PERIODICITY Flashcards
Define periodicity
periodicity is the repeating pattern of physical or chemical properties going across the periods.
Define 1st Ionisation energy
Ionisation energy is the minimum amount of energy required to remove one mole of electrons from one mole of gaseous atom to form (one of mole of gaseous +1 ions)
State the trend in atomic radius across a period
atomic radii decreases because:
- shielding remains constant
- nuclear charge increases
- outer electrons experience more attraction towards the positive nucleus
what’s the trend in melting points /boiling point across a period?
Na,Mg,Al-metallic bonding-gets stronger the more outer shell electrons released to the sea of electrons.Also a smaller sized ion with a greater positive charge makes the bonding strong.Higher energy required to break bonds
Si-macrolecular-many strong covalent bonds between atoms.High energy required to break covalent bonds-High mp/bp
Cl,S,P-simple molecular-weak vdw forces between molecules so little energy required to break it
Ar-weak vdw forces between atoms so little energy required to break
State the general trend in ionisation energy across a period
ionisation energy increases because: -nuclear charge increase -shielding remains constant -size decreases making it harder to remove electrons
why is their a drop in ionisation energy between Mg and Al?
Mg has its outer
electrons in the 3s sub shell, whereas Al is starting to fill the 3p sub shell. Al’s electron is slightly easier to remove because the 3p electrons are higher in energy.
why is there a drop in ionisation energy between phosphorous and sulfur ?
The electron being removed from p is in singly occupied orbital.However the electron being removed from s contains 2 electrons in its orbital creating repulsion so less energy is required to remove an electron from s than p , so the ionisation energy is lower.
