Geology Reference
In-Depth Information
When an atom with only one electron in its outer shell is near an atom with seven elec-
trons in its shell, the single electron will jump over to join and complete the almost-full
shell. This action results in the first atom having one more proton than electrons and,
therefore, a positive (or +1) charge. Meanwhile, the second atom has one more electron
than protons and, therefore, a negative (or -1) charge. (Later in the chapter, Figure 5-4 il-
lustrates this fact.)
Atoms or
molecules
(more than one atom joined together) with positive or
negative charge are called
ions.
The charge of the ion is determined by how the
electrons in its outer shell move to and from nearby atomic shells. An atom with a
positive charge is called a
cation,
and an atom with a negative charge is called an
anion.
Atoms, and even compounds, can have negative charges of 1, 2, 3, and even
4 (though 4 is rare) and positive charges up to +8. The interaction of ions with one
another is one way that atoms form bonds; keep reading to find out the details.
Chemical Bondage for Beginners
Very few atoms exist in nature all by themselves. Multiple atoms joined together are
called
molecules.
Some atoms of the same element pair up with each other to form mo-
lecules. An example of this is oxygen gas, which is composed of pairs of oxygen atoms,
written as O
2
. (The 2 indicates how many atoms of oxygen are in the molecule.)
In most cases, atoms of two or more different elements combine to form a
compound.
The compound is held together by a
chemicalbond.
In this section I explain the three
most common types of chemical bonding between atoms.
How two atoms bond together is determined by the number of electrons in
their outer orbital shells. For example, an atom with 13 total electrons such as alu-
minum (Al) will have two electrons in the first orbital shell, eight electrons in the
second orbital shell, and three electrons in the outermost orbital shell. The three
electrons in the outermost shell are the ones that participate in bonds with other
atoms.
Donating electrons (ionic bonds)
