Forming Compounds Ionic vs. Covalent

Understanding how atoms of elements combine when two atoms collide, valence electrons on each atom interact when two atoms collide, valence electrons on each atom interact Chemical bonds form if their valence e- make a new arrangement with a lower energy than their previous arrangement Chemical bonds form if their valence e- make a new arrangement with a lower energy than their previous arrangement For many atoms, the lowest energy arrangement is the same as the closest noble gas For many atoms, the lowest energy arrangement is the same as the closest noble gas Atoms achieve noble gas electron configuration bylosing/gaining/sharing electrons Atoms achieve noble gas electron configuration bylosing/gaining/sharing electrons

What is a bond? A bond is an attachment among atoms A bond is an attachment among atoms Atoms may be held together for several Atoms may be held together for several

COMPOUNDS and their BONDS Ionic Compounds Ionic Bonds Metals Nonmetals Covalent Compounds Covalent Bonds Nonmetals

Ionic Compounds Consist of positive ion + negative ion Consist of positive ion + negative ion Ions held together by strong attraction b/w oppositely charged ions = IONIC BOND Ions held together by strong attraction b/w oppositely charged ions = IONIC BOND Chemical and physical properties of the ionic compound are different from those of the individual elements Chemical and physical properties of the ionic compound are different from those of the individual elements Ex) Na soft, shiny metal Ex) Na soft, shiny metal Cl yellow, poisonous gas Cl yellow, poisonous gas NaCl white, crystalline (table salt) NaCl white, crystalline (table salt)

Charge Balance in Ionic Compounds Chemical Formula indicates: Number of ions Number of ions Kind of ions Kind of ions that make the ionic compounds Ex) NaCl Mg 2 O Mg 2 O

Nearly all ionic compounds involve bonds b/w metal cations + nonmetal anions positive negative charge charge The sum of ionic charges = zero The sum of ionic charges = zero (total positive charges = total negative charges) (total positive charges = total negative charges)

Properties of Ionic Compounds Cations and anions form a regular repeating pattern  creates a characteristic crystalline shape Strong attraction b/w charged ions extends throughout crystal  relatively high melting points When molten or dissolved in water, ions move freely  Conduct electricity In solid state, ions unable to move  Not electrical conductors in solid state

Subscripts in Formulas Ionic compounds made of 2 elements are called binary compounds Compounds that lose/gain more than 1 electron need to bond to more than 1 atom

Writing Ionic Formulas from Ionic Charges Subscripts represent the # of positive and negative ions that give an overall charge of zero Use the ionic charges to write the formula * The cation is always written first, followed by the subscript

Practice Naming Ionic Compounds The International Union of Pure and Applied Chemistry (IUPAC) = a global organization of scientists who set standards in chemistry The International Union of Pure and Applied Chemistry (IUPAC) = a global organization of scientists who set standards in chemistry Each compound has a unique name Each compound has a unique name The formula of the compound reflects its name The formula of the compound reflects its name

Naming Ions Monatomic Ions Ions consisting of a single atom with a + or - charge Cations (+) Most from Groups 1A, 2A, 3A Naming: Same as the name of the metal, followed by ion or cation Example: Sodium Ion, Potassium Ion Anions (-) Most from 5A, 6A, 7A Naming: Start with the stem of the element’s name ending with -ide Example: Fluoride, Chloride, Nitride

Naming Binary Ionic Compounds metal + nonmetal always 1 st always 2nd always 1 st always 2nd E lemental + Elemental + -ide ending E lemental + Elemental + -ide ending Name Name Name Name Na + F Na + F Sodium Fluorine Sodium Fluorine NaF  Sodium fluoride * Subscripts are never mentioned. They are understood as a result of the charge balance of the ions in the compound

Practice Naming Binary Ionic Compounds Write the name of each of the following ionic compounds. a) Na 2 Ob) Mg 3 N 2 Compound Ions and Names Name of Compound a) Na 2 O Na + O 2- SodiumOxide Sodium oxide a) Mg 3 N 2 Mg 2+ N 3- MagnesiumNitride Magnesium nitride

