Chemical Bonding

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Chemical Bonding

• Chapter 7

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The Octet Rule

• Atoms tend to gain, lose, or share electrons in
  order to acquire a full set of valence electrons.
• octet most atoms need 8 valence electrons for
  a full set
• Gaining or losing g ions ionic bonding
• Sharing covalent bonding

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Ionic Bonding
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Properties of Ionic Compounds

• High melting points
• Brittle
• Usually salts
• Many dissolve in water
• Can conduct electricity because ions separate and
  are charged in the solution

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Ionic Bonds

• Positively charged ion attracted to negatively
  charged ion
• Positive ions cations
• Negative ions anions
• Metal nonmetal
• Metals form cations
• Nonmetals form anions

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Types of Ions

• Monatomic one-atom
• H, Ca2, Br-, N3-
• Polyatomic many-atoms
• NH4, OH-, SO42-,

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Lewis Dot Structures

• Developed by American chemist Gilbert Lewis
  (1875-1946)
• Valence electrons represented by dots around the
  element symbol
• No more than two dots per side
• Can be used to show rearrangement of electrons
  during chemical reactions

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Binary Ionic Compounds

• Contain ions of only two elements
• Formula Cation written first, then anion
• Charges of ions written as superscripts, of
  atoms in a compound written as subscripts
• Ratio written in lowest terms empirical formula

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Binary Ionic Compounds

• Draw the Lewis Dot Structures for sodium and
  chlorine
• Using an arrow, identify how the transfer of 1
  electron can create 2 new ions

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• Sodium transfers an electron to chlorine.
• Sodium becomes a positive ion with a 1 charge.
• Chlorine becomes a negative ion with a -1 charge.

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Binary Ionic Compounds

• Na Cl- g NaCl
• The total (net) charge on the compound should be
  zero.
• You must determine how many of each ion will need
  to be in the compound to balance out the charges.

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Compound Formula Practice

• magnesium ion oxide ion
• Mg2 O2- g
• Mg2 O2- g MgO
• calcium ion and bromide ion
• Ca2 Br- g
• strontium ion and nitride ion
• Sr2 N3- g

Mg2O2
CaBr2
Sr3N2
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The Crisscross Method for Writing Compound
Formulas

• Write the ion symbols (with their charges as
  superscripts) for the cation and anion
• Criss-cross the two charges, moving them
  diagonally from one ions superscript to the
  other ions subscript
• Drop the sign!

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Crisscross Method Practice

• magnesium ion and chloride ion
• Mg2 Cl-1
• Mg Cl
• MgCl2

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Naming Ionic Compounds

• Name the cation using its element name.
• Name the anion by dropping the ending of the
  element name and adding ide.
• Ca3P2
• calcium phosphide
• If the anion is polyatomic, simply name it using
  the ions name
• Mg3(PO4)2
• magnesium phosphate

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Naming Ionic Compounds

• If the cation has more than one valence (it can
  have different charges), indicate the charge
  using roman numerals in parenthesis after the
  cation name.
• FeO iron (II) oxide
• Fe2O3 iron (III) oxide

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Covalent Bonding
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Covalent Bonds

• Formed by a shared pair of electrons between two
  atoms
• Make up molecules (which make up molecular
  substances)
• Between nonmetals

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Formulas

• Empirical formula gives the lowest ratio of types
  of atoms in a compound
• Molecular formula gives the exact number of atoms
  of each element in a single molecule of a
  compound
• Structural formula shows how atoms are bonded
  together

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Formula Example Glucose

• molecular formula
• C6H12O6
• empirical formula
• CH2O
• structural formula

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Lewis Dot Structures

• For molecules
• Show pairs of electrons that are shared between
  atoms using 2 dots or 1 dash.
• Leave electrons not involved in bonds as dots.

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Lewis Dot Structures

• Draw the Lewis dot structures for
• F2
• NH3
• H2O
• H2CO
• C2H2

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Exceptions to the Octet Rule

• Less than an octet
• BF3
• More than an octet
• SF4
• Odd number of electrons
• NO

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Properties of Covalent Bonds

• Polar covalent bonds
• Due to electronegativity difference
• More electronegative atom gets slightly negative
  charge (higher electron density)
• Less electronegative atom gets slightly positive
  charge (lower electron density)
• Nonpolar covalent bonds
• No electronegativity difference
• Share electrons equally

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Practice

• Look at page 184.
• Which compound has the more polar bond, HCl or
  F2? How do you know?
• Which atom in HCl has the higher
  electronegativity?
• Draw the Lewis Dot Structure for HCl and indicate
  the partial charges on the atoms.

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Naming Covalent Compounds (Molecules)

• Similar to naming ionic compounds, but prefixes
  must be added to tell the ratio of atoms in the
  compound.

mono- 1
di- 2
tri- 3
tetra- 4
penta- 5
hexa- 6
hepta- 7
octa- 8
nona- 9
deca- 10
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Naming Covalent Compounds (Molecules)

• Most electronegative element written last in
  formula and name.
• Drop ending of this elements name and add
• ide.
• Si2Br6
• disilicon hexabromide
• Dont include mono- prefix for 1st element
  listed.
• CF4
• carbon tetrafluoride

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Naming Covalent Compounds (Molecules)

• Shorten prefixes to make names easier to say.
• H2O
• dihydrogen monoxide
• not dihydrogen monooxide
• Sometimes common names are used.
• O2 oxygen
• NH3 ammonia

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Hydrates and Acids
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Naming Hydrates

• Hydrates are ionic compounds that absorb water
  into their solid structures.
• Anhydrous substances are water-free
• Naming
• Name the ionic compound
• Using the prefixes that you have learned,
  identify the degree of hydration
• MgSO4 s 7 H2O
• magnesium sulfate heptahydrate

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Naming Acids

• Acids are molecular substances that dissolve in
  water to produce hydrogen ions (H).
• Can separate into ions even though they are
  molecular compounds
• Hydrogen is the cation in acids.

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Naming Acids

• If the anion ends in ide
• Begin the name with hydro-
• Add the root name of the anion, but change the
  ending from ide to ic
• Add the word acid
• HBr
• HCl
• H2S

Hydrobromic acid
Hydrochloric acid
Hydrosulfuric acid
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Naming Acids

• If the anion ends in ate
• Do NOT begin with hydro-
• Keep the root of the anion, but change the ending
  from ate to ic
• Add the word acid
• HNO3
• H3PO4
• HC2H3O2

nitric acid
phosphoric acid
acetic acid
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Naming Acids

• If the anion ends in ite
• Do NOT begin with hydro-
• Keep the root of the anion, but change the ending
  from ite to ous
• Add the word acid
• HNO2
• H2SO3
• HClO2

nitrous acid
sulfurous acid
chlorous acid
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anion
_______ate
_______ide
________ite
add hydrogen ions (H)
acid
hydro____ic acid
______ic acid
______ous acid
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Metallic Bond, A Sea of Electrons
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Ionic Bonds One Big Greedy Thief Dog!
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Polar Covalent Bonds Unevenly matched, but
willing to share.
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Metallic Bonds Mellow dogs with plenty of bones
to go around.