2. Covalent bonds result from the sharing of valence electrons between two atoms.

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1 CHAPTER 2.8 NAMING AND WRITING FORMULAS FOR IONIC AND COVALENT COMPOUNDS, ACIDS, AND HYDRATES Alpharetta High School Dr. Sonha Payne Elements combine to form compounds by the interaction of their valence electrons. There are two different kinds of bonding: 1. Ionic bonds result from the transfer of valence electrons from one element to another. 2. Covalent bonds result from the sharing of valence electrons between two atoms. Ionic bonds form between: A metal on the left side of the periodic table. A nonmetal on the right side of the periodic table. Ionic versus Covalent Bonding Na Cl 2 NaCl Covalent bonds are formed when two nonmetals combine. A molecule is a discrete group off atoms that share electrons. The valence electrons are available to participate in bonding The valence electrons are in the outermost shell (the highest number n) of an atom. Configuration # of valence e He 1s 2 2 Ne 1s 2 2s 2 2p 6 8 = Ar 1s 2 2s 2 2p 6 3s 2 3p 6 8 = O 1s 2 2s 2 2p 4 6 = S 1s 2 2s 2 2p 6 3s 2 3p 4 6 = Mn 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5 2 Lu 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 14 5d 1 2 Elements in the same group have the same number of valence electrons Group # 1A 8A = # valence electrons (except He = 2) A Lewis (Electron) Dot Symbol is a Convenient Way to Represent the Valence Electrons Dots representing valence electrons are placed on the four sides of an element symbol. Ex: All elements in Group 2A have 2 valence electrons. Each dot represents one valence electron. Boron 1s 2 2s 2 2p 1 3 valence electrons B B B other reasonable Lewis dot symbols for boron B Lewis dot symbol for boron 1

2 For 1 to 4 valence electrons, single dots are used. With > 4 valence electrons, the dots are paired. Element: # of Valence electrons: Na O Electron-dot symbol: H 1 H For main group metals such as Na, the number of dots is the number of electrons that are lost. For nonmetals in the second period, the number of unpaired dots is the number of bonds the atom can form. C 4 C O 6 O Cl 7 Cl Atoms Combine in Order to Achieve a More Stable Electron Configuration The noble gases are chemically very stable. They do not react readily with other substances. He Ne Ar Kr Xe Rn Number of valence electrons Maximum stability results when a chemical species is isoelectronic with a noble gas. Na: 1s 2 2s 2 2p 6 3s 1 : 1s 2 2s 2 2p 6 10 electrons total, isoelectronic with Ne Cl: 1s 2 2s 2 2p 6 3s 2 3p 5 Cl : 1s 2 2s 2 2p 6 3s 2 3p 6 18 electrons total, isoelectronic with Ar Ions may also be represented by Lewis Dot Symbols Na Na 1s 2 2s 2 2p 6 3s 1 1s 2 2s 2 2p 6 Valence electron lost in the formation of the ion. Core electrons not represented in the Lewis dot symbol 2 O O O 1s 2 2s 2 2p 4 O 2 1s 2 2s 2 2p 6 Remember the charge Ionic compounds consist of oppositely charged ions that have a strong electrostatic attraction for each other. Ions are charged species in which the number of protons and electrons in an atom is unequal. There are two types of ions, cations and anions. Cations are positively charged ions. A cation has fewer electrons than protons. By losing electrons, a metal atom forms a cation with a completely filled outer shell of electrons. Anions are negatively charged ions. An anion has more electrons than protons. By gaining electrons, a nonmetal atom forms an anion with a completely filled outer shell of electrons. Octet Rule = 8 Valence Electrons Atoms will gain, lose or share sufficient electrons to achieve the same number of valence electrons as a noble gas (i.e. 8 electrons) p 11 e Na 11 p 10 e isoelectronic with neon 1s 2 2s 2 2p 6 Na 7 11 p 18 e isoelectronic with argon 1s 2 2s 2 2p 6 3s 2 3p

3 Formation of a Sodium Cation, Formation of a Magnesium Cation, Mg 2+ Cations (Positive Ions) Are Smaller Than Their Neutral Atoms Because They Have Lost Their Outermost Electrons Octet Rule = 8 Valence Electrons Atoms will gain, lose or share sufficient electrons to achieve the same number of valence electrons as a noble gas (i.e. 8 electrons) p 17 e Cl Cl p 10 e isoelectronic with neon 1s 2 2s 2 2p p 18 e isoelectronic with argon 1s 2 2s 2 2p 6 3s 2 3p Formation of a Chloride Anion, Cl - Anions (Negative Ions) Are Larger Than Their Neutral Atoms Because They Have Added Electrons 3