Metals with Variable Charge Transition metals typically form two or more kinds of positive ions because they lose their outer electrons from a lower level Transition metals typically form two or more kinds of positive ions because they lose their outer electrons from a lower level For these metals, it is not possible to predict the ionic charge from the group number For these metals, it is not possible to predict the ionic charge from the group number This is called variable valence This is called variable valence

Transition Metals Groups 3 – 12 Groups 3 – 12 Nearly all form more than one cation Nearly all form more than one cation Ex) Fe forms Fe 2+ and Fe 3+ Ex) Fe forms Fe 2+ and Fe 3+ Use the reverse cross-over method to determine the charge on the cation and write formulas for the ionic compounds Use the reverse cross-over method to determine the charge on the cation and write formulas for the ionic compounds

Charges must be determined by the number of electrons lost Can have varying charges for the same elements Naming: Two Methods -Stock System: Roman numerals in parentheses Example: Fe 2+ Written: Iron(II) ion Read: “Iron two ion,” Example: Cr 2+ Written: Chromium(II) ion Read: “chromium two ion” Transition Metals

Classical System: suffix used with root name to name the ion: Example: Fe2+Written: Ferrous Ion Example: Fe3+Written: Ferric Ion Example: Cr2+Written: Chromous Ion Example: Cr3+Written: Chromic Ion

Transition Metals Classical System: some names may seem unfamiliar Iron: Ferr- Copper: Cupr- Tin: Stann- Lead: Plumb- Some transition metals have only one charge Ag + Cd 2+ Zn 2+

Determining the charge on a cation: Example 1)FeCl 3 Fe 3+ Cl - The charge on the chloride anion is correct. Therefore the charge on the cation is correct. Example 2)FeO Fe + O - The anion charge is incorrect. Doubling the charges on both ions gives the correct charges.

Some common ions and their location on the periodic table

Practice Naming Ionic Compounds Write the name for each of the following ionic compounds: a. FeO Reverse Cross-over Fe charge + O 2- charge = 0FeO ? + (2-) = 0Fe 1+ O 1- (2+) + (2-) = 0 2x(Fe 1+ )(O 1- ) Fe 2+ O 2- Stock SystemClassic System Iron (II) oxide Ferrous oxide

b. Cu 2 S Reverse Cross-Over 2(Cu charge) + S 2- charge = 0Cu 2 S 2(?) + (2-) = 0Cu 1+ S 2- 2(1+) + (2-) = 0 Stock System Classic System Copper (I) sulfide Cuprous sulfide

Polyatomic Ions Ions composed of more than one atom Tightly bound groups of atoms that behave as one unit and have a charge All Anions ending in -ite or -ate contain Oxygen “-ites” have one less oxygen than “-ates” Examples: ClO 2- Chlorite ClO 3- Chlorate Cr 2 O 7 2- Dichromate PO 3 3- Phosphite

Polyatomic Ions When a polyatomic ion contains Hydrogen, it is like adding a H + with another polyatomic ion Examples: H + + CO >HCO 3 - CarbonateHydrogen Carbonate H + + PO >HPO 4 2- PhosphateHydrogen Phosphate

Binary Ionic Compounds An ionic or molecular compound composed of two elements Naming:Place the cation first followed by the anion. Formula:Cation first, Anion second Remember, total charge equals zero! Example: Cs2O = Cesium Oxide(Ionic) CuO = Copper(II) Oxide(Ionic) Hint: 1:1 ratio

Naming and Writing Formulas Binary Ionic Compounds

Naming and Writing Formulas Compounds with Polyatomic Ions Recall that a Polyatomic Ion acts as one unit Naming:Place the cation first followed by the anion. Formula:Cation first, Anion second Example: PbSO 4 = Lead(II) Sulfate K 2 HPO 4 = Potassium Hydrogen Phosphate

Naming and Writing Formulas Compounds with Polyatomic Ions

Naming Chemical Compounds Guidelines: 1) -ide generally indicates a binary compound 2) -ite or -ate means a polyatomic ion that includes O 3) A Roman numeral shows the charge of the cation 4) Prefixes generally indicate a molecular compound