points than ionic compounds.35 . E
The atomic radius of an atom increases down a group because the atomic radius of an atom
increases as the n value or shell increases. Cl and Na both have 3 shells, while the others have
only 2 shells. The atomic radius decreases across a period with increasing atomic number. This
is due to the increase in the effective nuclear charge. So Na has the largest atomic radius.
36 . E
The amount of energy needed to remove a single electron is the (first) ionization energy. The
shorter the wavelength of a photon, the higher its energy, so the question is asking which
element has the highest first ionization energy. Remember that the ionization energy of
elements generally increases from left to right across a period. Cl has the highest ionization
energy of the choices given and will require the highest-energy photon to ionize.
37 . A
Boron has a low electronegativity and often forms covalent compounds in which it has fewer
than 8 electrons (for example, BCl 3 , BH 3 ).
38 . C
The common oxoanion of phosphorus is PO 43 −.
39 . B
SiO 2 is a network covalent solid; it forms a nearly infinite network of alternating Si and O
atoms single-bonded to each other. Covalent network substances have very high melting
points and are generally insoluble in most solvents. You should definitely know the most
common examples of covalent network substances: SiO 2 (as quartz or glass, and also called
silica); C, as graphite (C atoms arranged in hexagons, in infinite sheets stacked on top of each
other) or diamond (tetrahedrally bonded C atoms in an infinite 3D network); and Si (pure
silicon has the same structure as diamond). Other examples are less familiar, but you’ll be
expected to recognize these four.
40 . B
All the ions are isoelectronic with Ne and have 10 electrons each, but they each have a
different number of protons in the nucleus. O2− has the lowest number of protons and the
weakest nuclear charge. So the O2− would be the largest ion.