Bonding + Structure

• Maximum number of electrons in the first 4 shells

  n=1 --> 2

  n=2 --> 8

  n=3 --> 18

  n=4 --> 32
• What is an orbital?

  Region around the nucleus that can hold up to 2 electrons with opposite spins

  
• What is the shape of an s-orbital?

  Spherical

  Each shell from n=1 has 1 s-orbital

  
• What is the shape of a p-orbital?

  Dumbbell

  Each shell from n=2 has 3 p-orbitals

  
• How many orbitals are in the d-orbital?

  Each shell from n=3 has 5 d-orbitals

  
• How many orbitals are in the f-orbital?

  Each shell from n=4 has 7 f-orbitals

  
• Why does the 4s subshell fill before the 3d subshell?

  Because 4s has a lower energy level

  
• How do you fill in orbitals with the same energy?

  Electrons are put in individually before pairing them. This is because the electrons will repel.
• What are the 2 exceptions in electron configuration?

  Chromium and Copper

  
• Where are electrons lost from first: 4s or 3d orbital?

  4s
• Define ionic bonding

  The electrostatic attraction between positive and negative ions

  
• What is a giant ionic lattice?

  A 3D structure that results from oppositely charged ions strongly attracting in all directions

  
• What are the physical properties of ionic compounds?

  - High melting and boiling point

  - Dissolve in polar solvents (e.g. water)

  - Conduct electricity only in liquid/aqueous state
• Explain the physical properties of ionic compounds

  - High temperatures are needed to provide a large quantity of energy and overcome the strong electrostatic forces between the oppositely charged ions in the ionic lattice. The melting points are higher for lattices containing ions with greater ionic charges. It also depends on the size of the atom

  - When an ionic compound dissolves in a polar solvents (such as water), polar water molecules break down the lattice and surround each ion. However, if the attractions in the giant ionic lattice is greater, then solubility decreases (as ionic charge increases)

  - In a solid state, ionic compounds do not conduct electricity as the ions are in fixed positions and there are no mobile charge carriers. But when liquid or molten they can conduct electricity as the ions are now free to move as mobile charge carriers
• What is a covalent bond?

  A strong electrostatic attraction between a shared pair of electrons and nuclei of bonded atoms

  
• Are covalent bonds in all directions or localised?

  They are localised as the attraction is solely between the shared pair of electrons and nuclei of the bonded atom
• Dative Covalent Bond

  A shared pair of electrons has been provided by one of the bonding atoms only (e.g. NH4+)

  
• Why do molecules have a fixed shape?

  Bonds repel each other equally
• Electron-pair repulsion theory

  Electron pairs repel one another so that they are arranged as far apart as possible.

  Bonded pair/bonded pair < bonded pair/lone pair < lone pair/long pair - Lone pairs repel more stronger than a bonding pair

  For every long pair, the bond angle decreases by 2.5

  
• Shapes of Molecules

  • Linear
  • Trigonal Planar
  • Tetrahedral
  • Octahedral
  • Trigonal Pyrimidal
  • Non-linear
• Linear


  Bonding Pairs --> 2

  Lone Pairs --> 0

  Bond Angle --> 180

  
• Trigonal Planar

  Bonding Pairs --> 3

  Lone Pairs --> 0

  Bond Angle --> 120

  
• Tetrahedral

  Bonding Pairs --> 4

  Lone Pairs --> 0

  Bond Angle --> 109.5

  
• Octahedral

  Bonding Pairs --> 6

  Lone Pairs --> 0

  Bond Angle --> 90

  
• Trigonal Pyramidal

  Bonding Pairs --> 3

  Lone Pairs --> 1

  Bonding Angle --> 107.5

  
• Non-linear

  Bonding Pairs --> 2

  Lone Pairs --> 2

  Bonding Angle --> 104.5
• What is electronegativity?

  The ability for of an atom to attract electrons towards itself in a covalent bond

  
• Non-polar bond

  Electrons are shared equally between the bonded atoms. A bond will be non-polar if:

  - Bonded atoms are the same

  - Bonded atoms have same/similar electronegativity

  
• Polar bonds

  Electrons are shared unequally between the bonded atoms. A bond will be polar if:

  - Bonded atoms are different

  - Bonded atoms have different electronegativities

  
• What is a dipole?

  The separation of opposite charges

  
• Why is H20 polar and CO2 not?

  - The two O-H bonds each have a permanent dipole. The two dipoles act in different directions but do not exactly oppose each other. This means overall the oxygen at the end of the molecule has a delta- charge and the hydrogen has a delta+

  - CO2 is non-polar. The 2 C-O bonds have a permanent dipole, however they act in opposite directions and oppose each other. This means the dipoles cancel and the overall dipole is 0

  
• What are the 3 intermolecular forces?

  - London forces

  - Permanent dipole-dipole interactions

  - Hydrogen bonding

  
• London forces

  London forces are the weakest out of the intermolecular forces and exist between all molecules (whether polar or non-polar).

  - Movement of electrons creates a changing dipole. At any instant, an instantaneous dipole will exist which induces a dipole on the neighbouring molecule. The induced dipole induces further dipoles on neighbouring molecules - which then attract each other

  
• Strength of London forces

  The more electrons in each molecule OR the bigger the atom, the larger the instantaneous and induced dipoles, the greater the induced dipole-dipole interactions and therefore the greater the attractive force. More energy is then needed to overcome the intermolecular forces - increasing the boiling point

  
• Permanent dipole-dipole interactions

  Acts between the permanent dipoles of different polar molecules
• Hydrogen Bonding

  The strongest intermolecular force between hydrogen on one molecule and the lone pairs of either N, O or F on the other molecule

  
• What are the anomalous properties of water

  1 - Ice is less dense than water

  2 - Water has a relatively high melting and boiling point

  
• Anomalous properties of water

  Hydrogen bonds hold water molecules apart in an open lattice structure. This means water molecule in ice are further apart than in water - therefore solid ice is less dense than liquid water and floats

  Water has London forces, permanent dipole-dipole interactions AND hydrogen bonding. This means that a large quantity of energy is needed to break the hydrogen bonds in water (therefore it has a higher melting and boiling point)
• Simple Molecular (covalent) Substances


  Made up molecules containing a few atoms that are covalently bonded.

  The molecules are held by weak intermolecular forces, but the atoms have strong covalent bonds.

  Examples include: Ne, I2, H2, H20, CO2

  
• Properties of Simple Molecular Substances

  - Low melting and boiling point: The weak intermolecular forces can be broken with little energy

  - Solubility: Simple molecule substances tend to be soluble in non-polar solvents (interactions between solvent and molecules weakens the intermolecular forces in the simple molecular lattice) and are not soluble in polar solvents (there is little interaction between molecules in the lattice and solvent molecules)

  - Does not conduct electricity: There are no mobile charged particles that can move and carry charge