The Periodic Table & Electron Configurations
• Periodic Law – when the elements are arranged in order of increasing
atomic number, their physical and chemical properties show a
periodic pattern
• Groups/families – vertical columns
• Periods – horizontal rows
• 7 periods & 18 groups
1
18
2
16 17
3
12
Metals, Nonmetals and Semimetals
• Metals
• Mostly solid at RT (exception Hg)
• Shiny, malleable, ductile
• Good conductors
• Nonmetals
• Often gases at RT, sometimes liquid or solid
• Not shiny
• Poor conductors
• Metalloids (semimetals)
• Properties between metals and non-metals (so identity disputed)
Valence electrons
• Valence electrons – electrons in the highest principal energy level that are
an element’s outermost electrons
• For H and He these are found in the 1s orbital
• H has 1 valence electron
• He has 2 valence electrons
Valence Electrons
• Oxygen has 6 valence electrons in its n=2 orbitals (outermost)
Valence Electrons
• Aluminum has 3 valence electrons in its n=3 orbitals (outermost)
Valence electrons
• Valence electrons are where all the chemistry happens
• These are the electrons that are involved in chemical reactions
Electron Configuration: Noble Gas Notation
• What is the electron configuration of He?
• 1s2
• This can also be written as: [He]
• This is understood to mean: 1s2
• Li = [He]2s1
• Be = [He]2s2
• B = [He]2s22p1 etc
• Until [He] 2s22p6 = [Ne]
Write the configurations for the first 4 alkali
metals using sublevel and noble gas notation
Element
Li
Na
K
Rb
Sublevel Notation
Noble Gas Notation
Write the configurations for the first 4 alkali
metals using sublevel and noble gas notation
Element
Li
Na
K
Rb
Sublevel Notation
1s22s1
1s22s22p63s1
1s22s22p63s23p64s1
1s22s22p63s23p64s23d104p65s1
Noble Gas Notation
[He] 2s1
[Ne] 3s1
[Ar] 4s1
[Kr] 5s1
• What pattern do you observe?
• The configuration of the valence electrons is the same for all of them.
• This accounts for the similar chemical behavior of the alkali metals
• This also explains group chemistry
Orbital Blocks
• Electron configurations are the key to the structure of the PT
• Each block is defined by a type of orbital
s-Block
• Alkali metals and alkaline earth metals
plus hydrogen and Helium
• Valence electrons only in s orbitals
• Two groups b/c max of 2 electrons
p-Block
• Groups 13-18 (except He)
• No p sublevel in first principal energy level
• Thus no p sublevel in period 1
• 6 groups because p orbitals in a level contain a max of 6 electrons
d-Block
• Groups 3-12
• First d orbital is 3d
• Up to 10 electrons so d block is 10 elements wide
f-Block
• Placed below main body of PT
• 28 elements
• f sublevel contains up to 14 electrons so 14 elements wide
• Lanthanides insert after Lanthanum
• Actinides insert after Actinium
• Adding electron to the f-block does not follow the nice rules we have
for elements further up the periodic table