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Chapter 8 Notes, part I Writing Ionic Formulas Compounds •Up until now, we have only looked at single elements. •There are only (to date) just over 100 elements, so how do we account for there being so many different types of stuff? Compounds •There are millions of different compounds—two or more elements that are combined chemically. •The two types of compounds we will discuss in this chapter are ionic compounds and covalent compounds. A compound is a pure substance made up of two or more elements that are chemically joined in definite proportions. 2 oxygen atoms Carbon dioxide is CO2 , while carbon monoxide (the poison) is CO . Ex. 1 oxygen atom Compounds do not look or act like the elements that form them. •Sodium is a silvery metal that reacts violently with water •Chlorine is a poisonous, green gas. •Does salt share any of those properties? Oxygen + Hydrogen -----> Water Hydrogen is explosive! Is water explosive? Ionic Compounds •Last chapter we discussed ions— elements that have a charge due to losing or gaining electrons. •Ionic compounds are made of ions. Ionic Compounds •Metals tend to form ions by losing electrons, giving them an overall positive charge. These are called cations. •Nonmetals tend to form ions by gaining electrons, giving them an overall negative charge. These are called anions. Ionic Compounds •An ionic compounds is formed from a cation and an anion, which means they are usually formed from a metal and a nonmetal. IONIC Compounds Ionic compounds consist of two oppositely charged ions. Li+1 F-1 Positive ion – metal Negative ion - nonmetal LiLi+10 3p+ 4n0 9p+ 10n0 0 F-1 Covalent compounds occur between two nonmetals. Both nonmetals share electrons 8p+ 8n0 6p+ 6n0 8p+ 8n0 Carbon dioxide Atoms are stable, or resistant to change if their outer energy level is completely filled with electrons. 10p 10n NEON 3p 4n Atoms of all the elements have 9p 10n from one to seven electrons in their outer energy level except the noble gases. When atoms lose or gain Electrons they become ions. Single or Monoatomic ions Ionic Compounds •Anions and cations can also be made up of a group of elements bonded together that carry an overall charge. •These groups of elements are called polyatomic ions. Polyatomic ions - groups of 2 or more elements that have a charge NH4+1 PO4-3 SO4-2 NO4-1 ClO3-1 C2H3O2-1 SO3-2 NO3-1 CO3-2 Ionic Compounds •Even though an ionic compound is made from charged particles, it is still electrically neutral. •This means that its total charge is always EQUAL TO ZERO!!! Ionic Compounds •SIDENOTE: The smallest part of an ionic compound is called a formula unit—just like the smallest part of an element is called an atom. Chemical Formulas •A chemical formula is like the recipe of a compound—it tells you the type and number of each element in the compound. Compounds are written as formulas. Formula - a group of symbols, possibly with subscripts, showing the number and type of atoms forming the compound. Na2SO4 Ba3(PO4)2 Formulas consist of a positive ion and a negative ion. The positive ion always comes 1st NaCl MgO AlP The positive ion is written first!!!!!!!! We read from left to right…. Metals are on the left. (LEFT = LOSE e- = positively charged ions) Metals are first !!!!! Na+1 Cl-1 Na+1 Cl-1 NaCl Nonmetals are on the right… and GAIN e- = negative ions Nonmetals are second!!!!! Subscript - a small lowered number that shows number of atoms of each element in the compound. Ba3P2 Ba Ba Ba P P A subscript of (1) is NEVER written. Na1Cl1 NO!!! Oxidation number - the charge of an atom, indicating whether the atom has lost (+) or gained (-) electrons and how many electrons it lost or gained. Al +3 Superscript Oxidation Numbers Group Lose or gain electrons How many Oxidation Number 1A lose 1 +1 Oxidation Numbers Group Lose or gain electrons How many Oxidation Number 1A lose 1 +1 2A lose 2 +2 Oxidation Numbers Group Lose or gain electrons How many Oxidation Number 1A lose 1 +1 2A lose 2 +2 3A lose 3 +3 Oxidation Numbers Group Lose or gain electrons How