Untitled - Kelly Walsh High School

16 CHEMISTRY FOR THE UTTERLY CONFUSED
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Our goal in this chapter is to help you learn about the composition of the atom,
the periodic table, and the writing and naming of chemical formulas. Check with
your instructor to see how many element names and symbols you need to know,
although you will learn many of them through practice. We will only give you an
abbreviated list of ions and molecules, so consult your text for a more extensive
list. Have a periodic table handy for the discussion throughout the chapter.
Practice, Practice, Practice.
2-1 Electrons, Protons, and Neutrons
Our modern model describes the atom as an electrically neutral sphere with a
tiny nucleus in the center containing positively charged protons and neutral
neutrons. The negatively charged electrons are moving in complex paths outside
the nucleus in energy levels at different distances from the nucleus. These
subatomic particles have very little mass expressed in grams; so we often use the
unit of an atomic mass unit (amu or simply u). An amu is 1/12 the mass of a carbon
atom that contains six protons and six neutrons. Table 2.1 summarizes the
properties of the three subatomic particles.
Many books and teachers omit the charges on the particle symbols.
Since the atom is electrically neutral, but is composed of charged particles, the
number of positively charged protons and negatively charged electrons are
equal. It is the number of protons in an atom that really defines the type of element.
For example, all sodium atoms (Na) contain 11 protons and 11 electrons
(to keep the atom neutral), but the number of neutrons may vary. Atoms of the
TABLE 2-1 Properties of the Subatomic Particles
Particle Symbol Charge Mass (g) Mass (amu) Location
Proton p 1 1.673 10 24 1.007 Nucleus
Neutron n 0 0 1.675 10 24 1.009 Nucleus
Electron e 1 9.109 10 28 5.486 10 4 Outside nucleus