AP Chemistry
A. AllanChapter 18 - The Representative Elements: Groups 1A through 4A
18.1 A Survey of the Representative Elements
A. Basic Trends
1. Metals tend to lose electrons and form cations
2. Nonmetals tend to gain electrons and form anions
3. Metalloids (semi-metals) have properties of both metals and nonmetals
a. B, Si, Ge, As, Sb, Te, Po, At
4. Metallic character tends to increase as atomic number increases within
a group
B. Atomic Size and Group Anomalies (Anomaly = oddity)
1. Hydrogen vs. Other Group I Elements
a. Very small, relatively high electronegativity (2.1)
b. Forms covalent bonds with nonmetals - other Group I elements
form ionic bonds with nonmetals
2. Beryllium vs. Other Group II Elements
a. Small, electronegativity of 1.5 produces covalent bonds with
many nonmetals (other group II's form ionic bonds)
b. BeO is amphoteric, other group II oxides are basic (form
hydroxides) in solution
3. Boron vs. Other Group III Elements
a. Boron is a nonmetal/semimetal, all others are active metals
4. Carbon vs. Silicon (Group IV Elements)
a. Carbon readily achieves the octet by forming π bonds with
oxygen in CO2
b. Silicon does not form π bonds with oxygen in discrete SiO2
molecules
(1) Si 3p orbitals do not easily overlap with oxygen 2p
orbitals
(2) Si forms interlocking SiO4 tetrahedra which make up the
crystalline structure of quartz
5. Nitrogen and Phosphorus (Group V)
a. Nitrogen forms a diatomic molecule with π bonds (N2)
b. Phosphorus forms aggregates based on the tetrahedral P4
molecule
(1) Single bonds
(2) Large atoms = weak π bonds
6. Oxygen and Sulfur (Group VI)
a. Oxygen forms a diatomic molecule with π bonds (O2)
b. Sulfur forms aggregates such as the cyclic S8 molecule, with all
single bonds
7. Halogens (Group VII)
a. Chlorine has an unexpectedly higher electron affinity than
fluorine
(1) Small size of fluorine atoms bring unshared (lone) pairs
close together, where they repel each other
