Ions
Ever wonder how a battery works? We know that a battery spits out
electricity, but where does it come from? In the power plant, some
companies either burn coal, use steam, or use nuclear energy to create
electricity. Clearly a battery does not employ any of those means to get
the electricity.
So what gives? What we're dealing with in a battery is ions, plain and
simple. Ions are essentially charged particles. Let's review what types
of charged particles there can be...
Key Concepts:
Energy levels - each row on the periodic table corresponds to a new energy
level. For instance, row one (which includes hydrogen and helium) is
energy level one. Row two (starting with litium and ending with neon) is
energy level two, and so on.
Electrons - these are negative charges that surround the nucleus of an
atom. Each electron is worth one negative charge.
Protons - these are positive charges located in the center of the nucleus
of an atom. Each proton is worth one positive charge.
Ionization energy - the energy it takes to remove one electron from the
atom. The lower the number, the easier it is to remove the
electron.
Okay, let's look at oxygen. It has 8 electrons in the ground state,
since
it's atomic number is 8. Notice that oxygen is in the second row of the
periodic table. This means that it is in energy level 2. We want to know
the number of valence electrons (that is to say, electrons that can be
involved in Bonding). When we move to a higher
energy level, some of the electrons become buried beneath the next level's
electrons. For instance, in the case of oxygen, two electrons from level
one are buried beneath the six electrons from level two. Do you know how
we know this?
If you don't, here's a quick summary. As we move left to right
through a
row on the periodic table, we increase the number of protons AND the
number of electrons. So, let's start with the simplest case, hydrogen.
Hydrogen has one electron and one proton. If we move to element #2, we
increase each proton and each electron by one. So, helium, element #2,
has two electrons and two protons. Similarly, when we get to the second
row, a new shell of electrons is added over the top of these two inner
electrons. For lithium, atomic number 3, there are two electrons buried
in the first shell, and one extra electron in an outer shell. There are
also three protons. So, an easy way to think of adding electrons is to
look at the atomic number. The atomic number corresponds to both the
number of electrons and the number of protons in the ground state of an
atom.
Now, when dealing with ions, we're dealing with cations (positively
charged ions) and anions (negatively charged ions). An ion with a -1
charge has one extra electron. An ion with a +1 charge has one fewer
electron. Notice that I didn't say one more proton. This is because when
we deal with ions, we're talking about the exchange of electrons. Since
the proton is buried deep in the atom, it does not have the ability to
leave the atom. However, since the electron is outside of the nucleus, if
it is given enough energy or is attracted to another molecule, it can
leave the atom. When this occurs, we say the atom was ionized. Since it
has one fewer negative charge than it normally has, it is a positive ion,
or cation.
Ions can be of molecules or of elements. For instance, oxygen combines
with one hydrogen to form a hydroxide ion, OH-. This
entire molecule has a one negative charge.
Ions are also involved in conductivity. Learn more about how ions transfer
charges in Conductivity.
A table of common cations/anions
| Cation Formula |
Common Name |
| NH4+ |
ammonium ion |
Ca+2
| calcium ion |
| Na+1
| sodium ion |
| H+
| hydrogen ion |
| Fe+2
| iron(II) ion |
| Fe+3
| iron(III) ion |
Sn+2
| tin(II) ion |
| Sn+4
| tin(IV) ion |
Hg+1
| mercury(I) ion |
| Hg+2
| mercury(II) ion |
| Ag+1
| silver ion |
| Al+3
| aluminum ion |
| Mg+2
| magnesium ion |
| Anion Formula |
Common Name |
| OH-
| hydroxide ion |
| OH-
| hydroxide ion |
| SO4-2
| sulfate ion |
| SO3-2
| sulfite ion |
| Cl-
| chloride ion |
| F-
| fluoride ion |
| NO3-
| nitrate ion |
| MnO4-
| permanganate ion |
| CN-
| cyanide ion |
| CO3-2
| carbonate ion |
| C2H3O2-
| acetate ion |
| PO4-3
| phosphate ion |
