2 Sharing is CaringThe atoms held together by sharing electrons are joined by a Covalent Bond.
3 2. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons. Oxygen AtomOxygen AtomOxygen Molecule (O2)
4 Molecules and Molecular Compounds Molecule is a neutral group of atoms joined together by covalent bonds.Diatomic molecule is a molecule consisting of two atoms.A compound composed of molecules is called a molecular compound.
5 PropertiesMolecular compounds tend to have relatively lower melting and boiling points than ionic compounds.Many are gases or liquids at room temperature.Most are formed from atoms of two or more nonmetals.
6 Molecular FormulasA molecular formula is the chemical formula of a molecular compound.It shows how many atoms of each element a molecule contains.CO2 Carbon Dioxide1 Carbon Atom2 Oxygen Atoms
11 In covalent bonding,atoms still want to achievea noble gas configuration(the octet rule).
12 But rather than losing or gaining electrons, In covalent bonding,atoms still want to achievea noble gas configuration(the octet rule).But rather than losing or gainingelectrons,atoms now share an electron pair.
13 The shared electron pair is called a bonding pair In covalent bonding,atoms still want to achievea noble gas configuration(the octet rule).But rather than losing or gainingelectrons,atoms now share an electron pair.The shared electron pairis called a bonding pair
16 Cl Cl Each chlorine atom wants to gain one electron to achieve an octet
17 Cl Cl do to achieve an octet? What’s the solution – what can they Neither atom will give up an electron –chlorine is highly electronegative.What’s the solution – what can theydo to achieve an octet?
18 Cl Cl do to achieve an octet? What’s the solution – what can they Neither atom will give up an electron –chlorine is highly electronegative.What’s the solution – what can theydo to achieve an octet?
38 OO=For convenience, the double bondcan be shown as two dashes.
39 This is the oxygen molecule, =this is so cool!!This is the oxygen molecule,O2
40 Multiple Covalent bonds Only 7 electrons doesNot meet Octet Rule!Need to shareAnother pair ofelectronsOOSharing One Pair of electronsOne Covalent BondOOOOA Double Bond can be represented by a double lineSharing Two Pairs of electronsTwo Covalent BondsA Double Bond
41 Multiple Covalent bonds NitrogenNNSharing Three Pairs of electronsThree Covalent BondsA Triple BondNNA Triple Bond can be represented by a Triple line
42 Coordinate Covalent Bond both electrons contributed by one atom of pairNH3 + H > NH4+H2O + H > H3O+
44 Drawing Lewis Dot Structures Predict the location of the atomsHydrogen is a terminal atomThe central atom has the smallest electronegativity.Count the valence electrons.Draw a single covalent bond between the central atom and the surrounding atoms.Subtract the number of electrons in the single covalent bonds from the total number of electrons in 2.Use the remaining electrons to complete the octets of each atom.If the central atom does not have a complete octet then try double or triple bonds.
45 Drawing Lewis Dot Structures Draw Lewis Dot Structures for:PH3H2SHClCCl4SiH4CH2Cl2
46 Bond Dissociation Energies The energy required to break the bond between two covalently bonded atoms.
47 Relate the strength of covalent bonds to bond length The more bonds located between 2 atoms, the shorter the bonds areThe shorter a bond is, the stronger it isH – H single bond, not too strongO=O double bonds, strongerNΞN triple bonds, strongest
48 Endothermic/Exothermic In chemical reactions, bonds are broken, then new bonds are formedEndothermicMore energy is required to break the old bonds than is released by the formation of new bondsEnergy is taken in (colder)ExothermicMore energy is released when forming new bonds than is used to break the old bondsEnergy is given off (hotter)
49 Exceptions to Octet Rule NO2 nitrogen dioxideresonance
52 INTRODUCTIONA) Lewis structures do not indicate the three dimensional shape of a molecule. They do not show the arrangement space of the atoms, what we call the molecular geometry or molecular structure.B) Molecules have definite shapes and the shape of a molecule controls some of its chemical and physical properties.
53 II. Valence Shell Electron Pair Repulsion Theory - VSEPR - predicts the shapes of a number of molecules and polyatomic ions.A) Assumptions of VSEPR Theory1) Electron pairs in the valence shell of an atom tend to orient themselves so that the total energy is minimized. This means that: the electrons will approach the nucleus as close as possible yet take positions as far away from each other as possible to minimize _______________ .
54 2) Because lone pairs of electrons are spread out more broadly than bond pairs, repulsions are greatest between two lone pairs, intermediate between a lone pair and a bond pair, and weakest between two bonding pairs of electrons.3) Repulsive forces decrease rapidly with increasing interpair angle - greatest at 90o, much weaker at 120o, and very weak at 180o.B) What are the ideal arrangements of electron pairs to minimize repulsions?
