1.01 Atomic Structure
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Which letter is used to represent the atomic number of an atom ?
Z.
What does the atomic number tell us about at element ?
The number of protons.
What letter represents the mass number of an atom ?
A.
How is mass number calculated ?
It is number of protons + number of neutrons.
Define relative atomic mass.
Average mass of all naturally occurring isotopes of an element compared to 1/12th the mass of an atom of Carbon 12.
What are isotopes of an element ?
Different forms of the same element, containing the same number of protons but different number of neutrons They still have the same chemical properties.
How many orbitals and electrons do these shells contain ? a) 1s b) 2p c)3s d)3d e)4s
a) 1s - 1 orbital 2 electrons b) 2p - 3 orbitals 6 electrons c) 3s - 1 orbital 2 electrons d) 3d - 5 orbitals 10 electrons e) 4s - 1 orbital 2 electrons
Does 3d or 4s have higher energy ? What does this mean ?
3d is higher energy. This means that the 4s orbital fills before the 3d orbitals.
What is an orbital ?
A region around the nucleus that can hold up to 2 electrons.
What would be the relationship between 2 electrons in the same orbital in terms of electron spin ?
Have opposite spin as repel each other as both negative.
Explain why chromium does not fit the trend for electron configuration.
It only has one electron in its 4s orbital before filling 3d Cr : 3p6 4s1 3d5.
Explain why copper does not fit the trend of electron configuration.
It only has one electron in its 4s orbital before filling 3d 3p6 4s1 3d10
What are the two types of ionisation for a mass spectrometer? How do they differ ?
• Electron impact: electron gun knocks off one electron from each particle’s higher energy electrons to form 1+ molecular ions • Electrospray: sample is dissolved in volatile solvent and is injected through a fine hypodermic needle. A high voltage is run through the solvent and particles gain a proton, producing HX+ ions Electron impact samples fragment and Electrospray ions rarely fragment.
When would you use the different types of ionisation in a mass spec ?
Electron impact is used for samples with a low formula mass Electrospray is used for substances with higher molecular mass including biological molecules.
Describe how a time of flight mass spectrometer works.
4 stages; Ionisation, acceleration, ion drift, detection Ionisation - Electron impact / electrospray Acceleration - Positive ions are attracted to a negative plate in the apparatus Ion drift - Ions pass through a whole in plate, form a beam with constant kE and travel to the detector. TOF is proportional to the sq. root of the mass. Detection - positive ions pick up electrons, creates current, m/z value and TOF recorded. Largest current is produced by the most abundant ions.
Define first ionisation energy.
The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous +1 ions.