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Chemistry test 2 Chemical Bonding Covalent Bonds If an atom does not have enough electrons to satisfy the octet rule it will share electrons Bonding electrons are shared electrons and lone pair electrons are unshared pair electrons Covalent bonds attractive force are shared electron pairs that connect the atoms in molecular covalent compounds H2 is held together by covalent bonds Single covalent bonds are formed when two atoms share one pair of electrons H2 F2 Cl2 are examples of single covalent bonds Multiple covalent bonds Double bond is when two shared pairs of electrons joint the same pair of atoms Triple bond three shared pairs Lewis structure for a molecule shows all valence electrons as dots or lines that represent covalent bonds Ionic Bonds Ionic bond electron transfer occurs and displacement is complete Polarity When two atoms are the same ex H2 or F2 there is an equal sharing of the bonding electron pair therefore the bond is a nonpolar covalent bond When two different atoms are bonded the sharing of the bonding electrons is usually unequal and results in displacement of the bonding electrons toward one of the atoms If the displacement is incomplete there is no ionic bond formed but the electrons are shared unequally and the bond is a polar covalent bond Non polar molecule if the polar bonds are oriented so that their polarities cancel each other If the molecule is non polar then the shape is symmetric Polar molecule if electron density is concentrated at one end of the molecule A polar molecular is a permanent dipole with a partial negative charge where the electron density is concentrated and a partial positive charge at the opposite end Drawing Electronegativity Electronegativity the ability of an atom in a covalent bond to attract shared electrons to itself The greater the difference in electronegativity between two atoms the more polar the bond will be Polar when molecules have dipoles Electronegativity increases diagonally upward and to the right in the periodic table Ionic compounds Ionic compounds are compounds whose composition consists of ions positive and negative Metals lose electrons therefore they are the least electronegative elements Non metals gain electrons therefore they are the most electronegative elements Positive ion cation Negative ion anion Monatomic ion is a single atom that has lost or gained electrons Polyatomic ion is a unit of two or more atoms that bears a net electrical charge Characteristic of an ionic compound 1 Composed of a metal cation and a nonmetal anion especially if the metal is combined with just one or two nonmetal atoms Ex NaCl CaCl 2 When a compound is composed of two or more nonmetals it is likely to be a molecular compound Ex H2O Organic compounds which contain carbon and hydrogen and possibly also oxygen nitrogen or halogens are molecular compounds If several nonmetals are combined into a polyatomic anion such as SO2 is combined with a metal ion such as Ca2 the compound will be ionic Ex CaSO4 and KOH Combined with cation such as NH form an ionic compound Ex NH4Cl 4 this cation can be combined with an anion to 4 and this anion 3 4 Metal atoms can be part of polyatomic anions When such polyatomic anions are combined with a metal ion and ionic compound results Ex K2Cr2O7 5 Metalloids can be incorporated into either ionic or molecular compounds 6 Hard and brittle solids 7 High boiling points 8 Poor conductors of heat Naming positive ions Naming negative ions 1 A Metals that form only one kind of cation the name is the name of the metal plus ion Ex Mg2 magnesium ion B For metals that can form more than one kid of cation the name of each ion must indicate its charge Roman numerals in parenthesis are given following the name Ex Cu2 copper II ion 2 A A monoatomic anion is named by adding ide to the stem of the name of the nonmetal element from which the ion is derived Ex Phosphorus phosphide Group 7 elements are halogens also known as halide ions B The names of the most common polyatomic ions are on the list Oxoanions are polyatomic ions containing oxygen Book p 96 Naming ionic compounds Covalent compounds The name of the cations comes first then the name of anion Calcium oxide is named from calcium rule 1a and oxide rule 2a Molecular compounds or covalent compounds are those in which the elements share electrons via covalent bonds Molecular compounds contain two or more nonmetal elements combine Compounds consisting only of carbon with hydrogen are called hydrocarbons Hydrocarbons have their own special nomenclature so they are treated differently from other molecular compounds Those are mostly gases liquids or solids Inorganic Nomenclature Prefix Number Mono 1 Di 2 Tri 3 Tetra 4 Penta 5 Hexa 6 Hepta 7 Octa 8 Nona 9 Deca 10 Ex CO carbon monoxide VSEPR Valence Shell Electron Pair Repulsion It is based on the idea that repulsion occurs among regions of electrons density such as the repulsions among pairs of bonding and lone pair electrons Electron pair geometry is determined by the number and arrangement of the electron pair around the central atom The molecular geometry is the arrangement of the atoms in space When atoms don t have any lone pair the electron pair geometry and molecular geometry are the same VSEPR concepts used to predict shape SiCl4 Drawing Multiple bonds Central atoms with bonding pairs and lone pairs Non covalent Interactions and Forces Non covalent interactions are all forces that are other than covalent ionic or metallic bonding Intermolecular forces occur when non covalent interactions act between one molecule and another Intermolecular forces do not result from sharing electron pairs so they are weaker than covalent bonds The strength of non covalent interactions between molecules intermolecular forces accounts for melting points boiling points and other properties of molecular substances There are three types of non covalent interactions 1 London forces dispersion forces attractions between all types of molecules even non polar ones London forces result from the attraction between the positive and negative ends of nonpermanent dipoles An induced dipole nonpermanent is caused in one molecule when the electrons of a neighboring molecule are momentarily unequally distributed resulting in a temporary dipole in the first molecule Boiling points increase as the total number of electrons increases Boiling points of liquids depend on the nature and strength of intermolecular forces 2 Dipole dipole forces


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Rio CHD 100 - Chemical Bonding

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