Topic 2- Atoms, molecules and stoichiometry Flashcards
Define relative atomic mass (Ar )
The mass of an atom of an element relative to the unified atomic mass unit
Define Unified atomic mass unit
1/12th of the mass of a Carbon -12 isotope. Does not have a unit
Define Relative Molecular mass
The ratio of the average mass of a molecule in a molecular compound relative to the unified atomic mass unit
Define Relative formula mass
The sum of the relative atomic masses in the formula unit of an ionic compound
What is an oxidation state?
A number assigned to an element in chemical combination which represents the number of electrons gained or lost by an atom of that element in a compound
Define
Electronegativity
the power of an atom to attract electrons to itself
Rules for oxidation states (5)
• Unconbined = 0
• Neutral = 0
• Sum of ion = charge of the ion
• More electronegative = negative oxidation state
• some elements when forming compounds always have the same oxidation number
Define Molecular formula
The formula that shows the number or type of each atom in a molecule
Define Empirical formula
The simplest whole number ratio of elements present in one molecule or the formula unit of a compound
Water of crystallisation?
When some compounds can form crystals which have water as part of their structure
Percentage yield
(Actual yield/ Theoretical yield) *100
Equation
Concentration
mol dm^-3
Moles / Volume (dm^3)
moles or mass
mol dm^-3 * mr = g dm^-3
What is the Limiting reagent?
the reagent that is not in excess
What is a standard solution?
a solution with a concentration that is known
What is standardising a solution?
finding the concentration of another solution using a standard solution
