2.1 Atoms And Reactions Flashcards
Relative Isotopic Mass
The mass of an atom of an isotope compared to one-twelfth of the mass of an atom of C-12 isotope
Amount of substance
Number of particles, measured in moles
Avagadro’s constant, Na
Number of particles per mole of a substance, 6.02 x10^23 mol^-1
Molar mass
The mass per mope of a substance in gmol^-1 = RFM
Mole
Amount of any substance with as many particles as there are C-atoms in exactly 12g of C-12 isotope,
Moles = Mass / RFM
Isotopes
Atoms of the same element with the same number of protons but different numbers of neutrons, and different masses
Acid
Proton donor - release H+ ions (protons) in solution, eg H2SO4, HCl, HNO3, CH3COOH (weaker)
Base
Proton acceptor - readily accepts H+ ions from acid in aq solution
Alkali
A soluble base that releases OH- ions in aq solution, eg NaOH, KOH, NH3
Neutralisation reaction ionic equation and observations
H+ (aq) + OH- (aq) –> H2O (l)
Metal dissolves, fizzing- CO2 (bubble through limewater cloudy to test), -H2 (lighted splint squeaky pop to test), temp rise and pH change?
Acid and carbonate forms…
Salt and carbon dioxide and water
Acid and metal oxide forms…
Salt and water
Acid and alkali forms…
Salt and water
Acid and metal forms…
Salt and hydrogen
Redox!
Salt
Produced when H+ ion of an acid is replaced by a METAL ion or another positive ion eg NH4+ ion
Hydrated
A crystalline compound containing water molecules
Anhydrous
A substance that contains no water molecules (the form without water)
Water of crystallisation
Water molecules that form an essential part of the crystalline structure of a compound
What do you need to work out empirical formula of hydrated compound?
Mass of anhydrous salt, and mass of WofC
Oxidation Number
A measure of number of electrons that an atom uses to bond with atoms of another element
Oxidation number rules
- -
Redox
Reaction where both oxidation and reduction occur
Oxidation
Loss of electrons, or increase in oxidation number
Reduction
Gain of electrons, or decrease in oxidation number
Relative Atomic Mass
Weighted mean mass of an atom of an element compared to one-twelfth of the mass of an atom of C-12
List soluble salts
All nitrates, all sodium/potassium/ammonium salts, Most chlorides (except Pb/Ag) Most sulphates (except Pb/Ba/Ca)
List of insoluble salts
Most oxides/hydroxides/carbonates (except Na/K/NH4+),
Lead/silver chloride
Lead/barium/calcium sulphate
Molar gas volume
Volume per mole of a gas, in dm^3mol^-1,
Moles of gas = vol dm3/24
Ideal gas law
pV=nRT
Pa x m^3 = JK^-1 x K
Why is 100% yield rare
Reaction at equilibrium, Other side reactions- byproducts, Impure reactions, Some r/p left behind in apparatus Separation and purification- lose product
Benefits for sustainability of high atom economy
More desireable product- less waste/toxic product (safer, less pollution),
Saves landfill and protects environment,
Expensive to dispose of waste,
Less separation costs,
Less expensive reactant wasted,
More sustainable (saves limited resources/materials/energy)
Strong acid
Dissociates completely in solution into constituent ions; very little of reverse reaction happens, so nearly all H+ ions are released
Weak acid
Only partially dissociates in solution into constituent ions; reverse reaction favoured so few H+ ions released
Shell
Group of atomic orbitals with same principal quantum number; shells further from nucleus have greater energy level than those closer to nucleus
Each shell holds up to … (electrons)
2n^2 electrons where n is the shell number
Each subshell holds up to … (electrons)
s- 1orbital, 2electrons,
p- 3orbitals, 6electrons,
d- 5orbitals, 10electrons,
f- 7orbitals, 14electrons
Subshell
Group of same type of atomic orbitals (s/p/d/f) within a shell
Orbital
Region around nucleus that can hold up to 2 electrons with opposite spins
First ionisation energy
Energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions
Factors influencing ionisation energy
Shells, shielding, nuclear charge and nuclear attraction
Why do successive IEs increase within each shell
Electrons are being removed from an increasingly positive ion- less repulsion among remaining ions so held more strongly by nucleus
Why are there big jumps in IE
A new shell is being broken into - an electron is being removed from a shell closer to the nucleus
Ionic bonding
Electrostatic attraction between oppositely charged ions (positive and negative ions)
Describe giant ionic lattices
millions of ions, each surrounded by ions of opposite charges, ions attract each other strongly in all directions, always solid
Properties of giant ionic lattices
high mp and bp - solid at room temp, lots of energy needed to break strong es forces between opp charged ions in sold lattice;
do not conduct as solids - ions in fixed positions, not free to move and carry charge;
conduct when molten/dissolved - ions free to move and carry charge;
soluble in polar molecules - eg water molecules surround each ion, which are pulled out of lattice, to form a soln (lattice breaks down)
Covalent bond
Strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms; directional so only acts between the 2 atoms involved
Lone pair
Outer shell pair of electrons not involved in chemical bonding; repels more than bp (2.5’ reduced due to extra repulsive effect)
Bond pair
Pair of electrons shared between 2 atoms; when only bp’s, all pairs repel each other equally
Dative covalent bond
Shared pair of electrons where both electrons have been provided by one of the bonding atoms only
Electronegativity
Ability of an atom to attract the bonding electrons in a covalent bond; increases towards F in the periodic table
Polar covalent bond (in terms of EN)
Bond between different molecules with a small difference in electronegativity
Ionic bond (in terms of EN)
Bond between different elements with a large difference in electronegativity
Electron pair repulsion theory CHECK
Shape of molecule is determined by number and arrangement of electron pairs in outer shell of central atom and hence the repulsion between them
Bond angle in linear molecule
180’
Bond angle in trigonal planar molecule
120’
Bond angle in tetrahedral molecule
109.5’
Bond angle in octahedral molecule
90’
Bond angle in pyramidal molecule
107’
Bond angle in non linear molecule
104.5’
Describe simple covalent molecules
strong covalent bonds within molecules; weak IMF (induced DD) between molecules break when they change state
Properties of simple covalent molecules
low mp and bp - induced DD;
don’t conduct - no charged particles to move/carry charge;
soluble in non polar solvents - form similar strength attractions (IDD) weakens lattice
