Chemical Bonding

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Chemical Bonding
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Atoms combine through chemical bonding

• Chemical bond - an interaction that holds atoms
  together
• When chemical bonds form, electrons are shared,
  gained or lost.
• Bonds are made by valence electrons (outermost
  electrons)

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Determining bond properties

• Atoms form bonds to achieve a full outer shell of
  electrons, (usually 8 electrons)
• A full outer shell puts the atom in a low energy
  state.
• Nobel gases (group 18) have a full outer shell,
  so are unlikely to bond.

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Determining valence electrons

• Group 1 and 2
• Group 13-18
• Group 3-12

• Same as group number
• Group number 10
• No consistent pattern due to many sub shells

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Ionic Bonds

• Ionic bonds are formed when valence electron(s)
  are transferred from one atom to another.
• Ions are charged particles formed after atoms
  gain or lose electrons.

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Positive ions

• Formed when atoms have electrons pulled off
• Positive ions have more protons than electrons
• Metals tend to make positive ions
• Positive ions are written with the atoms
  abbreviation and its charge Na, Ca2
• It takes energy to remove electrons and form a
  positive ion

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Negative ions

• Formed when atoms gain electrons
• Negative ions have more electrons than protons
• Non-metals tend to make negative ions
• Negative ions are written with the atoms
  abbreviation and its charge O2-, F-
• Energy is given off when non-metals gain
  electrons

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Ionic compounds

• When ionic compounds are formed, the positive and
  negative ions balance out to form a neutral
  compound
• Because positive and negatives attract each
  other, ionic compounds form a repeating 3-D
  pattern called a crystal lattice.
• http//jas.eng.buffalo.edu/education/solid/unitCel
  l/home.html
• http//www.worldofmolecules.com/interactive_molecu
  les/salt.htm

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Ionic compounds characteristics

• The strong attraction between ions in a crystal
  lattice give ionic compounds the following
  characteristics
• Brittleness
• High melting point
• High boiling point

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Ionic bonds links

• http//ithacasciencezone.com/chemzone/lessons/03bo
  nding/mleebonding/ionic_bonds.htm
• http//www.promotega.org/UGA06004/ionic_bonds.html
  
• http//www.teachmetuition.co.uk/Chemistry/Chemical
  structureandbonding/ionic_bonding.htm

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Covalent Bonds

• Formed when atoms share one or more pairs of
  electrons
• Formed between non-metals
• A large amount of energy is needed to remove an
  electron from a non-metal, so instead of
  transferring an electron, they share.

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Covalent bonds

• Substances formed by covalent bonds consist of
  individual particles called molecules.
• Molecule the smallest unit of a substance that
  keeps all the physical and chemical properties of
  the substance.

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Covalent bonds

• Characteristics of covalent bonds
• Low melting point
• Low boiling point
• Brittle in solid state
• This is because the individual molecules are not
  strongly attracted to one another (the atoms are!)

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Covalent bonds

• Molecules are composes of at least two covalently
  bonded atoms.
• Diatomic molecules are composed of exactly two
  atoms.
• Diatomic elements -elements found as diatomic
  molecules H2, O2, N2, F2, Cl2, Br2 and I2

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Metallic Bonds

• Metallic bonds are formed between metals.
• Since most metals are large atoms, their outer
  most electrons are very far from the nucleus.
• The outer most orbitals are so large, they
  overlap.
• The overlapping orbitals allow the nuclei to
  share any nearby electron.

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Metallic bonds

• The nuclei and the tightly held inner electrons
  have an overall positive charge, and repel each
  other. They line up in a pattern to maximize the
  distance between themselves.

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Metallic bonds

• The outermost electrons form a sea of electrons
  that are free to move from one overlapping
  orbital to another.

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Properties of Metallic bonds

• Conduct electricity- electrons are easy to move
• Ductile - can be drawn into wire
• Malleable- can be hammered into shape.

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