Bonding How can one distinguish between different bonding
Bonding How can one distinguish between different bonding types?
Bonding Concepts Through bonding, atoms attain a stable electron configuration n Energy must is required to break a chemical bond (endothermic) n Energy is released when a chemical bond is formed (exothermic) n
Metallic Bonding n Occurs in a pure metallic element (ex, Cu) n Positively charged ions surrounded by a “sea of mobile electrons” n Attraction between kernels (+) and electrons (-)
Properties of Metals n Generally n High Hard MP n Good Conductor of electricity and heat (in all phases) n Not soluble (cannot dissolve) in water
Ionic Bonding n Between Metal and Non-Metal n Electrons transferred from M to NM n Results in (+) and (-) ions
Properties of Ionic Compounds n Hard n High Melting Point n Cannot conduct electricity as a solid n Can conduct electricity as a liquid or in an aqueous solution n Generally dissolve well in water, but some cannot
Example Lewis Diagrams of Ionic Compounds
Compounds with BOTH Ionic and Covalent Bonding Ionic compounds that contain a polyatomic ion n Examples: Ca. CO 3, Mg. SO 4, *NH 4 Cl n
Covalent Bonding Non-Metal to Non-Metal n Electrons are shared between 2 atoms n Often results in the formation of n molecules n Although atoms are bonded tightly together within one molecule, multiple molecules are attracted by relatively weak intermolecular forces (IMFs)
Properties of Covalent (Molecular) Compounds Soft n Low MP/BP n Generally cannot conduct electricity n Polar molecules dissolve well in water n Non-polar molecules do not n
Network Solids n n Covalent bonding throughout a solid Diamond (Carbon) Silica (empirical formula of Si. O 2) Silicon Carbide (Si. C)
Properties of Network Solids n Very Hard n Very High MP n Poor conductor (cannot conduct electricity or heat) n Not soluble in water
Polar Covalent Bond Electrons are shared unequally n 2 atoms of different elements (NM) n More electronegative atom “hogs” electrons and is partially negative n The bond is more polar (has greater ionic character) with a larger difference in electronegativity n Ex. The bond in HCl is more polar than the bond in HBr n
Nonpolar Covalent Bond Electrons are shared equally n 2 atoms of the same element (same electronegativity value) n Neither atom “hogs” electrons, so no partial charges n Ex. Bond within the molecule of a diatomic element (HOFBr. INCl) n
Drawing Lewis Dot Diagrams of Covalent Compounds (Molecules) n n n Usually the first element is in the center Consider from the outside in: how many electrons are needed to become stable Give one to get one (single bond) Give two to get two (double bond) Give three to get three (triple bond)
VSEPR Theory n n n The valence shell electron pair repulsion theory helps to predict the shape of molecules The electron pairs around the central atom will move as far from each other as possible in three dimensions Bonding AND non-bonding pairs of electrons repel one another
Nonpolar Molecules n n “Zoom Out” and consider the shape Symmetrical molecules are nonpolar There is an equal distribution of charge n Partial charges cancel each other n One cannot assign opposite partial charges to opposite sides n Ex. H 2, O 2, CH 4, CF 4 n
Polar Molecules n n “Zoom Out” and consider shape Asymmetrical molecules are polar There is an unequal distribution of partial charge n Partial charges do not cancel out n One can assign opposite partial charges to opposite ends n Ex. H 2 O, NH 3, HCl, CH 3 Cl n
A nonpolar molecule can contain polar covalent bonds! Ex. CO 2 n ”Zoom Out”: CO 2 is symmetrical (nonpolar molecule) n “Zoom In”: C and O share electrons unequally (polar bond) n
Coordinate Covalent Bond n n Special covalent bond in which both of the shared electrons come from the same atom Examples: n hydronium
Intermolecular Forces of Attraction n Relatively weak attractions between multiple molecules n Stronger IMFs result in higher MPs and higher BPs
Intermolecular Forces of Attraction n Three Types of IMFs n London Dispersion Forces n Dipole – Dipole Attractions n Hydrogen Bonding n See page 25 in Bonding Packet
Molecule – Ion Attraction n n Like an intermolecular force of attraction In water, many ionic substances break apart Positive ions are attracted to the partial negative oxygen ends of water Negative ions are attracted to the partial positive hydrogen ends of water
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