Atomic structure and amount of substance Flashcards
(24 cards)
Define atomic number
Number of protons in the nucleus of an atom
Define mass number
The total number of protons plus neutrons in the nucleus
Define isotope
Atoms with the same number of protons but a different number of neutrons
What does a mass spectrometer help determine?
The mass of separate atoms (or molecules)
What is the job of the vacuum in a flight mass spectrometer?
The whole apparatus is kept under a high vacuum to prevent the ions that are produced from colliding with molecules from the air
What happens in the ionisation stage in a flight mass spectrometer?
An electron gun bombards the atom with a beam of electrons to knock off an electron from the atom’s outer shell to produce a singulary positive charged ion
What happens in the acceleration stage in a flight mass spectrometer?
The positive ions are attracted towards a negatively charged plate and accelerate towards it.
Lighter ions and more highly charged ions achieve a higher speed
What happens in the ion drift stage in a flight mass spectrometer?
The ions pass through a hole in the negatively charged plate, forming a beam and travel along the flight tube to a detector.
What happens at the detection stage in a flight mass spectrometer?
When the ions with the same charge arrive at the detector, the lighter ones are first as they have the higher velocities.
The flight times are recorded
The positive ions pick up an electron from the detector, which causes a current flow
What happens at the data analysis stage in the flight mass spectrometer?
The signal from the detector is passed to a computer which generates a mass spectrum
Define ionisation energy
The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous materials
What is ionisation energy a measure of?
The amount of energy needed to remove electrons from atoms
Define Avagadro’s number
The total number of particles in a mole of substance
Define a Mole
A quantity of a substance that contains the avagadro number of particles
What do solutions consist of?
A solvent with a solute dissolved in it
What does concentration tell you?
How much solute is present in a known volume of solution
What is the ideal gas equation?
pV=nRT
What is pressure measured in?
Pa
What is volume measured in?
m^3
What is temperature measured in?
K
Define atom economy
A reaction is found directly from the balanced equation. It is theoretical rather than practical
How do you work out % atom economy?
(Mass of desired product/Total mass of reactants)x100
What does % atom economy tell us?
How many atoms must be wasted in a reaction
What does the percentage yield of a chemical reaction tell us?
The practical efficiency of the process, how much is lost by: the practical process of obtaining a product, as a result of reactions that don’t go into completion
