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General Chemistry Mrs. Teates Newport High School

General Chemistry Mrs. Teates Newport High School. Unit 5 – Introduction to Chemical Bonding. Lesson 1 – Ions. Lesson Essential Questions: How are valence electrons and the octet rule important in bonding?

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General Chemistry Mrs. Teates Newport High School

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  1. General ChemistryMrs. TeatesNewport High School Unit 5 – Introduction to Chemical Bonding

  2. Lesson 1 – Ions • Lesson Essential Questions: • How are valence electrons and the octet rule important in bonding? Vocabulary: Ion, cation, anion, valence electron, electron dot structure, octet rule

  3. Review of Terminology • Valence electrons – electrons in highest occupied energy level • To find number of valence electrons, look at the group number. • Example: Neon is in group 8A, so it has 8 valence electrons. • All elements try to get 8 valence electrons by forming ions. • Example: Sodium is in Group 1A and has 1 valence electron. It will give that one valence electron up to have a full outer shell of 8.

  4. Octet Rule • Octet Rule: In forming compounds, atoms tend to achieve the electron configuration of a noble gas. • Metals tend to lose valence electrons. • Nonmetals either gain electrons or share electrons.

  5. Keeping Track of Electrons • Atoms in the same column... • Have the same outer electron configuration. • Have the same valence electrons. • The number of valence electrons are easily determined. It is the group number for a representative element • Group 2A: Be, Mg, Ca, etc. • have 2 valence electrons

  6. Electron Dot diagrams are… • A way of showing & keeping track of valence electrons. • How to write them? • Write the symbol - it represents the nucleus and inner (core) electrons • Put one dot for each valence electron (8 maximum) • They don’t pair up until they have to (Hund’s rule)

  7. Ne Lewis Structures • Electron Dot Diagrams • Pick the central atom • Count the valence electrons (they are what electron dot diagrams show) • Place electrons around the atom

  8. Ne Lewis Structures • Octet Rule • Most atoms form bonds in order to obtain 8 valence e- • Full energy level stability ~ Noble Gases

  9. The Electron Dot diagram for Nitrogen • Nitrogen has 5 valence electrons to show. • First we write the symbol. N • Then add 1 electron at a time to each side. • Now they are forced to pair up. • We have now written the electron dot diagram for Nitrogen.

  10. Formation of Cations • Metals lose electrons to attain a noble gas configuration. • They make positive ions (cations) • If we look at the electron configuration, it makes sense to lose electrons: • Na 1s22s22p63s1 1 valence electron • Na1+1s22s22p6 This is a noble gas configuration with 8 electrons in the outer level.

  11. Electron Dots For Cations • Metals will have few valence electrons (usually 3 or less); calcium has only 2 valence electrons Ca

  12. Electron Dots For Cations • Metals will have few valence electrons • Metals will lose the valence electrons Ca

  13. Electron Dots For Cations • Metals will have few valence electrons • Metals will lose the valence electrons • Forming positive ions Ca2+ This is named the “calcium ion”. NO DOTS are now shown for the cation.

  14. Electron Configurations: Anions • Nonmetals gain electrons to attain noble gas configuration. • They make negative ions (anions) • Halide ions are ions from chlorine or other halogens that gain electrons

  15. Electron Dots For Anions • Nonmetals will have many valence electrons (usually 5 or more) • They will gain electrons to fill outer shell. 3- P (This is called the “phosphide ion”, and should show dots)

  16. Stable Electron Configurations • All atoms react to try and achieve a noble gas configuration. • 8 valence electrons = already stable! • This is the octet rule (8 in the outer level is particularly stable). Ar

  17. Lesson 2 – Ionic Bonding • Lesson Essential Questions: • How do ionic bonds determine the properties of ionic compounds? Vocabulary: ionic compound, ionic bond, chemical formula

  18. Vocabulary • Chemical Bond • attractive force between atoms or ions that binds them together as a unit • bonds form in order to… • decrease potential energy (PE) • increase stability

  19. Vocabulary ION 2 or more atoms 1 atom Monatomic Ion Polyatomic Ion Na+ NO3-

  20. Vocabulary: • Ionic compound – composed of positive and negative ions that are combined so that the charges are equal.

  21. Ionic Bonding • Anions and cations are held together by opposite charges (+ and -) • Ionic compounds are called salts. • Simplest ratio of elements in an ionic compound is called the formula unit. • The bond is formed through the transfer of electrons (lose and gain) • Electrons are transferred to achieve noble gas configuration.

  22. Forming Ionic Compounds • Electron dot notation is used to note changes. • Form to create an atmosphere of stability

  23. Ionic Bonding Na Cl The metal (sodium) tends to lose its one electron from the outer level. The nonmetal (chlorine) needs to gain one more to fill its outer level, and will accept the one electron that sodium is going to lose.

