Chemistry Reference
In-Depth Information
Chemists come up with an average, based on the mass numbers of the iso-
topes and the relative abundance by which they appear. The fact that the
atomic number of hydrogen is so close to the mass number of the isotope
of hydrogen known as protium indicates that the vast majority of the hydro-
gen atoms found in nature (approximately 99%) are of this type.
Electrons (e
-
), which are located outside of the nucleus, have essentially
no mass and a charge of -1. Each electron has a charge that is the equal and
opposite to the charge of a proton but contains only about 1/1836th of the
mass of a proton. Because atoms typically have the same number of elec-
trons as protons, they normally have a net charge of zero and are said to be
neutral. For example, if an atom of oxygen has 8 protons (8 × +1 = +8)
and 8 electrons (8 × -1 = -8), then ((+8) + (-8) = 0) the atom of oxygen
has a net charge of zero.
Atoms will often gain or lose one or more electrons to become charged
atoms called ions. An atom that has lost some of its electrons would have
more protons than electrons and therefore have a net positive charge. We
call this type of atom a positive ion. Negative ions are formed when an atom
gains additional electrons, giving it a net negative charge. Figure 3
-
1c com-
pares neutral hydrogen to the positive and negative ions of hydrogen. Please
note that these images are not drawn to scale.
Comparing Neutral Hydrogen to Its Ions
-
-
+
-
+
+
Neutral Hydrogen
A neutral atom of
hydrogen contains one
proton and one electron,
for a net charge of “0.”
Negative Ion
Hydrogen gains an electron
to become the negative
hydride (H
-
) ion, with a net
charge of “1.”
Positive Ion
Hydrogen loses its only electron
to become the positive (H
+
)
ion, a bare proton with a net
charge of “+1.”
Figure 3-1c
Lesson 3
-
1 Review
1.
A(n) _______________ is an atom that has gained or lost one or
more electrons.
2.
A(n) _______________ is a neutrally charged subatomic particle
found in the nucleus.
