Which of the following is the type
of bond between sodium and bromine when they form a crystal of sodium bromide? (A) Hydrogen bond, (B) ionic bond,
(C) polar covalent bond, (D) nonpolar covalent bond, or (E) metallic bond.
There are several different types
of bonds in chemistry. The most common type is a covalent
bond, which involves the sharing of electrons. This type of bond typically occurs
between nonmetals. Covalent bonds can be nonpolar,
which is where the electrons and the bond are being shared evenly between the two
atoms participating in the bond. Or the covalent bond can be polar,
which is when the electrons are not shared evenly. This occurs due to differences in
electronegativity between atoms participating in the bond. The electrons will be pulled
towards the more electronegative atom.
If the electronegativity difference
between the atoms is very large, as is the case between metals and nonmetals,
instead of sharing the electrons, one of the species might steal the electron from
the other, resulting in positive and negatively charged ions. When this happens, it results in an
ionic bond. Substances with ionic bonds
typically come together in alternating positive and negatively charged ions, which
forms a structure known as a lattice. Substances featuring ionic bonding
form crystals under normal conditions.
Metallic bonding occurs when you
have just a metal, like a large collection of copper atoms, for example. In this kind of bond, the electrons
are freely shared between the metal atoms, resulting in what’s often referred to as
a sea of electrons. Covalent, ionic, and metallic bonds
are the primary ways that electrons can be shared between atoms of a substance. But there’s one other kind of bond
that happens a lot in chemistry that’s worth talking about. And that’s the hydrogen bond. Covalent, ionic, and metallic
bonding are all related to interactions between atoms within a substance. But hydrogen bonding is about
interactions that occur between molecules of a substance.
Hydrogen bonding occurs when you
have hydrogen and a highly electronegative atom like nitrogen, oxygen, or
fluorine. In hydrogen fluoride, for example,
hydrogen is far less electronegative than the fluorine is. Which means that the fluorine will
pull more on the electrons between the hydrogen and the fluorine, resulting in the
fluorine becoming partially negatively charged and the hydrogen becoming partially
positively charged. The fluorine here also has a lone
pair. So in addition to becoming
partially negatively charged due to the electronegativity difference, the lone pair
means that the fluorine has a very high density of negative charge around it.
This will cause the partial,
positively charged hydrogen from another hydrogen fluoride molecule to be attracted
to the partial, negatively charged fluorine from the other molecule. The species with the lone pair is
referred to as the hydrogen bond acceptor. And the species with the hydrogen
is referred to as the hydrogen bond donor. In this example, I’ve shown them
both to be the same type of molecule, but they don’t have to be.
So now that we’ve gone over all the
kinds of bonds that frequently show up in chemistry, let’s see what kind of bonding
the substance in this problem has. So we’re interested in the type of
bond that will occur between sodium and bromine. Sodium is a metal that’s found in
group one of the periodic table. And bromine is a nonmetal that’s
found in group 17 of the periodic table. The question also tells us that
this type of bond will form a crystal of sodium bromide.
All of this matches what we know
about ionic bonding, which typically occurs between metals and nonmetals, which is
what we have with sodium and bromine, which is answer choice (B). The type of bond that occurs
between sodium and bromine when they form a crystal of sodium bromide is an ionic