Week 11 Flashcards
Functional groups
A part of a molecule that has distinctive chemical properties
The same functional group will have similar chemical behaviour even when the rest of the molecule is different
Bond vibrations
Most bond vibrations correspond to absorbing IR light
Exact vibrational frequency depends on bond strength
Electric Dipole
An electric dipole is a separation of charges (positive and negative)
Unequal sharing or distribution of electrons between atoms
Dipole moment
The product of the separation of the ends of a dipole and the magnitude of the charges
Covalent bonds
Form when electrons are shared between atoms
Outer electrons are tightly held close to the nucleus
Delocalisation
Close overlap required
Short range, directional
Metallic bonding
Outer electrons a long way from the metal, not held tightly
Multiple atoms can overlap without nuclei repelling
Does not require close overlap
Electrons can delocalise across the whole system
- conduct electricity
Hydrogen bonding
creation of a hydrogen bond - intermolecular forces caused by dipole forming
Oxygen is electronegative so O-H bonds are polarised
Separation of charge to form a dipole
Can interact with other dipoles to form H-bonds
H-bonding is strong
Can der Waals interactions
Bond energy < 5 Kjmol-1
Polarisation of an electron cloud by adjacent nucleus
Weak electrostatic interaction
Waves
In phase waves are waves that are in sync and out of phase waves are waves that overlap but aren’t in sync
Standing waves
Oscillates in time
Peaks/troughs do not move in space
Location of any wave cannot be accurately determined
C = ^u
C = speed of light (3.00x10^8m/s)
^ = wavelength
V = frequency
Wave particle duality
Wave theory of light cannot explain the photoelectric effect
When light is shone at metal plate, an electron is emitted
Light is not continuous like a wave
Light is discrete, quantised
-photons - particle of light
Wave particle duality (2)
Night frequency waves = high energy particles
One photon with high enough energy can eject an electron
Many photons with low energy cannot eject an electron
E = hv
E = energy of photon
h = plancks constant (6.626 c 10^-34 m^2.kg/s)
V = frequency of a proton
Bohr model of the atom I
Potential energy of the electron in a hydrogen atom is quantised
Electron can only be found in specific energy levels - fixed distances from the nucleus
Energy increases with distance
Electron can move to higher level, but needs energy to do it
Photon of the exact specific energy absorbed
Bohr model of the atom (2)
Electron can return to lower level, but will give out energy if it does
Photon of the exact specific energy emitted
Rydberg constant (Rh) = 2.179 x 10^-18J
De broglie equation
^ = h/mv
^ = wavelength in m
H = plancks constant
M = mass of particle in kg
V = velocity of the particle in m/s
Absorption and emission spectra
White light can be separated by wavelength using a prism
Some photons are absorbed to promote electrons to higher levels
- absorption spectrum
Some photons are emitted as electrons return to lower levels
- emission spectrum
Electron as a standing wave
Electron in an atom is considered a circular standing wave
Must have an integer number of wavelengths
Wavelength related to energy
As n increases energy increases
Only certain energies are allowed - quantisation
Interference of standing waves results in covalent bonding
