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Chemistry: Atoms First Julia Burdge & Jason Overby Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 5 Naming Ionic and Covalent Compounds Kent L. McCorkle Cosumnes River College Sacramento, CA Homework: Chapter 5. 23, 25, 27, 55, 61, 63, 99 and 111
A compound is a substance composed of two or more elements combined in a specific ratio and held together by chemical bonds. Familiar examples of compounds are water and salt (sodium chloride).Compounds 5.1
Ionic Compounds and Bonding The resulting electrically neutral compound, sodium chloride, is represented with the chemical formula NaCl. The chemical formula, or simply formula, of an ionic compound denotes the constituent elements and the ratio in which they combine.
A monatomic ion is named by changing the ending of the element’s name to –ide. Cl – is chlorideO 2– is oxide Some metals can form cations of more than one possible charge. Fe 2+ : ferrous ion [Fe(II)] Fe 3+ : ferric ion [Fe(III)] Mn 2+ : manganese(II) ion Mn 3+ : manganese(III) ion Mn 4+ : manganese(IV) ion Naming Ions and Ionic Compounds 5.4
Formulas for ionic compounds are generally empirical formulas. Ionic compounds are electronically neutral.
Al 3+ O 2– Al 2 O 3 In order for ionic compounds to be electronically neutral, the sum of the charges on the cation and anion in each formula must be zero. Aluminum oxide: Sum of charges:2(+3) + 3(–2) = 0 Formulas of Ionic Compounds
Naming Ions and Ionic Compounds To name ionic compounds: 1) Name the cation omit the word ion use a Roman numeral if the cation can have more than one charge 2) Name the anion omit the word ion Examples: NaCN sodium cyanide FeCl 2 iron(II) chloride FeCl 3 iron(III) chloride
Polyatomic ions consist of a combination of two or more atoms. Formulas are determined following the same rule as for ionic compounds containing only monatomic ions: ions must combine in a ratio that give a neutral formula overall. Calcium phosphate: Covalent Bonding in Ionic Species 5.7 Ca 2+ PO 4 3– Ca 3 (PO 4 ) 2 Sum of charges:3(+2) + 2(–3) = 0
Worked Example 5.9 Strategy Begin by identifying the cation and anion in each compound, and then combine the names for each, eliminating the word ion. Name the following ionic compounds: (a) Fe 2 (SO 4 ) 3, (b) Al(OH) 3, and (c) Hg 2 O. Solution (a) Fe 2 (SO 4 ) 3 is iron(III) sulfate. (b) Al(OH) 3 is aluminum hydroxide. (c) Hg 2 O is mercury(I) oxide. Think About It Be careful not to confuse the subscript in the formula with the charge in the metal ion. In part (a), for example, the subscript on Fe is 2, but this is an iron(III) compound.
Covalent Bonding in Ionic Species Oxoanions are polyatomic anions that contain one or more oxygen atoms and one atom (the “central atom”) of another element. Starting with the oxoanions that end in –ate, we can name these ions as follows: 1)The ion with one more O atom than the –ate ion is called the per…ate ion. Thus, ClO 3 - is the chlorate ion, so ClO 4 - is the perchlorate ion. 2)The ion with one less O atom than the –ate ion is called the –ite ion. Thus, ClO 2 - is the chlorite ion. 3)The ion with two fewer O atom than the –ate ion is called the hypo…ite ion. Thus, ClO - is the hypochlorite ion. At minimum, memorize the oxoanions that end in –ate so you can apply these guidelines when necessary.
