Problem Set #1
1. Calculate the number of neutrons of the atom whose atomic number is 42 and whose mass number is 96.
Atomic Mass-Atomic Number = Neutrons 96 – 42 = 54 neutrons
2. Complete the following table concerning the three isotopes of silicon whose atomic number is 14.
Isotope
Si-28
Si-29
Si-30
# Protons
14
14
14
# Electrons
14
14
14
# Neutrons
14
15
16
3. How many moles are represented by each of the following.
a. 11.5 g Na which has an atomic mass of 22.99 amu.
11.5 g Na (1 mole ) = .5 mol Na
(22.99g)
b. 150 g S which has an atomic mass of 32.07 amu.
150 g S (1 mole ) = 4.68mol S
(32.07g)
c. 5.87 g Ni which has an atomic mass of 58.69 amu.
5.87 g Ni (1 mole ) = .1 mol Ni
(58.69g)
4. Explain why different atoms of the same element always have the same atomic number but can have different
mass numbers?
Atoms are made of three subatomic particles, protons, electrons, and neutrons, Protons and neutrons are found in
the nucleus and both have a mass of 1 amu. While the protons always remain the same (atomic identity) they can
vary in the amount of neutrons, these atomic variations are called isotopes. Isotopes occur naturally in nature and
since neutrons have mass, this variation changes the the atomic mass of the atom, but does not influence the atomic
number because the variation of neutrons does not affect the number of protons.
5. How is an ion different from its parent atom (use cation and anions as examples).
An ion is atom that has gained or lost electrons. A parent atom has the same amount of electrons and protons so the
atom is considered neutral, meaning it has no charge. An atom leaves this neutral state when it loses or gains
electrons. The gain of electrons now means that the atom has more electrons than protons and is considered more
negative than when it was in its neutral state—we call this an anion. The loss of electrons now means that the atom
has fewer electrons than protons and is considered more positive than when it was in its neutral state—we call this a
cation.
6. In your own words explain what a salt is and how it is formed.
A salt is an ionic compound , meaning it is formed between a cation and anion and when placed in water will
dissociate back into these cations and anions.
7. How can you use the periodic table to determine the charge of an ion?
When an atom becomes an anion it does so because it picks up additional electrons, only so much so that its outer
valence shell is full. So hy looking at the columns of the periodic table (not including the transitional elements) IVIII, those roman numeral number indicate how many electrons are present on the atom in its neutral state. To
determine the anionic charge you add the appropriate number to get to 8. Example Oxygen has 6 electrons and if it
forms an anion its charge with be negative 2, the amount of electrons needed to complete its outer (valence) shell.
8. How does a covalent bond differ from an ionic bond?
Covalent bonds and Ionic bonds are different in the way electrons are placed to complete the outer or valence orbital
of participating atoms when bonds are forming. In an Ionic bond, electrons are completely transferred from one
atom to another. This occurs because of the relative numbers of electrons found within the valence shells. Typically
in biochemistry, a atom that has one to two electrons in its valence shell or needs only one to two electrons to
complete it valence shell will most likely—but not always undergo Ionic bonding. As for covalent, the amount of
energy needed to fill a valence shell of lets say 3, 4 o 5 or to lose that many requires too much energy, therefore, the
sharing of electrons occurs between these two atoms—however they may not be shared equally.
9. Predict whether the bonds between the following pairs of elements are ionic, polar covalent, or nonpolar
covalent.
Na—F
H—I
N—O
Al—O
S—O
H—H
Cl—Br
Sr—O
Ionic
Covalent (Non-Polar)
Covalent (Non-Polar)
Ionic
Covalent (Polar)
Covalent (Non Polar)
Covalent
Ionic
10. What causes the formation of a chemical bond due to a mutual attraction of the nuclei?
The nuclei of atoms are positive and therefore not attracted to each other, but they share a mutual attraction to each
others electrons, this is especially apparent in a covalent bond when electrons are shared. When one of the atoms
nuclei is larger than the other it doesn’t share these electrons equally, so while the mutual attraction between nuclei
for each others electrons form a covalent bond, it forms a polar covalent bond.