many Oxidation Number 1A lose 1 +1 2A lose 2 +2 3A lose 3 +3 4A Lose or gain 4 +4 or -4 Oxidation Numbers Group Lose or gain electrons How many Oxidation Number 1A lose 1 +1 2A lose 2 +2 3A lose 3 +3 4A Lose or gain 4 +4 or -4 5A gain 5 -3 Oxidation Numbers Group Lose or gain electrons How many Oxidation Number 1A lose 1 +1 2A lose 2 +2 3A lose 3 +3 4A Lose or gain 4 +4 or -4 5A gain 3 -3 6A gain 2 -2 Oxidation Numbers Group Lose or gain electrons How many Oxidation Number 1A lose 1 +1 2A lose 2 +2 3A lose 3 +3 4A Lose or gain 4 +4 or -4 5A gain 3 -3 6A gain 2 -2 7A gain 1 -1 Oxidation Numbers Group Lose or gain electrons How many Oxidation Number 1A lose 1 +1 2A lose 2 +2 3A lose 3 +3 4A Lose or gain 4 +4 or -4 5A gain 3 -3 6A gain 2 -2 7A gain 1 -1 8A none none 0 The total charge on a compound must add up to ZERO. CaO +2 Ca Ca -2 O +2 -2 = 0 IONIC COMPOUNDS Ionic compounds consist of a Positive metal or positive polyatomic ion Negative nonmetal or negative polyatomic ion Binary compounds are composed of only two elements. (Look for 2 capital letters!) Ex. NaCl Ex. Mg3N2 sodium chloride magnesium nitride Polyatomic compounds are composed of three or more elements and contain at least one polyatomic ion. (Look for 3 or more capital letters) 2 3 4 1 NaC2H3O2 Polyatomic ions Ex. Na ClO3 Ex. Ca3 (PO4)2 sodium chlorate calcium phosphate Variable and Non-variable Metals (positive ions) A practical approach to determining if a metal is variable or non-variable. VARIABLE Look at the chart on the back of periodic table. If the metal is on the back of the periodic table with more than one oxidation number listed it is variable. EX: Cr= +2, +3, or +6 Fe= +2, or +3 Look at the chart on the back of periodic table. NON VARIABLE If it is not on the back of the periodic table OR Only one choice of oxidation number listed. EX: Ag+1, Zn+2, or Ni+2 Then it is non variable ROMAN NUMERALS Used when a metal has more than one potential oxidation number. The name of the metal must tell you the valence of the metal Chromium III chloride III The Roman numeral three tells you that the oxidation number of the metal is +3. Chromium VI chloride VI The Roman numeral six tells you that the oxidation number of the metal is +6. Writing and Naming Ionic Compounds Writing Chemical Formulas 1) Write the symbol for the elements and their oxidation number, positive ion first (the metal). EX: For a compound of Magnesium and Chlorine +2 Mg Cl -1 Writing Chemical Formulas 2) Criss cross the numbers and write them as subscripts without the signs. +2 2 Mg Cl -1 1 Writing Chemical Formulas 3) If there is a one charge, do not write it. Mg1Cl2 Writing Chemical Formulas 4) If you have subscripts that are multiples, reduce them down. +4 4 1 -2 2 Pb O2 Naming Ionic Compounds For ionic compounds where the metal always has the same oxidation number, 1) Name the metal. EX: BaBr2 Barium Naming Ionic Compounds For ionic compounds where the metal always has the same oxidation number, 2) Write the name of the non-metal, and change the end to –ide. EX: BaBr 2 Barium bromine ide Naming Binary Non variable Compounds 1. Name the positive ion 2. Name the negative ion changing the ending to IDE. AlBr3 Aluminum bromide No Roman numeral is needed -ides N - Nitrogen--> Nitride O – Oxygen --> Oxide F - Fluorine--> Fluoride P - Phosphorus--> Phosphide S - Sulfur--> Sulfide Cl - Chlorine-->Chloride Br - Bromine -->Bromide I - Iodine--> Iodide Naming Polyatomic Non variable Compounds 1. Name the positive ion 2. Name the negative ion changing the ending to -ate. AlPO4 Aluminum Phosphate No Roman numeral is needed Naming Ionic Compounds If there is a polyatomic anion, then you do not change the ending: EX: Ca(NO3)2 Calcium nitrate Name These: Na2O MgCl2 Na2CO3 Naming binary compounds of variable metals Determine the oxidation number of the variable metal using the crisscross method Cr2O3 Cr+ OThe oxidation number of the chromium is +3 The name is Chromium III oxide Naming Ionic Compounds 3)If a positive ion (a metal) can have more than one oxidation number, you have to designate its charge