Covalent Bonding

• Covalent bond

  A shared pair of electrons and it is the strong electrostatic force of attraction between the shared pair of electrons and the atoms' positive nuclei
• Single covalent bond

  a bond that involves 1 shared pair of electrons
• Double covalent bond

  a bond that involves 2 shared pairs of electrons
• triple covalent bond

  a bond that involves 3 shared pairs of electrons
• Lewis structures

  -dot and cross diagram

  -stick diagram

  -electrons must be in pairs in a stable molecule/ion
• Bonding pairs

  Shared pair of electrons
• Lone pairs

  Unbonded pair of electrons
• Number of covalent bonds that hydrogen can form

  1 covalent bond
• Number of covalent bonds that group 1 (apart from hydrogen) can form

  No covalent bonds, as ionic
• Number of covalent bonds that Beryllium can form

  2 covalent bonds
• Number of covalent bonds that group 2 (apart from beryllium) can form

  No covalent bonds, as ionic
• Number of covalent bonds that Boron can form

  3 covalent bonds
• Number of covalent bonds that aluminium can form

  3 covalent bonds (or ionic)
• Number of covalent bonds that carbon can form

  4 covalent bonds
• Number of covalent bonds that silicon can form

  4 covalent bonds
• Number of covalent bonds that nitrogen can form

  3 covalent bonds
• Number of covalent bonds that phosphorus can form

  3 or 5 covalent bonds
• Number of covalent bonds that oxygen can form

  2 covalent bonds
• Number of covalent bonds that sulfur can form

  2, 4 or 6 covalent bonds
• Number of covalent bonds that fluorine can form

  1 covalent bond
• Number of covalent bonds that chlorine can form

  1, 3, 5 or 7 covalent bonds
• Complex ions- if an ion is negative

  -if an ion is negative, it has gained an electron

  -the negative atom forms one less bond than normal

  -if a negative ion contains oxygen, the O has one extra electron and only forms one bond instead of 2
• Complex ions - if an ion is positive

  -if an ion is positive, it has lost an electron

  -positive ion forms one more bond than normal
• Dative covalent bond

  Where one atom donates 2 electrons to an atom or ion to form a bond, and both electrons in the covalent bond come from the same atom
• When does a dative covalent bond form?

  When one atom has a lone pair, and one atom has space to accept an electron pair
• Properties of molecules

  -molecules are structures held together by covalent bonds, but have a fixed formula (e.g CO2, NH3)

  -they have low melting and boiling points (usually gases or liquids at room temperature) because there are weak intermolecular forces (van der waals forces) between molecules so not much energy is needed to break these forces

  -they do not conduct electricity as there are no free electrons or ions to carry current
• Why do molecules have low melting and boiling points (usually gases or liquids at room temperature)

  because there are weak intermolecular forces (van der waals forces) between molecules so not much energy is needed to break these forces
• Why do molecules not conduct electricity

  as there are no free electrons or ions to carry current
• Giant covalent structure examples

  Diamond, graphite, silicon dioxide, graphene
• allotropes of carbon

  diamond and graphite
• allotropes of oxygen

  O2 and O3
• Diamond

  -tetrahedral shape

  -each carbon forms 4 bonds

  -it has a very high melting point and is very hard because it has a giant covalent lattice which has many strong covalent bonds so a lot of energy is needed to overcome these bonds

  -cannot conduct electricity because there are no free electrons or ions to carry a current

  -conducts heat well as it has a tightly packed, rigid arrangement
• What shape is diamond

  tetrahedral
• Why is diamond very hard and has a very high melting point

  because it has a giant covalent lattice which has many strong covalent bonds so a lot of energy is needed to overcome these bonds
• Why can diamond not conduct electricity?

  because there are no free electrons or ions to carry a current
• Why does diamond conduct heat well?

  as it has a tightly packed, rigid arrangement
• How many bonding pairs is a double covalent bond

  One bonding pair
• How many bonding pairs is a triple covalent bond

  One bonding pair
• Different name for silicon dioxide

  Silica, Si02, quartz, sand
• Silica

  -tetrahedral shape

  -each silicon is bonded to 4 oxygen atoms

  -each oxygen is bonded to 2 silicon atoms

  -it has a very high melting point and is very hard because it has a giant covalent lattice which has many strong covalent bonds so a lot of energy is needed to overcome these bonds

  -cannot conduct electricity because there are no free electrons or ions to carry a current