Naming Ions, Compounds and Molecules

Naming Ions  OBJECTIVES:  Identify the charges on monatomic ions by using the periodic table, and name the ions.  Define a polyatomic ion and write the names and formulas of the most common polyatomic ions.

Atoms and Ions  Atoms are electrically neutral.  Because there are the same number of protons (+) and electrons (-).  Ions are atoms, or groups of atoms, with a charge (positive or negative)  They have different numbers of protons and electrons.  Only electrons can move, and ions are made by gaining or losing electrons.

An Anion is…  A negative ion.  Has gained electrons (been reduced).  Nonmetals can gain electrons.  Charge is written as a superscript on the right. F 1- Has gained one electron (-ide is new ending = fluoride) O 2- Gained two electrons (oxide)

A Cation is… l A positive ion. l Formed by losing electrons (been oxidized). l More protons than electrons. l Metals can lose electrons K+K+ Has lost one electron (no name change for positive ions) Ca 2+ Has lost two electrons

Predicting Ionic Charges Group 1: Lose 1 electron to form 1+ ions H+H+H+H+ Li + Na + K+K+K+K+ Rb +

Predicting Ionic Charges Group 2: Loses 2 electrons to form 2+ ions Be 2+ Mg 2+ Ca 2+ Sr 2+ Ba 2+

Predicting Ionic Charges Group 13: Loses 3 Loses 3 electrons to form 3+ ions B 3+ Al 3+ Ga 3+

Predicting Ionic Charges Group 4: Do they lose 4 electrons or gain 4 electrons? Do they lose 4 electrons or gain 4 electrons? Neither! Group 4 elements rarely form ions (they tend to share)

Predicting Ionic Charges Group 15: Gains 3 Gains 3 electrons to form ions 3- ions N 3- P 3- As 3- Nitride Phosphide Arsenide

Predicting Ionic Charges Group 6: Gains 2 Gains 2 electrons to form ions 2- ions O 2- S 2- Se 2- Oxide Sulfide Selenide

Predicting Ionic Charges Group 7: Gains 1 electron to form Gains 1 electron to form 1- ions F-F-F-F- Cl - Br - Fluoride Chloride Bromide I-I-I-I- Iodide

Predicting Ionic Charges Group 0: Stable noble gases do not form ions! Stable noble gases do not form ions!

Predicting Ionic Charges Many transition elements have more than one possible oxidation state. Iron (II) = Fe 2+ Iron (III) = Fe 3+ Note the use of Roman numerals to show charges

Predicting Ionic Charges Some of the post-transition elements also have more than one possible oxidation state. Tin (II) = Sn 2+ Lead (II) = Pb 2+ Tin (IV) = Sn 4+ Lead (IV) = Pb 4+

Predicting Ionic Charges Some transition elements have only one possible oxidation state, such as these three: Zinc = Zn 2+ Silver = Ag + Cadmium = Cd 2+

Naming cations  Two methods can clarify when more than one charge is possible: 1) Stock system – uses roman numerals in parenthesis to indicate the numerical value 2) Classical method – uses root word with suffixes (-ous, -ic)

Naming cations  We will use the Stock system.  Cation - if the charge is always the same (like in the main group of metals) just write the name of the metal.  Transition metals can have more than one type of charge.  Indicate their charge as a roman numeral in parenthesis after the name of the metal

Naming Anions  Anions are always the same charge  Change the monatomic element ending to – ide  F - a fluorine atom will become a fluoride ion.

Practice by naming these:  Cl -  N 3-  Br -  O 2-  Ga 3+ chloride ion gallide ion gallium ion (not anion) oxide ion bromide ion nitride ion

Write symbols for these:  sulfide ion  iodide ion  phosphide ion  strontium ion This last one was to see if you were paying attention. This is a cation and thus stays with the actual element name, no change in ending! S 2- Sr 2+ P 3- I-I-I-I-

Naming Ionic Compounds  1. Name the cation first, then anion  2. Monoatomic cation = name of the element Ca 2+ = calcium ion  3. Monoatomic anion = root + -ide Cl  = chloride CaCl 2 = calcium chloride

Not all ionic compounds are that simple… Polyatomic ions are groups of atoms covalently bound, but because of the way they are together AS A UNIT, they have a charge… O ClO O The polyatomic ion chlorate is chlorine and oxygen sharing electrons but as a group have a -1 charge. (more on why this happens in a few classes!)

Polyatomic ions are…  Groups of atoms that stay together and have an overall charge, and one name.  Acetate (ethanoate): CH 3 CO O -  nitrate: NO 3 -  nitrite: NO 2 -  permanganate: MnO 4 -  hydroxide: OH - and cyanide: CN - (see the common polyatomic ions to know that I gave you in class.)

