Lecture 2611/04/05. 1) Write the spdf notation for Cl. 2) Which element is larger: Si or Ar?
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Transcript of Lecture 2611/04/05. 1) Write the spdf notation for Cl. 2) Which element is larger: Si or Ar?
Lecture 26 11/04/05
1) Write the spdf notation for Cl.2) Which element is larger: Si or Ar?
Trends in Ionization EnergyTrends in Ionization Energy
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 350
500
1000
1500
2000
2500
1st Ionization energy (kJ/mol)
Atomic NumberH Li Na K
HeNe
ArKr
IE increases across a period because Z* increases.
Metals lose electrons more easily than nonmetals.
Trends in Ionization EnergyTrends in Ionization Energy
IE decreases down a group Size increases easier to lose an electron
Electron Affinity
Electron affinity is the energy involved when an atom gains an electron to form an anion.
A(g) + e- ---> A-(g) E.A. = ∆E
Electron Affinity of OxygenElectron Affinity of Oxygen
∆E is exothermic
[He] O atom
EA = - 141 kJ
+ electron
O [He] - ion
Electron Affinity of Nitrogen
∆E is zero for N- due to electron-electron repulsions.
EA = 0 kJ
[He] N atom
[He] N- ion
+ electron
Trends in Electron Affinity
•Electron affinity becomes more negative across a period •Electron affinity becomes less negative down a group
•(except for some elements going from n=2 to n=3).
Fill in the table
On
Ch E M
Element Atomic radius (pm)
90
120
140
180
Compare the elements Na, Mg, and P.
a) Which has the largest atomic radius?b) Which has the most negative electron
affinity?c) Place the elements in the order of
increasing ionization energy.
A = [Ar]4s2 B = [Ar]3d104s24p5
a) Is element A a metal, metalloid, or nonmetal?b) Is element B a metal, metalloid, or nonmetal?c) Which element is expected to have a larger
ionization energy?d) Which element has a smaller atomic radius?
Valence Electrons Electrons in the outermost shell Determines the chemical properties of atoms Reactions involve loss, gain, or rearrangement of
electrons
Core Electrons Electrons in the inner shells Not involved in chemical reactions
Main group elements: Valence electrons = s and p electrons in outermost
shell Valence electrons are equal to the group number
Transition elements: Valence electrons = ns and (n-1)d electrons Valence electrons are equal to the group number
Valence electrons
Valence ElectronsValence
ElectronsB 1s2 2s2 2p1
Core = [He] , valence = 2s2 2p1
Br [Ar] 3d10 4s2 4p5
Core = [Ar] 3d10 , valence = 4s2 4p5
ExampleWrite the spdf, noble gas, and electron
orbital notation for carbon. Which are the valence electrons? Which are the core electrons?
Lewis Electron Dot Symbols
Represents valence shell electrons
Arrange electrons in pairs around the atom Maximum of eight electrons Octet rule
ExampleWrite the Lewis Dot Symbols for:NitrogenPhosphorous
Bonds
1. Atoms achieve noble gas configuration1. Quest for complete octet
2. Products tend to have a lower chemical potential than the reactants
3. The bond that forms has the lowest potential energy (greatest stability)
Bonding
Quest for complete octet
Covalent bonds:Molecular compoundsSharing of valence electronsCl2
Ionic bond Ionic compoundsValence electrons are transferred
from one atom to anotherMetal + non-metalNaCl
Bonding