chemical changes and structure Flashcards
how are elements arranged on the periodic table?
by increasing atomic number
which elements in the first 20 exist as a metallic lattice?
Lithium, Beryllium, Sodium, Magnesium, Aluminium, Potassium, and Calcium
Which elements in the first 20 are covalent molecules?
Hydrogen, Oxygen, Fluorine, Chlorine, Bromine, Nitrogen, Phosphorus, Sulfur and fullerenes.
which elements in the first 20 are covalent networks?
Boron, Silicon, and Carbon (as graphite or diamond)
which elements in the first 20 are monatomic?
noble gases
covalent radius + trends
covalent radius is the measure of the size of an atom.
across a period it decreases as nuclear charges increases.
going down a group it increases as the number of occupied shells increases.
first ionisation energy + trends
it’s the energy required to remove one mole of electrons from one mole of gaseous atoms.
it increases across a period as the nuclear charge increases.
it decreases down a group as screening effect increases.
second ionisation energy definition
energy required to remove the second mole of electrons from one mole of gaseous atoms
electronegativity + trends
it’s the measure of the attraction an atom in a bond has for the electrons in that bond.
it increases across a period as nuclear charge increases.
it decreases down a group due to increased screening effect
polar covalent bonds
form between atoms which have a difference in electronegativity. one atom will become slightly positive and the other slightly negative (atom with higher EN is negative as it pulls the electrons closer).
why aren’t all substances with polar covalent bonds polar molecules?
if they have a symmetrical arrangement of polar and non-polar bonds, as the polarity will cancel out. e.g carbon dioxide
states at room temperature
covalent molecules - gas/liquid
covalent networks - solid
ionic substances - solid
melting points
covalent molecules - low
covalent networks - high
ionic substances - high
solubility
decreases as size of molecule increases.
polar substances will dissolve in other polar substances etc (like dissolves like)
electrical conductivity
covalent bonds don’t conduct (except carbon as graphite)
ionic bonds can conduct when molten or in solution
intermolecular forces + three types
definition: forces that act between molecules
- london dispersion forces (weakest)
- permanent dipole-permanent dipole forces
- hydrogen bonding (strongest)
how are LDFs formed?
formed between a temporary and induced dipole, which are caused by the movement of electrons in atoms and molecules.
what affects the strength of LDFs?
they get stronger when an atom/molecule has more electrons (bigger molecules have more LDFs, and therefore higher mp/bp)
when are molecules described as polar?
when they have a permanent dipole
p.d-p.d interactions
form between oppositely charged ends of polar molecules, are in addition to LDFs and will increase a substance’s melting and boiling points.
hydrogen bonding
form between hydrogen and either nitrogen, oxygen, or fluorine.
they make melting and boiling points much higher than other compounds of a similar size.
why do ammonia and water have high boiling points?
they contain hydrogen bonding
oxidation and reduction definitions
oxidation: loss of electrons
reduction: gain of electrons
oxidising and reducing agents definitions
oxidising agent: substance that accepts electrons (is reduced itself)
reducing agent: substance that donates electrons (is oxidised itself)
