Module 17: Ionic and Covalent Bonds and Compounds

Compound

A substance made up of atoms of two or more DIFFERENT elements joined by chemical bonds; Examples are H20, CO2, and NaCl. O2 and Cl2 are not compounds because they are only made of one kind of element.

electrolytes

Dissolved ionic compounds; can carry an electric current.

Properties of Ionic Compounds

Form crystal lattices, conduct electricity in solution only, and have high melting and boiling points.

Covalent Bond

the force of attraction that holds together two atoms that share a pair of valence electrons. The shared electrons are attracted to the nuclei of both atoms. This forms a molecule consisting of two or more atoms. Covalent bonds form only between atoms of nonmetals.

molecule

the smallest particle of a compound that still has the properties of the compound.

Why Ionic Bonds form

Ionic bonds form only between metals and nonmetals. That's because metals "want" to give up electrons, and nonmetals "want" to gain electrons. Metals are on the left of the periodic table and they have a nearly empty outer electron shell so they like to give up electrons to become positively charged. Non-metals are on the right side of the periodic table. They have a nearly full outer electon shell so they like to gain electons to become negatively charged.

Naming Covalent Compounds

Start with the name of the element closer to the left side of the periodic table. Follow this with the name of element closer to the right of the periodic table. Give this second name the suffix -ide. Use prefixes to represent the numbers of the different atoms in each molecule of the compound. Examples: N2O3 is dinitrogen trioxide; CO2 is carbon dioxide; NO is nitrogen oxide

Naming Ionic Compounds

The name of the metal comes first (+ ion), followed by the name of the nonmetal (- ion) changing the nonmetal's ending to "ide".

Two charges of different types will always

attract each other

Uses of Ionic Compounds

making fireworks, detecting moisture, melting ice, used to replace ions lost in the body, used in batteries

Two charges of the same type will always...

repel or push away each other

Ionic Bond

the force of attraction that holds together positive and negative ions. It forms when atoms of a metallic element give up electrons to atoms of a nonmetallic element

Ionic Compound

A compound that consists of positive and negative ions; compounds in which electrons are transferred from one atom to another.

Covalent versus Ionic

Covalent has shared electrons, Ionic has tranfer of electrons to form ions; Covalent is made of nonmetals, Ionic is a metal and a nonmetal; Covalent is a poor conductor of electricity, Ionic is a good conductor in solution; Covalent can be solid, liquid, or gas, Ionic are solids only; Covalent has a low melting point, Ionic has a high melting point.

Properties of Covalent Compounds

Many covalent compounds, especially those containing carbon and hydrogen, burn easily. In contrast, many ionic compounds do not burn. Many covalent compounds do not dissolve in water, whereas most ionic compounds dissolve well in water. Unlike ionic compounds, covalent compounds do not have freely moving electrons, so they cannot conduct electricity. The individual molecules of covalent compounds are more easily separated than the ions in a crystal, so most covalent compounds have relatively low boiling points. This explains why many of them are liquids or gases at room temperature.

Covalent Compound

a chemical compound formed by the sharing of electrons of two or more nonmetallic elements, such as carbon and hydrogen. The largest, most complex covalent molecules have thousands of atoms. Examples include proteins and carbohydrates, which are compounds in living things. The smallest, simplest covalent compounds have molecules with just two atoms. An example is hydrogen chloride (HCl).

Covalent Molecule

a group of atoms in which the atoms are bound together by sharing one or more pairs of electrons; covalent molecules are formed only between atoms of nonmetals; when Examples are H20, CO2, and Cl2

crystal

a solid in which the atoms are arranged in a pattern that repeats again and again; consists of many alternating positive and negative ions bonded together in a matrix