Transcript ionic bond
Mr. Shields Regents Chemistry U09 L01 1 Elements found in Abundance in the Earth’s Crust Only Five Elements account for 93% of the mass of The earth’s crust What do you think they might be? 5 elements make up 93% of the earths crust And only 8 make up 99% of the entire mass But consider the diversity of compounds in our world! How Can there be so many different combinations? 2 Types of Bonds Compound diversity found in the world is a consequence of the many possible ways elements can combine with one another. Elements combine by forming what is called the CHEMICAL BOND So … What is a Chemical Bond? “ A Chemical Bond is a FORCE OF ATTRACTION holding two or more atoms together” 3 Types of Bonds There are several different types of Chemical Bonds: Ionic Metallic Network Covalent Polar Covalent All these bond types involve ONLY the electrons in the atoms valence shell, i.e. the valence electrons 4 Ionic Bonds In this unit we’ll discuss Ionic compounds first. Everyone is familiar with STATIC ELECTRICITY - Such as when you get a shock touching a doorknob after walking across a rug in the winter - In this case you’re neg. and the doorknob is + - Electrons are transferred in the process - So… From what to what? 5 Ionic Bonds Static electricity is also the basis for ionic bond formation In Ionic bonds there are metal atoms & non-metal atoms - We know metals want to lose electrons and Non-metals want to gain electrons. WHY? eRemember effective nuclear charge? - During the formation of IONIC BONDS metals TRANSFER valence electrons to the non-metal 6 Ionic bonds are formed by the Attraction between positive and negative ions 7 Electron Transfer between Sodium and Chlorine 2Na + Cl2 2NaCl How many electrons are transferred? And from where to where? 8 We know the valence electrons are involved in electron transfer to form the ionic bond BOTH NOW HAVE AN OCTET But WHICH electrons (i.e. what orbitals) are involved? Formation of The Octets A quantum mechanical representation of the electron transfer 9 Remember that the number of valence electrons an atom has determines its OXIDATION NUMBER What are The oxidation Nos. of These Atoms? 10 Group 1 & 17 The oxidation number determines how many atoms Are needed to form the ionic compound Ox. No: +1 -1 +1 -1 Chemical Formula: M1X1 (i.e. MX) -WHY? 11 Group 2 & 17 Ox. No: -1 +2 -1 Chemical Formula: M1X2 (i.e. MX2) - WHY? 12 Group 13 & 16 Ox. No: -2 +3 -2 +3 -2 Chemical Formula: M2X3 – WHY? 13 Ionic Bonds So… The driving force for ionic bond formation is the Attainment of the octet Remember: Metals with Low IE lose electrons more readily than non-metals with higher IE Non-metals with High Electronegativities attract electrons more readily than metals with Lower Electronegativities 14 And… for Metals lower Ionization energy means High Reactivity. For Non-metals lower Electronegativity means Lower Reactivity. Therefore Francium and Fluorine are the most Reactive elements. Na Dec. I.E. F Increasing Reactivity Fr Dec. EN Decreasing Reactivity I IE and EN decreases down a group and… IE and EN both increase L to R across a period 15 Electronegativity Difference The ability to fully transfer or accept electrons Defines ionic bonds we can determine which bonds are More ionic than others by calculating the difference in EN Between the Atoms For Example When the difference in Electronegativity Between 2 elements Is greater than 1.7 the Elements will form an Ionic bond Non-ionic ionic ionic Fr+ FEN Diff = 3.3 Most ionic compound 16 Least Ionic Most covalent Most Ionic – Least covalent 3.2 2.1 1.7 Diatomic molecules Like H2, O2, Cl2 etc ∆EN =0 17 We saw that when Na and Cl2 react there is a large amount of heat released We’ve burned Mg in air (O2) and saw that in this reaction there is also a lot of Heat & light released All IONIC REACTIONS are Characterized by the release of heat i.e. they are EXOTHERMIC Reaction of sodium metal and chlorine gas 18 Bond Formation When we release heat we are releasing energy Therefore ionic reaction products have less energy Than the starting reactants Bonds have An ideal bond Length. Push atoms Closer together & PE inc. Potential Energy - Decreasing energy means greater stability Na + Cl Potential Energy is Stored in the Chemical Bond NaCl 19