bonding

Chemical bonds

Chemical bonds are the attractive forces that hold atoms together in the form of compounds. A chemical bond is formed when electrons are shared between two atoms.

There are 3 types of bonds...covalent bonds, polar covalent bonds and ionic bonds.

The simplest example of bonding is demonstrated by the H₂ molecule. We can see that each hydrogen atom has a single electron from the periodic table. If two hydrogen atoms come together to form a bond, then each hydrogen atom effectively has a share in both electrons and thus each resembles an inert gas structure.

The two electrons that are shared are considered to be a chemical bond and can be represented with either two dots or a single dash between the two bonded atoms.

Recognizing the type of bond in a compound.

Most compounds that contain metals are ionic. For the purpose of this course, you may assume that all compounds that contain metals are ionic.

If a compound contains the ammonium ion, it will be ionic. That is why the compound ammonium nitrate is written as NH₄NO₃ rather than N₂H₄O₃. This alerts people to the fact that the compound contains the ammonium group and the nitrate group.

Methods of Showing Formulas of Compounds

Molecular formulas show only the type and number of atoms in a molecule.

Structural formulas show the atoms in their correct placement in the molecule.

Electron-dot formulas are similar to structural formulas but also include all of the non-bonding outer electrons. Knowledge of electron placement aids in understanding how molecules and elements react with one another.

Drawing Electron-Dot Formulas

1. Let us first look at the rules for drawing electron-dot formulas.

2. The first electron-dot formula we shall draw will be methane, CH₄.

3. Then let's try a compound that has non-bonding electron pairs...water.

4. The next example will be an ion with a negative charge, the hydroxide ion, HO^-.

5. Now let's see what happens when we have a positive charge and draw the ammonium ion, NH₄⁺.

6. Finally, let's draw a compound that requires multiple bonds and draw the formula for oxygen, O₂.

Problems

1. Define a covalent bond.

2. Define a polar-covalent bond.

3. Define an ionic bond.

4. Define electronegativity.

5. Why does electronegativity increase going from left to right in a row in the periodic table?

6. Why does electronegativity increase going from bottom to top in a column in the periodic table?

7. Describe the type of bond represented by the dash for each of the following compounds. Consider only the atoms to which the dash is directly connected.

H–H

H–CH₃

H–NH₂

Na–ONa

Na–Br

K–OH

H–OH

H–Br

F–CH₃

8. Draw the electron-dot formulas for the following compounds or ions and calculate the formal charges for every atom.

HF

H₂S

F^-

Br⁺

N₂

HCN

NC^-

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