Chapter 5 BONDING AND MOLECULES

Transcription

1 Chapter 5 BONDING AND MOLECULES

2 How Do Atoms Combine to Form Compounds? (5.1) Chemical bonds: a force of attraction between atoms or ions. Octet Rule: atoms tend to gain, lose, or share electrons in order to acquire a full set of valence electrons. (2 in s, 6 in p of highest energy level)

3 Elements and Compounds Element: substance that cannot be separated into simpler substances by a chemical change. (listed on the periodic table) Element symbol: consists of one or two letters 1 st letter always capitalized 2 nd letter never capitalized Compounds: two or more elements combined in a fixed proportion Elements and compounds are pure substances

4 Properties of Matter Identifying Characteristics Physical properties: can be observed without changing the identity of the substance. (Examples: density, color, melting point) Chemical properties: cannot be observed without altering the substance. (Examples: flammability, corrosiveness) Compounds have different properties than the elements they come from

5 Changes in Matter Physical change: does not alter identity Crushing, tearing, cutting, phase change Chemical change: changes identity Burning, exploding, corroding, etc.

6 Valence Electrons (5.2) Valence electrons: electrons in the outermost energy level of an atom

7 Gaining and Losing Electrons (5.3) Ions: atoms that are charged because they gained or lost electrons. Cations: positive ions (lost electrons) Anions: negative ions (gained electrons) Metals lose electrons Nonmetals gain electrons

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10 Complete symbol Mass number = 37 Atomic number = 17 Cl Element symbol

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13 Predicting Charges on Ions

14 Way Atoms bond (5.4) Ionic bond: Positive ion is attracted to a negative ion (usually a metal & a nonmetal) due to a transfer of electrons Cation: positive ion Anion: negative ion

15 Ionic Compounds Ionic compounds form crystals of indefinite size. Properties: Brittle High melting and boiling points Poor conductors of heat & electricity as solid Conducts as liquid or when dissolved Readily dissolve in water

16 Writing Formulas Monatomic ions: one atom ions Polyatomic ions: many atom ions Monatomic cations (+): name after element; for transition elements include a roman numeral for charge Na + Mg 2+ Fe 2+ Fe 3+ sodium ion magnesium ion iron (II) ion iron (III) ion

17 Writing Formulas Monatomic anions: name after element but change ending to ide Cl - O 2- N 3- chloride oxide nitride Polyatomic ions: atoms that are covalently bonded, but as a unit they form an ion. Use special names

18 Table 4.1

19 Table 4.2

20 Table 4.4

21 Binary Ionic Compounds Contain ions of only two elements Name: cation name & anion name CaF 2 MgO calcium flouride magnesium oxide Name does not tell ratio of ions Empirical formula: subscripts show ratio of ions Al 2 O 3 aluminum oxide two Al 3+ three O 2- Li 2 O lithium oxide Two Li + one O 2- no subscript means one Ionic compounds are neutral charges must equal

22 Crisscross method Calcium fluoride Ca 2+ F - \ / CaF 2 Magnesium Oxide Mg 2+ O 2- \ / MgO

23 Crisscross Method Calcium nitrate Ca 2+ NO 3 - \ / Ca(NO 3 ) 2 Aluminum nitrate Al 3+ NO 3 - \ / Al(NO 3 ) 3

24 Metallic Bonding (5.5) Metallic bond: a bond between metal atoms in which the valence electrons are free flowing.

25 Properties of Metals Good conductors of heat and electricity Ductile (shaped into wires) Malleable (shaped into thin sheets)

26 How do Nonmetals Bond? (5.6) Covalent bond: Electrons are shared between atoms of nonmetals Molecules and their Formulas Molecules: covalently bonded atoms Molecular formulas: tells how many atoms of each type are in a molecule oxygen O 2 2 O atoms sucrose C 12 H 22 O C atoms 22 H atoms 11 O atoms

27 More formulas Glucose Molecular formula C 6 H 12 O 6 Empirical formula CH 2 O Lactic Acid Molecular formula C 3 H 6 O 3 Empirical formula CH 2 O

28 Properties of Molecules Low melting points Many are liquids or gases at room temperature Many do not dissolve in water Not conductors of heat or electricity nonelectrolytes

29 Structural Formula Shows where atoms are bonded Lewis structures:

30 More Lewis Structures

31 Describing covalent bonds Use octet rule

32 C. Multiple Bonds Single bonds share one pair of electrons between atoms Double bonds share two pairs of electrons between atoms Triple bonds share three pairs of electrons between atoms

33 Double bonds

34 Triple bonds

35 Dots or Dashes? Dash represents a shared pair of electrons

36 More Lewis Structures

37 Exceptions to Octet Rule 1. Less than an octet

38 Exceptions to Octet Rule 2. More than Octet:

39 Exceptions to Octet Rule 3. Odd number of electrons:.... N.. + Ȯ.. :.... N=Ȯ :

40 Properties of Covalent Bonds Polar covalent bond: results from an unequal sharing of electrons; depends on electronegativity

41 Figure 12.5: Charge distribution in the water molecule.

42 Electronegativities

43 Properties of Covalent Bonds Nonpolar covalent bonds: results from equal sharing of electrons; occurs between same element or elements with the same electronegativity Examples: F 2, O 2, N 2

44 Properties of Covalent Bonds Electronegativity Difference Bond Type 0.4 nonpolar covalent Between 0.5 and 1.9 polar covalent 2.0 ionic

45 Table 12.1

46 Naming Molecular Compounds 1. Use prefixes (don t use mono on first element) 2. name in order written 3. always end second element in ide 4. common names exist O 2 H 2 O NH 3 oxygen water ammonia

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48 Diatomic molecules

49 Acids A molecular substance that dissolves in water to produce H + ions. Named after anion HCl H + + Cl - End in ide change to Hydro ic acid End in ate change to ic acid End in ite change to ous acid

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