B O N D I N G

1. BONDING

2. What is a chemical bond? • Why do elements bond? • To become stable. Bonds form between atoms in combination are more stable (have lower energy state) than if the atoms remain isolated. • What is bonding? • the interaction of atoms of different elements to form a compound • Elements in compounds are held together by forces of attraction called BONDS. • Each bond has TWO electrons

3. Types of bonding Intramolecular – within the molecule • Ionic • Covalent • Polar Covalent • Non-Polar Covalent • Co-ordinate or dative covalent • Metallic Intermolecular – between molecules • Hydrogen Bonding • London Dispersion forces (LDF) • Dipole- dipole • http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/bom1s2_11.swf Van der waals forces

4. The octet Rule • Atoms tend to gain or lose or share electrons until they have eight valence electrons, except H and He that must have two (2) • A simple dot diagram that shows the valence electrons • Na . Lewis Diagram

5. Ionic bonding • When two or more ions are held next to each other by electrical attraction. • One of the ions has a positive charge (called a "cation") and the other has a negative charge ("anion"). • Cations are usually metal atoms and anions are either nonmetals or polyatomic ions (ions with more than two atom). • Electrons are transferred from the metal to the non-metal • Example – Salt – Sodium Chloride, NaCl

6. Properties of Ionic compounds • form crystals • have high melting and boiling points • very hard and very brittle • conduct electricity when they dissolve in water or molten but not in the solid state • http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/atomic/ionicact.shtml

8. Learning Check • What does an ionic bond involve? • Sharing electrons between atoms. • Moving electrons between atoms. • Forming free electrons. • 2. Where do electrons lost by metal atoms during the formation of ions come from? • a. The highest occupied energy level. • b. The lowest occupied energy level. • c. The inner shell. • 3. Which of the statements below is correct? • a. Metal atoms form negative ions and non-metal atoms form positive ions.b. Metal atoms form positive ions and non-metal atoms form negative ions.c. Metal ions form positive atoms and non-metal ions form negative atoms.

9. Learning check continued • 4. An element forms ions with a 2+ charge. Which group is the element mostly likely to be in? • a. Group 2b. Group 16c. Group 0 • 5. What is an ionic bond? • A force of attraction between positive ions. • A force of attraction between negative ions. • A force of attraction between oppositely charged ions.

10. Covalent Bonding • Sharing of electrons with each atom contributing electrons • Formed when two nonmetals bond to each other. • Sharing of one pair – single bond e.g.H2 • Sharing of two pairs of electrons - double bond e.g. O2 • Sharing of three pairs of electrons – triple bond e.g.N2

11. Properties of Covalent compound • have much lower melting and boiling points than ionic compounds • soft and squishy (compared to ionic compounds, anyway) • more flammable than ionic compounds • don't conduct electricity in water. • Covalent compounds aren't usually very soluble in water. • http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/atomic/covalentbond.shtml

12. Covalent bonding learning check 1. What does a covalent bond involve? a. sharing electrons between atoms b. moving electrons between atoms c. forming free electrons 2. Where do the electrons in a covalent bond come from? • the highest occupied energy level • the lowest occupied energy level • the inner shell 3. Nitrogen is in group 15. How many covalent bonds can it form? • 8 b. 5 c. 3 4. The formula of sulfur dioxide is SO2. If an oxygen atom forms two covalent bonds, how many covalent bonds does sulfur form in sulfur dioxide? a. two bonds b. three bonds c. four bonds

13. Examples of Ionic and Covalent bonding • What type of bonding is present in the following? Draw Lewis diagrams to illustrate. • CaCl2 • H2O • NH3 • AlCl3 • Ca3N2 • CO2

14. Use Electronegativity values to determine type of Bond • The difference in Electronegativity values determine the type of bond. (pp. 632) • If the difference is greater than 1.7 --- IONIC BOND • If the difference falls between 0 and 0.7 --- COVALENT (non-polar) • If the difference falls between 0.7 – 1.7 --- COVALENT (polar) • Example:

15. Polar vs. Non-Polar Bonds • Polar Bond: unequal sharing of electrons.One atom in the molecule draws electrons closer to itself. Example: HF has a polar bond because Fluorine atom is more electronegative and so it draws electrons CLOSER to itself, giving the bond polarity • Non-polar bond: PERFECT SHARING OF ELECTRONS • Page 84 – Understanding concepts 1, 2, 3, 4

16. Illustration

17. Polar Molecules • If a molecule contains polar covalent bonds, the entire molecule may have a positive end and a negative end, in which case it would be classified as a polar molecule. • Not all molecules containing polar covalent bonds are polar molecules, • Carbon tetrachloride, CCl4(l), and HCl(g) • Molecules with non polar bonds are all non polar molecules

18. HOMEWORK • Page 71 Text, Questions 3, 5a,c,e,f,i • Page 73 Text, Questions 9a,b, 10a,c,d, 13 a - g • Read Section 2.3 (p.75 – 77) and make notes