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UNIT 7: Periodic trends (electrons) (General ideas (Coulomb's law…
UNIT 7: Periodic trends (electrons)
Zeff, radius
Zeff is the net nuclear charge experienced by an electron, which is got by Z (actual nuclear charge) - S (shielding, or inner core electrons b/n that electron and nucleus.)
Goes up right across due to increased nuclear charge but same shielding, a little up as go down due to less effective shielding from farther inner shells.
Higher Zeff also means a smaller radius because a stronger nucleus means pulled closer.
Decreases across period due to increasing nuclear charge; increases going down due to more "n" shells.
Anions will gain more radius due to increased repulsions/spread out. Cations lose radius due to less.
Non-bonding is distance b/n gaseous atoms bouncing off one another; bonding is distance b/n two chemically bonded atoms. Non-bonding > bonding.
Group characteristics:
Metallic character increases down and to the left
Know groups and what they are mostly: oxygen group is nonmetals (mostly solid), halogens are gases to solids to bottom, and noble gases.
GROUPS
METALS: Most metal oxides are basic (form bases in water). Met. O's also form salt + water w/acids; tend towards basic.
Alkali metals: Highly exothermic reactions w/water. Form hydrides (H-) and sulfides.) Li produces oxide, Na down produces peroxide (O2/2-), K down produces superoxide (O2-.)
Alkaline earth: denser, higher melt than alkali. Less reactive, ex. w/water: Be no react w/water, Mg w/steam, rest w/water.
React w/water to form hydroxide and H gas.
NONMETALS: Nonmetal oxides are ACIDIC; form acids in water and react w/bases.
Halogens: very high electron affinities. Cl reacts w/ water.
Noble gases: Xe is most "reactive" and Kr only one case; basically unreactive due to stability but F is only strong enuf.
Ionization energy/electron affinity
1st ionization energy is energy required to pull first valence electron off; will pull from highest subshell and least tightly bound.
Increases right because would be less stable if lost (also Zeff increases); decreases down because of larger radius and less pull.
2nd, 3rd, etc. are higher because the ion has become more positive overall (not really related to Zeff, but whatever)
Pulling from a former inner electron core is exponentially harder because it was STABLE!
Electron affinity is the ease at which gains an electron; more easy is more negative (energetically favorable.
Increases right because it would become more stable that way; note intermittent stability due to hund's rule.
General ideas
Coulomb's law (distance) + shielding (Zeff) = Ionization energy
Think: going across, shielding stays the same (inner cores) but nucleus protons increase. Therefore Zeff increases but radius decreases.
Blips: going to a 2-electron orbital from 1, as well as going to a 1 filled subshell from an empty shell can offer instability
Reactivity increases left and to right from middle due to decreasing ionization energy left and increasing electron affinity right.
OXIDATION NUMBER STAYS THE SAME THROUGHOUT REACTION!!! (for metal/nonmetal oxide or something)
EQUATIONS:
Binary compounds break into 2 pieces. Things often decompose into water, oxygen, CO2, or combination.
Metals + nonmetal = salt; metal oxide is basic, nonmetal oxide is acidic. (forms ___ with water, combines w/opposite base/acid to form salt and water)