Worked Example 5.10 Strategy Each species is either an oxoanion or an oxoacid. Identify the “reference oxidation” (the one with the –ate ending) for each, and apply the rules to determine appropriate names. Name the following species: (a) BrO 4 -, (b) HCO 3 -, and (c) H 2 CO 3. Solution (a) BrO 4 - has one more O atom than the bromate ion (BrO 3 - ), so BrO 4 - is the perbromate ion. (b) CO 3 2- is the carbonate ion. Because HCO 3 - has one ionizable hydrogen atom, it is called the hydrogen carbonate ion. (c) With two ionizable hydrogen atoms and no charge on the compound, H 2 CO 3 is carbonic acid. Think About It Make sure that the charges sum to zero in each compound formula. In part (a), for example, Hg 2+ + 2Cl - = (+2) + 2(-1) = 0; in part (b), (+2) + 2(-1) = 0; and in part (c), 3(+1) + (-3) = 0. Think About It Remembering all these names and formulas is greatly facilitated by memorizing the common ions that end in –ate. chlorateClO 3 - nitrate NO 3 - iodateIO 3 - carbonateCO 3 2- bromateBrO 3 - oxalate C 2 O 4 2- sulfateSO 4 2- chromate CrO 4 2- phosphatePO 4 3- permanganate MnO 4 -
Worked Example 5.11 Strategy The –ous ending in the name of an acid indicates that the acid is derived from an oxoanion ending in –ite. The oxoanion must be sulfite, SO 3 2-, so add enough hydrogen ions to make a neutral formula. Determine the formula of sulfurous acid. Solution The formula of sulfurous acid is H 2 SO 3. Think About It Remembering all these names and formulas is greatly facilitated by memorizing the common ions that end in -ate.
Hydrates A hydrate is a compound that has a specific number of water molecules within its solid structure. For example, in its normal state, copper(II) sulfate has five water molecules associated with it. Systematic name: copper(II) sulfate pentahydrate Formula: Cu(SO) 4 ∙ 5H 2 O Some other hydrates are BaCl 2 ∙ 2H 2 O LiCl ∙ H 2 O MgSO 4 ∙ 7H 2 O Sr(NO 3 ) 2 ∙ 4H 2 O
Hydrates When the water molecules are driven off by heating, the resulting compound, Cu(SO) 4, is sometimes called anhydrous copper(II) sulfate. Anhydrous means the compound no longer has water molecules associated with it.
A chemical formula denotes the composition of the substance. A molecular formula shows the exact number of atoms of each element in a molecule. Some elements have two or more distinct forms known as allotropes. For example, oxygen (O 2 ) and ozone (O 3 ) are allotropes of oxygen. A structural formula shows not only the elemental composition, but also the general arrangements. Covalent Bonding and Molecules
Molecular substances can also be represented using empirical formulas, the whole-number ratio of elements. While, the molecular formulas tell us the actual number of atoms (the true formula), the empirical formula gives the simplest formula. Molecular formula: N 2 H 4 Empirical formula: NH 2 The molecular and empirical formulas are often the same. Covalent Bonding and Molecules
Remember that binary molecular compounds are substances that consist of just two different elements. Nomenclature: 1) Name the first element that appears in the formula. 2) Name the second element that appears in the formula, changing its ending to –ide. Examples: HCl hydrogen chloride HIhydrogen iodide Naming Molecular Compounds 5.6
Greek prefixes are used to denote the number of atoms of each element present. Naming Molecular Compounds
The prefix mono- is generally omitted for the first element. For ease of pronunciation, we usually eliminate the last letter of a prefix that ends in “o” or “a” when naming an oxide. Example: N 2 O 5 is dinitrogen pentoxide not dinitrogen pentaoxide Naming Molecular Compounds
Worked Example 5.7 Strategy Each compound will be named using the systematic nomenclature including, where necessary, appropriate Greek prefixes. Name the following binary molecular compounds: (a) NF 3 and (b) N 2 O 4. Solution (a) nitrogen trifluoride (b) dinitrogen tetroxide Think About It Make sure that the prefixes match the subscripts in the molecular formulas and that the word oxide is not preceded immediately by an “a” or an “o”.
Worked Example 5.8 Strategy The formula for each compound will be deduced using the systematic nomenclature guidelines. Write the chemical formulas for the following binary molecular compounds: (a) sulfur tetrafluoride and (b) tetraphosphorus decasulfide. Solution (a) SF 4 (b) P 4 S 10 Think About It Double-check that the subscripts in the formulas match the prefixes in the compound names: (a) 4 = tetra and (b) 4 = tetra and 10 = deca.
