WLU CH110 Summaries.pdf - lOMoARcPSD|10729405 Terra...

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INTRODUCTON
Ions
- An ion is a charged chemical species (monatomic or polyatomic)
- Monatomic ions:
- A ion is charged because the number of electrons do not equal the number of protons
- An anion is an ion with a negatve charge (e.g. Cl
−
, O
2−
, H
−
, S
2−
, N
3−
)
Cl + e -  Cl
-
O + 2e -  O 2-
- A caton is an ion with positve charge (e.g. H + , Na + , Fe 2+ , He + )
H  H + + e -
Fe  Fe 2+ + 2e -
- Polyatomic ions
- Ex. H3O + , Cr
2
O
7
2− , NO 3− , CO
3
2− , MnO
4
− )
- These are groups of atoms in which the total number of electrons do not equal the number of protons

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5.1 ORBITAL ENERGIES
- Review of orbital energies for the hydrogen atom ( Z = 1, 1e − atom)
- The energy of an orbital with principal quantum number is given by
- The energy of the orbital increases as n increases (less stable)
- The most stable level is n = 1 (ground state)
- Less stable states n > 1 (excited states)
What about multelectron atoms?
- Basic idea is the same
- But energies cannot be calculated using the above equaton
- Variatons in nuclear charge ( Z ) and number of electrons infuence electrical forces between nucleus and
electrons
- Changes in electrical forces cause changes in orbital energies
Efect of Nuclear Charge:
- Increasing nuclear charge ( Z ) lowers the energy of orbitals
- Orbital energies are much lower for He +
- The larger nuclear charge of He + means larger forces of
atracton
- The He + orbitals are more stable
Efects of Other Electrons:
- Electron-electron repulsion:
- Each negatvely charged electron is atracted to the positvely charged nucleus (unlike charges atract)
- Each electron is repelled by all other electrons in the atom (like charges repel)
- Electron-electron repulsion accounts for the lower energy required to remove an electron from He
compared to He +
E
n
=−
2.10 × 10
− 18
J
n
2

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- All multelectron atoms have electron-electron repulsion
Screening:
- Screening is when electron-electron repulsion cancels or reduces the amount of atracton between an
electron and the nucleus
The nuclear charge that electron-B experiences is less
that the full +2 nuclear charge that electron-A
experiences
- Efectve Nuclear Charge ( Z
ef
) is the nuclear charge an electron experiences as a result of screening
Z
ef
= Z − efects of screening
Z
ef
(e
A
− ) = +2
Z
ef
(e
B
− ) < +2
- Screening and size of orbitals:
- Electrons in compact orbitals screen beter than electron in larger difuse orbitals
- Screening decreases as orbital size increases
- As the principle quantum number ( n) increases the screening ability of electrons in those orbitals
decreases
- The 1 s orbital screens the 2 s and 3 s orbitals
- The 2 s orbital screens the 3 s orbital
- The 3 s orbital screens larger orbitals (e.g. n = 4, 5, 6 etc.)
- Electrons in lower azimuthal quantum numbers ( l ) screen electrons in higher azimuthal quantum
numbers
- Electrons in s orbitals screen electrons in p , d and f orbitals
- Electrons in p orbitals screen electrons in d and f orbitals
- Electrons in d orbitals screen electrons in f orbitals
This part of the 3 p orbital screens the 3 d orbital