Chapter 4 Compounds and Bonds Valence Electrons – outermost electrons that determine chemical properties Electron Dot (Lewis) uses dots for valence electrons (see p. 113) Octet Rule- tendency of atoms to acquire a noble gas configuration (s 2 + p 6 = 8 valence) Ionization Energy—energy required to remove electrons to get to the stable octet

IONS Ions—one way to achieve the octet is to gain or lose electrons and become an ion (cations are pos. & anions are neg.) Ions and group numbers correspond Naming positive ions—stay the same name but transition metals (Ag and Zn are exceptions) get Roman Numerals to show charge Negative Ions—change the ending to ide (ex oxygen becomes oxide)

Ions Cont. Ions that stay together are called polyatomic ions and they are on your skill builder #2. Ionic formulas have the cation first and balance that with the charge of the anion by using subscripts (ex calcium fluoride would be CaF 2 ) Find the charge of a transition metal by looking at the anion (ex PbO 2 is lead (IV) oxide)

Covalent Bonding Covalent bonding occurs between two nonmetals and involves SHARING of electrons Electron Dot diagrams: 1.Write the number of valence electrons for each element 2.Multiply valence electrons by the number of atoms of that element 3.Add up the total number of valence electrons 4.Figure out which element will make the most bonds put it in the middle and attach the other atoms to it.

Naming Covalent Molecules and Geometry Look at the prefixes on page 134. Use these prefixes when you have more than one of the first element and always with the second element (ex CO is carbon monoxide) Change the ending of the second to be ide Shape of an atom can be determined by two factors 1. How many atoms are in the molecule? 2. How many lone pairs of atoms are on the central molecule?

Polarity Polarity only needs to be determined for covalently bonded molecules (nonmetals bonded together) First determine if any of the bonds are polar by finding the absolute value of the difference in their electronegativities. If you have one and only one polar bond then it is a polar molecule. If you have more than one polar bond, you need to also look at the shape of the molecule to see if the polar bonds “cancel.”