in the name! We do this by putting the charge as a roman numeral in parenthesis between the positive and negative ion. Naming Ionic Compounds Why do we need to do that? Name: Fe2O3 FeO These both exist in nature, so we have to show which one we mean. Naming Ionic Compounds IfReverse this is true, then what +3 criss was iron to begin with? Fe-22O3 cross to find the Name it: charge of the iron: Iron (III)oxygen ide Naming Ionic Compounds this is not true, the +2 -2 Ifnumbers Reverse criss must have been Fe-1O cross reduced.to find the Name it: charge of the iron: Iron ( II )oxygen ide Naming Ionic Compounds Metals that don’t need parentheses: Group I, II and IIIA Zn, Cd (always +2) and Ag (always +1) Which means transition, inner transition and other metals do! Naming polyatomic compounds of variable metals Determine the valence of the variable metal using the crisscross method Hg22SO4 1 Hg+ SO4- The oxidation number of the Mercury is +1 Mercury I sulfate Naming Ionic Compounds Final flowchart of how to name: Name the positive ion. Does it need a roman numeral? If so, reverse criss cross, if not, ignore. Name the negative ion and: If a nonmetal end in -ide; if not, end normally Name these: Na2S CuCl2 K2SO4 Pb(NO3)3 Finding formulas 1.Determine the charge of each side of the formula. Nonvariables: Aluminum oxide: Al+3 O-2 Potassium Chloride K+1 Cl-1 Calcium nitrate Ca +2 NO3-1 2. Add the oxidation numbers together. +3-2 = +1 +1-1 = 0 +2-1 = +1 2. Add the oxidation numbers together. Al+3 O-2 K+1 Cl-1 +3-2 = +1 +1-1 = 0 3. If the total = zero the formula is balanced with one ion each ex: KCl If the total does not equal zero use the crisscross method to determine the number of ions needed for each side of the formula. 3 Al+3 O-22 Al O If the total does not equal zero use the crisscross method to determine the number of ions needed for each side of the formula. 3 2 +3 -2 Al SO4 Al (SO4) Writing Chemical Formulas 5) If using polyatomic ions, put parentheses if there are more than one. +2 2 -1 1 Ca (NO3) Writing Chemical Formulas Here’s an example of a polyatomic that doesn’t have parentheses. +1 1 -3 3 Na PO4 Practice These: Barium and chlorine BaCl 2 Rubidium and nitrogen Rb3N Lithium and phosphate Li PO 3 4 Iron (III) and nitrate Fe(NO3)3 Manganese (IV) and sulfur MnS2 Chapter 8 Notes: Part III Bonding in Metals Metallic Bonds •Metallic bonds consist of metal cations with a free-floating “sea of electrons” •This explains many physical properties—why metals are good conductors, and why they are malleable and ductile Malleablilty/Ductility •Ductile – the ablity to be drawn into wires •Malleable – the ablity to be hammered into shapes Malleablilty/Ductility •Metals display these characteristics because when subjected to pressure, cations can easily slide past one another (unlike ionic solids, which have very strong attractive and repulsive forces) Alloys •Most metals you use everyday are a mixture of two or more elements, for example brass, bronze or steel. These are called alloys. Alloys •The importance of alloys are that often they have superior properties than the elements they are made of. Oxyanions An oxyanion is a polyatomic ion composed of an element, usually a nonmetal, bonded to one or more oxygen atoms. Many oxyaions contain the same nonmetal and have the same charges but differ in the number of oxygen atoms. These ions are easily named using the following conventions. • The ion with more oxygen atoms is named using the root of the nonmetal plus the suffix-ate. • The ion with fewer oxygen atoms is named using the root of the nonmetal plus the suffix-ite. Halogens form four oxyanions • The ion with the greatest number of oxygen atoms is named using the prefix per-, the root of the nonmetal, and the suffix –ate. • The ion with one less oxygen atom is named with the root of the nonmetal and the suffix –ate. • The ion two fewer oxygen atoms is named using the root of the nonmetal plus the suffix –ite. • The ion with three fewer oxygen atoms is named using the prefix hypo-, the root of the nonmetal, and the suffix – ite.