 1+. • copper (I) sulfide • Fe2O3 • Each O is 2- 3 x -2 = -6 • 2 Fe must = 6+, so each is 3+. • iron (III) oxide

Naming Binary Ionic Compounds • Write the names of the following • KCl • Na3N • CrN • Sc3P2 • PbO • PbO2 • Na2Se

Ternary Ionic Compounds • These will have polyatomic ions • At least three elements • name the ions • NaNO3 • CaSO4 • CuSO3 • (NH4)2O

Chapter 6 Chemical Names and Formulas