5.1 Ionic Bonds: Chemical Bonding The majority of elements occur in nature in chemical combination with other elements in the form of compounds Exceptions: Noble Gases: He, Ne, Ar, Kr, & Xe Some Metals: Cu, Ag, Au, Pt O2, N2 & S8 occur in nature as diatomic and polyatomic molecules The electrons of the interacting atoms are involved in compound formation in one of two ways: Transferring Electrons between Atoms - Ionic Compounds Sharing Electrons between Atoms - Covalent Compounds It is the Electronic Structure of Each Element that Gives Rise to the Chemistry (Reactivity) of Each Element in the Periodic Table continue…. S 5.0 Chemical Bonding and States of Matter, Pt I

5.1 Ionic Bonds: Ionic Bond Formation The noble gases have stability (low reactivity) that is related to the number and arrangement of electrons Metallic Elements lose electrons to form ions with the same number of electrons as the nearest noble gas Non-Metallic elements gain electrons to form ions with the same number of electrons as the nearest noble gas The Formation of Sodium Chloride: 2Nao + Cl2 2NaCl Sodium (11 e - ) loses 1 electron to form Na + (10 e - ) and attains the stability of Neon (10 e - ). Chlorine (17 e - ) gains 1 electron to form Cl - (18 e - ) and attains the stability of Argon (18 e - ). continue…. S 5.0 Chemical Bonding and States of Matter, Pt I

5.1 Ionic Bonds: - The Periodic Table Non-Metals Gain Electrons Metals Lose Electrons Noble Gases 5 continue….

5.2 Ionic Compounds: Ionic Compounds Ionic Compounds: “ Ionic compounds are composed of ions. An ion is any species (element or compound) that bear a charge “ Binary Ionic Compound: “ One composed of just two elements; formed when a metallic element reacts with a non-metallic element “ Cation Formation: “ The metal loses a certain number of electrons and becomes a positively charged cation “ Cation: “ A positively charged ion “ Anion Formation: “ The non-metal gains a certain number of electrons and becomes an anion “ Anion: “ A negatively charged ion “ In Effect, the Metal Atom Transfers Electrons to the Non-Metal Atom continue….

5.2 Ionic Compounds: Sodium Chloride (NaCl) Lattice Structure Form 2Nao (s) + Cl2 (g) 2NaCl (s) The Chemical Equation: The Particulate (Atomic) View Chlorine Ion ( Cl - ) Chlorine Atom (Cl) Sodium Ion ( Na + ) Na + and Cl - compound Shown in the Crystal Lattice Structure Form Sodium Chloride Crystal Sodium Atom (Na) continue….

5.3 Covalent Bonds Covalent compounds form when elements share electrons, which usually occurs between non-metallic elements. Covalent Bond: “ In a covalent bond the pair of electrons is mutually attracted by two nuclei. The electrons are “ shared ” between the two atomic elements “ H . + H . H : H or H2 The electron from each hydrogen atom is shared between both hydrogen atoms to give the helium noble gas configuration ( He: ) Hydrogen Atoms Diatomic Hydrogen Molecule continue…. S 5.0 Chemical Bonding and States of Matter, Pt I

Formation of a Covalent Bond between Two Hydrogen Atoms H . + H . H : H It is the attraction of the bonding electrons to two nuclei that holds the nuclei together in a covalent bond continue….

5.3 Covalent Bonds (cont) Lewis Structures: * “ The element displayed with an electron dot symbol to show the valence electrons “ * Also called Lewis symbols or Lewis diagrams. Group E.C. No V. e- Lewis Symbol 1A ns1 1 Li . 2A ns2 2 . Be . 3A ns2np1 3 . . B . 4A ns2np2 4 . . C . 5A ns2np3 5 . . N : 6A ns2np4 6 . : O : 7A ns2np5 7 . : F : . . 8A ns2np6 8 . . : Ne : E.C. = Electron Configuration No V. e- = Number of Valence Electrons continue……. S 5.0 Chemical Bonding and States of Matter, Pt I

5.3 Covalent Bonds (cont) . . The Reaction of Hydrogen and Fluorine: H2 (g) + F2 (g) 2HF (g) Covalent Bond Formation from a Lewis Structure Viewpoint: The octet of electrons around F is complete Vacant Orbital . : F : . . H . + H : F : A single line Is also used to describe the covalent bond H . . F : Each single bond (line) is made up of 2 shared electrons Octet Rule: “When atoms bond, they lose, gain, or share electrons to attain a filled outer shell of eight (or two) electrons “ This completes the noble gas configuration continue…….

5.3 Covalent Bonds (cont) . Molecules with Covalent Bonds: H . + Br . H : Br Hydrogen Bromide . . 2 H . + H : O : H . : O : Water continue……. S 5.0 Chemical Bonding and States of Matter, Pt I

5.3 Covalent Bonds (cont) . . Diatomic Molecules: . : F : + : F : F : The lone pairs are often not shown F . + F F Other Diatomic Molecules: Cl . + Cl Cl Br . + Br Br continue……. S 5.0 Chemical Bonding and States of Matter, Pt I

5.3 Covalent Bonds (cont) . N : . N : Multiple Bonds - Diatomic Oxygen Double Bonds are formed when 4 electrons (2 pairs of electrons) are shared between two atoms . : O : + . . . . : O : : O : Each oxygen atom has a complete octet of electrons There is a double bond between these two oxygen atoms O O Diatomic Nitrogen Triple Bonds are formed when 6 electrons (3 pairs of electrons) are shared between two atoms . . N : . . N : : N : : : N : Each nitrogen atom has a complete octet of electrons + There is a triple bond between these two nitrogen atoms N N continue……. S 5.0 Chemical Bonding and States of Matter, Pt I

