Chemical Bonding and Naming Compounds (Chapter 9) Types of Bonds Ionic Bonds Molecular Bonds Types of Compounds Ionic Molecular Acid Base Chemical Bonding Atoms will bond together using their valence electrons. Valence electrons are the electrons of an atom that occupy the highest energy level (orbital). To find an atom's number of valence electrons, simply look at what group it is in (for representative elements only). 1
Atoms will gain or loose valence electrons to achieve a stable octet like a noble gas (eight valence electrons). Ionic Bonding Monoatomic ions result from a single atom that looses or gains valence electrons. Metals from groups 1, 2 and 13 will lose electrons to form cations. Nonmetals in groups 15, 16 and 17 will gain electrons to form anions. Cation Anion 2
Ionic Bonds result from one atom transferring an electon(s) to another atom. This gives each atom an electronic charge which holds the compound together. Show using a Bohr Rutherford diagram how the following elements could form ionic bonds: 1. Sodium and hyrdogen 2. Lithium and fluorine 3. Magnesium and chlorine 4. Potassium and oxygen 3
Electron dot diagrams allow us a way to represent the valence electrons of an atom: Examples: Atom # e in neutral atom # Valence e Electron dot diagram Cation or anion? Sodium Chlorine Carbon Phophorus Cation an Anion Formation 4
Naming binary ionic compounds These compounds are composed of two elements that are bonded by ionic bonds. When writing these compounds, the cation's name is stated first followed by the anion's name. The name of an anion is not the same as the element's name. Instead the suffix ide is used. Example: F (fluorine) becomes fluoride S 2 (sulfer) becomes sulfide What about O 2, Br, As 3 The overall (or net) charge of an ionic compound will be zero. Example: NaCl is sodium cholride The crisscross method is used as a shortcut to write the names for binary ionic compounds. Example: Write the formula for barium nitrate Name: KCl Na 2 O Rb 2 S MnO Fe 2 O 3 MgCl 2 5
How do I know the charge on atoms? Memorize! Group 1 (alkali metals): Charge of +1 Groups 2 (alkaline earth metals): Charge of +2 Group 15 (representative elements): Charge of 3 Group 16 (representative elements): Charge of 2 Group 17 (halogens): Charge of 1 * Aluminum is +3 Transition Metals Cations can have more than one charge. We must state how many electrons are lost in the compound's name. 1 I Cu + Copper (I) 2 II Cu 2+ Copper (II) 3 III Fe 2+ Iron (II) Fe 3+ Iron (III) 4 IV Mn 7+ Manganese (VII) 5 V 6 VI 7 VII 8 VIII Roman numerals are ONLY used for Transition Metals! 6
Examples: Copper (II) chloride Lead (III) oxide Magnesium oxide Polyatomic Ions Polyatomic ions are made up of two or more nonmetals that are bonded tightly together. These groups of atoms will carry one charge. Most polyatomic ions end with the suffix ite or ate. 7
Examples: SO 3 2, sulfite NO 2, nitrite SO 4 2, sulfate NO 3, nitrate All polyatomic ions have a negative charge except for the ammonium ion, NH 4 +, which has a charge of +1. Naming Compounds with Polyatomic Ions These compounds are not binary since they contain more than two elements, however the overall charge is still zero. Examples: 1. Ca and CO 2+ 2 3 will form CaCO 3, calcium carbonate (calcium) (carbonate) 2. Mg and NO 2+ 3 will form Mg(NO 3 ) 2, magnesium nitrate (magnesium) (nitrate) *We need two nitrates for each magnesium and we must include parentheses. 3. K + and CO 3 2 will form K 2 CO 3, potassium carbonate Why are parentheses not needed here? 8
Molecular Compounds (Chapter 9.3) Binary molecular compounds are made up of two nonmetals. These non metals are not ions and can therefore not be named according to the ions they would form. Example: Na 2 O versus CO 2 Ionic Molecular Molecular compounds use covalent bonding. Colvalent bonds are formed by atoms sharing their electrons. Recap: 9
Naming Molecular Compounds When naming molecular compounds, prefixes are used in thename to tell us how many elements there are in the compound. 1 mono 2 di 3 tri 4 tetra 5 penta 6 hexa 7 hepta 8 octa 9 nona 10 deca Example: CO and CO 2 Carbon monoxide Carbon dioxide Only use these prefixes if you have two nonmetals!! Guidelines for Naming Molecular Compounds Make sure that the compound is only composed of two nonmetals. Name the elements in the order listed in the molecular formula. The name of the first element will not change, and the name of the second element will need the suffix "ide". Ex. CS 2 is carbon disulfide Use prefixes to indicate how many of each element there are. If there is just one of the first element, omit the prefix "mono". Ex. CO is carbon monoxide, not monocarbon monoxide Name: N 2 O Cl 2 O 8 10
Naming Acids and Bases An acid is an ionic compound that contains one or more hydrogen atoms that produce hydrogen ions (H + ) when dissolved in water. Acids will react with bases. A base is an ionic compound contains hydroxide ions (OH ). Remember OH is a polyatomic ion. An acid will begin with "H" or end in "COOH" Ex. HCl (hydrochloric acid) CH 3 COOH (acetic acid) Rules for Naming Acids 1. If the anion ends in ide, add the prefix hydro and change the ending to ic acid. Ex. Hydrobromic acid 2. If the anion ends in ite, change the ending to ous acid. Ex. Nitrous acid 3. If the anion ends in ate, change the ending to ic acid. Ex. Nitric acid 11
Practice: Name these acids: HNO 3 HMnO 4 HCN H 2 S Now you know how to name FOUR different types of compounds! Let's summarize! Ionic Molecular Acid Base Metal and a nonmetal Two nonmetals Begins with "H" or ends in "COOH" Contains "OH" Ionic bond (electrons transferred) Covalent bond (electrons shared) HCl NaOH NaCl *Use prefixes! CH 3 COOH CO 2 Mar 5 3:57 PM 12