Covalent Bonding SLO 4/14/16 Students will be able to draw Lewis Dot Structures of Covalent Compounds and explain resonance structures.
Classwork Check! Written Assignment: pg. 225, #1, 3, 4, 5, 6 1. Molecular forms tells us how many atoms of each elements are present. CO 2 is an example; 1 carbon, 2 oxygen 3. Noble gases exist on their own and we also call them monatomic elements. 4. NO has one nitrogen, N 2 O has two nitrogens 5. H 2 O 2 N 2 are found in earth s atmosphere 6. Molecular structure tells us how elements are combined and arranged together.
What rules do we already know about bonding? Octet Rule- elements will bond to reach a stable number of valence electrons, which is eight (8) Exceptions: H, He, Li, Be stable with 2 H stable with 0 B stable with 6 S and P often have more than 8 N can have 7 but isn t stable Noble gases don t form compounds because they have 8 valence electrons already They are stable alone
Lewis Dot Structures Lewis Dot Structures- similar to electron dot structures, except lines can be used to indicate the sharing of electrons for single, double, and triple bonds A pair of valence electrons that is not shared between atoms is called an unshared pair, also known as a lone pair or a nonbonding pair
Writing Lewis Dot Structures for Molecular Compounds (Covalent) 1. Count up total number of valence electrons 2. Determine the central atom C is often the central atom For now, the single atom will be the central atom 3. Bond atoms to satisfy the octet rule if possible 4. Fill in valence electrons to satisfy the octet rule for all atoms (keep the exceptions in mind) 5. If all atoms are not stable, try double or triple bonds 6. If you have extra electrons, put them on the central atom
8.2 Single Covalent Bonds The halogens form single covalent bonds in their diatomic molecules. Fluorine is one example.
8.2 Single Covalent Bonds The ammonia molecule has one unshared pair of electrons.
8.2 Double and Triple Covalent Bonds Each oxygen atom has two unshared pairs of electrons.
Coordinate Covalent Bonds Coordinate covalent bond- when both bonding electrons come from one atom In carbon monoxide, oxygen has a stable configuration but the carbon does not
Coordinate Covalent Bonds As shown below, to make the carbon stable, the oxygen donates one of its unshared pairs of electrons for bonding.
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8.2
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Compare and Contrast Ionic & Covalent Ionic is made up of metal and nonmetal; covalent is made up of 2 nonmetals Ionic involves transfer of electrons. Covalent involves sharing electrons Ionic involves attraction between charged ions; covalent involves attraction between neutral atoms Ionic has 1 type of bond. Covalent has 3 types of bonds Ionic has very strong attractions between ions because they are all bonded to each other; covalent has low attractions between molecules because molecules are not bonded to each other. Ionic- chemical formula is formula unit; covalentchemical formula is molecule
8.1 Molecules and Molecular Compounds
8.2 Resonance Ozone in the upper atmosphere blocks harmful ultraviolet radiation from the sun. At lower elevations, it contributes to smog.
Structure of Ozone Ozone is O 3 Draw the structure for ozone What kind of bonds do you see? Are those bonds the same length, based on what you have learned so far?
Resonance Scientists discovered all the bond lengths for ozone are the same! According to our structure, we expect single and double bonds to show up distinctly Single are longest, triple are shortest Bonds of ozone were BETWEEN the lengths of single and double bonds.
Resonance Resonance structures - two or more valid electron dot structures with the same number of electron pairs A double headed arrow is used to connect resonance structures and indicate that the actual bond is a hybrid http://www.mikeblaber.org/oldwine/chm1045/notes /Bonding/Resonan/Bond07.htm
Bond Dissociation Energy Bond Dissociation energy- total energy required to break the bond between two covalently bonded atoms Also represents the energy released when a bond forms- the opposite sign (-) is used Triple bonds are strongest, so they have a larger bond dissociation energy. Single bonds are weakest, so they have a smaller bond dissociation energy. Higher bond dissociation energy = less reactive Higher energy means it s harder to break apart
Covalent Bonding Practice Two Nitrogen (N) atoms exist as a diatomic molecule to create N 2.
Covalent Bonding Practice Two Carbon (C) atoms and six Hydrogen (H) atoms combine to form Ethane (C 2 H 6 )
Classwork! Reading Assignment: Sec 8.2 Written Assignment: pg. 238, #11-20
Do Now 4/9/15 Show the covalent bonding when one Silicon (Si) atom and two Oxygen (O) atoms are combined to form Silicon Dioxide (SiO 2 ).
Homework Check Time! pg. 238, #11, 12, 16, 17, 20 11. Atoms achieve a noble gas configuration by sharing electrons to form covalent bonds 12. In a coordinate covalent bond, the shared electron pair comes from one of the bonding atoms, and in other covalent bonds, each bonding atom provides an electron 16. Two dots are used to represent each covalent bond. 17. Two atoms are likely to form double or triple bonds when they can attain a noble gas structure by sharing two or three pairs of electrons 20.
Vocabulary Review Molecular Formula Covalent Bond Diatomic Molecule Single Bond Double Bond Triple Bond Chemical Formula Molecule Lewis Dot Structure Coordinate Covalent Bond Resonance Unshared pair
Independent Practice Complete the worksheet on bonding and naming.