The names of molecular compounds containing hydrogen do not usually conform to the systematic nomenclature guidelines. Many are called by the common, nonsystematic names or by names that do not indicate explicitly the number of H atoms present. Examples: B 2 H 6 Diborane SiH 4 Silane NH 3 Ammonia PH 3 Phosphine H 2 OWater H 2 SHydrogen sulfide Compounds Containing Hydrogen
One definition of an acid is a substance that produces hydrogen ions (H + ) when dissolved in water. HCl is an example of a binary compound that is an acid when dissolved in water. To name these types of acids: 1) remove the –gen ending from hydrogen 2) change the –ide ending on the second element to –ic. hydrogen chloride → hydrochloric acid
Compounds Containing Hydrogen A compound must contain at least one ionizable hydrogen atom to be an acid upon dissolving.
Our nomenclature discussion so far has focused on inorganic compounds, generally defined as those without carbon. Organic compounds contain carbon and hydrogen, sometimes in combination with other atoms. Hydrocarbons contain only carbon and hydrogen. The simplest hydrocarbons are called alkanes. Organic Compounds
Many organic compounds contain groups of atoms known as functional groups, which often determine a molecule’s reactivity.
A molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds H2H2 H2OH2ONH 3 CH 4 A diatomic molecule contains only two atoms H 2, N 2, O 2, Br 2, HCl, CO A polyatomic molecule contains more than two atoms O 3, H 2 O, NH 3, CH 4
Writing Chemical Formals One way to remember these elements is: Mr. BrINClHOF There are 7 elements that occur in nature as a diatomic molecule
A monatomic ion contains only one atom A polyatomic ion contains more than one atom Na +, Cl -, Ca 2+, O 2-, Al 3+, N 3- OH -, CN -, NH 4 +, NO 3 -
Guidelines for Writing Chemical Formulas for Binary Compounds 1.Except for Hydrogen, the element farther to the left in the periodic table appears first. Ie: KCl, PCl 3, Al 2 S 3, and Fe 3 O 4 2.If hydrogen is present, it appears last except when the other element is from group 16 or 17. Ie: LiH, NH 3, B 2 H 6, CH 4 H 2 O, HCl and HI 3.If both elements are from the same group, the lower one appears first. Ie: SiC and BrF 3
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 H2OH2O H2OH2O molecularempirical C 6 H 12 O 6 CH 2 O O3O3 O N2H4N2H4 NH 2
ionic compounds consist of a combination of cations and an anions the formula is always 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
Formula of Ionic Compounds Al 2 O 3 2 x +3 = +63 x -2 = -6 Al 3+ O 2- CaBr 2 1 x +2 = +22 x -1 = -2 Ca 2+ Br - Na 2 CO 3 1 x +2 = +21 x -2 = -2 Na + CO 3 2-
MUSTKNOWMUSTKNOW IonName (common name)IonName (Common name) NH 4 + AmmoniumCO 3 2- Carbonate H3O+H3O+ HydroniumHCO 3 - Hydrogen carbonate (bicarbonate) OH - HydroxideSO 3 2- Sulfite CN - CyanideHSO 3 - Hydrogen sulfite NO 2 - NitriteSO 4 2- Sulfate NO 3 - NitrateHSO 4 - Hydrogen sulfate ClO - Hypochlorite (often written OCl - ) SCN - Thiocyanate ClO 2 - ChloriteS 2 O 3 2- Thiosulfate ClO 3 - ChlorateCrO 4 2- Chromate ClO 4 - PerchlorateCr 2 O 7 2- Dichromate MnO 4 - PermanganatePO 4 3- Phosphate CH 3 CO 2 - Acetate (can be written C 2 H 3 O 2 - ) HPO 4 2- Hydrogen phosphate C 2 O 4 2- OxalateH 2 PO 4 - Dihydrogen phospate
Recognizing Ionic Compounds A compound is ionic if it contains a metal from group 1 Or group 2 or one of the polyatomic ions. Binary metal Oxides and sulfides also have ionic character
