Core Definitions and Core Knowledge - AS level Flashcards
Periodicity def
A repeated pattern or trend
Relative Atomic mass def
The relative atomic mass of an element is the average mass of its atoms, compared to 1/12th the mass of a carbon-12 atom
General formula def
formula for a family of compounds. E.g. alkanes‡ CnH2n+2 where n is the number of carbon atoms
Empirical formula def
shows the ratio of atoms in a compound. It is the simplest ratio in which atoms combine to form a compound
Molecular formula def
tells us how many of each type of atom there are in each molecule of the compound
Skeletal formula def
all the hydrogen atoms are removed from carbon chains, leaving just a carbon skeleton with functional groups attached to it
Displayed formula def
shows all the bonds in the molecule as individual lines (each line represents a pair of shared electrons)
Structural formula def
shows how the various atoms are bonded
Hydrated
A crystalline compound containing water molecules
Anhydrous def
A substance containing no water molecules
Water of crystallisation def
The water molecules bonded into a crystalline structure of a compound
How to improve results of water of crystallisation experiment
- Use a mass balance that calculates to a greater number of decimal places to get a more accurate mass reading
- Heat mixture until you record a constant mass
What happens if compound in water of crystallisation decomposes further?
How to stop this?
- Anhydrous solid mass at end will be less than it should be
- You could heat it more gently, or take mixture off of heat
First ionisation energy
The energy required to remove one electron from each atom in one mole of gaseous atoms to produce one mole gaseous 1+ ions
Second ionisation energy
The energy required to remove one electron from each 1+ ion in one mole of gaseous 1+ ions to produce one mole of gaseous 2+ ions
Atomic number def
Number of protons in the nucleus
Orbital def
A region within an atom that can hold up to two electrons with opposite spin
What is meant by one mole of substance?
- As many particles as there are carbon atoms in 12g of carbon - 12
- Or: 6.02x10^23 atoms
How do London Forces arise?
-there is an uneven distribution of electrons present in molecule
↳ this creates an instantaneous dipole
-these cause induced dipoles in neighbouring molecules
Trend in boiling points of chlorine, bromine and iodine
H
Oxidising agent def
A substance that oxidises another substance by attracting its electrons and becoming reduced in the reaction itself(absorbs electrons from other substances)
Reducing agent def
A substance that reduces another substance in a reaction but becomes oxidised in the reaction itself(loses electrons, donates them)
Metallic bonding def
The electrostatic attraction between between cations and delocalised electrons
Covalent bonding def
The electrostatic attraction between two atomic nuclei and a shared pair of electrons
