Topic 2: Atomic Structure Flashcards
Dalton’s Atomic Theory
- all matter is made up of tiny particles called atoms
- an element consists of atoms of a single type
- compounds are a combination of 2 or more types of atoms
- atoms can’t be created/destroyed in a chemical reaction, only rearranged
radioactive isotope
an isotope of a chemical element that has an unstable nucleus, which emits certain radiations.
uses of radioactive isotopes
- radiocarbon dating: C-14 exists in a set ratio to C-12 in living organisms, and when it dies, the C-14 isotopes decay, altering the ratio
- radiotherapy: Co-60 is a powerful gamma emitter used to treat cancer
- medical tracer: I-131 releases gamma and beta radiation and can be used to detect if the thyroid is functioning correctly + treat thyroid cancer
stages of mass spectrometer
- vaporisation
- ionisation
- acceleration
- deflection
- detection
Mass Spectrometer: Vaporisation
- high vacuum so particles don’t collide with air
- all particles are converted to gaseous state
Mass Spectrometer: Ionisation
- gaseous atoms are bombarded with high-energy electrons
- to generate positively-charged species
e. g. X (g) + e- -> M+ (g) + 2e-
Mass Spectrometer: Acceleration
- the ions are attracted to positively-charged plates
- accelerated in the electric field
- so they all have the same KE
Mass Spectrometer: Deflection
- the positive ions are deflected by an electromagnetic field
- degree of deflection depends on mass-to-charge ratio
- high deflection: low mass, high charge
the conditions in which the particle has high deflection on the mass spectrometer
high charge to low mass ratio
Mass Spectrometer: Detection
- the beam of ions passing through the detector plate is electrically detected
- species of a particular m:z ratio are identified
- results are called “mass spectrum”
electromagnetic spectrum
a spectrum of wavelengths comprised of the types of electromagnetic radiation
properties of electromagnetic radiation
- has electric and magnetic fields that oscillate perpendicularly to each other and to the direction of travel
- behaves like both a particle and like a wave
- velocity of EM waves = velocity of light
- can travel in a vacuum
characteristics of red light
highest wavelength, lowest frequency
characteristics of purple light
lowest wavelength, highest frequency
trends in electromagnetic spectrum
as wavelength increases:
- quanta energy decreases
- frequency decreases
procedure for absorption spectrum to be produced
- pass electromagnetic radiation (e.g. light) through a collection of cold gas
- atoms will absorb some radiation at a certain frequency
- the spectrometer will compare the transmitted radiation to initial radiation and produce the absorption spectrum
observations in absorption spectrum
- continuous spectrum of colours
- with vertical black lines at seemingly random intervals
- lines indicate absence of transmitted radiation
procedure for emission spectrum to be produced
- heat gas with electric sparks
2. observe the output through a spectrometer
what’s observed in emission spectrum
a black background with seemingly random vertical lines of colour (follows colour spectrum placements)
Bohr’s model
- electrons move in orbit around protons
- the forces of attraction are balanced by the acceleration of electrons at high velocity
- the closer the electron to the nucleus, the more stable the electron
- if energy was negligible, electrons could travel to any shell
Bohr’s model’s explanation of absorption and emission
- electrons absorb energy in the form of photons
- they get excited to a higher energy level if the photon’s energy >= energy difference between initial and final energy levels
- due to decreased stability in higher energy levels, electrons emit energy to go back to ground state
isoelectronic species
elements/ions that have the same electronic config.
Heisenberg’s Uncertainty Principle
it isn’t possible to measure the position AND velocity of a microscopic particle with 100% certainty.
reasoning behind Heisenberg’s Uncertainty Principle
it’s impossible to locate a microscopic body without disturbing its position/velocity
Schrodinger Model
- uses wave functions to describe electron behaviour
- shape of atomic orbitals depend on energy of electrons
principal quantum number
represented by “n”
- describes the main energy level (aka shell) occupied by the electron
- the higher the value of n = the farther the electron from the nucleus = the higher the energy associated with the shell
angular momentum quantum number
represented by "l" - describes the shape of the orbital (aka subshell) - formula: 0 to (n-1) n being principal quantum no - s, p, d, f, etc.
