1. CHAPTER 2, SECTION 2.2 MOLECULAR COMPOUNDS

2. MOLECULAR ELEMENT & MOLECULAR COMPOUND Diatomic: made up of two atoms. Molecular element: consists of molecules made up of two or more atoms of the SAME element. Ex: Nitrogen (N 2 ), Oxygen (O 2 ), Ozone (O 3 ). Molecular compound: consists of molecules made up of at least two different elements. Generally consist of only non-metallic elements. Ex: H 2 O, CO 2

3. HOW ARE COMPOUNDS CONSTRUCTED? ATOMIC LEVEL Understanding the shape and structure of molecule is critical as we explore its properties. Ex: Carvone (C 10 H 14 O) – two different structures. Are mirror images Found in different plants. Different physical properties – especially smell!

4. How can two molecules composed of the same atoms have such different smells? The two structures interact with different receptors in nose. That is why presenting the STRUCTURES of molecular compounds are important. They tell us a lot about their properties.

5. PROPERTIES OF MOLECULAR SUBSTANCES 1.Exist as gases, liquids, and solids at ambient (normal) temperature. 2.Can have various textures (malleable wax, brittle sugar). 3.Many do not dissolve readily in water. 4.Molecular elements: have low boiling points (so usually are gases). Ex: Oxygen 5.Molecular compounds: have relatively low melting and boiling points.

6. COVALENT BONDS Physical properties of molecular substances depend on …………………… 1) Molecular elements 2) Molecular compounds Atoms want to fulfill the Octet rule. Why?

7. 1) MOLECULAR ELEMENTS BONDING Example: H 2 (Hydrogen). How many protons and electrons are in a hydrogen atom? What is the Lewis dot diagram of hydrogen atom?

8. When two hydrogen atoms collide, the proton of each hydrogen atom attracts the electron of the other atom. Analogy: tug-of-war competition for electrons Neither atom completely wins.

9. SO WHAT HAPPENS? ELECTRON SHARING The 2 atoms share their electrons, and form a hydrogen molecule (H 2 ). Covalent bond: attractive force or bond that results from the sharing of an electron pair by two atoms. Result: each hydrogen atom achieves a full valence shell (and so giving a stable electron arrangement). Which noble gas is the nearest to H 2 ?

10. EXERCISE QUESTION How does diatomic element Chlorine form molecules? Which noble gas is it nearest to in terms of electron arrangement?

11. Bonding electron: an electron, in the valence shell of an atom, that is available to form a covalent bond with another atom. Ex: unbonded hydrogen has 1 unpaired valence electron. Unbonded chlorine also has 1 unpaired valence electron. Bonding capacity : number of covalent bonds an atom can form. The number of bonding electrons in an atom affects the number of bonds it can form.

12. Group114151617 Number of valence electrons Bonding Capacity Lewis Symbols Bonding Capacities & Lew Symbols of atoms forming covalent bonds (Table 2, p. 62)

13. Lewis structure representing covalent bonding based on Lewis symbols: 1) shared electron pairs are shown as lines/dash showing bond. Single dash (single covalent bond). Double dash (double covalent bond, meaning when two atoms share two pairs of electrons). Triple dash (triple covalent bond, meaning when two atoms share three electron pairs). 2) Unshared electrons are shown as dots ( called lone pairs ). Lone pair: pair of electrons that is NOT involved in covalent bonding.

14. EXAMPLE 1 Hydrogen (H 2 ) What kind of bond is formed? why?

15. EXAMPLE 2 Oxygen (O 2 ) + What kind of bond is formed? why?

16. EXAMPLE 3 Nitrogen (N 2 ) What kind of bond is formed? why? +

17. 2) MOLECULAR COMPOUNDS BONDING So we far we considered diatomic molecules of the same element (molecular element). Ex: H 2, Cl 2 Molecular compounds have different types of atoms and with variety of numbers of atoms, so there are some ways to draw Lewis structures.

18. 2) MOLECULAR COMPOUNDS BONDING Comparing with molecular elements: Form in the same way. The atoms though are not from the same elements. https://www.youtube.com/watch?v=p-X1lB_s2gc Ex: HCl (Hydrogen Chloride) +

19. THREE-ATOM MOLECULES Atoms in these molecules arrange themselves so they each have a complete valence shell. Each has two bonds. Water (H 2 0) Carbon Dioxide (CO 2 )

20. WHAT WE LEARNED How to represent a molecular substance using Lewis structure. Diagram shows BOTH : 1. Lone pairs of electrons surrounding each atom. 2. Covalent bonds (single, double, triple) between atoms.

21. SIMPLIFYING THINGS Lewis Structure: shows both covalent bonds and lone pairs. Structural formula: represents molecular diagrams by including ONLY the covalent bonds (without showing the lone pairs).

22. FURTHER SIMPLIFY Biological molecules are often huge (ex: sugar, lactic acid, wax). Large molecular compounds are usually liquids or solids.

23. HOW TO DRAW LEWIS STRUCTURES Consider bonding capacities. Central atom – tends to be one with highest bonding capacity (not always).

24. 1) LEWIS STRUCTURE FOR METHANAL (CH 2 O) Look at Sheet (Part 1)

25. STRUCTURAL FORMULA FOR METHANAL (CH 2 O) Just remove the lone pairs from the Lewis structure diagram

26. PRACTICE F 2 NO 2 HCN

27. 2) LEWIS STRUCTURE FOR POLYATOMIC ION CLO 3 - Look at Sheet (Part 2)

28. STRUCTURAL FORMULA FOR POLYATOMIC ION CLO 3 - Just remove the lone pairs from the Lewis structure diagram

29. MOLECULAR KIT INVESTIGATION

30. NOTES Benzene’s mysterious structure – ring shaped. Exceptions to the Octet rule: example is Nitrogen dioxide (NO 2 ). It is toxic. Physical properties of molecular compounds depend on the forces of attraction between individual molecules, and these forces depend on the covalent bsonds between atoms and how they are arranged.

31. PropertyIonic CompoundMolecular Compound State at ambient temperature Crystalline solidSolid, liquid, or gas Physical propertiesHard, brittleSolids can be soft, waxy, flexible, or crystalline. Relative melting point/boiling point HighLow Electrical conductivity when dissolved in water GoodPoo (for most molecular compounds) Electrical conductivity in the liquid state Good poor ExamplesSodium chloride, calcium carbonate Water, carbon dioxide, methane, sucrose.

32. Homework: Read section 2.2 Questions 1, 2 (a, d, i, m), 4 (c,d), 5, 6, 7, 8 (brief research).