4 Rules for Gaining or Losing Electrons Elements in the Same Group Form Ions of Similar Charge 1. Metals tend to lose electrons and form cations. 2. Nonmetals tend to gain electrons and form anions. 3. The number of electrons gained or lost rarely exceeds 3. Na 7 Cl 7+ The charge of a positive ion is equal to its Group number. Group 1A(1) = 1 + Group 2A(2) = 2 + Group 3A(3) = 3 + The charge of a negative ion is obtained by subtracting 8 or 18 from its Group number. Group 6A(16) = 6 8 = 2 or = 2 Cation Charge = Group Number Anion Charge = Group number 8 group 1A: M 1 valence e M + + e group 6A: X + 2e X 2 6 valence e charge = 6 8 = 2 group 2A: group 3A: M 2 valence e M e M 3 valence e M e group 7A: X + e X 7 valence e charge = 7 8 = 1 Remembering the Charges on Ions +1, +2, +3, Skip, -3, -2, -1, Zip Identify the element X in the following ions: a. X 2+, a cation with 36 electrons The +2 charge tells us it has lost 2 electrons. The ion must have 38 protons. So this element is strontium. b. X 3, an anion with 18 electrons The 3 charge tells us it has gained 3 electrons. The ion must have 15 protons. So this element is phosphorus. 4

5 Common Ions in the Human Body Write symbols for the following ions: First, figure out how many electrons have been gained or lost. a.the ion formed from a nitrogen atom gained 3 e b.the ion formed from an oxygen atom gained 2 e c.the ion formed from a lithium atom lost 1 e N 3- O 2 Li + Ionic compounds consist of oppositely charged ions that have a strong electrostatic attraction for each other. The attraction between oppositely charged ions constitutes an ionic bond. The Sum of the Charges in an Ionic Compound Must be Zero Overall In ionic compounds, the + s have to balance the s. The formula unit is the smallest whole-number repeating ratio of ions present in an ionic compound that results in charge neutrality. Ex: NaCl There really isn t such a thing as a specific ionic bond between specific pairs of ions. There are many ions attracted by ionic bonds to their nearest neighbors in a 3D array called a Lattice. Binary Ionic Compounds Compounds like NaCl, MgCl 2, LiF, KCl, CaF 2, LiBr, SrF 2, BaCl 2, NaI, etc. are called Binary Ionic Compounds Binary means two. Binary ionic compounds contain only 2 types of elements; one element is a metal and the other is a nonmetal. 5

6 How to write a formula for an ionic compound How to write a formula for an ionic compound Step [1] Identify which element is the cation and which is the anion. Step [2] Determine how many of each ion type is needed for an overall charge of zero. Metals form cations and nonmetals form anions. Use the group number of a main group element to determine the charge. K + Cl Ca 2+ O 2 metal nonmetal metal nonmetal group 1A group 7A group 2A group 6A When the cation and anion have the same charge, only one of each is needed. K + + Cl KCl Ca 2+ + O 2 CaO zero charge zero charge One of each ion is needed to balance charge. How to write a formula for an ionic compound Step [2] Determine how many of each ion type is needed for an overall charge of zero. When the cation and anion have different charges, Use the ion charges to determine the number of ions of each needed. Ca 2+ A +2 charge means 2 Cl anions are needed. Cl A -1 charge means 1 Ca 2+ cation is needed. How to write a formula for an ionic compound Step [3] To write the formula, place the cation first and then the anion, and omit charges. Example: KCl CaO CaCl 2 Use subscripts to show the number of each ion needed to have a zero overall charge. When no subscript is written, it is assumed to be 1. Ca 2+ + Cl CaCl 2 2 Cl for each Ca 2+ Writing Formulas of Ionic Compounds Case 1: the number of electrons lost by the metal atom is exactly the same number gained by the nonmetal. Ca 2+ O 2 In MgCl 2, Charge Balance in MgCl 2 A Mg atom loses two valence electrons Two Cl atoms each gain one electron Susbscripts indicate the number of ions needed to give charge balance +1 1 NaCl +2 2 CaO Case 2: the number of electrons lost by the metal atom is not the same number gained by the nonmetal. Mg MgCl 2 K + K + K + +3 K 3 N N 3 3 6

