9. Atomic and molecular interactions.

Question 1

Explain the types of atomic and molecular interactions and relate it to a diagram

Answer 1

We distinguish between attractive long range (=Couloumb) between outer shells and repulsive short range interactions between nuclei and inner shells.

The energy stored in a bond is potential energy and the sum of repulsive and attractive forces.

E_pot = E_attraction + E_repulsion = A/rⁿ + B/r^m

Parameters:

• A, B are atom-dependent interaction-specific constants
• n (attraction) > m (repulsion)
• r₀ = binding distance between both nuclei
• E_k = binding energy (= needed to disassemble the atoms/molecules)

Question 2

Describe primary bonds and give examples

Answer 2

Primary bonds are strong intramolecular bonds.

There are 3 kinds of intramolecular bonds:

• covalent: e^- are shared between the atoms, only small difference of ΔEN
• **metallic: **delocalized e^- spread around more than just 2 atoms → multi-atomic system
• **electrostatic: **
  
  • **​ionic bond: **Couloumb forces between ions, big ΔEN
  • dipole type charge distribution: intermediate ΔEN, partial charge = dipole moment

Question 3

Describe secondary bonds and give examples

Answer 3

Secondary bonds are weak intermolecular forces.

There are 3 main types of secondary bonds:

• **Van der Waals: **between atoms without permanent dipole moment → temporarily created dipole interacts with an apolar molecule or atom → converting it into a dipole (induced dipole)

Van der Waals radius: **r₀=r_A+r_B **

• **H-bonds: **H-atom interbridges to 2 other atoms: F, O, N (high EN)
• hydrophobic interactions:

weak Van der Waals interaction, but thermal motion would disrupt the system, ordered water molecules exclude the apolar structures (minimized contact surface)

Question 4

Define electronegativity and give the formula

Answer 4

Electronegativity is chemical property of atoms that describes the tendency to attract e^- towards themself.

EN = | E_i | + | E_ea |

electronegativity = ionization energy + electron affinity

The ionization energy of an atom or molecule describes the minimum amount of energy required to remove an e^- from the atom or molecule in the gaseous state.

Electronaffinity is the amount of energy released when an e^- is added to a neutral atom or molecule in the gaseous state to form a negative ion.