Mary J. Bojan Chem 110 1
Periodicity
Properties of elements • Sizes of atoms and ions
Electron Configuration of ions • Ionization Energy • Electron affinity • Reactivity • Metallic Character
Mary J. Bojan Chem 110 2
Electron Configuration and the Periodic Table
halogens (F, Cl, Br, I) have
noble gases (inert) have
Valence electrons determine the
chemistry!
Location on Periodic Table is related to electron configuration Elements in the same row (family) have the same valence shell configuration.
Example: alkali metals (row 1) have ns1 valence configuration
(H) 1s1 Li [He] 2s1 Na [Ne] 3s1 K [Ar] 4s1 Rb [Kr] 5s1 Cs [Xe] 6s1
Mary J. Bojan Chem 110 3
PROPERTIES OF ELEMENTS
Properties of elements are determined by: • Size (n) and shape () of orbitals • Atomic number (nuclear charge)
Electron configurations determine • the organization of the Periodic Table
AND • the properties of the elements:
reason for periodic trends in behavior
Elemental properties: atomic size ionization energy electron affinities reactivity
Mary J. Bojan Chem 110 4
ATOMIC SIZE
size decreases going from left to right across a period WHY ?
• • •
size increases going down group
WHY ?
Mary J. Bojan Chem 110 6
ELECTRON CONFIGURATIONS OF IONS
e-
Na Cl 1s2 2s2 2p6 3s1 1s2 2s2 2p6 3s23p5
core electrons valence electrons
Elements gain or lose electrons to form separate ions with complete octets.
Na+ Cl− 1s2 2s2 2p6 1s2 2s2 2p6 3s23p6
complete octets [Ne] [Ar]
Mary J. Bojan Chem 110 8
ION SIZES • anions are larger than
parent atoms Cl Cl− 0.99Å 1.81Å
• atom size increases going down family ion size also increases
Li+ F− Na+ Cl− size K+ Br− increases Rb+ I−
• cations are smaller than parent atoms Na Na+ 1.86Å 0.96Å
Mary J. Bojan Chem 110 10
ISOELECTRONIC SERIES
Example: O2− F− Na+ Mg2+ Al3+
# electrons? nuclear charge
size
Isoelectronic
Isoelectronic series a series of atoms or ions that have
Put these ions in order of increasing size. Ca2+ S2− K+ Cl−
Mary J. Bojan Chem 110 11
IONIZATION ENERGY Energy needed to remove an electron
I1 First ionization energy
I1
I2 Second ionization energy
I2 etc. -----------------------------------------------------
Mary J. Bojan Chem 110 12
IONIZATION ENERGY
Example: Mg 1s22s22p6 3s2
[Ne] valence electrons core electrons
I1= 738 kJ/mol Mg+(g) [Ne] 3s1 I2= 1451 kJ/mol Mg+2(g) [Ne] I3= 7733 kJ/mol Mg+3(g) 1s2 2s22p5
Mary J. Bojan Chem 110 14
IONIZATION ENERGY: TRENDS going down a family I1 (kJ/mol)
Li 510 Size? Na 490 I.E. K 418 increases
Rb 403 Cs 375
across the periodic table
Na Mg Al Si P S Cl Ar 490 735 580 780 1060 1005 1225 1550 I1 (kJ/mol) size
I.E I1 increases from left to right (some exceptions)
Electron further from the nucleus easier to remove, but takes extra energy to remove electrons from filled subshells (Mg, Ar) or half filled subshells (P)
Mary J. Bojan Chem 110 17
ELECTRON AFFINITIES
Halogens:
Group II metals (Be, Mg, Ca):
Group I metals :
Noble gases:
Energy needed to add an electron to an atom or ion in the gas phase.
Cl(g) + e− →Cl−(g) E.A. = −349kJ/mol
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METAL REACTIVITY
Li Be Na Mg K Ca Rb Sr
Reactivity ____ as ionization energy ____
(IE = energy need to form a positive ion)
2Li(s) +2H2O()→2Li+(aq) +2OH−(aq)+H2(g)
2Na(s)+2H2O()→2Na+(aq)+2OH−(aq)+H2(g)
2K(s) +2H2O()→2K+(aq) +2OH−(aq)+H2(g)
Mary J. Bojan Chem 110 21
HALOGEN REACTIVITY
Cl2 more reactive than Br2 or I2 Br2 more reactive than I2
F2 electron Cl2 reactivity affinity Br2 I2
Reactivity increases as electron affinity increases
2KCl(aq) + Br2(aq) →no reaction 2KCl(aq) + I2(aq) →no reaction 2KBr(aq) + I2(aq) →no reaction
2KBr(aq) + Cl2(aq) →2KCl(aq) + Br2(aq) 2KI(aq) + Cl2(aq) →2KCl(aq) + I2(aq) 2KI(aq + Br2(aq) →2KBr(aq) + I2(aq)