chem definitions Flashcards
(41 cards)
isotopes
are atoms of the same element with different numbers of neutrons and different masses
relative isotopic mass
is the mass of an isotope relative to 1/12 th of the mass of an atom of carbon - 12
relative atomic mass
is the weighted mean mass of an element relative to 1/12 th of the mass of an atom of carbon - 12
avogadro’s constant
6.02 x 10^23
molar mass
is the mass per mole of a substance (g mol^-1)
molecular formulae
the number of atoms of each element in a molecule
empirical formulae
is the simplest whole-number ration of atoms of each element in a compound
relative molecular mass
compares the mass of a molecule with the mass of an atom of carbon-12
relative formula mass
compares the mass of a formula unit with the mass of an atom of carbon-12
molar gas volume
is the volume per mole of gas molecules at a stated temperature and pressure
room temperature and pressure (RTP)
25 degrees Celsius / 298 K
101 kPa / 1 atm pressure
ideal gas equation
pV = nRT pressure (Pa) volume (m^3) amount of gas molecules (mol) R = gas constant (8.31 J mol^-1 K^-1) temperature (K)
celcius to kelvin
+ 273
kPa to Pa
x 10^3
percentage yield
= (actual yield) / (theoretical yield)
x100 for percentage
atom economy
is a measure of how well atoms have been utilised
= (sum of molar masses of desired products) / (sum of molar masses of all products)
x100 for percentage
strong acids
e.g HCL
releases all its hydrogen atoms into solution as H+ ions completely dissociates in aqueous solutions
weak acids
e.g ethanoic acid (CH3COOH)
only releases a small proportion of its available hydrogen atoms into solution as H+ ions.
partially dissociates in aqueous solution
alkali
is a base that dissolves in water releasing hydroxide ions (OH-) into the solution
acid + alkali
= salt + water
ionic bonding
is the electrostatic attraction between positive and negative ions.
it holds together cations and anions in ionic compounds
properties of ionic compounds
have high melting and boiling points
tend to dissolve in polar solvents: water
conduct electricity only in liquid state or in aqueous solution
covalent bonding
is the strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
dative covalent bond
is a covalent bond in which the shared pair of electrons has been supplied by one of the bonding atoms only.