Chem 151 Exam #3 NotesIonic Bonding- Valence electrons are transferred in a chemical reaction between two atoms- Atoms lose or gain electrons to form ions to achieve a more stable energy state- A strong net attractive force is present between the ionsCovalent- The atoms in a molecular compound are connected by shared electrons- Molecular compounds tend to form structures in which each atom has 8 valence electrons- The # of covalent bonds atoms form can be determined by electron configurations (full valence shell)Writing Lewis Structures for Molecular Compounds- Decide on the central atom----tends to be the atom with the lowestelectronegativity- Calculate the total number of electrons for the structure by adding thevalence electrons of each atom- Distribute the electrons among the atoms, giving octets (or duets in the caseof hydrogen) to as many atoms as possible- If any atoms lack an octet, form double or triple bonds as necessary to givethem octets.Hydrogen can have 1 bond and 0 lone pairs. Carbon: 4, 0Nitrogen: 3, 1Oxygen: 2, 2Fluorine: 1, 3- Double and triple bonds are commonly found in C, N, P, O, and SExceptions of the Octet Rule- Usually occur with Boron, elements of the higher periods, or compounds ofthe noble gases- Odd-electron species- Incomplete octets - Expanded octetsResonance: when you can write a Lewis structure multiple ways, but they are stillequivalent in strength and length. Between the structures, we draw a double-headed arrow. The true electronic structure is a hybrid/combination of theresonance structures.- Bond order= bonds/locationsThe formal charge of an atom in a Lewis Structure is the charge it would have if allbonding electrons were shared equally between the atoms.- The negative formal charge should be on the most electronegative element,making it the better structure. - The least electronegative atom should be in the center of the structure.- Smaller formal charges (whether positive or negative) are preferable to largeones- Like charges on adjacent atoms are not desirable- A more negative formal charge should reside on a more electronegative atom- The sum of the formal charges must equal the charge of the molecule- To determine the formal charge Valence electrons - assigned electronsBonding and Bond Lengths- As the bond between two atoms gets longer, it also gets weaker.- Bonding between a metal and non metal- ionic- Bonding between two nonmetals- covalent - Metals have a tendency to lose electrons, which means they have relativelylow ionization energiesElectron and Molecular GeometriesElectronGroupsBondingGroupsLone Pairs ElectronGeometryMolecularGeometryBondAngles2 2 0 Linear Linear 1803 3 0 TrigonalPlanarTrigonalPlanar1203 2 1 TrigonalPlanarBent <1204 4 0 Tetrahedral Tetrahedral 109.54 3 1 Tetrahedral TrigonalPyramidal<109.54 2 2 Tetrahedral Bent <109.5Intermolecular forces- Attractive forces that exist between all molecules and atoms- Hold liquids and solids together - Are responsible for the existence of condensed states- When thermal energy is high relative to intermolecular forces, the mattertends to be gaseous. When it is low, the matter tends to be a liquid or solidBond Polarity Cl is more electronagative than H. The bond is polar. Intramolecular- Forces within a molecule- Holds atoms togetherJust because a molecule has polar bondsdoesn’t mean the molecule is polar.H Cl- Determines the electron and molecular geometries- N≡N has strong intramolecular forcesIntermolecular- Forces between molecules to other molecules- The forces between many particles determine the macroscopic properties- Determine properties such as: boiling point, melting point, density, andsolubilityHydrogen Bonding- In molecules containing a H bonded to a very electronegative atom: N, O, or F- A very strong form of intermolecular attraction (special