Atomic Structure Flashcards
Dalton’s view on atoms
He believed atoms were indivisible solid spheres.
Thomson’s view on atoms
Atoms are a ball of charge with negative electrons embedded inside it.
Rutherford’s experiment and view on atoms
Rutherford and 2 of his student fired positive alpha particles at a thing gold sheet.
-Most went through suggesting most of the atom is empty space.
- Some were deflected suggesting the centre of the atom is positive
- Some bounced back suggesting the centre of the atom is small and dense.
His view on atoms: a small positive dense nucleus surrounded by a cloud of electrons and is mostly empty space. It goes against Thomspon’s. (Nuclear model.)
Bohr’s view on atoms
Similar to nuclear model, but the electrons are in orbitals, as the electrons would collapse without them.
Each shell has a iced energy.
The electrons can move between shells, the movement emitting and absorbing electromagnetic radiation.
As energy is fixed, radiation will have a fixed frequency.
The arrangement of subatomic particles, their charges and mass.
Protons and neutrons are found in the nucleus and are held together by strong nuclear forces.
Electrons are found in orbitals surrounding the atom.
Protons: 1 amu, +1
Neutrons: 1amu, 0
Electrons: 1/1840 amu, -1
What is atomic number?
Proton number.
Z
What is mass number?
Number of protons + Number of neutrons.
A
What is an isotope?
Different forms of the same element containing the same number of protons but different number of neutrons.
Why do isotopes have the same chemical property?
Chemical property is decided by electron configuration, and electrons are not affected by isotopes.
Why do isotopes have different physician properties?
Mass number is different and physical properties are dependent on mass.
Define relative atomic mass
Average mass of all isotopes of an element compared to 1/12 the mass of Carbon 12.
Ar = average mass on atom x 12/mass of one atom of carbon 12.
What are the 2 types of ionisation for a mass spectrometer? How do they differ?
- Electron impact: (electron gun) - hot wire filament with current through it emitting electrons. Knock of one electron from each particle to form +1 Molecular ions. These ions fragment.
- Electron spray - sample dissolved in volatile solvent (water methanol etc) and injected through a fine hypodermic needle to give an aerosol. Needle attached to positive terminal of high voltage power supply and particles gain a proton from the solvent as they leave the needle, producing XH+ ions (+1 charge and Mass of Mr 1.) Ions rarely fragment.
What is mass spectrometry?
Analytic technique used to identify different isotopes and find overall relative atomic mass of an element.
When would you use different type of ionisations during mass spectrometry?
Electron impact: organic and inorganic molecules with a low formula mass
Electrospray: Substances with higher molecular mass including biological molecules e.g., proteins
Describe how a time of flight Mass spectrometer works
Acceleration: accelerated by an electric field. Positive ions accelerated towards negatively charged detection plate. Increases kinetic energy of the ions. Lighter ions have a greater acceleration but all are given the same energy.
Ion Drift: Ions pass through a hole in a plate, form a beam with constant kinetic energy, travel along tube to detector . Time of flight is therefore directly proportional to the square root of mass. No electric field so not deflected. Just drift through.
Detection: lighter ions travel faster so they reach the detector first. When positive ions hit the negatively charged detection plate, they gain an electron, producing a flow of charge. The time taken to move down the drift chamber is used by the machine to determine the mass of the isotope. The size of the current produced when each isotope hits the detector is used to determine the abundance of each isotope. More abundant will create a greater current.
