1. Lecture 6 6/29

2. Agenda Chemical Bonds Forming Ionic and Molecular Compounds

3. Chemical Bonds Valence electrons are what form bonds between atoms. – Sometime they are shared and other times they are transferred. We will learn about 3 types of bonds: – Ionic – Covalent – Polar Covalent

4. Chemical Bonds Ionic Bonds: They are the result of a transfer of electrons from one atom to another. They form between a metal and nonmetal – Metals tend to lose the electrons while nonmetals tend to gain electrons. Perfect! In other words, it is a bond formed between two ions. For example: Na(+1) and Cl (-1)

5. Chemical Bonds Covalent Bonds: These bonds are the result of a sharing of electrons between two atoms Ions are not involved! Form between a nonmetal and another nonmetal – Also between a nonmetal and a metalloid and between metalloids

6. Chemical Bonds Polar Covalent: Still a more or less sharing of the electrons, but one atom is pulling a little bit harder. Still does not involve ions! Same types of atoms form polar covalent bonds as with regular covalent bonds. The way to distinguish between a polar covalent and a covalent is through electronegativities. – One atom likes the electron a little too much to completely share.

8. Forming Ionic Compounds Depends on the charge of the ions. The compound needs to be neutral. The compound also needs to have the smallest whole number ratios as possible. Steps: – Find out charges of ions. – Find out how many of each ion are needed to neutralize the compound.

9. Forming Ionic Compounds Let’s form a compound between Calcium and Fluorine. Step 1: Charges Ca (2+) and F (1-) Step 2: Neutralize CaF 2 (There needs to be 2 Fluorines)

10. Forming Ionic Compounds What is going on with the valence electrons? – Calcium has 2 – Fluorine has 7 Let’s draw it out on the board. As you can see, all atoms become happy with the octet rule. Law of definite proportions – A chemical compound always contains exactly the same proportion of elements by mass

11. Forming Covalent Compounds There are no ions, so no charges. – Nothing to cancel! – You cannot form covalent compounds with two atoms unless you know all of the possible ways you can form them. Law of multiple proportions – When two elements combine with each other to form more than one compound, the weights of one element that combine with a fixed weight of the other are in a ratio of small whole numbers. Law of definite proportions also applies.