Chemistry Reference
In-Depth Information
Finally, we must discuss the fact that many compounds contain both
ionic and covalent bonds. This occurs when compounds contain special ions
called polyatomic ions. Polyatomic ions are simply ions that are made up of
more than one atom. How do such ions form? Think back to the example
of oxygen, with six valence electrons. If an atom of oxygen “steals” two
additional electrons to complete its valence shell, it becomes the oxide
(O
2-
) ion. If it shares two pairs of electrons with two hydrogen atoms, it
becomes part of a neutral molecule of water (H
2
O). However, if it “steals”
one electron and shares one pair with an atom of hydrogen, you get a mo-
lecular compound, which is also an ion, the polyatomic ion called hydrox-
ide (OH
-
). A polyatomic ion can then attach to another ion with an opposite
charge, forming an ionic compound such as sodium hydroxide (NaOH),
which contains both ionic and covalent bonds.
Lesson 4- 2 Review
1.
_______________ compounds are formed from the electrostatic force
of attraction between charged particles.
2.
_______________ compounds are formed when atoms are held
together by covalent bonds.
3.
The relatively weak forces of attraction between the molecules of a
substance are called _______________ forces.
4.
_______________ ions are ions that are made up of more than one
atom.
5.
Which of the following compounds contain both ionic and covalent
bonds?
a) KCl
b) Al(OH)
3
c) NO
2
d) CH
4
Lesson 4-3: Lewis Dot Diagrams for Compounds
In Lesson 3-6, we learned how to produce Lewis dot diagrams for ele-
ments. In this lesson, we will go over the process of creating Lewis dot
diagrams for compounds. As you will learn in the next lesson, constructing
these diagrams for molecular compounds is a good way to predict the shape
of the molecules. These diagrams can also be useful when you need to
determine the ratio by which elements combine to form compounds. When
constructing these diagrams, you may want know which electrons come
with each atom. For this reason, I will be using dots of different shades to
represent electrons from different atoms in this lesson.
