Chemical bonds are the “glue” that hold groups of atomstogether. Some bond “facts”:All bonds form because of an electrostatic attractionbetween the positive and negative charges. IONIC and COVALENTChemical bonds are classified in TWO categoriesEnergy is required to break chemical bonds. Energyis released when bonds form.
BONDING IS ALL ABOUT ELECTRONSRecall: Electron configurations
To understand bonding you must have a very clear idea about valence electronsLewis dot diagrams are used to illustrate the number of valence electrons for an atom:1. Determine the number of valence electrons.2. Write the element symbol3. Place one dot to represent electrons around the four sides of the element symbol. Do not place two electrons together until each side has one (exception is helium).
Lewis Dot structures – complete on the first worksheet
The basis for an ionic bond is the electrostatic attraction between two oppositely charged ions. ATTRACTIVE FORCE + HOLDS IONS TOGETHER - Cation (metal) Anion (non-metal) Positive ion Negative ionHas “lost” electrons Has “gained” electrons
When metallic elements react with non-metallicelements . . . .Metal atoms have a tendency to lose valenceelectrons and form positive ions.Non-metals have a tendency to gain valenceelectrons and form negative ions. Mg Mg+2 Cl Cl-1To be most stable, atoms form ions by gaining or losing electrons soas to complete the outer valence shell. This usually means 8electrons so the rule is called the OCTET RULE.
The electrostatic attraction between the positivemagnesium and negative chloride ions is the basis forthe ionic bond. Mg2+ Cl-Notice that the overall electrical charge of the Mg-Clcombination is still +1. THE CHARGES ARE NOTBALANCED! (neutral)
The electrical charges will be balanced if two chlorideions combine with the magnesium ion.This is a convenient combination as the Mg atom has lost2 electrons whereas each chlorine atom gained 1. Cl- Mg2+ Cl-This combination is the formula unit for the compoundand has the formula MgCl2
The electrical charge is always balanced in the chemicalformula of an ionic compound.For example – what ionic compound forms betweencalcium and bromine?1. Locate the elements involved on the Periodic Table
2. Determine the ions that are formed by each element calcium is in group II : loses 2 e- to become Ca2+ bromine is in group VII: gains 1 e- to become Br-13. Criss-cross the oxidation number (charge) to find the numbers of each atom in the compound. You may need to simplify. Ca2+ Br-1 CaBr2
Write the chemical formula for calcium oxide1. Locate the elements involved on the Periodic Table2. Determine the ions that are formed by each element calcium is in group II : loses 2 e- to become Ca2+ oxygen is in group VI: gains 2 e- to become O-2 3. Criss-cross the ionic charges and simplify. Ca 2+ O -2 CaO
Ionic Bonding WorksheetReview ion formation, the octet rule, determining the number ofprotons, neutrons and electrons in atoms or ions AND showingionic bonding with dot diagrams See WIKI for answers
Naming Ionic CompoundsWe know how to write the chemical formula of a simple ioniccompound from its name. We must also know how to state thename of compound from it’s formula.What would be the name of the ionic compound MgCl2?write the name of the metallic element first magnesium chloride ide write the name of the non-metallic element but change its ending to “ide”
Calculating Formula MassWe know that the average atomic mass of a single atom is givenon the Periodic Table for each element.What would be the formula mass ofthe ionic compound MgCl2?The formula mass is the total mass of all the atoms in a singleformula unit . The formula unit is given by the chemical formula.Using data from your periodic tables for MgCl2 one Mg atom two Cl atoms ( 24.3) + (2 x 35.5) = 95.3
Calculating Formula MassPractice: 18.0 677.6 180.0
Ionic Compounds Containing Metals not in Group I, II or IIRecall Group I metals form +1 ions Group II metals form +2 ions Group III metals form +3 ions the transition metals and some others are interesting because they can have +1 more than one ionic charge +2 +3 iron for example can form both Fe2+ and Fe3+ions Fe
Ionic Compounds Containing Metals not in Group I, II or IISince iron can form both +2 and +3 ions, there are two possiblechemical formulas for iron oxide. What would they be? FeO iron II oxide and and Fe2O3 iron III oxideCalling both compounds “iron oxide”would be confusing. Different namesare required. Can you see from theexamples how these compounds werenamed?
Ionic Compounds Containing Metals not in Group I, II or II FeO iron II oxide and and Fe2O3 iron III oxide IIIIF a metal atom can form more +3than one possible ion, a ROMANNUMERAL indicates the ioniccharge. +2If the metal can only form onepossible ion (Group I, II, III, Znand Ag) then a roman numeral is +1NOT included.
Try naming these compounds BeCl2 beryllium chloride CuBr2 copper II bromide SnO2 tin IV oxide Pb3P2 lead II phosphide
Write the chemical formulas for these compounds sodium sulfide Na2S copper I oxide CuO nickel III chloride NiCl3 iron III nitride FeN
Structure of Ionic CompoundsIonic compounds are crystalline solids. Positive andnegative ions arrange themselves in regular geometricpatterns. This crystal lattice structure is held together strongly by the ionic bonds. These strong forces mean ionic compounds are brittle and have high melting points.
Crystals of sodium chloride are made of numerous Na+ and Cl-ions. Each ion is attracted to all the oppositely chargedneighboring ions.
Most ionic compounds are soluble and dissolve in water toform solutions
Solutions of ions are electrolytes. They conduct electricitybecause the dissolved ions are free to move.