Unit 6 Bonding and Intermolecular Attractions. SHS Chem

Transcription

1 Unit 6 Bonding and Intermolecular Attractions SHS Chem

2 Outcomes (KUD) Know! Definitions for all the vocab words found on the learning map. Correct usage of measuring devices All conversion factors related to a mole Charges for common monatomic and polyatomic ions. Prefixes for covalent naming. The difference between the types of bonding. The difference between intermolecular and intramolecular attractions. Trends in electronegativities. Understand! How type of element affects bonding. How and why ions combine to form ionic compounds. How and why atoms combine to form covalent compounds. Physical properties are dependent on the weak attractions between atoms and molecules. The relationship between our lab exercises, the concepts studied in the unit and life applications. How to name compounds in the IUPAC system. Do! Ionic and Metallic Bonding Ch 7, # s 40, 41 (and write the resulting formula), 46, 65 Covalent Bonding Ch 8, # s 44, 46, 54, 58, 70, 74 Chemical Names and Formulas Ch 9, # s 68, 70,

3 LEQ s Bonding How do the three basic types of bonding compare? Ionic Bonds and Ionic Compounds How are ionic compounds formed? What are the basic properties of ionic compounds? Molecular Compounds How are covalent compounds formed? VSEPR How does hybridization direct molecular shapes? Polar Bonds and Physical Properties How does the polarity of a molecule affect its physical properties?

4 Bonding How do the three basic types of bonding compare? Covalent Metallic ionic

5 Ionic Bonds and Ionic Compounds How are ionic compounds formed? Write the abbreviated electron configurations for O F Ne Na Mg How do they differ?

6 How an ionic bond forms Loss of electron(s) Mg [Ne]3s 2 Mg 2+ [He] 2s 2 2p 6 (an octet) Gain of electron(s) F [He]2s 2 2p 5 F 1 [He]2s 2 2p 6 Electrostatic Attraction (an octet) Mg 2+ F 1 (need two F 1 s) to form MgF 2 Electrons gained = electrons lost

7 Nomenclature MgF 2 is a binary ionic compound you name by naming the two ions Mg 2+ = magnesium + F 1 = fluoride The subscript does not affect the name for ionic compounds. Magnesium fluoride Create and name the ionic compound that is formed from aluminum and nitrogen.

8 Common Cations and Anions

9 Derive the following ionic compounds and name them or write the formula (level 1) Sr & Br Al & O K and N francium fluoride rubidium sulfide barium chloride

10 Multiple Charges and Polyatomics Treat the same way as other ions except Metallic ions with multiple charges have a roman numeral equal to their charge in the name Mn 2+ is called manganese(ii) while Mn 3+ is called manganese(iii) Polyatomic ions just go by their common name NO 3 1 is nitrate, NO 2 1 is nitrite Create and name the ionic compound that is formed from lead(iv) and phosphate. Go to the Chem I website and try the Unit 6 Ionic Compound Naming (Practice Quiz).

11 Another type of ion (Polyatomic)

12 Derive the following ionic compounds and name them or write the formula (level 2) Sn 2+ & Br Pb 4+ & O Ca and PO 4 3 iron(iii) fluoride copper(ii) nitrate cobalt(iii) sulfate

13 Ionic Bonds and Ionic Compounds What are the basic properties of ionic compounds? known as salts hard and brittle conduct when molten or dissolved very high melting and boiling points solids at room temperature most are soluble in polar solvents such as water so they are considered electrolytes

14 Experiment: Electrolytes vs. Nonelectrolytes

15 Molecular Compounds How are covalent compounds formed? molecular orbital theory (MO theory) accurately describes the shapes of covalent molecules by explaining how and why atoms bond. atomic orbitals s,p,d,f overlab to form molecular orbitals electrons are not assigned to individual bonds between atoms, but are treated as moving under the influence of the nuclei in the whole molecule electrons are shared to form stable configurations, for the majority of atoms as an octet (8 electrons)

