Unit 1 – Day 3 Bonding

The Stable Octet Atoms are most stable when they have a full outer shell of electrons. This is why noble gases, which have a full shell, do not react. For other elements, they will need to gain or lose electrons to obtain a full outer shell.

Ions When an atom gains or loses electrons, it becomes a charged ion. If an atom loses negative electrons, it becomes positive. If an atom gains negative electrons, it becomes negative. Example: Na  Na+ + e- S + 2e-  S2-

Metals Metals are elements on the left side of the periodic table, like sodium or iron. They have less than 4 electrons in their outer shell. They tend to lose electrons and become positive ions.

Non-metals Non-metals are elements on the right side of the periodic table, like oxygen or chlorine. They have more than 4 electrons in their outer shell. They tend to gain electrons and become negative ions.

Ionic Bonds Metals tend to give their electrons to non-metals, so they can both get a full outer shell. The metal and non-metal ions are opposite charges, and they attract. This attraction is called an ionic bond.

Properties of Ionic Compounds An ionic bond is very strong. As well, the ions arrange themselves so that molecules attract to other molecules nearby.

Properties of Ionic Compounds Because of this, it is very difficult to pull apart ionic molecules. This affects many properties. Melting Point: Ionic compounds are very difficult to melt, because in order to make a liquid, molecules need to move farther apart.

Properties of Ionic Compounds Smell Ionic compounds have no smell, because in order to enter the air, molecules would need to leave the surface. Hardness Ionic compounds are hard to crush, because the network of molecules supports each other in a crystal.

Properties of Ionic Compounds Solubility Ionic compounds dissolve in substances like water. The charges from a water molecule pull apart the ions.

Properties of Ionic Compounds Electrical Conductivity When melted or dissolved, ionic compounds separate into ions. These ions can carry electrical charges.

Covalent Bonds Non-metals need to gain electrons to fill their outer shell, so they sometimes share electrons with each other. When two non-metals share electrons, it is called a covalent bond.

Pure Covalent Bonds If the atoms are the same, they share equally. This is called a pure covalent bond. Ex: H2, O2, N2 , CH bonds Pure covalent compounds have no charges, so the molecules don’t attract each other as well as ionic compounds do.

Pure Covalent Properties Pure covalent compounds have the following properties: Strong odour (molecules escape into the air easily) Crush easily (no crystal support) Do not dissolve in water (no charges to attract) Do not conduct electricity (no ions) Low melting pt. (molecules are easy to separate)

Polar Covalent Compounds Sometimes when atoms share electrons, the electrons are closer to one atom than the other. This results in one atom having a slight negative charge, and the other having a slight positive charge.

Polar Covalent Properties Pure covalent compounds have the following properties: No odour (slight charge holds molecules in place) Hard (charges have some crystal support) Dissolve in water (slight charges attract water) Do not conduct electricity (no ions) Average melting point (molecules are easier to separate than ionic, but not as easy as pure cov.)

Table of Properties Use your notes to summarize into a table the properties of the three types of compounds.