  24. Ionic Bonding Na+ Cl - Note: Remember that NO DOTS are now shown for the cation!

  25. Do they Conduct? • Conducting electricity means allowing charges to move. • In a solid, the ions are locked in place. • When melted, the ions can move around. • Melted ionic compounds conduct. • NaCl: must get to about 800 ºC. • Dissolved in water, they also conduct (free to move in aqueous solutions)

  26. - Page 198 The ions are free to move when they are molten (or in aqueous solution), and thus they are able to conduct the electric current.

  27. Ionic Nomenclature Ionic Formulas • Write each ion, cation first. Don’t show charges in the final formula. • Overall charge must equal zero. • If charges cancel, just write symbols. • If not, use subscripts to balance charges. • Use parentheses to show more than one polyatomic ion.

  28. Ionic Nomenclature Ionic Names • Write the names of both ions, cation first. • Change ending of monatomic ions to -ide. • Polyatomic ions have special names.

  29. Ionic Nomenclature Common Ion Charges 1+ 0 2+ 3+ NA 3- 2- 1-

  30. Ionic Nomenclature • potassium chloride • magnesium nitrate • copper(II) chloride  KCl • K+ Cl- • Mg2+ NO3-  Mg(NO3)2  CuCl2 • Cu2+ Cl-

  31. Ionic Nomenclature • NaBr • Na2CO3 • FeCl3 • sodium bromide • sodium carbonate • iron(III) chloride

  32. Lesson 3 – Metallic Bonding • Lesson Essential Questions: • How can you model the valence electrons of metal atoms? • How does the order of metal atoms affect the structure of the metal? Vocabulary: Metallic bond, alloy

  33. Characteristics of Metallic Bonds • Metal ions held together by attraction to free floating electrons. (Sea of electrons) • Good conductors of electricity – Why?

  34. Characteristics of Metallic Bonds Cont. • Malleable • Ductile • Bond strength – The stronger the bond, the more energy it takes to break it.

  35. Alloys • A mixture of two or more substances, one of which must be a metal. • Common alloys include steel, 14K gold, 18K gold, cast iron, sterling silver, and bronze. • Within different alloys, there can be different types of mixtures – ex. Steel • Where do we find alloys?

  36. Lesson 4 – Covalent Bonding • Lesson Essential Questions: • How are molecular compounds different from ionic compounds? Vocabulary: Covalent bond, molecule, diatomic molecule, molecular compound, molecular formula

  37. Types of Bonds COVALENT IONIC e- are transferred from metal to nonmetal e- are shared between two nonmetals Bond Formation Type of Structure true molecules crystal lattice Physical State liquid or gas solid Melting Point low high Solubility in Water yes usually not yes (solution or liquid) Electrical Conductivity no Other Properties odorous

  38. Types of Bonds METALLIC e- are delocalized among metal atoms Bond Formation Type of Structure “electron sea” Physical State solid Melting Point very high Solubility in Water no yes (any form) Electrical Conductivity malleable, ductile, lustrous Other Properties

  39. Ionic vs. Covalent Ionic • High melting temperature • High boiling point • Hard • Brittle, because slight shift of crystal can cause it to break • Conduct electricity when dissolved in water Covalent • Low melting temperature • Low boiling point • Do not conduct electricity • Not as brittle

  40. Compare/Constrast • Use the 3 circle Venn diagram to compare and contrast ionic, metallic, and covalent bonding.

  41. Covalent bonds • Nonmetals hold on to their valence electrons. • They can’t give away electrons to bond. • But still want noble gas configuration. • Get it by sharing valence electrons with each other = covalent bonding • By sharing, both atoms get to count the electrons toward a noble gas configuration.

  42. F Covalent bonding • Fluorine has seven valence electrons (but would like to have 8)

  43. F F Covalent bonding • Fluorine has seven valence electrons • A second atom also has seven

  44. F F Covalent bonding • Fluorine has seven valence electrons • A second atom also has seven • By sharing electrons…

  45. F F Covalent bonding • Fluorine has seven valence electrons • A second atom also has seven • By sharing electrons… • Both end with full orbitals that have 8 valence electrons.

  46. Molecular Compounds • Covalent compounds are called molecular compounds • Molecular compounds are not as strong a bond as ionic. • The formula for water is written as H2O • The subscript “2” behind hydrogen means there are 2 atoms of hydrogen; if there is only one atom, the subscript 1 is omitted • Molecular formulas do not tell any information about the structure (the arrangement of the various atoms).

  47. A Single Covalent Bond is... • A sharing of two valence electrons. • Only nonmetals and hydrogen. • Different from an ionic bond because they actually form molecules.

  48. H O Water • Each hydrogen has 1 valence electron - Each hydrogen wants 1 more • The oxygen has 6 valence electrons - The oxygen wants 2 more • They share to make each other complete

  49. O Water • Put the pieces together • The first hydrogen is happy • The oxygen still needs one more H

  50. O Water • So, a second hydrogen attaches • Every atom has full energy levels Note the two “unshared” pairs of electrons H H

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