16 Sigma(σ), pi(π) and delta(δ) bonds

17 Formation of MO in ethene

18 Creating Lewis dot structures Add up the total number of valence electrons(dots) and divide them into pairs. Place the atoms in the appropriate locations, central element is one written first in the formula (except H compounds) Place the dots such that each atom has eight around it (H will want only 2) Atoms can share 2, 4, or 6 electrons(dots). Tutorial: /folder_structure/bo/m2/s1/index.htm

19 Lewis Tutorial Questions (by slide number) Create a study guide by completing the following in your notes. 1. What do dots represent? 2. What are lone pairs? 3. Why do atoms lose, gain or share electrons? 4. In SCl 2 which atom goes in the center? 5. How many electrons does chlorine contribute to the molecular orbital in SCl 2? 6. In SCl 2 what type of bond is between S and each Cl? 7. After SCl 2 is formed, how many electrons are around each atom? 8. Create a graphic organizer that will help you draw Lewis structures. (hint: look at the top of the site page) 9. In COCl 2, which atom goes in the center? Why? 10. How many electrons does oxygen contribute to the molecular orbital in COCl 2? 11. What is the first step in placing electrons (dots) in COCl 2? 12. Where do you start placing lone (unshared) pairs? 13. How is it possible to give C 8 electrons without taking one from O? 14. Draw the structures for the three compounds on the site slide. 15. Answer the quiz questions in complete sentences.

20 Draw structures for H 2 O H 2 S NH 3 CH 4 CO 2 HCN NO 2

21 VSEPR How does hybridization direct molecular shapes? Hybridization is a description of the s, p, d and f orbitals that combine, overlap that arrange themselves as far apart from each other as possible to create the following shapes.

22 Finding Molecular Shapes VSEPR activity Create (Lewis) dot structures. Identify # of bonding and non bonding groups around the central atom. Treat single, double and triple bonds the same. Arrange the groups around the central atom as far from each other as possible. (Steric repulsion) Groups of non bonding electrons take up more space the atoms. Account for that in deciding shapes.

23 Polar Bonds and Physical Properties How does the polarity of a molecule affect its physical properties? It is somewhat inaccurate to describe bonds as being either ionic or covalent instead it is better to describe them as having a % ionic character. Linus Pauling defined the pull an atom has on an electron (electronegativity) As the difference increases so does polarity until

24 Electronegativities (Pauling units)

25 Polar Bonds and Molecules How does the polarity of a molecule affect its physical properties? Intramolecular Forces: Attractive forces inside a molecule (metallic, ionic or covalent) Intermolecular Forces: Attract molecules to each other London Dispersion Forces Dipole Interaction Hydrogen Bonding Responsible for : Boiling Pt Freezing Pt Viscosity Surface Tension Capillary Effect Density of ice lower than water

26 Intermolecular Forces (IMF) Dispersion Forces (London Forces) weakest intermolecular force (one hundredth one thousandth the strength of a covalent bond) momentary dipoles occurring due to uneven electron distributions in neighboring molecules as they approach one another the weak residual attraction of the nuclei in one molecule for the electrons in a neighboring molecule. (Important) The more electrons that are present in the molecule, the stronger the dispersion forces will be.

27 Intermolecular Forces (IMF) Dipole Interaction are stronger intermolecular forces than Dispersion forces occur between molecules that have permanent net dipoles (polar molecules), for example, dipole dipole interactions occur between SCl 2 molecules, PCl 3 molecules and CH 3 Cl molecules. The partial positive charge on one molecule is electrostatically attracted to the partial negative charge on a neighboring molecule.

28 Intermolecular Forces (IMF) Hydrogen Bonding Generally one sixth the strength of a single covalent bond. Occur between molecules that have a permanent net dipole resulting from hydrogen being covalently bonded to either fluorine, oxygen or nitrogen. For example, hydrogen bonds operate between water. Hydrogen atom is strongly attracted to the fluorine, oxygen or nitrogen atom, leaving a highly localized positive charge on the hydrogen atom and highly negative localized charge on the fluorine, oxygen or nitrogen atom.

29 Physical Properties How does intermolecular attractions affect Boiling Pt Freezing Pt Viscosity Surface Tension Capillary Effect Density of ice lower than water

30 Chemical Bonding (Ch 8 & 9) How are the energies of compounds described? (8.5,8) Intramolecular Forces

31 The Strength of Attractive Forces