Writing Ionic Compound Formulas Example: Barium nitrate (note the 2 word name) 1. Write the formulas for the cation and anion, including CHARGES! 2. Check to see if the charges are balanced. 3. Balance charges, if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Use the criss-cross method to balance subscripts. (The charge of the cation becomes the subscript of the anion, and vise versa, of course, you don’t have to write the charge or subscript of “1”) Ba(NO 3 ) 2

Writing Ionic Compound Formulas Example: Ammonium sulfate 1. Write the formulas for the cation and anion, including CHARGES! NH 4 + SO Check to see if charges are balanced. 3. Balance charges, if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Use the criss-cross method to balance the subscripts. Remember the charge and subscript of “1” are not actually written in. (NH 4 ) 2 SO 4

Writing Ionic Compound Formulas Example: Iron (III) chloride 1. Write the formulas for the cation and anion, including CHARGES! Fe 3+ Cl - 2. Check to see if charges are balanced. 3. Balance charges, if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Use the criss-cross method to balance the subscripts. FeCl 3

Writing Ionic Compound Formulas Example: Aluminum sulfide 1. Write the formulas for the cation and anion, including CHARGES! Al 3+ S Check to see if charges are balanced. 3. Balance charges, if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Use the criss-cross method to balance the subscripts. Al 2 S 3

Writing Ionic Compound Formulas Example: Magnesium carbonate 1. Write the formulas for the cation and anion, including CHARGES! Mg 2+ CO Check to see if charges are balanced. (Since they balance they are in a 1:1 ratio! No need for subscripts, remember ionic are shown as the lowest ratio of atoms.) MgCO 3

Writing Ionic Compound Formulas Example: Zinc hydroxide 1. Write the formulas for the cation and anion, including CHARGES! Zn 2+ OH - 2. Check to see if charges are balanced. 3. Balance charges, if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Use the criss-cross method to balance the subscripts. Zn(OH) 2

Writing Ionic Compound Formulas Example: Aluminum phosphate 1. Write the formulas for the cation and anion, including CHARGES! Al 3+ PO Check to see if charges are balanced. AlPO 4

Naming Ionic Compounds  some metals can form more than one charge (usually the transition metals)  use a Roman numeral in their name: PbCl 2 – use the anion to find the charge on the cation (chloride is always 1-) Pb 2+ is the lead (II) cation PbCl 2 = lead (II) chloride (Metals with multiple oxidation states)

Things to look for: 1) If cations have ( ), the number in parenthesis is their charge. 2) If anions end in -ide they are probably off the periodic table (Monoatomic) 3) If anion ends in -ate or –ite, then it is polyatomic

Practice by writing the formula or name as required…  Iron (II) phosphate  Potassium sulfide  Ammonium chromate  MgSO 4  FeCl 3 Fe 3 (PO 4 ) 2 (NH 4 ) 2 CrO 4 K2SK2S Magnesium sulfate Iron (III) chloride

Practice by writing the formula for the following:  Magnesium hydroxide  Mg(OH) 2  Iron (III) hydroxide  Fe(OH) 3  Zinc hydroxide  Zn(OH) 2 (Zinc is always +2, see slide 16)

Hydrates  Some compounds contain H 2 O in their structure. These compounds are called hydrates.  The H 2 O can usually be removed if heated.  A dot separates water: e.g. CuSO 4 5H 2 O is copper(II) sulfate pentahydrate.  A Greek prefix indicates the # of H 2 O groups  Sodium sulfate decahydrate is  Na 2 SO 4 · 10H 2 O

How well do you know your Greek prefixes?

Prefixes 1: mono2: di3: tri 4: tetra5: penta6: hexa 7: hepta8: octa9: nona 10: deca

Hydrates Give the name of the following: 1. CuSO 4. 5H 2 O Copper (II) sulfate pentahydrate 2.MgCl 2. 6H 2 O Magnesium chloride hexahydrate 3.Na 2 SO 4. 10H 2 O Sodium sulfate decahydrate Write the formula for the following: Write the formula for the following: 1. zinc chloride hexahydrate 1. zinc chloride hexahydrate calcium phosphate dihydrate 3. copper (I) chloride pentahydrate ZnCl 2. 6H 2 O Ca 3 (PO 4 ) 2. 2H 2 O CuCl 2. 5H 2 O

Covalent Bonding Covalent Bond: –a bond formed by the sharing of electrons between atoms. (does NOT form charges) –Made up of nonmetals Molecule: a neutral group of atoms joined together by covalent bonds. (Compounds formed with ionic bonds do NOT have molecules) Molecular Formula: chemical formula for a molecular compound. It shows how many atoms of each element a molecule contains.

Molecular Nomenclature Prefix System (binary compounds) 1.Less electronegative atom comes first. 2.Add prefixes to indicate # of atoms. Omit mono- prefix on first element. 3.Change the ending of the second element to -ide. most

PREFIX mono- di- tri- tetra- penta- hexa- hepta- octa- nona- deca- NUMBER Molecular Nomenclature Only use “mono” on the second element.

Naming Covalent Binary Compounds P 2 O 5 = CO 2 = CO = N 2 O = diphosphorus pentoxide carbon dioxide carbon monoxide dinitrogen monoxide PCl 5 N2H4N2H4 Cl 2 O 7 IO 2 phosphorous pentachloride = dinitrogen tetrahydride = dichlorine heptaoxide = iodine dioxide =

Basic reminders in naming Covalent Compounds First name: name of the first element in the formula Usually the least electronegative Requires a prefix if more than one of them Second name: ends in –ide ALWAYS requires a prefix Now try this on your own. Complete the Chemistry worksheet on naming compounds you were given in class and posted in Moodle