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Ionic, Covalent and Metallic Summary (Unit 5.2, 5.3, 5.5)
IONIC COMPOUNDS
Ionic bonds are formed when a metal atom transfers one or more of its valance
electrons to a non-metal. The metal becomes a positive ion (cation) and the non-metal
becomes a negative ion (anion.) The cations and anions become electrostatically attracted
to each other and form a structure known as a crystal lattice. (See picture to the right.)
Ionic compounds have high melting points. The electrostatic between cations and
anions is strong. It takes a lot of energy to overcome this attraction in order to allow the
ions to move more freely and form a liquid.
Ionic compounds are not conductive in solid form, but they are capable of conducting electricity in liquid form. In order
for a substance to conduct electricity, it must contain mobile and charged particles. Solid ionic compounds do not
conduct electricity because the ions (charged particles) are locked into place in the lattice. The ions cannot move out of
the lattice, so the solid cannot conduct electricity. When the ionic solid is melted into a liquid, the ions are free to move
out of the lattice structure and are able to conduct electricity.
Ionic solids are brittle meaning they break under pressure. When a stress is applied to the ionic lattice, one or
more of the layers shift slightly. When the layers shift ions that have the same charge will end up next to each other.
Ions of the same charge will repel each other, so the crystal lattice will break apart. (See diagram below.)
Shift
Repel
COVALENT COMPOUNDS
Covalent bonds are formed between two or more non-metals. These nonmetals share one or more sets of valance electrons in order to become stable.
Covalently bonded atoms form neutral groups of atoms called molecules. (See the
diagram to the right.)
Covalent compounds have a low melting point. Unlike ionic substances
which are made of oppositely charged ions, covalent substances are made of
neutral molecules. These neutral molecules have very little attraction for each
other, so it requires very little energy to move them away from each other.
Covalent compounds are not good conductors. In order for a substance to conduct electricity, it must contain
mobile and charged particles. Covalent substances contain only uncharged (neutral) molecules that are unable to carry
electricity.
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METALLIC COMPOUNDS
Metallic bonds are formed between two or more
metal atoms. Each metal atom donates its electrons to the
space between the atoms. These electrons are collectively
known as the electron sea. Once the atoms lose their
valance electrons, they become positively charged cations.
These cations are electrostatically attracted to the negative
electron sea that surrounds them. (See diagram to the
right.)
Metallic substances have a high melting point. The
metal cations (+) and the electron sea (-) have a very strong electrostatic attraction. This electrostatic attraction keeps
the metal ions in place. It takes a lot of energy to overcome this attraction in order to allow the metal ions to move more
freely and form a liquid.
Metallic substances are good conductors. In order for a substance to conduct electricity, it must contain mobile
and charged particles. Metallic substances have delocalized electrons (-) that are free to move throughout the electron
sea. These mobile electrons are able to carry electricity.
Metallic substances are malleable. The metal ions are not attracted to each other the way ions in an ionic
substance are. Instead the metal ions are attracted to the electron sea that surrounds them. If they are forced to move,
the electron sea can move with them and they will remain attracted.
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Ionic, Covalent Metallic Summary Questions (5.2, 5.3, 5.5)
Directions: Use the article that you read to answer the following questions in complete sentences!
1) Compare and contrast how ionic and covalent bonds form. What occurs that “bonds” the atoms to each other in each
case.
2) How do the melting points of ionic, covalent and metallic bonds compare? What causes each type of compound to
have the melting point that it does?
3) Conductivity is the ability of a substance to allow an electrical current to pass through it. What must a compound
contain in order to be a good conductor? Are ionic, covalent, or metallic compounds good or bad conductors? Why?
4) Ionic and metallic substances tend to be solids at room temperature. Ionic solids are brittle while metallic solids are
malleable, why?