Chemical Nomenclature Ionic Compounds –often a metal + nonmetal –anion (nonmetal), add “ide” to element name BaCl 2 barium chloride K2OK2O potassium oxide Mg(OH) 2 magnesium hydroxide KNO 3 potassium nitrate
Cations of Variable Charge Transition metals such as copper may form cations Of different charge. This is represented by placing a Roman numeral after the transition metal in Parentheses after the name of the metal. CuO Copper(II) oxide Cu 2 O Copper(I) oxide
Transition metal ionic compounds –indicate charge on metal with Roman numerals FeCl 2 2 Cl - -2 so Fe is +2 iron(II) chloride FeCl 3 3 Cl - -3 so Fe is +3 iron(III) chloride Cr 2 S 3 3 S -2 -6 so Cr is +3 (6/2)chromium(III) sulfide
Molecular compounds nonmetals or nonmetals + metalloids common names H 2 O, NH 3, CH 4, C 60 element further left in periodic table is 1 st element closest to bottom of group is 1 st if more than one compound can be formed from the same elements, use prefixes to indicate number of each kind of atom last element ends in ide
HIhydrogen iodide NF 3 nitrogen trifluoride SO 2 sulfur dioxide N 2 Cl 4 dinitrogen tetrachloride NO 2 nitrogen dioxide N2ON2Odinitrogen monoxide Molecular Compounds TOXIC ! Laughing Gas
An acid can be defined as a substance that yields hydrogen ions (H + ) when dissolved in water. HCl Pure substance, hydrogen chloride Dissolved in water (H + Cl - ), hydrochloric acid An oxoacid is an acid that contains hydrogen, oxygen, and another element. HNO 3 nitric acid H 2 CO 3 carbonic acid H 2 SO 4 sulfuric acid HNO 3
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
Hydrates A hydrate is an ionic compound that has water molecules Incorporated into their solid structures Writing the formula: name of ionic compound-# H 2 O Copper(II)sulfate. pentahydrate Olmsted Williams
Writing Chemical Formulas For non ionic compounds with more than 2 atoms Write Carbon first Hydrogen second All other elements in alphabetical order 4 Hydrogen 2 Carbons 4 oxygens 1 Fluorine 1 Sulfur C 2 H 4 FlO 4 S 4 Carbons 1 Bromine 8 Hydrogen 1 Chlorine 2 Nitrogen 4 Oxygens C 4 H 8 BrClN 2 O 4 Let’s try some……………… 4 Iodines 6 Carbons 10 Hydrogens C 6 H 10 I 4
Structural Formulas for Carbon Containing Compounds Draw a line to show a connection between all elements in a molecule Carbon makes 4 connections (this makes them central or inside atoms) Oxygen and Sulfur make 2 Halogens and Hydrogen make 1 (terminal atoms) Nitrogen makes 3 Let’s try some………………… C 2 H 5 FlO (This molecule contains an alcohol (OH) H-C-C-O-H Fl H H H C 4 H 7 ClN (This molecule contains An amine, NH 2 ) Cl-C-C-C-C-N HH H HH H H H HH
Line Formulas for Carbon Containing Compounds All ends and corners represent a Carbon Hydrogens on Carbons are NOT shown All other elements and Hydrogens not on a Carbon are shown Let’s try some………………… (It always helps to draw the structural formula first) C 2 H 5 FlO (This molecule contains an alcohol (OH) H-C-C-O-H Fl H H H C 4 H 7 ClN (This molecule contains An amine, NH 2 ) Cl-C-C-C-C-N HH H HH H H H HH F O H Cl N H H
Naming Carbon Compounds Prefixes for number of carbons 1Meth- 2Eth- 3Prop- 4But- 5Pent- 6Hex- 7Hept- 8Oxt- 9Non- 10Dec- If there are only single bonds The ending is ane Hydrogens are understood All other groups attached to a carbon are listed before the carbon based name If the compound is circular the Prefix cyclo is attached If there is an –OH group attached The compound ends in ol Let’s try some problems……………………….