Chapter 5 - Electrons + bonding

• What are electron shells?

  an energy level of electrons at a characteristic average distance from the nucleus of an atom
• What is the principle quantum number?

  describes the size of the electron orbital and represents the relative overall energy of each orbital
• What are atomic orbitals?

  region around the nucleus that can hold up to 2 electrons, with opposite spins
• What shape is the p orbital?

  dumbbell
• What shape is the s orbital?

  spherical
• What does the shape of an orbital represent?

  Where electrons have the highest probability of being found
• What are the 3 rules of electron configurations?

  1) electrons fill orbitals in order of increasing energy (4s sub-shell has a lower energy than 3d sub-shell, so is filled first)

  2) each orbital can contain a maximum of 2 electrons with opposite spins

  3) in orbitals of the same energy, orbitals are filled singularly before pairing
• Where do p-block elements have the highest energy electrons?

  p sub-shell
• What block are the transition elements in?

  d block
• What are the 2 exceptions to the electron configuration rules?

  chromium- has only one electron in each orbital of the 4s and 3d sub-shells

  copper- has only one electron in the 4s orbital and a full 3d orbital
• What happens when d-block elements form ions?

  they lose the highest energy electrons
• What are the rules associated with the 4s and 3d sub-shells?

  -when sub-shells are empty, the 4s sub-shell is lower in energy than 3d sub-shell so 4s orbital is occupied before 3d sub-shells

  -when orbitals are occupied, 4s electrons are higher in energy than 3d electrons so 4s electrons are lost before 3d electrons
• How are ions formed?

  When atoms lose or gain electrons
• What is ionic bonding?

  The electrostatic attraction between oppositely charged ions
• Describe the structure of ionic compounds

  each ion attracts oppositely charged ions in all directions, forming a giant ionic lattice
• What properties do ionic compounds have?

  -high melting and boiling points

  -many compounds are soluble in polar solvents

  -don't conduct electricity when solid, but do conduct electricity when molten or dissolved in water
• What causes the variation in melting points for ionic compounds?

  lattices that have ions with greater charges form stronger ionic bonds, which require a lot of energy to overcome so have higher melting points
• Why are many ionic compounds soluble in water (a polar solvent)?

  water molecules break down the lattice and surround ions. The solubility is dependent on the strength of the attractions
• Why don't ionic compounds conduct electricity when solid?

  the ions are fixed in position and are unable to move to carry a charge
• Define covalent bonding

  The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
• What is a molecule?

  smallest part of a covalent compound that can exist, whilst retaining the chemical properties of the compound
• What are lone pairs?

  paired electrons that are not involved in bonding
• How many covalent bonds do carbon and nitrogen form?

  carbon- forms 4 covalent bonds

  nitrogen- forms 3 covalent bonds
• Why is boron considered an exception when bonding?

  it only has 3 outer-shell electrons to be paired, so only forms 3 covalent bonds. Thus, it can only have a maximum of 6 outer-shell electrons
• Why are phosphorous, sulfur and chlorine exceptions when bonding?

  because they are in period 3, they have access to 18 electrons so can form multiple different covalent bonds
• What is expansion of octet?

  when the d sub-shell becomes available for bonding
• What is a dative covalent bond?

  A covalent bond in which a shared pair of electrons is supplied by one of the bonding atoms only
• Describe the reaction of ammonia with a hydrogen ion

  -in a dative covalent bond, the shared pair of electrons is originally a lone pair of electrons

  -the lone pair on the central nitrogen atom of the ammonia molecule is donated to the H+ ion
• What is average bond enthalpy?

  A measure of the average energy of a covalent bond
• Draw the dot and cross diagram for NH4+