LECTURE 13 (Forces) Flashcards
What are Valence electrons?
The outermost electrons that participate in chemical bonding
What are the two main types of chemical bond?
- COVALENT BOND = when one or more of the valence electrons from each atom are shared between the two atoms
- IONIC BOND = when one or more of the valence electrons are completely stripped away from an atom and are “donated” to the neighbouring atom
Describe the Quantum mechanical point of view
Cloud represents the probability of finding the electron at a given point in space -> denser the cloud -> higher the probability of finding the electron at that point at any moment in time
Describe the Colloquial point of view
Electron spends on average more time where the cloud is dense and less time where the cloud is thin
What is a Polar bond?
A type of covalent bond where one atom has a stronger pull on the shared electrons
Explanation: One of the atoms may have a stronger pull on the electrons than the other because one atom has a more +vely charged nucleus or because the nucleus is more exposed to, or closer to the shared electrons
Describe a case where ions in solution bond to specific ionised regions of biomolecules
Na+ binds to negative phosphate groups of DNA double helix backbone -> Na+ ions help stabilise the double-helical structure by reducing repulsive force between the -vely charged phosphate groups
What movements does flexibility of covalent bonds allow?
- Free rotation
- Bending
- Compression
- Extension
- Twisting
What gives rise to covalent bonds vibrating at specific frequencies?
When a force causes one of these motions in a molecule, the balance between the force causing the motion and the restoration force can result in vibrations of atoms back and forth -> various vibrational states in the molecule
What are the different molecular forces?
- Coulomb potential
- Charge-dipole interaction
- Induced dipoles
- Dispersion forces
- Hydrophobic forces
- Hydrophilic forces
What is Coulomb’s law?
F = k q1q2/r^2
F - electrostatic force
q - electric charge
r - distance between charge centers
k - Coulomb constant
WHAT IT STATES:
- magnitude of electric charge is directly proportional to electrostatic force
- distance is inversely proportional to electrostatic force -> as distance increases, attraction/repulsion decreases
What is Permittivity?
A measure of how easily a medium is polarised by an electric field
Medical correlation: regions of low permittivity (e.g cell membranes) exclude ions due to the cost of increasing Gibbs energy to place ions there -> use of ion channels which allow ions to pass by creating a tunnel of high permittivity through the membrane
What is a dipole moment?
Equal to the magnitude of the charge at one end of the dipole times the fixed distance between the two charges
d = QdL
Qd - magnitude of the charge at one end of the dipole
L - distance between the two charges
What are the properties of Dipole-dipole forces?
- When two dipoles interact there is a total of 4 charges interacting (compared to 3 in point charge dipole)
- Two different angles to consider for each dipole (compared to a single angle in a point charge dipole)
What are the two angles to consider?
- Each dipole can orient itself toward or away from the other dipole
- Each dipole can turn to the right or left relative to the other dipole
What is a Pi Bond?
A Pi bond is formed by sideways overlap of atomic orbitals which results in electron density above and below the plane of the nuclei of the bonding atoms
