physics 1 Flashcards
What is the Bohr model?
- neg electrons orbit the pos nucleus at fixed distances
- each electron occupies a shell which has discrete energy state
- letters go: K,L,M,N and are numbered 1,2,3,4
How much can each shell in the Bohr model hold?
the rule is 2n squared, n is the quantum number of the shell
What is the rule called within the Bohr model?
orbital filling rule
- 2
C. 4
Carbon
12.0107
6 - atomic number (no of protons)
C - carbon
12.0107 - atomic weight (mean mass of isotopes)
2/4 electron shells
How does 6 = 12?
An element generally has the same number of protons as neutrons (unless an isotope) so multiply the ‘6’ number by 2, so carbon would be 12
how is the chemical behaviour of atoms determined?
- number and arrangement of electrons around nucleus
- that no depends on protons in nucleus
what is nuclear force? what does it do?
an attractive force that acts between all nuclear particles at the short distances between them (about 2 x 10-15m)
this makes sure that the nuclei are stable, even though there is electrostatic forces between protons
what is binding energy?
a measure of the strength of the strong nuclear force holding the nucleons together
it is the loss of mass which results when nucleons form a nucleus
what to remember about the nucleus in relation to binding energy?
the mass of any nucleus is always less than the sum of the masses of the individual constituent nucleons which make it up.
what are isotopes?
- atoms of the same element having different no of neutrons
- they are different forms of the same element
- behave identically
what are radioactive isotopes?
- they contain too many neutrons to hold together, unstable
what do radioactive isotopes undergo?
- nuclear fission, splitting into lighter atoms and releasing energy
what are radioactive isotopes useful for?
- in biology to:
1. trace atoms through living systems
what are radioisotopes bad for?
- too much radiation exposure can lead to damaging living tissue
1. cell destruction
2. mutation
3. cancer
in the graph for electron energy levels, what are they referring to?
the shells, K is 1, L is 2 etc ..
the 0 is unbound
the number at bottom, k shell - tightly bound
what is Neil’s Bohr hypothesis?
- electron outside atom has 0 energy
- electrons in energy levels closer to nucleus have lower and neg energy
- electrons can only exist at specific energy levels
what is transition energy?
The energy required to move an electron from the innermost orbit (K-shell) to the next orbit (L-shell)
is the difference between the binding energies of the two orbits
what does diagram on slide 11 with outermost or valance shell show?
- diff shells represent varying energy states or levels of potential energy
- orbitals are specified with regard to energy, electrons can’t exist between
what are valence electrons?
electrons that are found in the outermost energy levels of an atom.
all elements within a group or family have? referred to as?
have the same number of electrons in their outermost energy levels.
This outermost energy level is referred to as an element’s valence shell.
what is the max number of electrons that can occupy the outermost energy level?
8!
what is special about group VIII
all group 8 are Nobel gases, filled valance shell and do not react in oxidation-reduction
how does electron excitation look like?
ground state
absorption of photon
excited state
What is an orbital?
An orbital is also an area of space in which an electron will be found 90% of the time.
explain electron excitation
atom: Ground State, the electrons are occupying their customary shells.
If the atom is subjected to energy, an electron may be moved to one of the higher energy levels, the atom is now said to be Excited.
If the electron returns to it’s usual energy level, the atom returns to its Ground State and releases it’s absorbed energy as a form of electromagnetic radiation.
what to remember about electron excitation!!!
energy released by each transition is equal to the difference in binding energy between the original and final shells of individual electrons.
how does ionisation look like?
yah! u got this
what is ionisation?
If atom absorbs sufficient energy then an electron may be raised to an electron level (or shell) where it is freed from the atom.
what is ionisation energy?
The minimum energy required to ionise an atom in its ground state
what is the SI unit for work?
the joule
3 forms of energy?
- potential
- kinetic
- heat
what is potential energy?
- same as stored energy
what is an example of potential energy? how does it link to kinetic energy?
When you lift a heavy object against the gravitational field, you exert energy or give the object energy as you lift it. This potential energy later becomes kinetic energy if you let go of the object and it falls
what is gravitational potential energy?
Ep = mgh
Ep - potential energy in joules
m - mass in kg
g - acceleration gained gravity mps
h - height lifted m
what is Ek = ½mv2?
Ek - kinetic energy in joules
m = mass in kg
v - velocity of object mps
what is power? measured in?
- the rate at which energy is expended
- is the rate at which work is done
joules per second: the watt
what is thermal equilibirum?
- more molecules with kinetic energy = hotter and low = colder
- if in contact, energy transferred from hot to cold
- The body at the lower temperature receives a net increase in its molecular kinetic energy with a rise in temperature whilst the hotter body cools
what is specific heat capacity? and formula?
- heat energy in joules required raise temp of 1kg body by 1 degree kelvin
what is thermal capacity?
“heat required increasing the temperature of whole substance” and we show it with “C”.
what is the formula for specific heat capacity? what does it mean?
c = Q
m(T2-T1)
Q being the heat energy required to raise the temperature of the body of mass (m) from T1 to a temperature T2
c - constant for given material and SHC
What is conduction?
transfer of heat between bodies via physical contact
main process of heat transfer in a solid
results in transfer of kinetic energy by interatomic collision
inc of kinetic energy causes vibrations, further transfer of kinetic energy to other atoms in the material
What is convection?
- main process by which heat is transferred in fluids like liquid and gases
- only occurs when molecules are free to move around
- conduction needed for convection
what happens when you increase thermal energy?
- fluid expands, becoming less dense than surrounding fluid
- hydrostatic pressure, heated liquid rises and transfers heat to surrounding molecules by conduction
- temp of small section of heated fluid returns to same temp as surroundings
- convection currents thus set up
what is radiation?
- process of heat transfer through electromagnetic radiations
- only transfer process able to pass through vacuum
define electromagnetic radiation
- visible light, radio waves and x-rays are different types of electromagnetic radiation
- EMR no mass, not affected by electric or magnetic fields and travels at a constant speed in given medium
- travels in straight lines
define EMR wave characteristics
- wavelength λ :
- frequency v (f)
- velocity c
- amplitude a
define wavelength λ
distance between successive corresponding points on the wave
define frequency v (f)
no of waves produced per second
define velocity c
distanced travelled per second by waves
amplitude a
energy of the waves - height of the peak
define Quantum nature of EMR
- EMR delivers energy in discrete packets called quantum: photon
explain E=hv
the shorter the wavelength the greater the energy possessed by the photons.
Short wavelength means
1.high frequency
2. high photon energy.
Long wavelength means
1. low frequency
2. small photon energy
define inverse square law
- an object twice the distance from a light source will receive a quarter amount of illumination
inverse square law definition in RADIOGRAPHY
The intensity of a beam of radiation emitted from a small isotropic source is inversely proportional to the square of the distance from the source providing there is no absorption or attenuation by the medium through which it passes.
What is band theory of conduction?
- electrons exist in specific energy states
- when two atoms are close, energy levels are modified
- electrons influenced by electric fields of both atoms
energy band theory can be used to?
describe the difference between conductors, insulators and semiconductors.
what happens in metallic solid conductors?
- all atoms fully ionised
- 1 electron detached from each nucleus in lattice
- delocalised valence electrons shared between all atoms in lattice, free to move atom to atom
- in metallic solid, valence band partially filled
- conduction bands overlap
what are examples of good conductors?
copper, aluminium and silver:
what happens in insulators?
- valence band completely filled
- energy gap very large
- electrons cannot move under influence of applied potential difference
- high electrical resistance
- no electric current conduction