7 In Na 2 S, Charge Balance in Na 2 S Two Na atoms lose one valence electron each One S atom gains two electrons Susbscripts shoe the number of ions needed to give charge balance Summary: Writing Ionic Formulas An ionic formula/compound consists of positively and negatively charged ions is neutral has charge balance total positive charge = total negative charge The symbol of the metal is written first, followed by the symbol of the nonmetal written second. Write the Formula for the Compound Formed from Na and N Charge balance is used to write the formula for sodium nitride, a compound containing and N N 3 = Na 3 N 3(1+) + 1(3 ) = 0 If is combined with N 3, you will need 3 ions for every 1 N 3 ion to balance the charges; therefore, the formula must be Na 3 N. Writing Formulas of Ionic Compounds Select the correct formula for each of the following ionic compounds: A. Mg 2+ and O 2 check: Mg 2+ + O 2 = 1(2+) + 1(2 ) = 0 1) Mg 2 O 2 2) MgO 3) MgO 2 B. Al 3+ and 1) AlCl 3 2) AlCl 3) Al 3 Cl check: Al = (3+) + 3(1 ) = 0 C. Mg 2+ and N 3 1) MgN 2) Mg 2 N 3 3) Mg 3 N 2 check: 3Mg 2+ +2N 3 = 3(2+) + 2(3 ) = 0 Writing Formulas for Ionic Compounds Using the Crisscross Method Writing Formulas for Ionic Compounds Using the Crisscross Method 1. Write the symbol for the metal cation and its charge. 2. Write the symbol for the nonmetal anion and its charge. 3. Charge (without sign) becomes subscript for other ion. 4. Reduce subscripts to smallest whole number ratio. 5. Check that the total charge of the cations cancels the total charge of the anions. 1. Ba +2 column 2A 2. Cl- column 7A 3. Ba +2 Cl - 4. BaCl 2 5. Ba = (1) (+2) = +2 Cl = (2) ( 1) = 2 1. Write the symbol for the metal cation and its charge. 2. Write the symbol for the nonmetal anion and its charge. 3. Charge (without sign) becomes subscript for other ion. 4. Reduce subscripts to smallest whole number ratio. 5. Check that the total charge of the cations cancels the total charge of the anions. 1. Al 3+ column 3A 2. O 2- column 6A 3. Al 3+ O 2-4. Al 2 O 3 5. Al = (2) (+3) = +6 O = (3) ( 2) = 6 7

8 Writing Formulas for Ionic Compounds Using the Crisscross Method 1. Write the symbol for the metal cation and its charge. 2. Write the symbol for the nonmetal anion and its charge. 3. Charge (without sign) becomes subscript for other ion. 4. Reduce subscripts to smallest whole number ratio. 5. Check that the total charge of the cations cancels the total charge of the anions. 1. Ca 2+ column 2A 2. S 2- column 6A 3. Ca 2+ S 2-4. Ca 2 S 2 CaS 5. Ca = (1) (+2) = +2 S = (1) ( 2) = 2 Practice Writing Formulas of Binary Ionic Compounds Potassium iodide Gallium bromide Strontium fluoride Aluminum selenide Potassium nitride Magnesium phosphide Zinc chloride Calcium nitride Naming Cations Main group cations (in groups 1 (IA), 2 (IIA), and 13 (IIIA)) are named by identifying the metal, followed by the word ion. Examples: Li Lithium Li + Lithium ion Ca Calcium Ca 2+ Calcium ion Al Aluminum Al 3+ Aluminum ion Naming Anions Nonmetal anions are named by adding the suffix -ide to the stem of the nonmetal, followed by the word ion. Element Stem Formula of ion Name of ion Bromine brom- Br bromide ion Chlorine chlor- chloride ion Fluorine fluor- F fluoride ion Iodine iod- I iodide ion Nitrogen nitr- N 3 nitride ion Oxygen ox- O 2 oxide ion Phosphorus phos- P 3 phosphide ion Sulfur sulf- S 2 sulfide ion Naming Binary Ionic Compounds Name the cation and then the anion. Practice Naming Binary Ionic Compounds Do not specify the charge on the ion. Do not specify how many ions of each type are needed to balance charge. Metal sodium Mg 2+ magnesium + Nonmetal Stem+ide + F fluoride Cl chloride NaF sodium fluoride MgCl 2 magnesium chloride NaCl KI CaS Li 3 N CsBr MgO CsF AlCl 3 LiH Sodium chloride Potassium iodide Calcium sulfide Lithium nitride Cesium bromide Magnesium oxide Cesium fluoride Aluminum chloride Lithium hydride 8

