Ch. 4: Compounds and Their Bonds

1. Ch. 4: Compounds and Their Bonds Chem. 20 El Camino College

2. Octet Rule • 8 e-s is a magic number • Main Group elements (except H and He) will give, take, or borrow electrons to reach 8 electrons in the outermost shell • Noble Gases (except He) have 8 electrons in the outer shell, so they don’t give or take electrons

3. Cations: Positive Ions • Atoms are neutral • Ions have a charge • Cations are positive, Anions are negative • Metals lose e-s easily to form cations • When electrons are lost, the particle left over has a positive charge.

4. Main Group. Cations: Positive Ions • Ex. Sodium atom has one valence electron. When Na loses 1 e-, a cation with a positive charge forms • The name of Na+ is sodium ion • Note, for a +1 charge, just show +.

5. Main Group. Cations: Positive Ions • Ex. Mg atom has 2 valence electrons • When Mg loses 2 electrons, a cation with a +2 charge forms • The name of Mg2+ is magnesium ion • Note, show the number, then the charge.

8. Anions: Negative Ions • Nonmetals gain electrons easily to form anions • When electrons are gained, the particle has a negative charge • Example: When Cl gains 1 e-, an anion with -1 charge forms • The name of Cl- is chloride ion.

10. Anions: Negative Ions • Ex. How many valence e-s does N have? • 5 • How many e-s will N gain to reach 8? • 3 • The formula for nitride ion is N3-

11. Names of Ions • For metal ions in groups. 1, 2, and 3, the name is the metal plus the word “ion” • K+ is potassium ion • Ca2+ is calcium ion • What is the name of Al3+? • aluminum ion

12. Names of anions • For anions (nonmetal ions), the name is the nonmetal in ide form, plus the word “ion” • F- is fluoride ion • O2- is oxide ion • What is the name of S2-? • sulfide ion

13. Name These • lithium • lithium ion • phosphide ion • phosphorus • barium ion • barium • Li • Li+ • P3- • P • Ba2+ • Ba

14. Charges from Group number • Gp 1 (1A) metals form + ions • Gp 2 (2A) metals form 2+ ions • Gp 13 (3A) metals form 3+ ions • Gp 15 (5A) nonmetals form 3- ions • Gp 16 (6A) nonmetals form 2- ions • Gp 17 (7A) nonmetals form - ions

16. Ionic Compounds • An ionic bond occurs when one atom gives electrons to another • Compounds always have zero charge.

19. Predicting Ionic Formulas • Determine the charge of each ion • Combine ions to get zero charge overall • Use the lowest numbers possible • Ex. A compound contains sodium ions and sulfide ions. Write the formula. • Sodium ion is Na+, sulfide ion is S2- • It will take 2 Na+ ions to cancel the charge in one S2- ion • The formula is Na2S.

21. Write the Formulas • KI • CaCl2 • AlN • BeF2 • Li2S • Al2O3 compound contains • potassium ions, iodide ions • chloride ions, calcium ions • aluminum ions, nitride ions • beryllium ions, fluoride ions • sulfide ions, lithium ions • aluminum ions, oxide ions

22. Naming Ionic Compounds • The 1st word is the cation name (metal ion) • The 2nd word is the anion name • Never use the word “ion” in a name • lithium bromide • magnesium fluoride • calcium sulfide • calcium phosphide • potassium oxide • aluminum chloride • LiBr • MgF2 • CaS • Ca3P2 • K2O • AlCl3

24. Transition Metal Ions • Some transition metals may form many cations • Know these transition metal ions • Cr2+, Cr3+ chromium(II) ion, chromium(III) ion • Fe2+, Fe3+ iron(II) ion, iron(III) ion • Cu+, Cu2+ copper(I) ion, copper(II) ion • Sn2+, Sn4+ tin(II) ion, tin(IV) ion • Pb2+, Pb4+ lead(II) ion, lead(IV) ion

25. Transition Metal Ions • Chromium can form two ions: Cr2+, Cr3+ • To name, use a Roman numeral in parentheses and the word “ion” • The name of Cr3+ is chromium(III) ion • What is the name of Pb4+? • lead(IV) ion (note--parentheses are only for elements that form more than one ion such as Cr, Fe, Cu, Sn, Pb) • What is the name of Ag? • silver • What is the name of Ag+? • silver ion

