periodicity - chemistry courses — penn state...

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


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


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


ATOMIC SIZE

size decreases going from left to right across a period WHY ?

•  •  • 

size increases going down group

WHY ?


Trends in Radii


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]


Charges of Common Ions


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


Ionic Radii


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−


IONIZATION ENERGY Energy needed to remove an electron

I1 First ionization energy

I1

I2 Second ionization energy

I2 etc. -----------------------------------------------------


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


IONIZATION ENERGY


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)


Ionization Energy


Trends in I.E.


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


Electron Affinities


Metal vs. Nonmetal


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)


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)

periodicity - chemistry courses — penn state...

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