1. Molecular Geometry Ms. Murphy Chemistry Newington High School

2. The Octet Rule Atoms want to have a completely filled s and p sublevel 8 valence electrons Two ways to achieve Ionic Compounds Give or take electrons to acquire a complete shell Covalent Compounds Share electrons to acquire a complete shell

3. Exceptions Covalent compounds may have atoms that have less than 8 when in a bond Some central atoms may have more than 8 when in a bond The rule: The maximum number a atom can have in its valence shell is twice the number of valence electrons it brings into the covalent compound

4. Incomplete Octets Elements in groups 1A-3A that have a high enough electronegativity to share electrons will have “incomplete octets” An “Incomplete Octet” means the atoms will have ______ than 8 valence electrons Examples: Hydrogen: will have ____ valence electrons Beryllium: will have _____ valence electrons Boron: will have _____ valence electrons less

5. Expanded Octets Some elements can have _____ than 8 valence electrons when in covalent compounds. These elements can also create complete octets. Lewis Dot Diagrams P P

6. When Will An Expanded Octet Occur? To create symmetry Electrons remain after outside atoms receive 8

7. Electrons Electrons occur in pairs Single bond = 2 electrons Double bond = 4 electrons Triple bond = 6 electrons Nonbonding Pair= 2 electrons

8. Drawing Lewis Diagrams First step is to tally the total valence electrons CO 3 2- COCO 1313 xxxx 4646 = 4 = 18 22 24

9. Drawing Lewis Diagrams The second step is to determine the central atom To create symmetry The element with the lowest electronegativity (also the element with the lowest number of valence electrons) CO 3 2- 4 valence e- 6 valence e- ICl 3

10. Drawing Lewis Diagrams The third step is to connect all other atoms to the central atom with a single bond A single bond is drawn as a line. Each line serves the represent ______ electrons. All atoms can only be connected to the central is there is only one central atom Multi-central atoms usually contain multiple carbons 2 C OO O

11. Drawing Lewis Diagrams Determine how many electrons remain Subtract 2 electrons (from the total valence electrons tallied earlier) for each bond drawn 24 - (3 bonds x 2 e-) = 24 - 6 = 18 e- remaining

12. Drawing Lewis Diagrams Place the remaining electrons in pairs around the outside (terminal) atoms first to give each of the outside a total of 8 electrons This usually means placing 3 pairs around each terminal atom (6 electrons + 1 bond = 8 total) Pairs of dots that represent pairs of electrons are called “nonbonding pairs”

13. Drawing Lewis Diagrams Subtract the number of electrons used from the tally Place the remaining electrons (if any) on the central atom Central atoms can take more than 8

14. Drawing Lewis Diagrams If the central atoms has less than 8 and the central element is in groups 4A-8A.. Double and triple bonds can be added to satisfy the Octet Rule Each time a line is drawn as a bond, a nonbonding pair must me erased.

15. Practice

16. Tips & Tricks To predict the number of bonds, the number of valence electrons can be used. The total number of lines (individual bonds) will be the same as 8- the number of valence electrons Example: Oxygen 6 valence electrons Should have a total of 2 lines 2 single bonds 1 double bond

17. Tips & Tricks co. For elements in groups 4A, which each have _____ valence electrons, and therefore, need _____ The potential combinations are ______ single bonds ______ single bond(s) and _____ double bond ______ double bonds ______ single bond and ______ triple bond For elements in group 5A, which each have ______ valence electrons, and therefore, need _____ ______ single bonds ______ single bond(s) and _____ double bond ______ double bonds only ______ single bond and ______ triple bond 4 4 4 2 2 1 1 1 5 3 3 1 1 0 0 1

18. Tips & Tricks co. For elements in group 6A, which each have ______ valence electrons, and therefore, need _____ ______ single bonds ______ single bond(s) and _____ double bond ______ double bonds only ______ single bond and ______ triple bond For elements in group 7A, which each have ______ valence electrons, and therefore, need _____ ______ single bonds ______ single bond(s) and _____ double bond ______ double bonds only ______ single bond and ______ triple bond 6 2 00 2 0 1 1 1 1 7 0 0 0 0 0

19. VSEPR Theory Valence Shell Electron Pair Repulsion The valence shell electron pairs repel each other The outermost electrons, which occur in pairs, push as far away from each other as possible

20. Molecular Shapes To understand how molecules function and react, we must understand their shape. VSEPR Theory explains the reasoning behind their shapes Geometry helps give us specific shape names and helps us determine the angles between pairs of electrons. This is called “Molecular Geometery”

21. Determining Molecular Geometry Count the number of domains around the central atom

22. Determining Molecular Geometry How many atoms are connected to the central atom? “Bonding sites” or “Bonding Domains” How many nonbonding pairs are on the central atom? Use the reference packet

23. Determining Bond angles The areas around the central atom strive to be as far away from each other as possible. The bonding pairs are all _______________ in charge and ____________ each other

24. Determining Bond Angles

25. Multi-central Molecules Multi-central molecules are most often organic compounds (carbon-based molecules) For many multi-central molecules, the carbons can be connected together in a chain.

26. Structural Formulas Structural Formulas give insight into where specific elements occur in the compound. For example: C 4 H 10 Often written as CH 3 CH 2 CH 2 CH 3 CC C C H H H H H HH H H H

27. Element Order The order in which elements should be listed is C, H, O, N, P For example, if carbon was directly bonded to and Oxygen and a Hydrogen, It would be listed in the structural formula as CHO. If the order is different, it is because the (out of order) elements are NOT directly connected to Carbon C H H C H H O Written: CH 3 CHO C C H H H H H O H Written: CH 3 CH 2 OH