Basics of the Table : Basics of the Table http://www.wwnorton.com/chemistry/overview/ch6.htm
Groups and Periods
Metals, nonmetals and metalloids
s,p,d, and f-blocks
The Groups: Group IA Alkali Metals : The Groups: Group IA Alkali Metals Configurations end in s1
Soft, silvery colored metals
Highly reactive (not found free in nature)
Less dense than water
Note: K+ important in cell function, Li2CO3 treats manic depression, K2Cr2O7 in “breathalizers”, soap making (NaOH, KOH) Li Na K Rb
The Groups: Group IIA Alkaline Earth Metals : Configurations end in s2
Soft, silvery colored metals
Less reactive than Group IA
Note: flares, flashbulbs, rocket parts, sheet rock, sacrificial anodes, cement, stalactites/stalagmites, hard water The Groups: Group IIA Alkaline Earth Metals Be Mg Ca Sr
Periodic Trends : Periodic Trends Properties of elements increase or decrease across periods and down groups.
Don’t have to memorize data
Atomic size, Ionization energy, Electronegativity & Electron affinity, solubility
What determines how tightly electrons are held? : What determines how tightly electrons are held? See the following link Depends on the force of attraction between nucleus and electrons
How do we determine the strength of this force of attraction?
Three things to consider…. : Three things to consider…. The number of protons in an atom (Z)
The extent of shielding
The configuration of the atom
Shielding : Shielding Shielding - the reduction of the force of attraction between the nucleus and the valence electrons caused by electrons in between them.
Slide 8 : Shielding See the following graphic
Atomic radius: the trend : Atomic radius: the trend Across the period: atomic number increases, no increase in shielding, atomic radius decreases
Down the groups: shielding increases and the atoms get larger
Slide 10 : http://www.wwnorton.com/chemistry/overview/ch6.htm
Ionic radii : Ionic radii W hat kind of ions do metals tend to form? How about nonmetals?
How does this affect the size of the atom?
Ionic radii problems : Ionic radii problems 1) Which is bigger?
a) Mg Mg2+ b) F F-
c) F- Cl- d) Na+ K+
e) Br- Se2-
Ionization Energy : Ionization Energy The energy required to remove an electron, measured in kJ / mole
Process of removing an electron is endothermic
The larger the atom, the easier it is to remove an electron
Ionization Energy: The trend : Ionization Energy: The trend Across period: atomic number increases, no shielding increase, ionization energy increases
Down group: decreases as shielding increases
Excepton:The stability of a full or ½ full sublevel causes an exception to the trend across the periods in Groups III and VI
Ionization energy problems : Ionization energy problems 1)Compare the ionization energies of the elements in the following pairs:
a) Li Na b) C O
c) Ar K d) Be B
e) N O
2nd and 3rd ionization energies : 2nd and 3rd ionization energies Electrons are held more tightly as each one is removed.
It takes more energy to remove the second and third electrons from an atom than the first.
Be aware of exceptionally high ionization energies for elements with half or full sets of orbitals.
Ionization energy problems : Ionization energy problems 2)Consider the following elements:
O Mg N F Na Ne
Which one would have the:
a)Highest 1st ionization energy?
b)Lowest 2nd ionization energy?
c)Highest 3rd ionization energy?
Electronegativity : Electronegativity The relative tendency of an atom to attract a bonding pair of electrons when the atom is chemically combined with another atom
Electronegativity: the trend : Electronegativity: the trend Across the period: increases as atomic number increases
Down the groups: decreases as shielding effect gets larger strength of the nucleus becomes less
Slide 22 : http://www.wwnorton.com/chemistry/overview/ch6.htm
Self check : Self check 1)Which element in each of the following pairs has the highest electronegativity?
A) C or O
B) Be or Mg
C) Na or F
D) O or Al
2) Which element is the least electronegative in the periodic table?
Electron affinity : Electron affinity Measure of how badly an atom wants an electron
Electron Affinity: the trend : Electron Affinity: the trend Going across the period: becomes greater as atomic number increases
Going down the groups: gets smaller as elements become larger and shielding increases.
Exception: elements with full and ½ full configurations are especially stable and thus will have lower electron affinities than expected.
Check : Check 1) Which of the following elements has the greatest electron affinity?
A) Li or Be
B) O or F
C) Al or S
D) N or O
E) Ne or F
F) Mg or Al
Review Summary : Review Summary http://www.wwnorton.com/chemistry/overview/ch6.htm {slide 10 Q2-4}
First ionization energy : First ionization energy
Slide 30 : Electronegativity
Slide 31 : Electron affinity increases decreases