MUST KNOW Definitions Flashcards
Relative Atomic Mass Ar
the weighted average of the masses of its isotopes relative to 1/12 of the mass of a C12 atom
Relative Molecular Mass Mr
the weighted average of the masses of the atoms in a molecule relative to 1/12 of the mass of a C12 atom
Mass Number (A)
the sum of protons and neutrons in the nucleus of an atom
Atomic Number (Z)
the number of protons in the nucleus of an atom
Isotopes
atoms with the same atomic number but a different mass number
Empirical Formula
the simplest whole number ratio of elements in a compound
Molecular Formula
the actual number of atoms of each element in the formula of a compound
Ionic Bond
Oppositely charged ions held together by an electrostatic attraction
Covalent Bond
the electrostatic attraction between a positively charged nucleus and a shared pair of electrons, one electron supplied by each atom either side of the bond
Dative Bond
a shared pair of electrons, both electrons being supplied by one atom in the bond
First Ionisation Energy
the minimum amount of energy required in order to remove one mole of gaseous electrons from one mole of gaseous atoms to form one mole of gaseous positive ions
Electronegativity
the ability of an atom to attract the pair of electrons in a covalent bond to itself
Electron Affinity
The enthalpy change when one mole of gaseous atoms acquires one mole of electrons to form one mole of gaseous negative ions
Exothermic Reaction
the heat of a reaction is given out to the surroundings
Endothermic Reaction
the heat of a reaction is absorbed from the surroundings
Average Bond Enthalpy
The energy required to break one mole of a particular covalent bond in the gaseous state to form gaseous atoms (under standard conditions)
it is an average value as it will be affected by neighbouring atoms
Standard Enthalpy Change of a Reaction
the heat energy change under standard conditions (P= 100 kPa T=298K)
Standard State
the state of an allotrope of an element or compound at standard conditions
Standard Enthalpy of Formation
the enthalpy change when one mole of compound is formed in its standard state from its elements in the standard states
Standard Enthalpy of Combustion
the enthalpy change when one mole of a substance undergoes complete combustion in its standard state (at STP)
Standard Enthalpy of Atomisation
the enthalpy change when one mole of gaseous atoms is formed from the elements in its standard states (at STP)
Lattice Enthalpy
the amount of energy required to dissociate one mole of an ionic compound to its gaseous ions (at STP)
Electron Affinity
the enthalpy change when one mole of gaseous atoms accepts a mole of gaseous electrons (at STP)
Rate of Reaction
change in concentration of reactant (or product) with time
Activation Energy
the minimum amount of energy that colliding reactants require to exceed in order for a reaction to occur
Oxidation
the loss of electrons
gain of oxygen
loss of hydrogen
Reduction
the gain of electrons
the loss of oxygen
the gain of hydrogen
Oxidising Agent
causes the other reacting species to be oxidised and itself reduced
Reducing Agent
causes the other reacting species to be reduced and itself oxidised
Delocalisation
electrons in p orbitals forming pi bonds but shared between more than two nuclei
Resonance
when more than one Lewis Structure can represent the position of a double bond
Sigma Bond
Results in the axial (end to end) overlap of orbitals, electron density is concentrated between the nuclei of bonding atoms
Hybridisation
the mixing of atomic orbitals to form new orbitals of intermediate energy
Pi Bond
results in the sideways overlap of parallel p orbitals, electron density is concentrated above and below the nuclei of bonding atoms