27. Transition Metals in Compounds • When a compound contains a transition metal with variable charge, you must determine what the charge is • Ex. Name FeCl2 • Is that Fe2+ or Fe3+? • Since chloride ion is Cl- and there are 2 of them, this must be iron(II) ion • Iron(II) chloride • Write the formula for iron(III) bromide • FeBr3

28. Examples • Name CuO, Cu2O, Fe2S3, FeO, PbS, PbS2, AgCl • copper(II) oxide • copper(I) oxide • iron(III) sulfide • iron(II) oxide • lead(II) sulfide • lead(IV) sulfide • silver chloride

29. Formulas Jumbo Practice 1 • chromium(III) bromide, chromium(II) sulfide, zinc oxide, tin(II) nitride, tin(IV) nitride, tin(II) oxide • CrBr3 • CrS • ZnO • Sn3N2 • Sn3N4 • SnO

30. Polyatomic Ions • Polyatomic ions are ions that contain more than 1 atom • Never change the numbers inside or the charge of a polyatomic ion • If you need more than one polyatomic ion, use parentheses.

32. OH- • Hydroxide ion is OH- • To write the formula of sodium hydroxide • Sodium ion is Na+ • Hydroxide ion is OH- • NaOH

33. OH- • To write the formula of calcium hydroxide • Calcium ion is Ca2+ • Hydroxide ion is OH- • Ca(OH)2 • Note: Writing CaO2H2 or CaOH2 is incorrect

34. Other Polyatomic Ions • Nitrate ion NO3-, sulfate ion SO42-, phosphate ion PO43- • Write the formulas for sodium nitrate, sodium sulfate, and sodium phosphate • NaNO3 • Na2SO4 • Na3PO4 • Write the formulas for calcium nitrate, calcium sulfate, and calcium phosphate • Ca(NO3)2 • CaSO4 • Ca3(PO4)2

35. Other Polyatomic Ions • Be careful with similar sounding ions • sulfate ion SO42-, sulfite ion SO32-, sulfide ion S2- • hydrogen sulfate ion HSO4- • carbonate ion CO32- • hydrogen carbonate ion HCO3- • acetate ion C2H3O2- • ammonium ion NH4+

37. Examples • Name CuNO3, Cu2SO3, ZnSO3, Sn(C2H3O2)4, KHCO3 • copper(I) nitrate • copper(I) sulfite • zinc sulfite • tin(IV) acetate • potassium hydrogen carbonate

38. Formulas • chromium(III) hydrogen sulfate, iron(II) phosphate, zinc hydroxide, tin(II) carbonate, ammonium acetate • Cr(HSO4)3 • Fe3(PO4)2 • Zn(OH)2 • SnCO3 • NH4C2H3O2

39. Ionic vs. Covalent • All the compounds we’ve looked at so far are ionic • The cation of an ionic compound is a metal ion or ammonium ion • The anion of an ionic compound is a nonmetal ion or polyatomic ion • In ionic compounds, e-s are given from one atom to another.

40. Ionic vs. Covalent • Covalent compounds are made of 2 nonmetals • In covalent compounds, e-s are shared (not given away) • Covalent compounds are called molecules • Ionic compounds are never called molecules.

42. H2 hydrogen N2 nitrogen O2 oxygen F2 fluorine Cl2 chlorine Br2 bromine I2 iodine Diatomic Molecules are Formed by Covalent Bonds • There are 7 elements that form diatomic molecules • Formulas for these elements are always shown with subscript “2”

43. Fig. 6-1, p. 137

46. Examples • Write the formulas • gold • iodine • helium • nitrogen • oxygen • potassium • Au • I2 • He • N2 • O2 • K

47. Naming Compounds • A compound is 2 or more elements bonded together • The rules for naming covalent (nonmetal-nonmetal) compounds are different than the rules for ionic (metal-nonmetal) compounds • Always check the periodic table to decide which rules to use.

48. Molecular Compounds (Nonmetal-Nonmetal) • We’ll only be naming binary molecular (nonmetal-nonmetal) compounds (made of 2 elements) • The 1st word is the name of the 1st element • The 2nd word is the name of the 2nd element in “ide” form • Use a prefix for the number.

49. One: mono- Two: di- Three: tri- Four: tetra- Five: penta- Six: hexa- Seven: hepta- Eight: octa- Nine: nona- Ten: deca- Prefixes in Molecular Compounds

50. Putting it all Together • CO2 is a molecular compound • The 1st word is the name of the 1st element: carbon (the prefix mono is omitted in the 1st word) • The 2nd word is the 2nd element in “ide” form, with the prefix “di” • The name is carbon dioxide.