Bond, Chemical Bond

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Bond, Chemical Bond

• CPS Chemistry
• Part 1

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What is bond?

• A chemical bond is an attractive force between
  atoms that connects them together.
• This attractive force comes from the absence or
  abundance of electrons in the outer most electron
  level of an atom, it involves the valance
  electrons
• Atoms bond so their valence electrons will
  redistribute in ways that make the atom more
  stable

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Types of connections

• Intermolecular Forces
• Forces of attraction between molecules
• Dipole-Dipole
• Hydrogen Bonding
• London Dispersion Forces

• Types of Bonds
• between atoms to form molecules and compounds
• Ionic
• Covalent
• Polar
• Non Polar
• Metallic

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Ionic Bonds

• Ionic Bonding
• Atoms either loose or gain electrons to form
  complete outer energy levels
• It is the result of large numbers of cations and
  anions that are attracted due to electrical
  imbalances

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Covalent bonding

• Covalent Bonding when electrons are shared
  between atoms, think cooperation
• Two types Polar Non Polar

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Non-Polar Covalent Bond

• Electrons are shared evenly between both atoms
• the charge is evenly distributed around the
  molecule

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Polar-Covalent Bond

• While the electrons are shared, they are unevenly
  distributed around the molecule
• One side of the molecule is more positive than
  the other side (has less electrons)

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Metallic Bond

• In metallic bonding instead of sharing electrons
  between two atoms the electrons in the outer
  shells are shared amongst all the atoms in a
  lattice with all the atoms positively charge.
  These atoms are attracted to the negatively
  charged 'cloud' of electrons.

• The movement of the free electrons means that
  metallic bonded materials have good thermal and
  electrical conduction.

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Bond Properties - Covalent

• Forms molecules
• Low melting points boiling points
• Softer, more flexible
• Doesnt conduct electricity
• Doesnt easily dissolve in water
• Exceptions HCl, NH3, sugars
• Have weak molecular forces between molecules
• Examples H2O, O2, CH4

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Bond Properties - Ionic

• Creates compounds
• High melting points boiling points
• Creates rigid crystalline solids
• Conducts electricity
• Soluble in water
• Has strong forces between ionic compounds
• Will conduct electricity when molten or dissolved
  in water
• Examples NaCl, CaF, KCl

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Metallic Bond Properties

• Metals are good conductors of heat and
  electricity. This is directly due to the mobility
  of the electrons.
• The "cement" effect of the electrons determines
  the hardness of the metal.  Some metals are
  harder than others the strength of the "cement"
  varies from metal to metal.
• Metals are lustrous.  This is due to the uniform
  way that the valence electrons of the metal
  absorb and re-emit light energy.
• Metals are malleable (can be flattened) and
  ductile (can be drawn into wires) because of the
  way the metal cations and electrons can "flow"
  around each other, without breaking the crystal
  structure.

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What type?

• Using the electronegativity of elements, you can
  determine the type of bond created
• By finding the difference (subtract one from the
  other) will express what type of bond is made
• Difference 0 ? 0.3 Nonpolar Covalent
• Difference 0.3 ? 1.7 Polar Covalent
• Difference 1.8 ? and above Ionic

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Electronegativity chart
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A Way to remember

• Think of electrons as bones.What would your dog
  do?
• Ionic bonds One big greedy thief dog!
• Non-Polar Covalent bonds  Dogs of equal
  strength.
• Polar Covalent bonds Unevenly matched but
  willing to share.
• Metallic bonds  Mellow dogs with plenty of bones
  to go around.

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Intermolecular Forces

• Once a molecule is made, it does not live in
  isolation, it will connect with other molecules
• Intermolecular forces is the forces of attraction
  between molecules
• Types
• Dipole-Dipole
• Hydrogen bonding
• London Dispersion Forces

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Dipole-Dipole

• A dipole (d) is created by equal in magnitude,
  but opposite in charge molecules, separated by a
  short distance

• The direction of a dipole is from its positive
  side to its negative side
• They are short range forces, only affect near by
  molecules
• Strongest of the intermolecular forces

Br
F
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Hydrogen Bonding

• A type of dipole-dipole bonding
• A hydrogen atom bonded to a highly
  electronegative atom, and then attracted to
  unshared pair of electrons of a near by
  electronegative molecule
• Examples HF, Water

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London Dispersion

• Intermolecular attraction resulting from the
  constant motion of electrons and creations of
  instantaneous dipoles.
• This is the only type of attraction detected with
  Noble Gasses non-polar molecules
• It is a relatively weak force

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Louis Structure Electron Dot

• A short hand representation of the valence
  electrons available for bonding
• The goal is to have a complete set of valence
  electrons
• Each group has its valence number 1-8

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Electron Dot

• Valence Electron E-dot Example
• 1 X Na
• 2 X Mg
• 3 X B
• 4 X C
• 5 X N
• 6 X O
• 7 X F
• 8 X Ne

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Louis Structure

• You can use electron dot diagram to show
  molecules
• A shared pair can be show by
• HH or H-H
• A double shared pair can be shown by
• CO or C O
• A triple shared pair can be shown by
• NN or NN

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Terms and Extras

• If you need further definitions and explanations
  look at the slides beyond this point

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molecule

• A molecule is a neutral group of atoms held
  together by covalent bonds

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Electronegativity

• Electronegativity is a measure of the tendency of
  an atom to attract a bonding pair of electrons.

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Valence Electron

• Electrons that are in the outermost energy level
  of the atom
• Valance electrons are either shared or
  gained/lost in chemical bonds

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Ions

• Ion an atom with a charge, either positive or
  negative due to the number of electrons (negative
  charge) it has in relation to the number of
  protons (positive charge)
• Cation an ion with a positive charge, so it has
  less electrons than a neutral atom of that
  element, usually non-metals
• Anion an ion with a negative charge, so it has
  more electrons than a neutral atom of that
  element, usually metals