Chemical Bonding

1. Page 2 Chemical Bonding

2. Chemical Bond • attractive force between atoms or ions that binds them together as a unit • bonds form in order to… • decrease potential energy (PE) • increase stability

3. CHEMICAL FORMULA IONIC COVALENT Formula Unit Molecular Formula NaCl CO2

4. COMPOUND more than 2 elements 2 elements Binary Compound Ternary Compound NaCl NaNO3

5. ION 2 or more atoms 1 atom Monatomic Ion Polyatomic Ion Na+ NO3-

6. Chemical bonds are formed when valence electrons are: • transferred from one atom to another (ionic) • shared between atoms (covalent) • mobile within a metal (metallic)

7. Sodium has one valence electron and chlorine has seven. Sodium want to lose 1 electron and chlorine needs to gain 1. Sodium transfers its valence electron to chlorine Forming an Na+ and a Cl- ion – sodium chloride NaCl Ionic bonds are formed when metals transfer their valence electrons to nonmetals.The oppositely charged ions attract each other to form an ionic bond.

8. Electron-dot diagrams (Lewis structures) can represent the valence electron arrangement in elements, compounds, and ions. atom ion molecular compound ionic compound

9. Dots represent valence electrons.Everything else (inner shell electrons and nucleus) is called the Kernel and is represented by the symbol. Phosphorous has 5 valence electrons so we draw 5 dots around the symbol for phosphorous.

10. Draw the Lewis Dot Structures of the first 18 elements.

11. When metals lose electrons to form ions, they lose all their valence electrons. The Lewis Dot Structure of a metal ion has no dots. The charge indicates how many electrons were lost. Magnesium atom Magnesium ion

12. When nonmetals gain electrons, they fill up their valence shell with a complete octet (except hydrogen.) The ion is placed in brackets with the charge outside the brackets.

13. A + metal ion is attracted to a – nonmetal ion (opposites attract) forming an ionic compound. We can use Lewis dot structures to represent ionic compounds. The formula for magnesium fluoride is MgF2

14. Two major categories of compounds are ionic and molecular (covalent) compounds. (5.2g) • Ionic compounds are formed when a metal combines with a nonmetal. • Ionic compounds have ionic bonds. • Molecular compounds are formed between two nonmetals. • Molecular compounds have covalent bonds.

15. Comparing the properties compounds with ionic bonds and compounds with covalent bonds. • Properties of ionic compounds • Solids with high melting and boiling points (strong attraction between ions) • Electrolytes: Do not conduct electricity as solids but do when dissolved or molten – ions are charged particles that are free to move • No individual molecules • Properties of molecular compounds • Low melting and boiling points (weak attraction between molecules) • Nonelectrolytes: Do not conduct electricity as solids or when dissolved or molten – no charged particles (ions) to move • Solids are soft • Forms molecules

16. Ionic solids conduct electricity when dissolved or molten. Molecular solids do not. Solution doesn’t conduct electricity Solution conducts electricity Ionic Solid dissolved in water Molecular Solid dissolved in water

17. Nomenclature “Or How Do We Name Compounds”

18. Systematic Naming • Compound is made up of two or more elements • Name should tell us how many and what type of atoms • Too many compounds to remember all the names

19. Anion • Negative ion • Has gained electrons • Non metals form anions Cation • Positive ion • Formed by losing electrons • Metals form cations

20. Ionic Compounds • Made of cations and anions • Metals and nonmetals • Electrons lost by the cation are gained by the anion

21. Na + Cl Ionic Compounds Sodium is cation 1- 1+ Na + Cl Chlorine is anion

22. Charges on Ions

23. Naming Ions • Metal ion is written first in both name and formula • It is named directly from element which formed the ion. • Will nearly always be the positive ion or “cation” • Transition metals can have more than one type of charge • Indicate the charge with roman numerals in parenthesis. Iron(II) or Iron(III) • Exceptions: • Silver always +1 • Cadmium and Zinc always +2

24. Name these • Na 1+ • Ca 2+ • Al 3+ • Fe 3+ • Fe 2+ • Pb 2+ • Li 1+ • Sodium • Calcium • Aluminum • Iron (III) • Iron (II) • Lead (II) • Lithium

25. Write Formulas for these • Potassium ion • Magnesium ion • Copper (II) ion • Chromium (VI) ion • Barium ion • Mercury (II) ion • K1+ • Mg2+ • Cu2+ • Cr6+ • Ba2+ • Hg2+

26. Naming Anions • Anions are always the same. • Change the element ending to -- ide • F1- Fluorine to Fluoride

27. Name These • Cl1- • N3- • Br 1- • O2- • I1- • Sr2+ • Chloride • Nitride • Bromide • Oxide • Iodide • Strontium

28. Write These • Sulfide ion • Iodide ion • Phosphide ion • Strontium ion • S2- • I1- • P3- • Sr2+

29. Polyatomic Ions • Tightly bound groups of atoms acting as a single ion. • Names given in table in book. (pg 123) • Most are anions that contain oxygen. Names end in –ate(one more O), or –ite (one less O). • SO32- = sulfite; SO42- = sulfate • Exceptions: Ammonium cation NH4+, Cyanide CN-, and hydroxide OH-

30. Naming Binary Ionic Compounds • 2 elements involved • Ionic – metal (cation) and a non-metal (anion) • Naming is easy with representative elements in A groups • NaCl = Na+ Cl-= sodium chloride • MgBr2 = Mg2+Br-= magnesium bromide

31. Naming Binary Ionic Compounds • The problem comes with the transition metals. • Need to figure out their charges • All ionic compounds will have a neutral charge • Same number of + and – charges • Use the anion to determine the charge on the positive ion.

