Chapter 3 Flashcards
Atoms, molecules, and stoichiometry
What is unified atomic mass unit?
One twelfth of the mass of a carbon-12 atom.
1 unified atomic mass unit = 1 u = 1.66 x 10^-27 kg
What is relative atomic mass?
The ratio of the average mass of the atoms of an element to the unified atomic mass unit.
Ar = weighted average mass of atoms in a given sample of an element / unified atomic mass unit.
What is relative isotopic mass?
The mass of a particular atom of an isotope compared to the value of the unified atomic mass unit.
What is relative atomic masses?
The weighted average mass of atoms in a given sample of an element compared to the value of the unified atomic mass unit.
What is formula unit?
The simplest formula for a covalent giant structure of an ionic giant structure, e.g. SiO2, MgCl2
What is relative molecular mass Mr?
The weighted average mass of a molecule in a given sample of that molecule compared to the value of the unified atomic mass unit.
Mr = weighted average mass of molecules in a given sample of a mole / unified atomic mass unit.
What is relative formula mass?
The weighted average mass of one formula unit compared to the value of the unified atomic mass unit.
What is water of crystallisation?
A specific number of moles of water assosciated with a crystal structure.
What is hydrated compound?
Compound which contains a definite number of moles of water in their structure (water of crystalisation).
What is anhydrous?
Containing no water of cystallisation.
What is relative isotopic abundance?
The proportion of one particular isotopes, usually expressed as a percentage. The heights of the peaks in a mass spectrum show the proportion of each isotope present.
What is molecular ions (M+)?
The ion that is formed by the loss of an electron from the original complete molecule during mass spectrometry. This gives us the relative molecular mass of an unknown compound.
What is fragmentation?
The breaking up of a covalent compound during mass spectrometry into smaller positive charged species, e.g. CH3+.
What is the equation of mass spectrometry?
n = 100/1.1 x abundance of [M+1]+ ion/abundance of M+ ion
What is mole?
The amount of a substance which contains 6.02 x 10^23 specified particles (atoms, molecules, ions or electrons).
