1 What is electronegativity? What types of bonds did you read about last night?

2 CHEMICAL BONDING Cocaine

3 Chemical Bonding Problems and questions — How is a molecule or polyatomic ion held together? Why do water molecules stick together? Why are atoms distributed at strange angles? Why are molecules not flat? Can we predict the structure? How is structure related to chemical and physical properties?

4 Atoms want to be stable…. Stability occurs when they have a full outer electron shell They want to be like the noble gasses This means having eight electrons in their outer shell (Octet rule) The exception is Hydrogen (The duet rule) They share or give or take electrons to achieve this stability

5 Drawing Lewis Dot Structures Determine the amount of Valence electrons by referring to the periodic table Draw the element Place one dot one each side of the element to represent an electron Pair them up as needed Ex: P 5 electrons Draw I! When you are drawing a bonding molecule you use a line to represent the bond

6 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!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 1s 2 2s 2 2p 1 ; so the outer energy level is 2, and there are 2+1 = 3 electrons in level 2. These are the valence electrons!B is 1s 2 2s 2 2p 1 ; 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] 4s 2 3d 10 4p 5 How many valence electrons are present?Br is [Ar] 4s 2 3d 10 4p 5 How many valence electrons are present?

7 Bond and Lone Pairs Valence electrons are distributed as shared or BOND PAIRS and unshared or LONE PAIRS.Valence electrons are distributed as shared or BOND PAIRS and unshared or LONE PAIRS. HCl lone pair (LP) shared or bond pair This is called a LEWIS structure.

8 Steps for Building a Dot Structure Ammonia, NH 3 1.Decide on the central atom; Never H! 2.Therefore, N is central on this one 2. Add up the number of valence electrons that can be used. H = 1 and N = 5 H = 1 and N = 5 Total = (3 x 1) + 5 Total = (3 x 1) + 5 = 8 electrons / 4 pairs = 8 electrons / 4 pairs

9 3.Form a single bond between the central atom and each surrounding atom (each bond takes 2 electrons!) H H H N Building a Dot Structure H H H N 4.Remaining electrons form LONE PAIRS to complete the octet as needed (or duet in the case of H). 3 BOND PAIRS and 1 LONE PAIR. Note that N has a share in 4 pairs (8 electrons), while H shares 1 pair.

10 We are going to discover how different molecules bond together You will create the molecule listed Draw Picture of what you see Draw the Lewis dot structure for each Note: Do not make any random molecules. Make sure that you put all pieces back! Make sure you don’t press the bonds into the atoms Note: Carbon is black, Chlorine is green, Oxygen is red, Nitrogen is blue Hydrogen is yellow Wood dowels are single bonds, springs are double bonds When you are finished write a pargraph about what you discovered about the structure of molecules in relation to valence electrons, type of bond(double single triple) and electronegativity of elements

11 Note: Carbon is black, Chlorine is green, Oxygen is red, Hydrogen is Yellow, Nitrogen is Blue!! Draw Picture of what you see Draw the Lewis dot structure for each When you are finished write a paragraph about what you discovered about the structure of molecules in relation to valence electrons, type of bond(,double, single triple) and electro negativity of elements

12 What did you discover about Molecule Shape? Do you like Robin Eggs? What factors do you believe influence molecule shape? Why do robin eggs turn your lips blue?

13 Ionic Bonds Positive cations and the negative anions are attracted to one another (remember the Paula Abdul Principle of Chemistry: Opposites Attract!) between metals and nonmetals (opposite ends of the periodic table).

14 Covalent Lewis structures…. A shared electron is noted by a line….A shared electron is noted by a line…. HCl lone pair (LP) shared or bond pair

15 Lewis dot structures for Ionic Bonds.. Look differently than covalent bonds Use Brackets and show electron gain or loss Ex NaCl Try NaO

16 How do you create Lewis Dot Structures for –Covalent Bonds –Ionic Bonds –How do you know what type of Lewis Dot structure to create –Create a lewis dot structure for – KBr –C 6 H 12

17 Why does water do the things that it does? How many pennies? What do you observe between water and hexane?

18 The type of bond can usually be calculated by finding the difference in electronegativity of the two atoms that are going together.

19 Electronegativity Difference If the difference in electronegativities is between: – 1.7 to 4.0: Ionic – Covalent Bonds – 0.1 to 1.7: Polar Covalent – 0.0: Non-Polar Covalent Example: NaCl Na = 0.8, Cl = 3.0 Difference is 2.2, so this is an ionic bond!

20 Bond Polarity 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 (-  ) and H has slight positive charge (+  )

21 This is why you can dissolve NaCl in water and not hexane… One is polar thus they will be attacted to each other The other is non-polar, thus they will repel each other. Bond Polarity

22 Bond Polarity “Like Dissolves Like”“Like Dissolves Like” –Polar dissolves Polar –Nonpolar dissolves Nonpolar

23 What holds molecules together? What holds several molecules together? Intramolecular Forces (Those bonds that hold molecules or compounds together internally) vs. Intermolecular Forces (Those forces that exist BETWEEN molecules).

24 Intermolecular Forces and Bonding in Solids

25 “Measure” of intermolecular force boiling point melting point  H vap  H fus  H sub Intermolecular Forces Intermolecular forces are forces between molecules (Intermural sports are between different schools). Intramolecular forces hold atoms together in a molecule. Intramural sports are competition at a specific school. Intermolecular vs Intramolecular 41 kJ to vaporize 1 mole of water (inter) 930 kJ to break all O-H bonds in 1 mole of water (intra) Generally, intermolecular forces are much weaker than intramolecular forces.

26 S O O What type(s) of intermolecular forces exist between each of the following molecules? HF HF is a polar molecule: dipole-dipole forces. Hydrogen is bounded to F. Hydrogen bonds exist. There are also dispersion forces between HBr molecules. CH 4 CH 4 is nonpolar: dispersion forces. SO 2 SO 2 is a polar molecule: dipole-dipole forces. There are also dispersion forces between SO 2 molecules. Intermolecular Forces