Chemical Bonding Seventh Grade Science

Chemical Bonds Chemical bonds are the glue that holds the atoms of elements together in compounds Chemical bonds differentiate compounds from mixtures

Types of Chemical Bonds Ionic Bonds Covalent Bonds Polar Covalent Bonds

Ionic Bonds Ionic bonds form when positive ions of one element are attracted to the negative ions of another element Ions are attracted to one another by electrical attraction of the positive and negative charges

Compounds with Ionic Bonds Compounds with ionic bonds are very stable Compounds with ionic bonds have very strong crystals Ionic compounds form crystals with different regular patterns

Quick Check for Understanding What are some characteristics of a compound with an ionic bond?

Naming Ionic Compounds The name of the ionic compound is based on the names of the ions it is made of. For example, sodium ions bond with chlorine ions to make sodium chloride

Naming Ionic Compounds (cont.) To name an ionic compound, the name of the positive ion is placed first, followed by the name of the negative ion. The negative ion’s name is changed from its original name by adding the suffix “ide.”

Ionic Compound Naming Practice Remember, take the positive ion’s name and put it first. Then, take the negative ion’s name and add “ide” to the end of it Third, put the two names together and you have your compound’s name

Practice Naming Ionic Compounds The positive ion is potassium, so we’ll keep that as the first name of our compound The negative ion is bromine, so we’ll change that to bromide and add it to our positive ion to get our compounds’ name Potassium + Bromine = Potassium bromide

Practice Naming Ionic Compounds What ions are you dealing with? Remember, the number of protons tells you the atom’s identity! Your positive ion is … Your negative ion is … Your ionic compound’s name is …

Practice Naming Ionic Compounds Magnesium + Fluorine= Magnesium fluoride The positive ion is magnesium because magnesium has 12 protons. The negative ion is fluorine. Your ionic compound’s name is magnesium fluoride.

Quick Check for Understanding Name the ionic compounds formed: Calcium + Sulfur = Beryllium + Chlorine = Potassium + Fluorine = Sodium + Chlorine = Lithium + Iodine = Magnesium + Sulfur =

Covalent Bonds Another way in which atoms can bond together is by sharing electrons. Nonmetal atoms usually form bonds with each other by sharing electrons. A pair of shared electrons between two atoms is called a covalent bond. The shared electrons are attracted to both positively charged nuclei.

Covalent Bonding The number of covalent bonds an atom can form depends on the number of electrons available for sharing. Halogen family and hydrogen have only one electron available for sharing.

Covalent Bonding Group 16 has two electrons available for sharing; therefore, it can form two covalent bonds. Group 15 has three electrons available for sharing; so they can form three covalent bonds.

Covalent Bonding Carbon and Silicon in Group 14 have four electrons available for bonding; therefore, they can form four covalent bonds.

Sharing Pairs of Electrons Sometimes, atoms may share more than one pair of electrons with another atom. For example, the carbon atom in carbon dioxide (CO2 ) forming double bonds with the oxygen atoms.

Double Bonds A double bond consists of four (two pairs)of shared electrons. For example, ethylene, chemical formula C2H4 has two double bonds of carbon bonded with four hydrogen atoms

What is a molecule? A molecule is a group of atoms held together by covalent bonds. Most molecules contain two or more elements. Some molecules contain atoms of only one element, such as H2; N2; O2; F2; Cl2; Br2; I2.

Quick Check for Understanding How does a covalent bond differ from an ionic bond? What are molecules? Which compounds can exist as individual elements?

Polar Covalent Bonds A covalent bond in which the electrons are shared unequally is called a polar covalent bond. The word polar refers to anything that has two extremes or poles. Water is the most common polar covalent compound.

Comparing Compounds Ionic Compounds Have a regular crystal shape The ratio of ions give the crystal its shape Some crystals are rigid and shatter rather than bend when enough force is applied Covalent Compounds Exist as individual molecules (ex. O2) Each molecule has a specific three-dimensional shape called its molecular structure Shape of the molecule depends on the atoms it contains and the bonds holding it together

Covalent, Ionic or Polar Covalent Compound?

Quick Check for Understanding How do polar covalent bonds differ from covalent bonds? What type of structure do compounds with covalent bonds have? Which type of compounds have a crystalline structure? Which compounds can exist as individual elements?

Metallic Bonds Metals bond together by equally sharing electrons in all directions This equal sharing allows electrons to move easily among the atoms of the metal

Properties of Metallic Compounds Good conductors of electricity Electrons in a metal flow through the material carrying the electric current Good conductors of heat Have high melting point All are solids at room temperature except for mercury

Additional Properties of Metals Metals can be easily shaped by pounding Can be drawn into a wire

Quick Check for Understanding How are the metallic bonds unique? How do metallic bonds affect the properties of metals? What are some characteristic properties of metals?