3Section 1 Learning Targets 8.1.1 – I can distinguish between the melting points and boiling points of molecular compounds and ionic compounds – I can describe the information provided by a molecular formula.
4Molecules and Molecular Compounds Covalent bond – atoms held together by sharing electrons.Molecule – neutral group of atoms joined together by covalent bonds.
5Molecular compound – compound composed of molecules. Diatomic molecule – molecule consisting of two atoms.
6Molecular compounds tend to have relatively lower melting and boiling points than ionic compounds.
7Molecular FormulasMolecular formula – chemical formula of a molecular compound.A molecular formula shows how many atoms of each element a molecule contains.
11Section 2 Learning Targets 8.2.1 – I can describe how electrons are shared to form covalent bonds and identify exceptions to the octet rule – I can demonstrate how electron dot structures represent shared electrons – I can describe how atoms form double or triple bonds.
12Section 2 Learning Targets 8.2.4 – I can distinguish between a covalent bond and a coordinate covalent bond and describe how the strength of a covalent bond is related to its bond dissociation energy – I can describe how oxygen atoms are bonded in ozone.
13The Octet Rule in Covalent Bonding In covalent bonding, electron sharing usually occurs so that atoms can attain the electron configuration of the noble gases.
14Single Covalent BondsStructural formula – represents the covalent bonds by dashes and shows the arrangement of covalently bonded atoms.
15An electron dot structure, such as H:H represents the shared pair of electrons of the covalent bond by two dots.
16Single covalent bond – two atoms held together by sharing a pair of electrons. Unshared pair – (lone pair) or nonbonding pair of electrons.
17In the water molecule the two hydrogen atoms share electrons with the one oxygen to attain a noble gas electron configuration.
18The halogens form single covalent bonds because they have seven valence electrons and need one more to attain the electron configuration of a noble gas.
19Ammonia has three bonds and one unshared pair of electrons.
20Carbon behaves differently than expected. What you expect is:What happens is:This movement of electrons allows carbon to make four covalent bonds.
22Double and Triple Covalent Bonds Atoms form double or triple covalent bonds if they can attain a noble gas structure by sharing two or three pairs of electrons.Double covalent bond – bond that involves two shared pairs of electrons.Triple covalent bond – bond formed by sharing three pairs of electrons.
23Oxygen forms a double bond by sharing two pairs of electrons.
24Nitrogen’s three 2p electrons allow it to form triple bonds.
25Some elements exist as diatomic molecules. There are seven of them.
26Double and triple bonds can exist in molecules that are not diatomic.
34Bond Dissociation Energy Bond dissociation energy – energy required to break the bond between two covalently bonded atoms.A large bond dissociation energy corresponds to a strong covalent bond.Type of BondDissociation Energy (kJ/mol)C-CCarbon single347C=CCarbon double657C≡CCarbon triple908H-HHydrogen single435
35ResonanceResonance structures – structure that occurs when it is possible to draw two or more valid electron dot structures.Usually seen with double bonds – where they could shift around.
36The actual bonding in ozone (O3) is a hybrid, mixture, of the extremes represented by the resonance forms.
37Exceptions to the Octet Rule The octet rule can not be satisfied in molecules whose total valence electrons in an odd number.There are also molecules in which an atom has fewer, or more, than a complete octet of valence electrons.
41Section 3 Learning Targets 8.3.2 – I can describe how VSEPR theory helps predict the shapes of molecules.
42VSEPR Theory VSEPR (Valence Shell Electron Pair Repulsion Theory VSEPR videoAccording to VSEPR the repulsion between electron pairs causes molecular shapes to adjust so that the valence-electron pairs stay as far apart as possible.
43Unshared pairs are just as important as bonds because they help determine the shapes of the molecules.Unshared pairs of electrons are held closer to the nucleus and push bonded atoms out of their way.Tetrahedral angle – a bond angle of 109.5° that results when a central atom forms four bonds.
45I’m giving you a handout instead of this table for your notes Linear TriatomicTrigonal PlanarBent TriatomicPyramidalTetrahedralTrigonal BipyramidalSawhorse or SeesawOctahedralSquare PyramidSquare PlanarT-ShapedI’m giving you a handout instead of this table for your notes
48How many bonds do each of these make? Let’s PracticeOn the back of your yellow paper answer the following:How many bonds do each of these make?CarbonNitrogenOxygenFluorinePhosphorusSulfurChlorineBromineIodineHydrogenGroup 5Group 6Group 7
49Draw the molecules and tell their molecular shape COBF3Shape =Shape =
50Draw the molecules and tell their molecular shape SO2CH4Shape =Shape =
51Draw the molecules and tell their molecular shape NH3H2OShape =Shape =
52Draw the molecules and tell their molecular shape PF5SF4Shape =Shape =
53Draw the molecules and tell their molecular shape BrF3XeF2Shape =Shape =
54Draw the molecules and tell their molecular shape SF6BrF5Shape =Shape =
55Draw the molecules and tell their molecular shape XeF4Shape =
56VSEPR VideoPage 233 in your text book may help with the matching on your daily work if you’re struggling.
61Section 4 Learning Targets 8.4.1 – I can describe how electronegativity values determine the distribution of charge in a polar molecule – I can describe what happens to polar molecules when they are placed between oppositely charged metal plates.
62Section 4 Learning Targets 8.4.3 – I can evaluate the strength of intermolecular attractions compared with the strength of ionic and covalent bonds – I can identify the reason why network solids have high melting points.
63Bond Polarity Electrons are not always shared equally in compounds. Nonpolar covalent bond – when atoms in the bond pull equally the bonding electrons are shared equally.
64Polar covalent bond (polar bond) – covalent bond between atoms in which the electrons are shared unequally.
65The more electronegative atom attracts electrons more strongly and gains a slightly negative charge. Slight charges are represented by Greek delta symbols (δ+ δ-)
66The electronegativity difference can tell you the kind of bond between two atoms. Page 177 or Chapter 6 Section 3 has this information.What kind of bonds are these?
67Polar MoleculesPolar molecule – one end of the molecule is slightly negative and the other end is slightly positive.Dipole – a molecule that has two poles.
68When polar molecules are placed between oppositely charged plates, they tend to become oriented with respect to the positive and negative plates.
70Attractions Between Molecules Intermolecular attractions are weaker than either ionic or covalent bonds.
71Van der Waals ForcesVan der Waals forces – the two weakest attractions between molecules.After Dutch chemist Johannes van der Waals (1837 – 1923).Two kinds of van der Waals forces:Dipole interactionsDispersions forces
72Dipole interactions – polar molecules are attracted to one another. Dispersion forces – weakest of all, caused by the motion of electrons.Neighbor electrons influence other neighbors momentarily.Grey dashes represent dipole interactions
73Hydrogen BondsHydrogen bonds – attractive forces in which a hydrogen covalently bonded to a very electronegative atom is also weakly bonded to an unshared pair of another electronegative atom.
74Hydrogen bonds are the strongest of the intermolecular forces. HINT: hydrogen needs to already be in a compound first then attracted to an unshared pair.Red lines represent hydrogen bonding
75Intermolecular Attractions and Molecular Properties Because the kinds of covalent bonds vary so do the properties of covalent (molecular) compounds.Network solid – (network crystal) solid in which all of the atoms are covalently bonded to each other.
76Melting a network solid would require breaking covalent bonds throughout the solid. For example: the melting point of diamond is 3500°C and then it vaporizes instead of melting.