CK-12 Physical Science Concepts - For Middle School

http://www.ck12.org Chapter 3. Chemical Interactions

Formulas for Ionic and Covalent Compounds

TheTable3.1 shows four examples of compounds and their chemical formulas. The first two compounds are ionic
compounds, and the second two are covalent compounds. Each formula shows the ratio of ions or atoms that make
up the compound.

TABLE3.1:Compounds and Their Chemical Formulas

Name of Compound Type of Compound Ratio of Ions or Atoms of

Each Element

Chemical Formulas

Sodium chloride ionic 1 sodium ion (Na+) 1

chloride ion (Cl−)

NaCl

Calcium iodide ionic 1 calcium ion (Ca^2 +) 2 io-

dide ions (I−)

CaI 2

Hydrogen peroxide covalent 2 hydrogen atoms (H) 2

oxygen atoms (O)

H 2 O 2

Carbon dioxide covalent 1 carbon atom (C) 2 oxy-

gen atoms (O)

CO 2

There is a different rule for writing the chemical formula for each type of compound.

Ionic compounds are compounds in which positive metal ions and negative nonmetal ions are joined by ionic bonds.
In these compounds, the chemical symbol for the positive metal ion is written first, followed by the symbol for the
negative nonmetal ion. The video at the following URL gives a fuller explanation of ionic compounds and their
formulas: http://www.youtube.com/watch?v=vscoYh6m46M.

MEDIA

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URL: http://www.ck12.org/flx/render/embeddedobject/79969

• Q:The ionic compound lithium fluoride consists of a ratio of one lithium ion (Li+) to one fluoride ion (F−).
  What is the chemical formula for this compound?


• A:The chemical formula is LiF.

Covalent compounds are compounds in which nonmetals are joined by covalent bonds. In these compounds, the
element that is farther to the left in the periodic table is written first, followed by the element that is farther to the
right. If both elements are in the same group of the periodic table, the one with the higher period number is written
first. The following URL gives a fuller explanation of covalent compounds and their formulas: http://www.youtu
be.com/watch?v=ZTMHbKtgI-M.

MEDIA

Click image to the left for use the URL below.

URL: http://www.ck12.org/flx/render/embeddedobject/79970