32. Naming Binary Ionic Compounds • Try naming these • KCl • Na3N • CrN • ScP • PbO • PbO2 • Na2Se • Potassium chloride • Sodium nitride • Chromium (III) nitride • Scandium (III) phosphide • Lead (II) oxide • Lead (IV) oxide • Sodium selenide

33. Tertiary Ionic Compounds • Will have polyatomic ions • At least 3 elements • Use blue sheet • Name these ions • NaNO3 • CaSO4 • CuSO3 • (NH4)2O • LiCN • Fe(OH)3 • (NH4)2CO3 • NiPO4 • Sodium nitrate • Calcium sulfate • Copper (II) sulfite • Ammonium oxide • Lithium cyanide • Iron (III) hydroxide • Ammonium carbonate • Nickel (III) phosphate

34. Polyatomic ions are groups of atoms covalently bonded together that have a negative or positive charge.

35. Polyatomic ions are held together by covalent bonds but form ionic bonds with other ions. + Ionic bond H - Covalent bonds H N H Cl H

36. Writing Formulas • Charges have to add up to zero. • Get charges on pieces from Periodic Table • Cations from element name on table • Anions from table change ending to –ide, or use name of polyatomic ion • Balance the charges • Put polyatomics in parenthesis

37. Writing Formulas • Write formula for calcium chloride • Calcium is Ca2+ • Chloride is Cl1- • Ca+2Cl-1would have a +1 charge • Need another Cl1- • Ca+2Cl2-1 = CaCl2

38. Writing Formulas • Crisscross method Calcium chloride CaCl2 Ca2+ Cl1- No need to write the one Iron (III) sulfide Fe 3+ S2- Fe 2 S3 Fe2S3

39. Write Formulas for These • Lithium sulfide • Tin (II) oxide • Tin (IV) oxide • Magnesium fluoride • Copper (II) sulfate • Iron (III) phosphide • Iron (III) sulfide • Ammonium chloride • Ammonium sulfide • Li2S • SnO • SnO2 • MgF2 • CuSO4 • FeP • Fe2S3 • (NH4)Cl • (NH4)2S

40. Things to Look For • If cations have ( ), the roman numeral is their charge. • If anions end in –ide they probably are off the periodic table (monoatomic) • If anion ends in –ate or –ite it is a polyatomic ion

41. Molecular Compounds Writing Names and Formulas

42. Covalent Bonding / Compounds • Compounds in which the electronegativity difference is less than 2.0 • Between a nonmetal and nonmetal • Can’t be held together because of opposite charges • Can’t use charges to figure out how many of each atom

43. Water H2O Carbon Dioxide CO2 Ammonia NH3 Covalent Bonding • Smallest piece of a covalently bonded compound is a molecule • Electrons are shared between atoms in bond

44. In a multiple covalent bond, more than one pair of electrons are shared between two atoms. (5.2e) • Diatomic oxygen has a double bond O=O (2 shared pairs) because oxygen needs 2 electrons to fill its valence shell • Diatomic nitrogen has a triple bond NN (3 shared pairs) because nitrogen needs 3 electrons to fill its valence shell • Carbon dioxide has two double bonds

45. Regents Question: 08/02 #17 Which molecule contains a triple covalent bond? (1) H 2 (2) N 2 (3) O 2 (4) Cl 2 þ

46. Molecular polarity can be determined by the shape of the molecule and the distribution of charge. • Possible shapes • Linear (X2 HX CO2) • Bent (H2O) • Pyramidal (NH3) • Tetrahedral (CH4 CCl4) A polar molecule is called a dipole. It has a positive side and a negative side – uneven charge distribution.

47. Symmetrical (nonpolar) molecules include CO2 , CH4 , and diatomic elements. .. Symmetrical molecules are not dipoles.

48. Asymmetrical (polar) molecules include HCl, NH3 , and H2 O. (5.2l) The negative side of the molecule is the side that has the atom with the higher electronegativity.

49. - + Na + Cl Na + Cl Differences between ionic and covalent bonding: • Ionic bonding • electron is “stolen” • high electronegativity difference • between metal & nonmetal • Formation of crystal structure • think proportions of atoms in formula unit NaCl 1:1

50. Molecules are easier to name and work with • Ionic compounds use charges to determine how many of each. • Have to figure out charges • Have to figure out numbers • Molecular compound’s name tells you the number of atoms.