55 Note that each atom has a single, unpaired electron. Bond FormationA bond can result from an overlap of atomic orbitals on neighboring atoms.ClH•••+Overlap of H (1s) and Cl (2p)Note that each atom has a single, unpaired electron.
56 Double and even triple bonds are commonly observed for C, N, P, O, and S H2COSO3C2F4
57 Some Common Geometries LinearTetrahedralTrigonal Planar
60 Structure Determination by VSEPR Water, H2OThe electron pair geometry is TETRAHEDRAL2 bond pairs2 lone pairsThe molecular geometry is BENT.
61 Structure Determination by VSEPR Ammonia, NH3The electron pair geometry is tetrahedral.The MOLECULAR GEOMETRY — the positions of the atoms — is TRIGONAL PYRAMID.
62 Bond Polarity Cl has a greater share in bonding electrons than does H. HCl is POLAR because it has a positive end and a negative end. (difference in electronegativity)Cl has a greater share in bonding electrons than does H.Cl has slight negative charge (-d) and H has slight positive charge (+ d)
63 Bond PolarityThis is why oil and water will not mix! Oil is nonpolar, and water is polar.The two will repel each other, and so you can not dissolve one in the other
65 Electronegativity Difference If the difference in electronegativities is between:1.7 to 4.0: Ionic0.3 to 1.7: Polar Covalent0.0 to 0.3: Non-Polar CovalentExample: NaClNa = 0.8, Cl = 3.0Difference is 2.2, sothis is an ionic bond!
66 Remember: BrINClHOF Diatomic Elements These elements do not exist as a single atom; they always appear as pairsWhen atoms turn into ions, this NO LONGER HAPPENS!HydrogenNitrogenOxygenFluorineChlorineBromineIodineRemember: BrINClHOF
67 Polar Covalent Bonds: Unevenly matched, but willing to share.
68 Van der Waals ForcesSmall, weak interactions between molecules
69 Van der Waals Forces Intermolecular: between molecules (not a bond) Intramolecular: bonds within molecules (stronger)
70 3 Types of Van der Waals Forces 1) dipole-dipole2) dipole-induced dipole3) dispersion
71 Dipole-DipoleTwo polar molecules align so that d+ and d- are matched (electrostatic attraction)Ex: ethane (C2H6) vs. fluromethane (CH3F)Occurs when polar molecules are attracted to one another.The slightly region of a polar molecule is weakly attracted to the slightly positive region of another polar molecule.Similar to but much weaker than ionic bonds.
72 Dispersion ForcesThe weakest of all molecular interactions, are caused by the motion of electrons.Dispersion is the ONLY intermolecular attraction that occurs between non-polar molecules
73 Review Dipole – between two polar molecules Dispersion- between two non-polar molecules
74 Hydrogen Bonding STRONGEST Intermolecular Force!! A special type of dipole-dipole attractionBonds form due to the polarity of water.IceLiquid
75 Hydrogen Bonding con’t Hydrogen bonds keep water in the liquid phase over a wider range of temperatures than is found for any other molecule of its size
76 How many drops can you get on a penny? Water?Why is there a difference???Water has strong Hydrogen Bonds and TTE has weaker intermolecular forces
77 How is surface tension affected by soap? Breaks the surface tension!
78 Intermolecular Attractions and Molecular Properties The physical properties of a compound depend on the type of bonding it displays-in particular, on whether it is ionic or covalent.Network Solids are solids in which all of the atoms are covalently bonded together.Melting a network solid would require breaking covalent bonds throughout the solid.Diamond does not melt; rather it vaporizes to a gas at 3500 degrees Celsius and above.
79 Review of Chemical Bonds There are 3 forms of bonding:_________—complete transfer of 1 or more electrons from one atom to another (one loses, the other gains) forming oppositely charged ions that attract one another_________—some valence electrons shared between atoms_________ – holds atoms of a metal togetherMost bonds are somewhere in between ionic and covalent.
80 Review of Valence Electrons Number of valence electrons of a main (A) group atom = Group number
81 Review of Valence Electrons Remember from the electron chapter that valence electrons are the electrons in the OUTERMOST energy level… that’s why we did all those electron configurations!B is 1s2 2s2 2p1; so the outer energy level is 2, and there are 2+1 = 3 electrons in level 2. These are the valence electrons!Br is [Ar] 4s2 3d10 4p5 How many valence electrons are present?
82 Bond and Lone PairsValence electrons are distributed as shared or BOND PAIRS and unshared or LONE PAIRS.•••HClshared orbond pairlone pair (LP)This is called a LEWIS structure.