Inorganic Unit 2.1: Periodicity
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define periodicity
the pattern in properties across a row, which is repeated in each row
how are elements classified as s, p or d block?
according to their proton number & which orbitals the highest energy e-s are in
what is the trend in atomic radius across a period & why?
atomic radius decreases across a period increase in # of protons same shielding outer e- in same principle energy level stronger attraction b/w outer shell e-s & nucleus, pulling the e-s in
what is the general trend in 1st ionisation energy across a period & why?
of protons increases general trend: ionisation energy increases across period atomic radius decreases same shielding so stronger attraction b/w outer shell e-s & nucleus it takes more energy to remove it
what groups deviate from the general increase in IE across the period & why?
group 2–>3 dip 1IE of Al<Mg Mg: 1s2 2s2 2p6 3s2 the outer e- in Mg is in an s orbital al: 1s2 2s2 2p6 3s2 3p1 Al outer e- is in a p orbital p orbital is higher in energy than s orbital so less energy needed to remove the outer e- in Al group 5–>6 dip 1IE of S<P p: 1s2 2s2 2 p6 3s2 3p3 P outer e- is from an orbital with one e- s: 1s2 2s2 2p6 3s2 3p4 S outer e- is from an orbital with 2 e-s paired up, which repel each other so less energy is needed to remove outer e- in S
what is the trend in electronegativity across a period & why?
electronegativity increases bc increase in # of protons atomic radius decreases same shielding so stronger attraction b/w nucleus & the 2e-s in covalent bond
what is the trend in melting & boiling point across a period & why? split into 4 parts
• Na, Mg, Al (metals) higher mp & bp bc strong metallic bonding Al>Mg>Na bc from Na–>Al ion size decrease, positive charge of ion increases & # of delocalised e-s increases • Si highest mp & bp in period bc macromolecular/giant covalent structure lots of thermal energy is needed to break v many v strong covalent bonds • P4, S8, Cl2 low mp & bp bc simple molecular strucures weak Van der Waal’s forces b/w molecules S8>P4>Cl2 bc S8 biggest & has most e-s so strongest VDWs b/w molecules decrease in # of e-s = weaker VDWs • Ar lowest mp & bp bc monatomic weakest VDW b/w atoms