Molecules and Bonds

1
Chapter 3

• Molecules and Bonds

2
Objectives

• Ionic Bonding
• Describe the characteristics of an ionic bond
• Understand and explain the octet rule
• Covalent Bonding
• Describe the characteristics of a covalent bond
• Describe the difference between polar and
  nonpolar covalent bonds
• Naming Chemical Compounds
• Write names for ionic compounds, molecular
  compounds, and acids

3
CHEMICAL BONDS

• In almost all stable chemical compounds each atom
  attains a ________________________. This forms
  the basis of our understanding of chemical
  bonding.
• Atoms are held together in a substance by strong,
  attractive forces called
• Many types of bonds
• Two major types

4
Bonding

• In reactions, _______ are exchanged to form new
  compounds
• __________ can be traded or stolen in the
  formation of those compounds
• Octet rule
• Electronegativity

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Ionic Bonding

• All atoms want to be
• Complete set of
• This is for most atoms
• H and He need only WHY?
• Elements will gain, lose, or share electrons to
• Which elements will gain electrons?
• Which elements will lose electrons?
• Which elements might share electrons?

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Ionic Bonding

• Ionic bond the electrostatic attraction between
  positive and negative ions
• Cation
• Anion
• a

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Ionic Bonds

• Result from one atom
• This is done to satisfy octet
• Lewis structures to show

8
Ionic Bonding

• Attraction between electrostatic charges is a
  strong force which holds atoms together
• Transfer of electrons from one atom to another

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Ionic Bonding

• Lewis Dot Diagrams
• Show
• Use dots (Figure 7-9)
• Move in clockwise direction (12, 3, 6, 9) with
  one dot in each spot before filling with pairs
• Draw Lewis Structures of

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Practice

• Show the electron transfer between
• Show the electron transfer between

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Predicting Charges of Ions

• Look at column
• Remember the octet rule
• Look at

12
Predicting Formulas

• Math Method
• Ion charges must balance to 0

• Criss-Cross Method
• Ion charges must balance to 0

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Stock System

• Look at Cu
• Use Roman Numbers to show the charge

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Naming

• Use the stock system
• For binary ionic compounds
• Name of positive () ion
• Name of negative (-) ion

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Polyatomic Ions

• Primarily negatively charged
• NO3-1, SO42-
• See table 3.2 p 75

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Polyatomic Ions

• Naming nonmetallic elements that combine with
  oxygen to form more than one polyatomic ion
• Ion with smaller proportion of
• Ion with large proportion of

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Polyatomic Ions

• When a series of negative ions extends to 3 or 4
  members prefixes are also used
• ClO-
• ClO2-
• ClO3-
• ClO4-

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Are Ionic Compounds Important?

• TSP
• Bones
• Nerves
• Drugs

• Seasoning
• Preservatives
• Soaps
• Electrolytes
• Blood

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The Covalent Bond

• A pair of electrons
• Most common type of bond
• Stronger than ionic bond
• Electron orbital __________ to include both
  nuclei
• most often found between two nuclei
• Negative charges allow positive
  nuclei to be drawn close to each other

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The Covalent Bond

• Molecule group of atoms that are
• Molecular Formula
• Also tells total
• C6H12O6
• Structural Formula indicates kind, number,
  arrangement, and bonds of atoms in a molecule
• Lewis Structures

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The Covalent Bond

• LEWIS STRUCTURES of covalent bonds
• Use

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The Covalent Bond

• Single bond 2 electrons shared between 2 atoms
• Double bond 2 pairs (4 electrons) shared
  between 2 atoms
• Triple bond 3 pairs (6 electrons) shared
  between 2 atoms
• Multiple bonds are stronger than single bonds
• Harder to break
• Draw Lewis structure and put puzzle together to
  know single, double, or triple bonds

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Bonding

• Molecule
• Diatomic molecule
• All but 8 elements use their atomic symbols to
  denote the neutral atom, its elemental state
  (found uncombined_
• BUT 8 are found to be diatomic (never uncombined
  in nature) and are expressed as neutral elements
  in the following forms

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Naming Covalent Compounds

• Common names
• Use

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Naming Molecular Compounds(Covalent Bonds)

• Use prefixes to indicate number of atoms in
  molecule
• Dont use mono for first atom

Prefix Meaning Prefix Meaning
Mono 1 Hexa 6
Di 2 Hepta 7
Tri 3 Octa 8
Tetra 4 Nona 9
Penta 5 Deca 10
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Lewis Structures
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Rules

• Choose the central atom
• Usually
• Draw the Lewis atom
• Position the remaining atoms around the central
  atom

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Rules

• Draw a line connecting
• This is
• Represents
• Remaining electrons left around the central atom

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Showing Covalent Bonds

• Lewis structures
• H2

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Multiple Central Atoms

• C3H8

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Multiple Bonds

• C2H4

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Bonding

• Molecular Compound
• Polyatomic ions charged group of covalently
  bonded atoms

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Polyatomic Ions

• Still have to satisfy the octet rule

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Ionic? Covalent?
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Predicting Bonds

• How do you know which bond will result?
• Compare
• Electronegativity
• Atoms have different
• Electrons will spend more time near atoms
• Soone atom assumes a partial positive charge
• The other assumes a partial negative charge

36
Electronegativity

• Electronegativity trends and periodic table
• Generally
• Decreases
• Highest is
• Lowest is

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Electronegativity

• Polarity is determined by difference in
  electronegativity
• Nonpolar Covalent Bond
• Polar Covalent Bond ( )
• One electronegativity is larger.
• Ionic Bond ( )
• Electronegativity is so great that no
• sharing occurs
• Electrons are lost or gained instead

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Ionic, Polar, NonPolar?

• Look at difference in electronegativity

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Representation of Polar Bonds

• Use an arrow,
• Use arrows for
• Dipole moment (book)
• Electrical force causing the attraction within a
  polar molecule

40
Overall Polarity

• Examine all of the bonds within a molecule
• Contributes to the shape

• CO2

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Shapes
42

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VSEPR and Shape

• Shapes of interest
• Linear
• Bent
• Trigonal planar
• Trigonal pyramid
• Tetrahedral

44
Floating

• Polarity manifested in properties
• Compare