Naming and Formulas Chapter 9
General Concepts • Chemical Symbols- a universal shorthand used to identify the known elements on earth. Ex. C H Fe • Rules for Chemical Symbols: 1. 1st letter capitalized 2. 2nd letter lowercase
Monoatomic Elements- most of the elements can exist alone & are written w/ no subscript. Ex. Fe Ne C • Diatomic Elements/Molecules- there are seven elements that exist in nature • Exist with a subscript– a number to the right & slightly below a symbol that tells the number of atoms present H2, N2, O2, F2, Cl2, Br2, I2
Chemical Formulas • When elements combine, the newly formed compounds give both qualitative and quantitative information. Qualitative - Cannot be counted or measured Ex. What elements are in the compound Quantitative- Can be counted or measured Ex. # of atoms of each element that are present in the compound Ex. CO CO2 H2SO4
Types of Formulas • Simplest whole-number ratio Empirical Formula H2O CH2O CH4 • Actual ratio of atoms in a molecule Molecular Formula H2O C6H12O6 C2H8
How do elements form compounds? • Atoms are electrically neutral (equal # of p+ and e-) however, they are not necessarily stable/happy. • Most atoms form ions when in solutions or combining with other atoms in a chemical reaction. • More with what ions are on the next slide • The ions that are formed are predictable… Using the periodic table.
Ions Ions – atoms with either a positive or negative charge due to gaining or losing electrons • Cations – carry a positive charge (lost e-) • Generally metalsEx. Na1+ • Anions– carry a negative charge (gain e-) • Generally nonmetals Ex. Si4- You can determine the ions (oxidation states) from the PT. Group 1 Group 2 Group 16 Group 17
How do elements form compounds? • By the attraction of oppositely charged ions • Monatomic or polyatomic ions attract each other in a ratio that produces a neutral compound Ex. Sulfuric acid Methane
Coefficients Coefficients – written in front of a formula. • Tells how many units of the formula are present; applies to the entire formula Ex. 4H2O 6NH33C2H6 To determine the # of atoms present: • Consider the formula without the coefficient • Multiple each value by the coefficient to find the total of each type of atom.
How Do We Determine the Chemical Formula? Steps: • Look up charges on PT • Balance positive and negative charges so that they = zero • Write formula using subscripts to tell how many of each element was used. Ex. Calcium and ChlorineEx. Aluminum and Oxygen
9.1 Monatomic Ions • How are the charges of Group A metal and nonmetal ions related to their positions in the periodic table? • When the metals in Groups 1A, 2A, and 3A lose electrons, they form cations with positive charges equal to their group number. • Monatomic ions consist of a single atom with a positive or negative charge resulting from the loss or gain of one or more valence electrons, respectively. • The names of the cations of the Group 1A, Group 2A, and Group 3A metals are the same as the name of the metal, followed by the word ion or cation.
9.1 Monatomic Ions • These elements have ionic charges that can be obtained from their group numbers.
9.1 Monatomic Ions • Anions • The charge of any ion of a Group A nonmetal is determined by subtracting 8 from the group number. • Anionnames start with the stem of the element name and end in-ide. Ex. Fluoride Chloride Sulfide Bromide Iodide Nitride
9.1 Monatomic Ions • These Group A elements form anions.
9.1 Ions of Transition Metals • How are the charges of some transition metal ions determined? • The charges of the cations of many transition metal ions must be determined from the number of electrons lost. Transition Metals – roman numeral tells the charge Ex. Iron (III) ion = Fe3+
9.1 Naming • Two methods are used to name the ions of transition metals. 1.) The Stock system 2.) The classical method
Stock System • In the Stock system, a Roman numeral in parentheses is placed after the name of the element to indicate the numerical value of the charge. Ex. Mercury (II) oxide Mercury (I) oxide Mercury (II) chloride Mercury (I) chloride Note that mercury (Hg) is a transition metal
Classical Method • In an older less, useful method, the classical name of the element is used to form the root name for the element. • With different suffixes on the end Ex. Iron ferrum is Latin for iron ferr- is the root name for iron
9.1 Monatomic Ions
Practice Write the symbol for the ion formed by each element. K+ : cation, potassium ion I- : anion, iodide ion S2-: anion, sulfide ion Pb4+: cation, lead(IV) or plumbic ion • Potassium • Iodide • Sulfur • Lead, 4 electrons lost
9.1 Polyatomic Ions • What are the two endings of the names of most polyatomic ions? Polyatomic ions – a group of atoms bonded together that carry a charge (See RT p.1 Table E) Ex. OH- NO3- SO4-2 • Some ions, called polyatomic ions, are composed of more than one atom. • The names of most polyatomic anions end in -ite or -ate.
9.1 Polyatomic Ions • These models show the structures of four common polyatomic ions.
Were You Paying Attention? 1.When metals from groups 1A, 2A, and 3A form cations, the charge on the ion is equal to • 8 minus the group number. • the group number minus 8. • the period number. • the group number.
Were You Paying Attention? 2.Which of the following are positively charged polyatomic ions? • (I) ammonium ion • (II) perchlorate ion • (III) ferric ion • I only • II only • III only • I and III
Were You Paying Attention? 3. If the name of an ion ends in -ite or -ate, the ion is a • polyatomic cation. • polyatomic anion. • transition metal cation. • monatomic anion.
Binary Ionic Compounds Essential Questions: • How are the names of binary ionic compounds determined? • How do you write the formulas for binary ionic compounds?
