CHEM H90 Lecture Notes - Lecture 9: Electron Configuration, Metallic Hydrogen, Diatomic Molecule
Lecture #9
• pattern emerges
o for each value of l, there are 2/+1 orbitals
o for each value of n, l ranged from 0 to n-1
o for each n, there are n2 orbitals
o for each n, electrons have 2n2 places to go
o if n is 1, 2n2 is 2
o if n is 2, 2n2 is 8
• a very deep thing
o everything in our material world is made from atoms
o all the interesting stuff happens because you can combine their electrons in almost
infinitely many ways
o all their chemical properties are determined by their position in periodic table
o the shape of the periodic table is due to quantum mechanics
• what we should have learned
o electron ‘orbits’ described by wavefunctions
o only certain wavefunctions are allowed, labeled with quantum numbers
o allowed orbit wavefunctions are called orbitals
o only 2 electrons fit in an orbital
o the energy of the orbitals of particular n goes as s<p<d
o periodic table follows the ‘filling’ of the orbitals
• trends in reactivity
o elements in the same group resemble each other because they have the same outer
electron configuration
o but groups 3A, 4A, 5A, and 6A have more diversity because they include metals,
nonmetals, and metalloids
• hydrogen
o electron configuration: 1s1
o forms H+ ion (proton) and H- ion (hydride)
o exists as a diatomic molecule H2
o not a metal
o metallic hydrogen is predicted to exist at very high pressures
o however, researchers have shown that it is still not at metal at 100K and 3.2
million atmospheres
▪ this is close to the pressure at the center of the earth
• alkali metals (group 1A)
o electron configuration: [x]ns1, n > 2, n=2
o easily form +1 ions
o the alkali metals are so reactive they are not found in nature in element form
o alkali metals react with water to produce hydrogen gas and a metal hydroxide
• alkali earths (group 2A)
o electron configuration: [x]ns2, n > 2, n=2
o easily form +2 ions
o less reactive than group 1A, but follow same kinds of trends
o Be does not react with water, Mg reacts with steam, while Ca, Sr, and Ba can react
with liquid water
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