Transcript Chapter 7: Periodic Properties of the Elements

Chapter 7: Periodic Properties of the Elements
Chapter 7: Periodic Properties of the Elements
Dimitri Mendeleev (1834-1907)
• ordered known elements
according to atomic weight
=> in the modern version, elements
are ordered according to atomic number
• elements with similar properties
fell into vertical groups
Chapter 7: Periodic Properties of the Elements
Properties (e.g. reactivity) of atoms depends on…
… number of electrons
… electron configuration
… how tightly electrons are bound to nucleus
(and many more properties)
Chapter 7: Periodic Properties of the Elements
How tightly electrons are bound to nucleus…
… is measured by effective nuclear charge, Zeff
Core electrons shield (mask) nuclear charge
7N:
-
-
-
++
++
+ ++
-
core
valence electrons
1s22s22p3
core electron configuration:
[He] = 1s2
Effective Nuclear Charge:
-
Zeff = +7 – 2 = 5 +
#protons
# core electrons
Chapter 7: Periodic Properties of the Elements
What happens to Zeff along a period in the periodic table?
11Na
12Mg
13Al
14Si
….
Chapter 7: Periodic Properties of the Elements
What happens to the atomic radius along a period ?
The effective nuclear charge increases along a period and draws in the
surrounding electrons, making the atom more compact
Lithium
Fluorine
Chapter 7: Periodic Properties of the Elements
What happens to the atomic radius as we go down a group ?
11Na
19K
37Rb
=> Zeff essentially remains constant
=> but - more main shells are added
atomic radius increases as we go down a group
atomic radius increases
Chapter 7: Periodic Properties of the Elements
atomic radius increases
Chapter 7: Periodic Properties of the Elements
which radius is largest?
which radius is smallest?
Chapter 7: Periodic Properties of the Elements
Chapter 7: Periodic Properties of the Elements
How about the radii of ions?
cations are always smaller than their parent ions
anions are always larger than their parent ions
Chapter 7: Periodic Properties of the Elements
Which of the following has the largest radius?
S2-, S, O2-
Why does the ionic radius decrease along the following series?
O2-
F-
Na+
Mg2+
Al3+
Chapter 7: Periodic Properties of the Elements
Ionization Energies measure the energy required to remove
electrons from an atom in the gas phase
1st ionization energy: energy required to remove 1st electron
K (g)
K+ (g) +
Mg (g)
Mg+ (g) +
ee-
I1 = 419 kJ/mol
I1 = 738 kJ/mol
2nd ionization energy: energy required to remove 2nd electron
3rd ionization energy: energy required to remove 3rd electron …
Chapter 7: Periodic Properties of the Elements
Trends in 1st Ionization Energies
Chapter 7: Periodic Properties of the Elements
Why does the ionization energy increase sharply after removal
of the 5th electron for Nitrogen?
What would a similar graph look like for beryllium (Be)?
Nitrogen
Chapter 7: Periodic Properties of the Elements
Some Group trends:
• Melting point of alkali metals decreases with increasing
atomic number:
• Reactivity of alkali metals increases with increasing
atomic number
Chapter 7: Periodic Properties of the Elements
General Properties of Metals:
• compounds made of metals and non-metals tend to be …
…ionic substances
2 Ni (s) + O2 (g)
→
2 NiO (s)
• Metal oxides dissolve in water to make metal hydroxides:
Na2O (s) + H2O (l)
→
2 NaOH (aq)
strong base!
Chapter 7: Periodic Properties of the Elements
• Metal oxides tend to make basic solutions in water
Na2O (s) + H2O (l)
→
2 NaOH (aq)
• Non-metal oxides tend to make acidic solutions in water
CO2 (g) + H2O (l)
→
H2CO3 (aq)
SO2 (g) + H2O (l)
→
H2SO3 (aq)
SO3 (g) + H2O (l)
→
H2SO4 (aq)
natural water
is always slightly
acidic !
contribute to
acid rain!