9.2 Naming Binary Ionic Compounds • A binary compound is composed of two elements and can be either ionic or molecular. • To name any binary ionic compound, place the cation name first, followed by the anion name. Do Not Modify Compound Formula: KCl MgS AlN Modify to end in -ide Compound Name: Potassium Magnesium Aluminum chloride sulfide nitride Ex. Tin(II) sulfide Sn2+F1- SnF2 Sodium nitrate Na1+NO31- NaNO3
Writing Formulas for Binary Ionic Compounds • Write the symbol of the cation and then the anion. Add whatever subscripts are needed to balance the charges. Balance the formula using appropriate subscripts: Ion Formula: Mg2+ Cl- Ca2+ OH- Compound Formula: MgCl2 Ca(OH)2
Practice Write formulas for these binary ionic compounds: a.) beryllium chloride b.) potassium iodide c.) calcium oxide
Practice Name each of the following binary ionic compounds: a.) NaBr b.)AlF3 c.) MgS
9.2 Compounds With Polyatomic Ions How do you write the formulas and names of compounds containing polyatomic ions? Write the symbol for the cation followed by the formula for the polyatomic ion and balance the charges. Ex. calcium nitrate calcium cation polyatomic nitrate anion (Ca2+) (NO3–) • two nitrate anions, each with a 1– charge, are needed to balance the 2+ charge of each calcium cation. • The formula for calcium nitrate is Ca(NO3)2.
Writing Formulas for Compounds with Polyatomic Ions • Write the formula for each ion in the order listed in the name. • Use subscripts to balance the charges. • If more than one polyatomic ion is needed to balance a formula, place the polyatomic ion formula in parentheses, followed by a subscript showing the number needed. Ex. Magnesium Hydroxide, aka Milk of magnesia
Practice Write formulas for these compounds: a.) tin(II) hydroxide b.) lead(II) nitrate c.) sodium phosphate
Naming Compounds with Polyatomic Ions To name a compound containing a polyatomic ion, state the cation first and then the anion, just as you did in naming binary ionic compounds. Ex. NaClO Na+ ClO- sodium hypochlorite
Practice Write names for each of the following compounds: a.) Sn(OH)2 b.) Ca(NO3)2 c.) K2CrO4
Were You Paying Attention? 1. The correct name for CrCl3 is • chromium chlorine. • chromium(III) chloride. • monochromium trichloride. • chromium(III) trichloride.
Were You Paying Attention? 2. What is the correct formula for strontium nitride? • Sr3N2 • SrN2 • Sr2N3 • Sr3N
Were You Paying Attention? 3. Which one of the following compounds is named correctly? • sodium chlorite, NaClO • potassium nitrate, KNO2 • sodium acetate, NaC2H3O2 • lithium sulfate, Li2SO3
9.3 Naming and Writing Formulas for Molecular Compounds • One milligram of gold is worth only about one cent, but one kilogram of gold is worth approximately $12,500. The correct prefix ( milli- or kilo-) makes quite a difference! Prefixes are important in chemistry, too. The prefixes in the name of a binary molecular compound tell you its composition.
9.3 Naming Binary Molecular Compounds What does a prefix in the name of a binary molecular compound tell you about the compound’s composition? A prefix in the name of a binary molecular compound tells how many atoms of an element are present in each molecule of the compound.
9.3 Naming Binary Molecular Compounds • Some guidelines for naming binary molecular compounds: • Name the elements in the order listed in the formula. • Use prefixes to indicate the number of each kind of atom. • Omit the prefix mono- when the formula contains only one atom of the first element in the name. • The suffix of the name of the second element is -ide.
9.3 Writing Formulas for BinaryMolecular Compounds How do you write the formula for a binary molecular compound? Use the prefixes in the name to tell you the subscript of each element in the formula. Then write the correct symbols for the two elements with the appropriate subscripts.
Practice Name each of the following binary molecular compounds: a.) O2F2 d.) SF2 b.)SiF4 e.) H2S c.)S4N4 f.) P4O10 Sulfur difluoride Dioxygen difluroide Silicon tetrafluoride dihydrogen sulfide Tetrasulfur tetranitride Tetraphosphorous decaoxide
9.4 Naming Acids What are the three rules for naming acids? What are acids? • An acid is a compound that contains one or more hydrogen atoms and produces hydrogen ions (H+) when dissolved in water. Acids have various uses.
9.4 Naming Acids • Three rules can help you name an acid with the general formula HnX. RULE #1 When the name of the anion (X) ends in -ide, the acid name begins with the prefix hydro-. The stem of the anion has the suffix-icand is followed by the wordacid. Ex. HCl(aq) Anion: Cl-1 = chloride Hydrochloric acid Practice: H2S(aq) Anion: S-2 = sulfide Hydrosulfuric acid
9.4 Naming Acids RULE #2 When the anion name ends in -ite, the acid name is the stem of the anion with the suffix -ous, followed by the word acid. Ex. H2SO3(aq) Anion: SO3 = sulfite Sulfurous acid Practice: HNO2(aq) HClO2 Anion: NO2 = nitrite nitrous acid Anion: ClO2 = chlorite chlorous acid
9.4 Naming Acids RULE #3 When the anion name ends in -ate, the acid name is the stem of the anion with the suffix -icfollowed by the word acid. Ex. HNO3(aq) Anion: NO3 = nitrate nitric acid Practice: H2SO4 H2CO3 Anion: SO4 = sulfate sulfuric acid Anion: CO3 = carbonate carbonic acid
9.4 Naming Acids • A Summary of the Three Rules for Naming Acids.
9.4 Writing Formulas for Acids • How are the formulas of acids determined? • Use the rules for writing the names of acids in reverse to write the formulas for acids. • What is the formula for hydrobromic acid? Following Rule 1, hydrobromic acid (hydro- prefix and -ic suffix) must be a combination of hydrogen ion (H+) and bromide ion (Br–). The formula of hydrobromic acid is HBr.