18-2 Chemical Bonds

Chemical Bonds

Types of Bonds

Ions

Recap:
Some atoms can become more stable if they give up or gain electrons.
Atoms are more stable with a complete outer shell of 8 electrons (or 2 if small)

Atoms that give up or gain electrons are called ions.

Giving up electrons makes a positively charged ion called a cation.
(Metals typically give up electrons)

Gaining electrons makes a negatively charged ion called an anion.
(Nonmetals typically gain electrons)

Multiple Select

Select the cations.

• Ca

• Be $$^{2+}$$

• Ca $$^{2+}$$

• F $$^-$$

• Li $$^+$$

Multiple Select

Select the anions.

• S $$^{2-}$$

• Be $$^{2+}$$

• P

• F $$^-$$

• Li $$^+$$

Transfer of electrons

What would happen if potassium (K) and iodine (I) meet?

As a group 1 metal, potassium has 1 electron in its outer shell that it can give
up. Losing that electron would create a potassium ion, K+.

As a group 17 halogen, iodine has 7 electrons in its outer shell and would
really like to have another to make 8. Taking in an electron from potassium
would create an iodide ion, I-.

The oppositely charged ions attract each other to form the neutral compound,
potassium iodide, or KI. It’s neutral because the 1+ cancels out the 1-.

This attraction is called an ionic bond.

The Ionic Bond

Ionic compounds still need to have zero net charge. That means the cations
have to balance out the anions to make zero. Let’s look at magnesium
chloride.

Magnesium is a group 2 metal, losing 2 electrons to become Mg2+.

Chlorine is a group 17 halogen, gaining one electron to become Cl-.

To form a neutral compound requires two chloride ions to balance out each
magnesium ion.

So, the chemical formula is MgCl2.

Multiple Choice

What is the charge of an ionic compound?

• positive

• negative

• neutral

• covalent

Dropdown

Sodium forms a $$1^+$$ cation. Sulfur forms a $$2^-$$ anion.

The chemical formula for sodium sulfide is ​

Select answer

.

Molecules

Some nonmetals are unlikely to lose or gain electrons.
Losing an electron causes the remaining electrons to be held more tightly,
requiring more energy to separate.

For instance, carbon would have to gain or lose 4 electrons to be chemically
stable.

These elements can more easily become chemically stable by sharing
electrons rather than becoming ions.

Shared electrons form what is known as a covalent bond. The neutral
compound formed is called a molecule.

The Covalent Bond

A single covalent bond is a pair of shared electrons.

One shared electron comes from each atom in the bond.

Water (H2O) is a great example of covalent bonding. Take a
look at the dot diagram for oxygen (group 16). Notice the two
unshared electrons.

Now look at the diagram for hydrogen (group 1). Notice the
one unshared electron. Maybe two of those could share
electrons with oxygen…

It’s customary to replace a shared pair of electrons with a
single line to show the single covalent bond.

Multiple Covalent Bonds

In some cases, elements can share more than one pair of electrons.

Two shared pairs (4 e-) form a double covalent bond. Diatomic oxygen (O2)

Three shared pairs (6 e-) form a triple covalent bond. Diatomic nitrogen (N2)

Drag and Drop

In this ethene molecule, carbon and hydrogen share a ​

Placeholder

bond and carbon and carbon share a ​

Placeholder

bond.

Drag these tiles and drop them in the correct blank above

single

double

triple

ionic

quadruple

Equal sharing

Different atoms attract shared electrons in a covalent bond with different
strengths. When electrons are shared by identical (or very similar) atoms, the
result is a nonpolar bond.

Unequal sharing

When atoms with different attractive strengths share electrons, the covalent
bond formed is a polar bond. The shared electrons spend more time near the
stronger atom, resulting in a small negative charge at that end and a small
positive charge at the other, like a little magnet.

δ+

δ-

Dropdown

O-O is a​

Select answer

bond. H-F is a​

Select answer

bond.

Cl-Cl is a​

Select answer

bond. N-O is a

Select answer

bond.

Polar and Nonpolar molecules

A polar molecule has a slightly positive end and a slightly negative end. A
molecule with a single polar bond would also be a polar molecule.

However, multiple polar bonds can sometimes cancel each other out because
of how the bonds are arranged. For example, carbon dioxide looks like this:

The oxygen atoms are stronger than the carbon atom,
pulling electrons away from the carbon. Since each oxygen
pulls equally in the opposite direction, their pulls cancel out
resulting in a nonpolar molecule.

Nonpolar Molecules

Remember what water looked like?

For reasons we won’t go into this year, water is a bent molecule. Oxygen is
stronger than hydrogen, so each bond is slightly negative to the oxygen and
slightly positive to the hydrogen. Overall, this produces a polar molecule.
Many of water’s special properties are due to its polarity.

δ-

δ+

You might recall from the electromagnetic waves chapter
that microwave ovens work by flipping water molecules like
little magnets in an a vibrating electric field. Now you know
why water molecules behave like little magnets!

Multiple Choice

This is trichloromethane, $$CHCl_3$$ . It's a carbon bound to 3 chlorines and a hydrogen. This molecule is...

• polar

• nonpolar

Dropdown

This is carbon tetrachloride, $$CCl_4$$ . It is a carbon atom bonded to four chlorine atoms in a tetrahedron. This is a

Select answer

molecule.​

Next time…

We’ll learn how to write chemical formulas and name some compounds!