9 Some Metals Form More than One Type of Cation Some transition metals, inner-transition metals, and a few other metals form more than one type of charged ion. Examples: Fe 2+ and Fe 3+, Cu + and Cu 2+, Au + and Au 3+, Mn 2+ and Mn 7+, etc. To name binary ionic compounds that contain these elements, we must indicate which ion is present. There are two ways to do this: a modern system, and an older system that is still in use. Modern (Systematic) Naming System Indicate the ionic charge of the metal by putting a roman numeral in parentheses following the name of the metal. Ionic charge of metal = roman numeral Examples: Fe FeCl 2 Iron(II) chloride Fe FeCl 3 Iron(III) chloride Only metals which can form more than one ion need the Roman numeral. Metals with a fixed ionic charge do NOT need the Roman numeral. Ag +, Zn 2+, and Cd 2+ form only one ion and do not require a Roman numeral Most Transition Metals and Group 4(14) Metals Form 2 or More Positive Ions Naming Binary Ionic Compounds Using the Older Common Name System The suffix -ous is added to the root metal name with the ion of lower charge. The suffix -ic is added to the root metal name with the ion of higher charge. Compound Modern Name Older Name FeCl 2 FeCl 3 CuF CuF 2 CoBr 2 CoBr 3 iron(ii) chloride iron(iii) chloride copper(i) fluoride copper(ii) fluoride cobalt(ii) bromide cobalt(iii) bromide ferrous chloride ferric chloride cuprous fluoride cupric fluoride cobaltous bromide cobaltic bromide How to Name an Ionic Compound That Contains a Metal with Variable Charge 1. Determine the charge of the cation from the anion. 2. Name the cation by the element name, and use a Roman numeral to show its charge. Ionic charge of metal = roman numeral Cu? F +1 1 CuF Cu? +2 F F 2 CuF 2 Practice Naming Ionic Compounds Containing a Transition Metal Cr 2 O 3 Fe 2 S 3 CuO Copper(I) fluoride Copper(II) fluoride 9

10 Polyatomic Ions A Polyatomic ion is a cation or anion that contains more than one atom. Both the formulas and the charges of the polyatomic ion must be memorized. NH 4 + OH CO 2 3 SO 2 4 CN NO 3 PO 3 4 ammonium ion hydroxide ion carbonate ion sulfate ion cyanide ion nitrate ion phosphate ion Rules For Naming Polyatomic Ions The names of common polyatomic anions End in ate ClO 3 - chlorate With one less oxygen end in ite ClO 2 - chlorite With two less oxygen end in ite and have prefix hypo ClO - hypochlorite With one more oxygen end in ate with prefix per ClO 4 - perchlorate With hydrogen attached use prefix hydrogen (or bi) HCO 3 - hydrogen carbonate (bicarbonate) Ionic Compounds Containing Polyatomic Ions The + s have to balance the s. In the formula, parentheses are used around the polyatomic ion if more than one is used. NaOH K 2 HPO 4 Ca(MnO 4 ) 2 NH 4 NO 3 contains OH contains K + HPO 2 4 contains Ca 2+ MnO 4 contains NH + 4 NO 3 Naming Compounds Containing Polyatomic Ions Polyatomic ion present Positive ion is present Negative ion is present Both ions are polyatomic 1. Polyatomic ion name 2. Stem of nonmetal name 3. Suffix ide 1. Full metal name 2. Possible Roman numeral 3. Polyatomic ion name 1. Positive polyatomic ion name 2. Negative polyatomic ion name NH 4 Cl Ammonium chloride Ca(MnO 4 ) 2 Calcium permanganate NH 4 NO 3 Ammonium nitrate 10

11 Flowchart for Naming Ionic Compounds Practice Naming Ionic Compounds MgS MgSO 3 MgSO 4 Ca(ClO 3 ) 2 CaCl 2 Ca(ClO 2 ) 2 Mg(NO 3 ) 2 PbO 2 Fe 2 (SO 4 ) 3 Ba 3 (PO 4 ) 2 Writing Formulas for Compounds Containing Polyatomic Ions Write the formula of each of the following substances: Determine the charge on the given metal ion Determine the charge on the given polyatomic ion In ionic compounds, the + s have to balance the s. Writing Formulas for Compounds Containing Polyatomic Ions Select the correct formula for each: a. Aluminum nitrate 1) AlNO 3 2) Al(NO) 3 3) Al(NO 3 ) 3 b. Copper(II) nitrate 1) CuNO 3 2) Cu(NO 3 ) 2 3) Cu 2 (NO 3 ) a. Sodium bicarbonate, HCO 3 - NaHCO 3 b. Aluminum hydroxide Al 3+, OH - Al(OH) 3 c. Lithium carbonate Li +, CO 3 2- Li 2 CO 3 c. Iron(III) hydroxide 1) FeOH 2) FeOH 3 3) Fe(OH) 3 d. Tin(IV) hydroxide 1) Sn(OH) 4 2) Sn(OH) 2 3) Sn 4 (OH) Writing Formulas for Ionic Compounds Potassium bromate Calcium carbonate Sodium phosphate Iron(III) oxide Summary: Ionic versus Covalent Bonding Transfer of electrons Metal and nonmetal Formula units Empirical formula Sharing of electrons 2 nonmetals Molecules Molecular formula Iron(II) nitrate Iron(II) hydroxide Copper(II) bromide Lithium phosphate Empirical Formula The simplest integer ratio of elements in a compound. Molecular Formula Represent the actual number of atoms of each element in a molecule of compound. 11

