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
actual and relative masses of protons/neutrons
relative mass: 1
actual mass: 1.673 x 10^-24
actual and relative masses of electrons
relative mass: 1/2000
actual mass: (negligible mass)
actual and relative charge of protons
relative charge: +1
actual charge: + 1.602 x 10^-15
actual and relative charge of electrons
relative charge: -1
actual charge: - 1.602 x 10^-15
isotope
- atoms of the same element with diff neutron no.
- identical chem properties but diff physical properties compared to other atoms of same element
- since mass differs, other physical properties (e.g. density) also differs
radioactive isotope
- isotope with unstable nucleus
- 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
- all particles passing through get converted to gaseous state
- high vacuum here so particles don’t collide with air
Mass Spectrometer: Ionisation
- the 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
- thus they’re 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
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
thus: shorter wavelength = higher frequency = higher energy
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 (line spectrum)
- only contains emissions at particular wavelengths
- lines tend to converge at lower wavelengths (violet)
- follows colour spectrum placements
explanation of emission spectra
- electrons get excited by the photon energy supplied
- go from ground state to excited state
- electrons can only exist at certain fixed energy levels
- when dropping back to ground state they emit energy
- this corresponds to a particular wavelength and shows up as a line on the emission spectrum
why does the line spectrum converge?
because energy levels themselves converge at higher levels
continuous spectrum
a spectrum in which there are no gaps, each region blends directly into the next
line spectrum
a representation of light appearing as a series of discrete coloured lines
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
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
Schrodinger Model
- uses wave functions to describe electron behaviour
- shape of atomic orbitals depend on energy of electrons
types of wave functions
- principal quantum no. (n)
- azimuthal no. (l)
- magnetic no. (m1)
- spin no. (ms)
principal quantum number
represented by “n”
- describes 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
azimuthal 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)
first ionization energy
energy needed to remove 1 mol of e-s from the ground state of 1 mol of gaseous atoms
e.g. H (g) –> H+(g) + e-
from and to what energy levels do removed electrons move to during ionisation?
from n = 1 to n = infinite!