5.3 Covalent Bond: Bond Length & Bond Strength Triple bonds are shorter than double bonds Double bonds are shorter than single bonds Bond Lengths and Bond Energies Bond Type C C C C C C N N Bond Length (nm) 0.154 0.134 0.120 0.109 Bond Strength (kcal/mol) 83 146 200 225 Bond Strength: Triple bonds are stronger than double bonds Double bonds are stronger than single bonds continue……. S 5.0 Chemical Bonding and States of Matter, Pt I

5.4 Shapes of Molecules: Electron Pair (EP) Repulsion Molecular shape plays an important role in determining the macroscopic properties of a chemical substance Valence Shell Electron-Pair Repulsion (VSEPR) Theory The electron pairs that are drawn in a Lewis structures, distribute themselves around a particular atom so that they are as far apart from each other as possible These are the locations of lowest potential energy This arrangement is called electron-pair (or region) geometry This lowest energy condition also holds for regions of electron density other than electron pairs (ie, double bonds) Electron Pair (or region) Geometries No. Electron Regions Geometry Electron-Pair Angles 2 Linear 180 o 3 Trigonal Planar 120 o 4 Tetrahedral 109.5 o continue…. S 5.0 Chemical Bonding and States of Matter, Pt I

5.4 Shapes of Molecules: Electron Pair Geometry Two Electron Pairs (or Regions) Around an Atom Linear Geometry Electron Regions are 180 o apart from each other Three Electron Pairs (or Regions) Around an Atom Trigonal Planar Geomety Electron Regions are 120 o apart from each other continue…. S 5.0 Chemical Bonding and States of Matter, Pt I

5.4 Shapes of Molecules: Electron Pair Geometry (cont) Four Electron Pairs (or Regions) Around an Atom Tetrahedral Geometry Electron Regions are 109.5 o apart from each other continue…. S 5.0 Chemical Bonding and States of Matter, Pt I

5.4 Shapes of Molecules: Electron Pair Geometry (cont) Linear 2 atoms on opposite sides of central atom 180° bond angles Trigonal Planar 3 atoms form a triangle around the central atom Planar 120° bond angles Tetrahedral 4 surrounding atoms form a tetrahedron around the central atom 109.5° bond angles 180° 120° 109.5° S 5.0 Chemical Bonding and States of Matter, Pt I

5.4 Shapes of Molecules: Molecular Shape Linear Electron Pair Geometry 2 Regions of electrons around the central atom, both bonding Or two atom molecule as trivial case ( N2, O2, etc ) Trigonal Electron Pair Geometry 3 Regions of electrons around the central atom All Bonding = trigonal planar ( CO3 2- ) 2 Bonding + 1 Lone Pair = trigonal bent ( O3 ) Tetrahedral Electron Pair Geometry 4 Regions of electrons around the central atom All Bonding = tetrahedral 3 Bonding + 1 Lone Pair = trigonal pyramid ( NH3 ) 2 Bonding + 2 Lone Pair = tetrahedral bent or V-shaped ( H2O ) continue……. S 5.0 Chemical Bonding and States of Matter, Pt I

5.5 Polar and Nonpolar Bonding Nonpolar Bond: “ A bond in which bonding electrons are shared equally is a nonpolar bond “ A bond between identical atoms ( H2 , F2, etc) is always nonpolar Polar Bond: “ A bond in which bonding electrons are shared unequally “ Electrons Distributed Evenly Unevenly 11 Chlorine attracts the bonding electrons more strongly than hydrogen Chlorine is More Electronegative than Hydrogen continue……. S 5.0 Chemical Bonding and States of Matter, Pt I

5.5 Polar and Nonpolar Bonding (cont) Electronegativity: - “ A measure of how strong an atom attracts bonded electrons to itself. A measure of how stingy an atom is for bonded electrons Covalent bonding between unlike atoms results in unequal sharing of the electrons One end of the bond has greater electron density than the other The end with the larger electron density gets a partial negative charge The end that is electron deficient gets a partial positive charge H F •   continue…. S 5.0 Chemical Bonding and States of Matter, Pt I

The Polar Nature of Water Covalent Bond Formation - 1) The Distribution of Bonding Electrons In a covalent bond formed from different atoms the sharing of electrons is not equal One atom will prefer to have a greater share of the electrons (one atom is more electronegative than the other) Since the oxygen atom is more electronegative than hydrogen the bonding electrons will spend more time around oxygen This unequal sharing creates partially charged “ poles “ at the end of each O  H bond Partial Negative Charge on Oxygen The Water Molecule O H H Partial Positive Charge on Hydrogen Electrons have Shifted the Average Position Nearer to Oxygen continue…….

The Polar Nature of Water (cont) Covalent Bond Formation - 1) The Distribution of Bonding Electrons (cont) The bond polarity is represented by a polar arrow pointing to the negative pole from a plus sign on the arrow The Two O  H Bonds in Water are Polar Water has a bent shape Covalent Bond Formation - 2) The Overall Shape of the Water Molecule The combined effects of bent shape and polar bonds makes water a polar molecule Water is a Polar Molecule The Overall Vector Component of Polarity continue…….