Topic 2: Atomic Structure

• 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

relative mass: 1 actual mass: 1.673 x 10^-24

relative mass: 1/2000 actual mass: (negligible mass)

relative charge: +1 actual charge: + 1.602 x 10^-15

relative charge: -1 actual charge: - 1.602 x 10^-15

• 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

• isotope with unstable nucleus - emits certain radiations

• 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

• vaporisation • ionisation • acceleration • deflection • detection

• all particles passing through get converted to gaseous state • high vacuum here so particles don’t collide with air

• the gaseous atoms are bombarded with high-energy electrons • to generate positively-charged species e. g. X (g) + e- -> M+ (g) + 2e-

• the ions are attracted to positively-charged plates • thus they’re accelerated in the electric field • so they all have the same KE

• 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 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”

a spectrum of wavelengths comprised of the types 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

highest wavelength, lowest frequency

lowest wavelength, highest frequency

as wavelength increases: • quanta energy decreases • frequency decreases thus: shorter wavelength = higher frequency = higher energy

• 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

• continuous spectrum of colours • with vertical black lines at seemingly random intervals • lines indicate absence of transmitted radiation

• heat gas with electric sparks 2. observe the output through a spectrometer

• 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

• 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