periodicity Flashcards
how are elements in periodic table arranged
elements arranged according to proton number
what is a period
horizontal row
what is periodicity
study of trends within periodic table. often these trends are linked to elements’ electronic configuration
what is the trend in atomic radius along a period
along a period, atomic radius decreases
why does the atomic radius decrease along a period
atomic radius decreases due to an increased nuclear charge for the same number of electron shells
this means that the outer electron are pulled in closer to the nucleus because the charge produces a greater attraction
as a result the atomic radius is reduced
trend in atomic radius going down group
going down a group, atomic radius increases
why does atomic radius increase down a group
with each increment down a group, an electron shell is added
increases the distance between the outer electrons and the nucleus, reducing the power of attraction
more shells also increases electron shielding, whereby the inner shells create a ‘barrier’ that blocks the attractive forces
the nuclear attraction is reduced further and atomic radius increases
what is the trend in ionisation energy along a period
along a period, ionisation energy increases
why does ionisation energy increase along a period
increases because atomic radius decreases, hence nuclear charge increases
this means that the outer electrons are held more strongly so more energy is required to remove the outer electron and ionise the atom
what is the trend in ionisation energy going down a group
decreases
why does ionisation energy decrease going down a group
nuclear attraction between the nucleus and outer electrons and shielding also increases
both of these factors mean less energy is required to remove the outer electron
what does melting point of period 3 element depend on
- structure of element
- bond strength
what happens to melting points across period 3 between sodium and aluminium
Na, Mg an dAl are all metals with metallic bonding
their melting points increase due to greater positive charge of their ions
means more e- released in the form of free e-
increases attractive electrostatic forces from Na to Al, therefore more energy needed to break them
why does melting point increase dramatically for silicone in period 3
silicon has a very strong covalent structure
more energy is required to break the strong covalent bonds - giving very high melting point
why does the melting point decrease in Period 3 between phosphorous and chlorine
phosphorous, sulphur and chlorine are all simple covalent molecules held with weak van der waals forces
less energy is needed to overcome these weak intermolecular forces, so these molecule have relatively low melting points
