1. Electrons & Bonding Chapters 7 and 8

2. Valence Electrons Electrons located in the outermost energy level (the last shell) Number of valence electrons = group number

3. We only show valence electrons because these are the electrons involved with bonding. The only exception to this rule is He, which has a full outer shell with only 2 valence electrons (remember that the first energy level only holds 2 electrons). Electron dot structures use dots to represent the valence electrons in an atom.

4. Why are noble gases unreactive in chemical reactions? – They have a full valence shell which makes them stable Other atoms want to be like the noble gases. They want to have 8 valence electrons. This is known as the Octet Rule, which states that atoms tend to achieve the same number of valence electrons as a noble gas (8). Metals tend to lose valence electrons, while nonmetals tend to gain or share valence electrons.

5. Lewis Dot Diagrams Use dots to represent the valence electrons Steps to drawing dot diagrams: – Write the chemical symbol – Determine the number of valence electrons – Draw out the dots in the following configuration Cl

7. Ions – atoms that carry a charge because electrons have been gained or lost Cations – positively charged ions Electrons lost Metals lose all of their valence electrons Anions – negatively charged ions Electrons gained Non-metals gain enough electrons to fill out their outer shell (8 electrons total)

8. Cation Formation Sodium AtomSodium Ion 11 p + 12 n 0 11 p + 12 n 2 e - 8 e - 1 e -

9. Anion Formation Fluorine Atom 9 p + 10 n 0 Fluoride Ion 9 p+ 10 n 0 2 e - 7 e - 8 e - 1 e -

10. Ionic Bonding Repeating 3-D patterns Very stable Electrically neutral High melting & boiling point Conduct electric current Metal + non-metal Cation + anion Forms a salt (NaCl, MgCl 2 ) Elements held together by electrostatic forces Crystalline solids

11. Ionic Bonding Cations ______ valence electrons. Anions ______ valence electrons. Show the movement of electrons using arrows. lose gain DIRECTIONS: DRAW DOT DIAGRAM MOVE ELECTRONS FROM METAL TO NON-METAL USING ARROWS MAKE SURE ALL DOTS ARE REMOVED FROM METAL MAKE SURE NON-METAL HAS 8 DOTS

12. Examples NaCl NaCl Na O Na 2 O Mg O MgO

13. Mg N N Mg 3 N 2

14. Covalent Bonding Single bond (1 pr. shared electrons) F Double bond (2 pr. shared electrons) O Triple bond (3 pr. shared electrons) N 2 non-metals Electrons are shared Lower melting points and boiling points Diatomic molecules: two molecules of the same element chemically combined (H 2,Cl 2, I 2, F 2, Br 2, O 2, N 2 )

15. Covalent Bonding Two ____________. Form bonds by ___________ electrons. Show how electrons are shared with circles. nonmetals sharing DIRECTIONS: DRAW DOT DIAGRAM SHOW HOW UNPAIRED (SINGLE) ELECTRONS ARE SHARED WITH CIRCLES. MAKE SURE EACH ATOM HAS EIGHT ELECTRONS TOTAL.

16. P Unshared electron pairs Cl PCl 3

17. C O O CO 2

18. C HH CH 4 H H

19. Bonding Theories VSEPR – valence shell electron pair repulsion theory – Electrons will shift so they are as far apart from each other as possible – Think of magnets (electrons have a negative charge, so they repel each other) – This repulsion of electrons causes the molecules to “bend” giving them different shapes

20. Polarity Polar Covalent – Covalent bond between atoms in which the electrons are shared unequally – The more electronegative element is slightly negative and the less electronegative element is slightly positive. HCl δ+ δ- – HCl H 2 O δ- δ- – δ+ O δ+H – O– OH

21. Polarity Con’t. Non-polar Covalent – Occurs when the atoms in the bond pull equally on each other – The bonding electrons are shared equally H – H Br – Br Cl ClC Cl Cl

22. Metallic Bonding Between 2 non-metals Results in alloys (metal mixtures) Solids at room temperature Valence electrons are free- floating and loosely attracted to the metal cations – “sea of electrons” Good conductors of electricity Ductile Maleable

23. Sea of Electrons