12 Covalent bonds result from the sharing of electrons between two nonmetal atoms. In covalent bonding, atoms share electrons until both atoms achieve a noble gas configuration. (8e except H which only needs 2e ) The resulting collection of atoms is called a molecule. Remember the Octet Rule Atoms will gain, lose or share electrons to achieve the same number of valence electrons as a noble gas (i.e. 8 electrons). Example: By sharing the two electrons, each H achieves 2e, the electron configuration of He. 7 Elements that Exist as Diatomic Molecules Example How to Name a Covalent Compound Name each covalent molecule: (a) NO 2 (b) N 2 O 4 Step [1] Name the first nonmetal by its element name and the second using the suffix IDE. (a) NO 2 (b) N 2 O 4 Nitrogen oxide nitrogen oxide Have No Fear Of Ice Cold Beer H 2 N 2 F 2 O 2 I 2 Cl 2 Br 2 Step [2] Add prefixes to show the number of atoms of each element. Mono is usually dropped when it appears at the beginning. (a) NO 2 (b) N 2 O 4 Nitrogen dioxide dinitrogen tetroxide Greek Prefixes Used to Indicate Number of Atoms in Covalent Compounds Naming Binary Covalent Compounds SO 3 NI 3 S 2 O 7 CCl 4 N 2 O 5 CO 2 CO sulfur trioxide nitrogen triiodide disulfur heptoxide carbon tetrachloride dinitrogen pentoxide carbon dioxide carbon monoxide 12

13 Writing Formulas of Binary Covalent Compounds Sulfur tetrafluoride Tetraphosphorus decasulfide Sulfur trioxide Disulfur decafluoride Compounds Containing Hydrogen 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. B 2 H 6 Diborane SiH 4 Silane NH 3 Ammonia PH 3 Phosphine H 2 O Water H 2 S Hydrogen sulfide An acid is a substance that produces hydrogen ions (H + ) when dissolved in water. Ex: HCl Naming Binary Acids hydro - nonmetal root ic acid 1. The word hydrogen in the anhydrous compound name is dropped. 2. The prefix hydro- is attached to the stem of the name of the nonmetal that is combined with hydrogen. 3. The suffix -ide on the stem of the nonmetal that is combined with hydrogen is replaced with the suffix -ic. 4. The word acid is added the the end of the name as a separate word. 5. If the nonmetal is sulfur or phosphorus, the stems sulfand phosph- are expanded to sulfur- and phosphor- for pronunciation reasons before the -ic suffix is added. Naming Binary Acids HCl HBr hydrogen chloride hydrogen bromide hydro + chlor + ic acid hydro + brom + ic acid hydrochloric acid hydrobromic acid H 2 S hydrogen sulfide hydro + sulfur + ic acid hydrosulfuric acid A compound must contain at least one ionizable hydrogen atom to be an acid upon dissolving. Naming Oxyacids 1. All hydrogens that are written as the first part of the formula of the acid are dropped. 2. The polyatomic ion that remains is named. 3. If the polyatomic ion ends with the suffix -ate, the suffix is replaced by the suffix -ic, and the word acid is added. 4. If the polyatomic ion ends with the suffix -ite, the suffix is replaced by the suffix -ous, and the word acid is added. 5. If the polyatomic ion contains sulfur or phosphorus, the stems sulf- and phos- are expanded to sulfur- and phosphor- for pronunciation reasons before the -ic or - ous suffixes are added. 13

14 Naming Oxyacids Names and Formulas of Common Acids H 2 SO 4 SO 4 2 = sulfate ion sulfuric acid HNO 3 NO 3 = nitrate ion nitric acid HNO 2 NO 2 = nitrite ion nitrous acid A hydrate is an ionic compound that has a specific number of water molecules within its solid lattice structure. BaCl 2 2H 2 O MgSO 4 7H 2 O Sr(NO 3 ) 2 4H 2 O CuSO 4 5H 2 O Name the ionic compound followed by a Greek prefix indicating the number of water molecules and the word hydrate. Copper(II) sulfate pentahydrate 14