3 Periodicity Flashcards
where in the periodic table is the largest atom
bottom left
(to the right, nuclear charge incr and hence greater pull)
what is the electron shell theory
atomic radii decr across a period as atomic number incr
explain shielding effect
electrons in the inner shells repel the electrons in the outermost shells
ionic radius down a period
incr with incr NEGATIVE
decr with incr POSTIVE
so more negative is bigger
why does ionic radius increase as charge becomes more negative
atoms accept more electrons, nuclear charge remains the same
= new electrons experience repulsion
4 factors influencing ionisation energy
- size of nuclear charge
- distance of outer electrons from nucleus
- shielding effect
- spin-pair repulsion
recall ionisation energy trends esp anomalies
theyre in 7 i think
define electron affinity
(the opposite of ionisation energy)
amt of energy RELEASED when ONE MOLE of electrons is gained by ONE MOLE of atoms of an element in the GASEOUS state to form ONE MOLE of GASEOUS IONS
electron affinities are measured under standard conditions which are ___ K and ____ kPa
298k (25C)
100kPa
units for electron affinity
kilojoules / mole
kJ / mol
the first electron affinity is always (exo/endo thermic)
EXOthermic
why can second electron affinity by endothermic
energy is required to overcome repulsion between electron and negative ion
the most exothermic electron affinities belong to ….
group 17! they also have the highest electronegativities
what elements are missing from electron affinity charts
noble gases! they do not form negative ions
which 2 groups does electron affinity peak
2 and 5
electron affinities (incr/decr) down a grp
decrease – less exothermic
- atoms larger = incr shielding = decr effective nuclear charge
why is the electron affinity for fluorine less than expected?
fluorine is a small stom
additional electron in 2p subshell = considerable repulsion w other valence electrons
define electronegativity
ability of an atom to attract a pair of electrons towards itself in a covalent bond
what is the most electronegative atom
fluorine
(4.0 on the Pauling scale!)
2 factors affecting electrongeativity
nuclear charge
- more protons = incr nuclear attraction = more electroneg
atomic radius
- closer = more strongly attracted = incr electroneg
electrongeativity down a group
decrease down a group
- nuclear charge incr BUT extra shell = shielding
- incr dist
decr effective nuclear charge
how does electronegativity change across a period
increases
protons added = incr nuclear charge
same shielding
incr attraction
smaller atomic radii
the larger the electrongeativity, the _____ the atomic radii
smaller
electronegativity vs electron affinity
chemical character, only covalent bonds!
thermodynamic value measurable – formation of negative ions
low _________ ________ and low __________________ of metals can account for delocalisation of electrons
ionisation energies (less energy req to seperate)
electronegativities (Attraction low)
high __________ and high __________ explain tendency to form covalent bonds in nonetals
electronegativity
electron affinity
change in acid-base character across a period
basic –> amphoteric –> acidic
aluminum oxide is acid/base?
amphoteric! can act as both
why are metal oxides basic
largest difference in electronegativity with oxygen – forms ionic bond
eg Na and Mg – purely ionic bonding = alkaline
oxide ions become hydroxide ions
why are nonmetal oxides acidic
close electrongeativity to oxygen = covalent bond
forms acid, donates H+
reaction of NO2 with water?
2NO2 + H2O –> HNO3 + HNO2
reaction of SO2 and SO3 in water?
SO2 + H2O –> H2SO3
SO3 + H2O –> H2SO4
more electronegative = more/less ionic?
less ionic (electroneg is for COVALENT!)
transition metals have an incomplete ____ subshell
d
within the d block elements, which ones are transition elements?
exclude the last group of both sides
- they only form one ion with empty/complete d subshell
transition elements definition
incomplete d subshell
form at least one stable cation with an incomplete d subshell
between 3d and 4s subshells, remove electrons from? when forming cations
4s
5 characteristics of transition elements
- variable oxidation states
- form complex ions
- form coloured compounds
- behave as catalysts
- have magnetic properties
what is a ligand
a molecule / ion surrounding the central metal atom/ion
colours of…
[Cr(OH)6]3- complex
[Cr(NH3)6]3+ complex
dark green
purple
what makes transition elements good catalysts
variable oxidation states
why do transition elements lose electrons from the 4s subshell first
when orbitals are occupied, repulsion betw electrons
pushes 4s to higher energy state (slightly higher than 3d)
= +2 is a common oxidation state
describe transition metals with oxidation state +3 and above
polarising
high degree of covalent charater (bonds)
high charge density – pull electrons towards themselves