magnetic quantum number
represented by (ml, l in subscript) - describes the orientation of an orbital around the nucleus - formula: -l to l l being azimuthal/angular quantum no e.g. the x or y in 2px or 2py
spin quantum number
represented by “ms” (m subscript s)
- describes the spin orientation of the electron
- value: either spin up or spin down (0.5 or -0.5)
wave functions
- principal quantum no. (n)
- azimuthal no. (l)
- magnetic no. (m1)
- spin no. (ms)
relative masses of subatomic particles
proton : neutron : electron
1 : 1 : 0.0005
relationship between EM wave velocity, frequency, and wavelength
speed = frequency x wavelength
line spectrum
a representation of light appearing as a series of discrete coloured lines
continuous spectrum
a spectrum in which there are no gaps, each region blends directly into the next
Pauli’s Exclusion Principle
no 2 electrons in an atom can have the same values for all 4 quantum numbers
Hund’s rule
- electron pairing will not occur in orbitals in the same subshell
- until all orbitals are filled with at least one electron
factors affecting ionisation energy
- effective nuclear charge
- size of atom
- shielding effect
ionisation energy
the amount of energy required to remove the most loosely bound electron from an isolated gaseous atom of an element
successive ionisation energy
the energy required to remove subsequent electrons from the atom in the gaseous state
effective nuclear charge
the net positive charge experienced by electrons
periodic trends of ionisation energy
- increases along a period, as nuclear charge increases and atomic size decreases
- decreases gradually down a group, as while nuclear charge increases, atomic size and shielding effect also increases
exceptions to periodic trends of ionisation energy
IE of Be > B
IE of N > O
because B and O configurations are half-filled, while Be and N configurations are completely filled
atomic mass
- top left in a chemical symbol
- no. of protons + no. of neutrons
atomic number
- bottom left in chemical symbol
- no. of protons/electrons
relative abundance of an isotope
- the fraction of a single existing element
- that has a specific atomic mass
- can be found with mass spectrometry
how is atomic mass calculated
- multiplying relative abundance of each isotope of an element
- by its atomic mass
- and summing up all the products
- then finding the average
what does a mass spectrometer do
- ionises atoms/molecules
- with high energy electron beam
- then deflects the ions through a magnetic field
- based on mass to charge ratio of ion
- the mass spectrum of a sample shows its relative abundance on y axis and m:z ratio on x axis
law of conservation of mass
matter is not created nor destroyed in a closed system
law of constant composition
a pure compound will always have the same proportion (ratio) of the same elements
Plum pudding model of atom
- negatively charged electrons embedded
- in positively charged “pudding”
Aufbau principle
- electrons are placed into orbitals
- in order of lowest energy first
relationship between wavelength and frequency
c = νλ
c: speed of light
ν: frequency
λ: wavelength
disproportionation reaction
- type of redox reaction
- in which a substance is both oxidised and reduced in the same reaction
Planck equation
E(photon) = hν E = energy h = Planck constant ν = frequency
OR
E(photon) = hc/λ c = speed of light λ = wavelength
why is glass transparent?
- 2 most common elements, Si and O2: SiO2 (Quartz)
- when heated to b.pt, becomes amorphous solid when cooled (neither liquid nor solid)
- visible light consists of photons, which are absorbed by electrons
- amorphous solids can’t absorb photons so they just pass through
- this is due to the large gap between electron shells of glass atoms
- photons don’t have enough energy to pass through shells so they just go in and out of the atom
concept of energy quantification
- energy can only be absorbed/released in small, discrete packages (quantum)
- instead of a continuous flow
relationship between photon energy and wavelength
- inversely proportional
- the greater the photon’s energy, the smaller its wavelength
what is the wave function?
- series of mathematical functions describing electrons
- associates possible energy states that electrons can occupy
- represented by ψ
- ψ^2 denotes the probability of finding an e- in a region of space at a given radius “r” from the nucleus
atomic orbital
- the means of describing an electron’s wave functions
- denotes a region in the space around the nucleus
- where the probability of finding the electron is maximum
difference between orbit and orbital
- orbit: 2-D concept
- orbital: 3-D regions
nature of light
- light behaves like waves: the diffraction of light that occurs when passing through a small slit can only be explained with a wave model
- light behaves like particles: scattering of electrons that occur when light hits a metal surface can only be explained using particle models
patterns between energy levels and sub-levels
nth energy level is divided into nth sub-levels
identification of elements
- atoms of diff elements give out a distinctive colour of light when electric discharge is passed through its gaseous form
- when heated, metals produce different-coloured flames depending on the element
reason for convergence in an atomic spectrum
energy levels inside atoms are closer together at higher energies
exchange energy
- the shifting of e-s from 1 orbital to another
- in the same subshell
NOTE: positions can only be changed in linear order, e.g. electrons from the 4th shell can’t move to 2nd shell but the opposite may occur
relationship between energy of photon and the kinetic energy & work function of an electron
E(photon) = KE(electron) + E(W.F.)
difference between work function and ionisation energy
- I.E.: energy required to remove an electron from an atom
- work function: energy required to remove an electron from a metal’s surface
- the electrons in metal are a “sea” of electrons, they don’t belong to any one atom
