AP Chemistry Periodicity valence orbitals outershell orbitals elements

AP Chemistry Periodicity

valence orbitals: outer-shell orbitals -- elements in the same group have the same valence-shell electron configuration -- since valence e– are involved in bonding, elements within a group have many of the same properties Sodium and potassium react w/water to produce hydrogen gas.

Development of the Periodic Table -- few elements appear in elemental form in nature (Au, Ag, Hg, a few others) -- most are in combined forms with other elements -- In 19 th century, advances in chemistry allowed more elements to be identified. Au Ag Hg

r dr Approximate bonding atomic radii for the elements have been tabulated. The distance between bonded nuclei can be approximated by adding radii from both atoms. e. g. , Bonding atomic radii are as follows: C = 0. 77 A, Br = 1. 14 A So the approximate distance between bonded C and Br nuclei = 0. 77 + 1. 14 = 1. 91 A

Atomic Radius As we go down a group, atomic radius… increases. -- principal quantum number increases (i. e. , a new energy level is added) As we go from left to right across the Table, atomic radius… decreases. -- effective nuclear charge increases, but principal quantum number is constant more p+, but no new (i. e. , farther away) energy levels

Coulombic attraction depends on… amount of charge 2+ 2– 1+ 1– distance between charges 2+ 2+ + H He – ++ + + – – 2– 2– As we go , more coulombic attraction, no new energy level, more pull, smaller size

Arrange the following atoms in order of increasing atomic radius: Sr, Ba, Cs Sr < Ba < Cs

Ionization Energy: the minimum energy needed to remove an e– from an atom or ion M+(g) + e– M+(g) + 2 nd I. E. M 2+(g) + e– M 2+(g) + 3 rd I. E. M 3+(g) + e– I. E. M(g) + 1 st I. E. Successive ionization energies are larger than previous ones. -- (+) attractive force remains the same, but there is less e–/e– repulsion e–

The ionization energy increases sharply when we try to remove an inner-shell electron. e. g. , For Mg, 1 st IE = 738 k. J/mol 2 nd IE = 1, 450 k. J/mol 3 rd IE = 7, 730 k. J/mol (strong evidence that only valence e– are involved in bonding) As we go down a group, 1 st IE… decreases. -- more e–/e– repulsion and more shielding

Generally, as we go from left to right, 1 st IE… Exceptions: Be: 1 s 2 2 s 2 B: 1 s 2 2 p 1 e. g. , B < Be 2 p B doesn’t like Subshells prefer to be either completely filled OR half-filled. (easier to remove B’s single 2 p e– than one of Be’s two 2 s e–s) …than any of these. N: 1 s 2 2 p 3 More stable to have O: 1 s 2 2 p 4 than to have 2 p This e– is easier to remove…

First ac r os s a pe rio d… down a group… ac s s ro a pe … d rio

Electron affinity: the energy change that occurs when an e– is added to a gaseous atom For most atoms, adding an e– causes energy to be… released. A + e– A– Exceptions: e Ie. E – ne. r gy eq. for e– affinity: een–e rg y noble gases: the added e– must go into a new, higher energy level group 2 metals: the added e– must go into a higher-energy p orbital group 15 elements: the added e– is the first one to double-up a p orbital

The halogens have the most (–) electron affinities, meaning that they become very stable when they accept electrons. O F more (–) more willing to – 141 – 328 = – e affinity accept an e– S Cl – 200 – 349 Electron affinities don’t vary Se Br much going down a group. – 195 – 325 Te I – 190 – 295 He + Ne + Ar + Kr + Xe +

Group Trends Alkali Metals -- the most reactive metals (one e– to lose) -- obtained by electrolysis of a molten salt e. g. , chloride ion is oxidized and sodium ion is reduced 2 Na. Cl(l) 2 Na(l) + Cl 2(g)

-- react with hydrogen to form metal hydrides: 2 M(s) + H 2(g) 2 MH(s) -- react with water to form metal hydroxides: 2 M(s) + 2 H 2 O(l) 2 MOH(aq) + H 2(g) -- react w/O 2: Li yields Li 2 O, others yield (mostly) peroxides (M 2 O 2) 2 M(s) + O 2(g) M 2 O 2(s) Potassium in water, forming flammable hydrogen and soluble potassium hydroxide.

Alkaline-Earths -- not as reactive as alkalis (two e– to lose) compared to alkalis: harder, denser, higher MPs -- Ca and heavier ones react w/H 2 O to form metal hydroxides Ca(s) + 2 H 2 O(l) -- Mg. O is a protective oxide coating around substrate Mg Ca(OH)2(aq) + H 2(g) Mg ribbon Mg. O

Hydrogen -- a nonmetal, but belongs to no family -- reacts w/other nonmetals to form molecular (i. e. , covalent) compounds The Hindenburg (She burned up in (She was scuttled in May 1937, June 1919, along withkilling 71 other 36 passengers. ) German ships. )

Halogens -- At isn’t considered to be a halogen; little is known about it -- at 25 o. C, F 2 and Cl 2 are gases, Br 2 is a liquid, I 2 is a solid -- their exo. reactivity is dominated by their tendency to gain e– -- Cl 2 is added to water; the HOCl produced acts as a disinfectant -- HF(aq) = weak acid; HCl(aq) HBr(aq) = strong acids HI(aq) A small amount of a halogen is mixed with a noble gas to fill halogen lamps. The halogen sets up an equilibrium with the tungsten filament to prevent the heated tungsten from being deposited on the inside of the bulb.

Noble Gases -- all are monatomic; have completely-filled s and p orbitals -- He, Ne, and Ar have no known compounds; Rn is radioactive -- Kr has one known compoud (Kr. F 2); Xe has a few (Xe. F 2, Xe. F 4, Xe. F 6) professional-grade Rn detector Fan for Rn mitigation

Ionic Radius smaller than parent atoms; Cations are _______ larger than parent atoms. anions are ______ Ca atom 20 p+ 20 e– Ca 2+ ion 20 p+ 18 e– Cl atom 17 p+ 17 e– Cl– ion 17 p+ 18 e– Ca Ca 2+ Cl Cl– EX. Compare the sizes of Fe, Fe 2+, and Fe 3+. Then compare Br with Br–. Fe > Fe 2+ > Fe 3+ Br– > Br

Electronegativity electronegativity: the tendency for a bonded atom to attract e– to itself Electronegativity increases going. . . up and to-the-right. o r t c e l e ty i v i t a neg s e s a e incr Linus Pauling quantified the electronegativity scale. Most electronegative element is. . . fluorine (F).