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Unformatted text preview: Chapter 3 Structure and Properties of Ionic and Covalent Compounds Denniston Topping Caret 5 th Edition Edited by Ahmad Audi Edited by Ahmad Audi For CHEM1070 For CHEM1070 3.1 Chemical Bonding • Chemical bond- the force of attraction between any two atoms in a compound • This attractive force overcomes the repulsion of the positively charged nuclei of the two atoms participating in the bond • Interactions involving valence electrons are responsible for the chemical bond 3.1 Chemical Bonding Lewis Symbols • Lewis symbol (Lewis structure) - a way to represent atoms using the element symbol and valence electrons as dots • As only valence electrons participate in bonding, this makes it much easier to work with the octet rule • The number of dots used corresponds directly to the number of valence electrons located in the outermost shell of the atoms of the element 3.1 Chemical Bonding Lewis Symbols • Each “side” of the symbol represents an atomic orbital, which may hold up to two electrons • Using Lewis symbols – Place one dot on each side until there are four dots around the symbol – Now add a second dot to each side in turn – The number of valence electrons limits the number of dots placed – Each unpaired dot (unpaired electron of the valence shell) is available to form a chemical bond Lewis Dot Symbols for Representative Elements 3.1 Chemical Bonding 3.1 Chemical Bonding Principal Types of Chemical Bonds: Ionic and Covalent • Ionic bond- a transfer of one or more electrons from one atom to another • Forms attractions due to the opposite charges of the atoms • Covalent bond- attractive force due to the sharing of electrons between atoms • Some bonds have characteristics of both types and not easily identified as one or the other Ionic Bonding • Representative elements form ions that obey the octet rule • Ions of opposite charge attract each other creating the ionic bond • When electrons are lost by a metal and electrons are gained by a nonmetal – Each atom achieves a “Noble Gas” configuration – 2 ions are formed; a cation and anion, which are attracted to each other 3.1 Chemical Bonding 3.1 Chemical Bonding Consider the formation of NaCl Na + Cl Æ NaCl Sodium has a low ionization energy it readily loses this electron Na x Æ Na + + e- When sodium loses the electron, it gains the Ne configuration Chlorine has a high electron affinity When chlorine gains an electron, it gains the Ar configuration » ¼ º « ¬ ª o . ¡ : .. .. Cl : e .. .. Cl : Ionic Bonding 3.1 Chemical Bonding Essential Features of Ionic Bonding • Atoms with low I.E. and low E.A. tend to form positive ions • Atoms with high I.E. and high E.A. tend to form negative ions • Ion formation takes place by electron transfer • The ions are held together by the electrostatic force of the opposite charges • Reactions between metals and nonmetals (representative elements) tend to be ionic Ion Arrangement in a Crystal • As a sodium atom loses one electron, it becomes a...
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- Spring '08
- Atom, Ion, Chemical bond, Drawing Lewis Structures