Cornell Notes
Topic/Objective: Chemistry of Compounds
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Essential Question: What Are Compounds?
Questions:
Notes: A compound is a unique substance that forms when two or more elements combine
chemically. Compounds form as a result of chemical reactions. The elements in compounds
are held together by chemical bonds. A chemical bond is a force of attraction between atoms
or ions that share or transfer valence electrons.
Water is an example of a common chemical compound. As you know, each water molecule
consists of two atoms of hydrogen and one atom of oxygen. Water always has this 2:1 ratio
of hydrogen to oxygen. Like water, all compounds consist of a fixed ratio of elements. It
doesn’t matter how much or how little of a compound. If the same elements combine in
different ratios, they form different compounds.
Same Elements, Different Compounds: Look at the Figure below of water (H2O) and
hydrogen peroxide (H2O2), and read about these two compounds. Both compounds consist
of hydrogen and oxygen, but they have different ratios of the two elements. As a result,
water and hydrogen peroxide are different compounds with different properties. If you’ve
ever used hydrogen peroxide to disinfect a cut, then you know that it is very different from
water!
Carbon Dioxide and Carbon Monoxide are another example of “Same Elements,
Different compounds”
Summary:
Questions:
Notes: Types of Compounds
There are two basic types of compounds that differ in the nature of the bonds that
hold their atoms or ions together. They are covalent and ionic compounds. Both
types are described below.
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Covalent compounds consist of atoms that are held together by covalent
bonds. These bonds form between nonmetals that share valence electrons.
Covalent compounds exist as individual molecules. Water is an example of a
covalent compound.
Ionic compounds consist of ions that are held together by ionic bonds. These
bonds form when metals transfer electrons to nonmetals. Ionic compounds
exist as a matrix of many ions, called a crystal. Sodium chloride (table salt)
is an example of an ionic compound.
Summary
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A compound is a unique substance that forms when two or more elements
combine chemically.
A compound always consists of the same elements in the same ratio. If the
same elements combine in different ratios, they form different compounds.
Types of compounds include covalent and ionic compounds. They differ in
the nature of the bonds that hold their atoms or ions together.
Vocabulary : compound: Unique substance that forms when two or more elements
combine chemically.
Review (answer these questions on the left side of your notebook)
1. What is a compound?
2. A mixture is a combination of two or more substances in any proportions.
An example of a mixture is lemonade, which contains water, lemon juice,
and sugar. How do compounds differ from mixtures such as lemonade?
3. Compare and contrast ionic and covalent.
Summary: