Chapter 8
Periodic Properties of the Elements
H E
Energy of an atomic orbital
For an atom, electrons are in atomic orbitals.
Orbital Energy Levels for the Hydrogen Atom
H atom: E only depends on n degenerate
E depends on n and l
same n, l↑ ↔ E↑
H E
i fE E hv
A Picture of the Spinning Electron
Spin quantum number ms
ms = +1/2 or −1/2
4 quantum numbers are used to specify an electron.
How do electrons fill up atomic orbitals?
Pauli Exclusion Principle
In a given atom, no two electrons can have the sameset of four quantum numbers.
An orbital can hold only two electrons, they must haveopposite spins.
1s1
2s1
2p1
electron configuration
Lowest energy: ground state
Excited states
↑1s
↓2s
H atom
orbital diagram
↑2p
Now we can write the ground state electronconfigurations and draw orbital diagrams accordingto Pauli principle.
Electron configurations explain many chemicalproperties.
For degenerate orbitals, the lowest energy is attainedwhen the number of electrons with the same spin is maximized.
Hund’s rule
Valence electrons: electrons in the outermost shell formain group elements.They are involved in bonding and reactions.
Core electrons: inner electrons
Elements in the same group have similar valenceelectron configuration — similar chemical properties.
Noble gases have 8 (He 2) valence electrons. Stablestructure.
Number of valence electrons = main group number
Metals: tend to lose valence electrons to reach 8(2) valence electron.
Nonmetals: tend to gain electrons to reach 8(2) valence electrons.
Number of filled shells = period number
Review Problem Set 10
Periodic trends in atomic properties
• Atomic radius
Atomic Radii (in Picometers) for Selected Atoms
Atomic radius
In a period: decreases from left to right
In a group: increases from top to bottom
On the basis of periodic trends, choose the larger atom in each pair (if possible). Explain your choices.
(a) N or F (b) C or Ge (c) N or Al (d) Al or Ge
EXAMPLE 8.5 Atomic Size
Choose the larger atom or ion from each pair.
(a) S or S2– (b) Ca or Ca2+ (c) Br– or Kr
EXAMPLE 8.7 Ion Size
Periodic trends in atomic properties
• Atomic radius
• Ionization energy
Energy required to remove an electron froma gaseous atom or ion.
X(g) → X+(g) + e−
X+(g) → X2+(g) + e−
Ionization energy
first ionization energy
second ionization energy
Ionization energy
In a period: increases from left to right
In a group: decreases from top to bottom
(general trend)
Periodic trends in atomic properties
• Atomic radius
• Ionization energy
• Electron affinity
Energy change associated with the additionof an electron to a gaseous atom.
X(g) + e− → X−(g)
Electron affinity
∆E = Ef − Ei = EA < 0
X(g) + e−
X−(g)
EEi
Ef
stable X−
Electron affinity
In a period: increases from left to right
In a group: no clear trend
(very rough trend)
Periodic trends in atomic properties
• Atomic radius
• Ionization energy
• Electron affinity
Remember the trends
Problem Set 11
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