Chapter 3 Molecules, Compounds, and Chemical Equations

Molecular View of Elements and Compounds 2

How do atom join together to form a compound? compounds are made of atoms held together by chemical bonds ionic bonds result when electrons have been transferred between atoms, resulting in oppositely charged ions that attract each other Metal + Nonmetal covalent bonds result when two atoms share some of their electrons Nonmetal + Nonmetal 3

Representing Compounds with Chemical Formula compounds are generally represented with a chemical formula all chemical formulas tell what elements are in the compound ◦ use the letter symbol of the element Empirical Formula describe the kinds of elements found in the compound and the ratio of their atoms ◦ Simplest form of a molecule or compound ◦ they do not describe how many atoms, the order of attachment, or the shape ◦ the formulas for ionic compounds are empirical Molecular Formula describe the kinds of elements found in the compound and the numbers of their atoms ◦ they do not describe the order of attachment, or the shape 4

Chemical Formulas 5 Hydrogen Peroxide Molecular Formula = H 2 O 2 Empirical Formula = HO Glucose Molecular Formula = C 6 H 12 O 6 Empirical Formula = CH 2 O

Ionic Compounds metals + nonmetals no individual molecule units, instead have a 3-dimensional array of cations and anions made of formula units many contain polyatomic ions ◦ Two or nonmetals are bonded and carried charge Writing Formulas for Ionic Compounds 6

Some Common Polyatomic Ions 7 NameFormula acetateC2H3O2–C2H3O2– carbonateCO 3 2– hydrogen carbonate (aka bicarbonate) HCO 3 – hydroxideOH – nitrateNO 3 – nitriteNO 2 – chromateCrO 4 2– dichromateCr 2 O 7 2– ammoniumNH 4 + NameFormula hypochloriteClO – chloriteClO 2 – chlorateClO 3 – perchlorateClO 4 – sulfateSO 4 2– sulfiteSO 3 2– hydrogen sulfate (aka bisulfate) HSO 4 – hydrogen sulfite (aka bisulfite) HSO 3 –

Examples Complete the names of the following ions: Ca 2+ Al 3+ ________ __________ N 3  Se 2  _________ __________ Polyatomic ions NH 4 + CO 3 2- ____________________________ HPO 4 2- CN - _____________________________ 8

Writing Ionic compound Identify the cation and anion Combine the cation and anion together to produce an electrically charged compound. ◦ If the charges on the cation and anion are NOT equal in magnitude, use the charge on the cation as the subscript for the anion. Use the charge on the anion (omitting the negative sign) as the subscript for the cation. ◦ Place parentheses around a polyatomic ion if you need more than one of them in the final formula. ◦ Do not show the charges of the ions when you write the final formula for the compound Make sure that the subscripts for the cation and anion are the smallest whole number ratio.

Examples What are the formulas and names for compounds made from the following ions? potassium ion with a nitride ion Ammonium ion with a sulfide ion 10

Examples Write a formula for the combination of the following ions then give a systematic name for each compound NH 4 + and SO 4 2- Al 3+ and PO 4 3-

Transitional Metal Cations Metals with Invariant Charge ◦ metals whose ions can only have one possible charge  Groups 1A +1 & 2A +2, Al +3, Ag +1, Zn +2, Sc +3 ◦ cation name = metal name with Roman numeral in parenthesis 12

Examples Write formulas and provide their names 1. Pb 4+ and S Cu 2+ and F -

Example – Naming Binary Ionic with Invariant Charge Metal CsF 1. Identify cation and anion Cs = Cs + because it is Group 1A F = F - because it is Group 7A 2. Name the cation Cs + = cesium 3. Name the anion F - = fluoride 4. Write the cation name first, then the anion name cesium fluoride 14

Example – Naming Ionic Compounds Containing a Polyatomic Ion Na 2 SO 4 1. Identify the ions 2. Name the cation 3. Name the anion 4. Write the name of the cation followed by the name of the anion 15

Name the following compounds 1. TiCl 4 2. Au 2 S 3 3. MnO 16

Practice - What are the formulas for compounds made from the following ions? 1. iron(III) ion with a bromide ion 2. aluminum ion with a sulfate ion 3. chromium(II) with hydrogen carbonate 17

Hydrates hydrates are ionic compounds containing a specific number of waters for each formula unit water of hydration often “driven off” by heating in formula, attached waters follow ∙ CoCl 2 ∙6H 2 O in name attached waters indicated by suffix -hydrate after name of ionic compound CoCl 2 ∙6H 2 O = cobalt(II) chloride hexahydrate CaSO 4 ∙½H 2 O = calcium sulfate hemihydrate 18 PrefixNo. of Waters hemi½ mono1 di2 tri3 tetra4 penta5 hexa6 hepta7 octa8 Hydrate CoCl 2 ∙ 6H 2 O Anhydrous CoCl 2

Practice 1. What is the formula of magnesium sulfate heptahydrate? 2. What is the name of NiCl 26H 2 O? 19

Naming Covalent Compounds N2F4N2F4 The second element listed is more anionlike and takes the name of the element with an “ide” modification to the ending. The first element listed is more cationlike and takes the name of the element. The prefix is added to the front of each to indicate the number of each atom. dinitrogen tetrafluoride 20

Naming Chemical Compounds Binary Molecular Compounds dinitrogen tetroxideN2O4N2O4 carbon monoxideCO Whenever the prefix for the first element is “mono,” drop it. Whenever the prefix ends in “a” or “o” and the element name begins with a vowel, drop the “a” or “o” in the prefix. carbon dioxideCO 2 21

Subscript - Prefixes 1 = mono- ◦ not used on first nonmetal 2 = di- 3 = tri- 4 = tetra- 5 = penta = hexa- 7 = hepta- 8 = octa- 9 = nona- 10 = deca-

Name the following 1. NO 2 2. PCl 5 3. I 2 F 7 23

Example – Binary Molecular dinitrogen pentoxide Identify the symbols of the elements nitrogen = N oxide = oxygen = O Write the formula using prefix number for subscript di = 2, penta = 5 N2O5N2O5 24

Write formulas for the following 1. dinitrogen tetroxide 2. sulfur hexafluoride 3. diarsenic trisulfide 25

Acids acids are molecular compounds that form H + when dissolved in water ◦ to indicate the compound is dissolved in water (aq) is written after the formula  not named as acid if not dissolved in water sour taste dissolve many metals ◦ like Zn, Fe, Mg; but not Au, Ag, Pt formula generally starts with H ◦ e.g., HCl, H 2 SO 4 26

Acids Contain H +1 cation and anion ◦ in aqueous solution Binary acids have H +1 cation and nonmetal anion Oxyacids have H +1 cation and polyatomic anion 27

Naming Binary Acids write a hydro prefix follow with the nonmetal name change ending on nonmetal name to –ic write the word acid at the end of the name E.g HCl HCN 28

Naming Oxyacids if polyatomic ion name ends in –ate, then change ending to –ic suffix if polyatomic ion name ends in –ite, then change ending to –ous suffix write word acid at end of all names E.g H 2 SO 4 vs. H 2 SO 3 29

Writing Formulas for Acids when name ends in acid, formulas starts with H write formulas as if ionic, even though it is molecular hydro prefix means it is binary acid, no prefix means it is an oxyacid for oxyacid, if ending is –ic, polyatomic ion ends in –ate; if ending is –ous, polyatomic ion ends in –ous E.g Hydrosulfuric acidvs. Carbonic acid 30