1. The Periodic Table
Understanding the Periodic Nature of the Elements

2. DETERMINING THE RADIUS OF AN ATOM 
Br2 = A (1.14 A)  
C-C = 1.54 A (0.77 A) 
C-Br = 1.91 A

3. TRENDS IN ATOMIC SIZE
Atomic size correlates to the number of energy levels (n) in an atom and the effective nuclear charge (Z eff) of that atom

4. Li:1s22s1
n = 2, Z eff = 1
Na:1s22s22p63s1
n = 3, Z eff = 1
Be:1s22s2
n = 2, Z eff = 2
Mg:1s22s22p63s2
n = 3, Z eff = 2
B:1s22s22p1
n = 2, Z eff = 3
O:1s22s22p63s23p1
n = 3, Z eff = 3

5. The energy required to remove an electron from a gaseous atom:
IONIZATION ENERGY (I1,2,…n)
The energy required to remove an electron from a gaseous atom:
M(g)  M(g) + + e-
Si:
1s2
2s2
2p6
3s2
3p2

6. Ionization energy increases from left to right across a period
Ionization energy decreases going down a group

7. These 2e- do a better job of shielding the 2p1
electron than they do of shielding each other
Be:1s22s2
n = 2, Z eff = 2
1s2
2s2
B:1s22s22p1
n = 2, Z eff = 3
1s2
2s2
2p1
 decrease in I1

8. These 2e- repel one another 1s2 2s2
N:1s22s22p3
n = 2, Z eff = 5
These 2e- repel one another
1s2
2s2
O:1s22s22p4
n = 2, Z eff = 3
1s2
2s2
2p1
 decrease in I1

9. ELECTRON AFFINITY (E a)
The energy change that occurs when an electron is added to a gaseous atom:
M(g) + e-  M-

10. Adding one or more electrons is an exothermic process for most neutral atoms and for all positively charged ions.
Adding one or more electrons is an endothermic for process for some neutral atoms and for all negatively charged anions ions.
The greater the attraction between the species and the added electron, the more negative the electron affinity.

11. Electron affinity undergoes very little change going down a group
Electron affinity generally increases from left to right across the periodic table
Electron affinity undergoes very little change going down a group
Note that VA elements are less negative (don’t attract electrons as well as)
IVA elements
C:1s22s22p2
n = 2, Z eff = 4
N:1s22s22p3
n = 2, Z eff = 5
Adding this electron would increase the electron-electron repulsion and reduce the
electron-nucleus attraction for the added electron
 less negative Ea
In general, atoms with filled or half-filled subshells have more positive electron
affinities than do elements on either side of them in the periodic table

12. Metallic Elements
Distinguishing luster
Good thermal and electrical conductivity
Most metallic oxides are basic
Exist in solution as cations.
Nonmetallic Elements
Nonlusterous
Solids are brittle
Most nonmetal oxides are acidic
Exist in solution as cations.

13. Group Trends: The Active Metals
Alkali metals are prepared by passing an electric current (electrolysis)
through molten salt
Active metals are soft, possess low densities and low melting points
Alkali metals possess the lowest ionization energies of the elements
Alkali metals readily combine with most nonmetals
2M(s) + H2  2MH(s)
2M(s) + S  M2S(s)
2M(s) +Cl2  2MCl(s)
Alkali metals react vigorously with water
2M(s) + H2O  2MOH + H2(g)
Alkali metals react with oxygen to form oxides, peroxides, and superoxides
4Li(s) + O2  2Li2O
2Na(s) + O2  2Li2O2
K + O2  KO2

14. Group Trends: The Alkaline Earth Metals
Alkaline Earth metals are very reactive but less so than alkali metals
Alkaline metals harder, more dense than, and melt at higher temperatures that alkali metals.
Alkaline earth metals possess higher ionization energies than alkali
metals
Some Alkaline metals react directly with water
Beryllium and magnesium do not react with water, however,
Mg will react with steam.
Mg(s) + H2O(g)  2MgO(s) + H2(g)
Calcium, Strontium, and barium react directly with water
Ca(s) + H2O(g)  2CaOH(s) + H2(g)

15. Transitional Elements: Comparing 1A and 1B Elements
K:1s22s22p63s23p64s1
Note that both elements have 4s1 valence electrons
Cu:1s22s22p63s23p64s13d10
Because the ‘d electrons’ partially shield the 4s electron in Cu and because there is a greater nuclear charge, the 4s electron experiences a larger effective nuclear charge than its counterpart in potassium

16. Group Trends: Selected Nonmetals
Hydrogen is a nonmetal and is diatomic in nature
Hydrogen possess no electron shield and therefore possess a higher
ionization energy than other iA elements (I1= 1312 kJ/mol )
Hydrogen generally reacts with nonmetals to produce molecular
compounds
Hydrogen reacts with active metals to from solid metal hydrides
Mg(s) + H2(g)  2NaH
Ca(s) + H2(g)  CaH2

17. Group Trends: Selected Nonmetals
Oxygen is a colorless diatomic gas. All the other VIA elements
are solid
Both oxygen and sulfur exist as allotropes (different forms of the
same element)
O2(g) O3(g) H = kJ
Oxygen and Sulfur to a lesser degree, possess the ability to attract electrons. Tends to react with metals to produce a metal oxide. Also forms nonmetal oxides

18. Group Trends: Selected Nonmetals
Halogens are generally known as salt formers
Halogens exist as diatomic molecules
Melting points of Halogens increase with increasing atomic number