Ionic and Metallic Bonding Mr. Bostrom West Forsyth High School
Why do atoms bond? To answer this question we must first look at the elements: Do we normally find matter in its elemental form? No – why? Most atoms are unstable!!!!!!!! Why?
Let’s look at a stable element! What makes Ne stable? Valence Electrons – it has a complete set!!!!
Back to the original question Atoms form bonds in order to increase stability!!!!!!!!!! Example: H2O
Another Example NaCl or Salt
Atoms bond together to increase stability!!! There are three types of bonds Ionic Bond Covalent Bond Metallic Bond We are going to concentrate on Ionic and Metallic Bonds today
What is an Ionic Bond? Na :Cl: NaCl . . .. An ionic bond is formed between oppositely charged atoms in which one atom transfer(s) electrons to the other Na :Cl: NaCl - Formed between a metal and a non- metal . . ..
What changes about the atom The atom that loses electrons gains a positive charge Na has 11 p+ and 11 e- which gives a 0 charge If Na loses 1 electron it now has 10 e- vs 11 p+ giving Na+1 Sodium is now an ion
Ion An atom or group of atoms that has a positive or negative charge Examples Single Ion = Na+1 Sodium Ion Polyatomic Ion = NH4+1 Ammonium Ion Polyatomic Ions get treated as 1 ion, not separate elements There is a list of common polyatomic ions in your reference tables
Are all Ions Positively Charged? No!!!!! Positive Ions are called Cations Mainly formed from metals Formed when an atom loses an electron Negative Ions are called Anions Mainly formed from metalloids or non metals Formed when atoms gain electrons
Anions When Chlorine gains an electron, it now has 12 e- and 11p- giving it a -1 charge Cl-1
How do you know how many electrons you need to gain or lose? In order to be stable you must obey the octet rule!!!! When forming compounds atoms tend to achieve a noble gas configuration Must have 8 valence electrons Oct = 8 Exception is Helium because Helium only has 2 total electrons and one energy level Octet refers to the ns2 np6 configuration Trying to achieve a noble state configuration
Example Cation Na – e- Na+1 1s2 2s2 2p6 3s1 1s2 2s2 2p6 1s2 2s2 2p6 = Neon Anion Cl + e- Cl+1 1s2 2s2 2p6 3s2 3p5 1s2 2s2 2p6 3s2 3p6 1s2 2s2 2p6 3s2 3p6 Argon
Worksheet
Formation of Ionic Compounds 1s2 2s2 2p6 3s1 1s2 2s2 2p6 3s2 3p5 Na Cl: 1s2 2s2 2p6 1s2 2s2 2p6 3s2 3p6 .. . . ..
Writing Ionic Chemical Formulas First, find the oxidation numbers of the elements Second, place the element with the positive oxidation first Third, add the two oxidation number together – if they equal zero get rid of the numbers and combine the elements Fourth, if the oxidation numbers don’t equal zero, criss cross the numbers and write them as subscripts
Example Fluorine and Lithium F-1 Li +1 Li +1 F-1 +1 + -1 = 0 LiF
Example Sulfur and Potassium S-2 K+1 K+1 S-2 +1 + -2 don’t = 0 Criss Cross Oxidation #’s SK2
Naming Ionic Compounds These rules are for binary ionic compounds First, write the cation’s elemental name Second, to the anion, drop the ending and add –ide Write the formula with the cation first and anion second
Example: Na2Se Na = Na+ = Sodium Se = Se- = Selelenium = Selenide Sodium Selenide
Properties of Ionic Compounds Solid Crystals at room temperature Generally have high melting points Ionic compounds can conduct electricity
Activities Crystal Lab Water Hardness
Bonding In Metals Valence electrons of metal atoms can be modeled as a sea of electrons
Metallic Bonds Unlike ionic bonds which are formed between a metal and non-metal, metallic bonds are formed between metal atoms