Solving these two problems results in a mass number of 1 and a nuclear charge of 0; this set of
values corresponds to the neutron . As for the wrong choices, in choice A, the beta particle
is a nuclear electron and thus has mass and charge numbers of 0 and –1, respectively. The
positron, choice B, has the mass of an electron but the opposite charge; the numbers are thus
0 and +1, respectively. Alpha particles are helium nuclei; choice C corresponds to a mass
number of 4 and a nuclear charge of +2. Choice E, gamma ray, is short-wavelength
electromagnetic radiation, i.e., light; as such, it has no mass and no charge.46 . D
Cr metal in its elemental state has an oxidation number of 0. In K 2 Cr 2 O 7 , O has an oxidation
number of –2 and K has an oxidation number of +1.
Cr must cancel out the –12, so the two Cr molecules must have a charge of +12. 12/2 = +6 for
each Cr molecule.47 . A
When a Ca molecule loses an electron to become Ca+, it goes from 20 to 19 electrons. K in its
elemental state has 19 electrons.
48 . C
This question requires you to know something about the periodicity of the elements. Basically,
all you are asked is why all the halogens behave so similarly in reactions. You know from
studying the periodic table that there must be something that repeats or the table would not
be periodic. What is it about the elements in a column that are the same? The number of
valence electrons. Since the identity of the valence electrons is the same in each column, or
group, and columns in the s block have valence s electrons, columns in the p block have
valence s and p electrons, and columns in the d block have valence s and d electrons, the only
thing that can make them act similarly is the number of electrons in these shells. Furthermore,
the number of electrons in the valence shell affects the reactivity and stability of the shell. The
number of electrons affects the ionization energy and electron affinity, whether the atom will
form cations or anions, and even the number of bonds the atom can participate in.