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Chemical Bonding

Chemical Bonding. Chemical Bonding. Molecules Atoms joined together that act as one unit Molecules come in three sizes: Small Made of two atoms only Medium Made of 3-100,000 atoms Large Made of over 100,000 atoms Called macromolecules

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Chemical Bonding

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  1. Chemical Bonding

  2. Chemical Bonding • Molecules • Atoms joined together that act as one unit • Molecules come in three sizes: • Small Made of two atoms only • Medium Made of 3-100,000 atoms • Large Made of over 100,000 atoms Called macromolecules Even large molecules cannot be seen with the naked eye!

  3. Chemical Bonding • Small Molecules • Examples: • NaCl • KI • CO • LiF

  4. Chemical Bonding • Medium molecules • Sugar • Water • Octane • Alcohol

  5. Chemical Bonding • Large molecules (macromolecules) • Plastics • Proteins • Medicine • Viruses • DNA

  6. Chemical Bonding • Molecule formation • Molecules form when atoms gain, share, or lose electrons from their valence shell (ring farthest away from nucleus) so their structure resembles a Noble Gas which is very stable • Octet Rule- all atoms want to have 8 valence electrons • Atoms with 1-3 valence electrons will lose them • Atoms with 4 valence electrons will share them • Atoms with 5-7 valence electrons will gain more

  7. Chemical Bonding When atoms lose or gain electrons, they form ions, or charged particles. Cations- positive ions formed from metals Have more protons than electrons Anions- negative ions formed from nonmetals Have more electrons than protons

  8. Trends in Ion Formation • When metals lose electrons, they become positively charged. • Group 1 loses 1 e  +1 Group 13 loses 3 e  +3 • Group 2 loses 2 e  +2 • When nonmetals gain electrons, they become negatively charged. • Group 17 gains 1 e  -1 Group 15 gains 3 e  -3 • Group 16 gains 2 e  -2

  9. Chemical Bonding When atoms rearrange their electrons, they can form forces of attraction with other atoms. These forces of attraction are called chemical bonds.

  10. Chemical Bonding • Chemical Bonds • Ionic Bonds • Formed from positive and negative ions joining together • Involves a metal with a nonmetal

  11. Ionic Bonds • Ionic bonds are formed in 2 steps: • 1. Metal transfers an electron to a nonmetal, forming ions • 2. Oppositely-charged ions attract, forming a bond

  12. Chemical Bonding • Covalent bonds • Sharing electrons to form a bond • Usually occurs between nonmetals or metalloids • Can also occur between two atoms of the same element

  13. Bell ringer • A magnet has two poles. What does that mean?

  14. Chemical Bonding • Polarity • How electrons are shared in a chemical bond • Covalent bonds can be separated by polarity into: • Polar bonds- unequal sharing of electrons • Nonpolar bonds- equal sharing

  15. Chemical Bonding • Nonpolar bonds share the electrons equal amounts of the time • In polar bonds, one element is stronger than the other and controls the electrons for more of the time. This creates a dipole.

  16. Chemical Bonding • Polarity of a bond can be represented in three ways: • Bubble method • Partial charge method • Polarity arrow method • Arrow always faces element with larger EN

  17. Polarity • Polarity is determined by the EN difference between the 2 elements in the bond. • 0.0-0.3 nonpolar (share equally) • 0.4-1.6 polar (shared but not equally) • 1.7+ ionic (completely transferred)

  18. Lewis Structures • 1. Count the # of valence electrons • 2. Draw a simple structure to represent the molecule • 3. Place 8 e around the central atom • 4. Fill the outside atoms • 5. Move lone pairs to make multiple bonds • 1. CCl4 C- 4 Cl- 7 x 4 • 2. Cl Cl C Cl Cl • 3. Cl Cl C Cl Cl • 4.

  19. Chemical Bonding Molecular Geometry Shape of a molecule in 3D space Bonded pair Lone pair C : Br Br :

  20. Chemical Bonding Linear Tetrahedral Trigonalbipyramidal Bent Trigonal pyramidal Octahedral Trigonal planar

  21. Bell ringer • What makes up aluminum foil?

  22. Metallic Bonding • Between atoms of the same metal • Atoms share the electrons around, known as the “sea of electrons” • Responsible for many properties of metals- malleability, conductivity

  23. Comparing Bonds Do not usually conduct High Longer due to space between ions Liquid, gas, soft solid Conduct when dissolved in water Crystalline solid Low High High Conduct very well Shorter due to overlap Low Solid High Long and flexible

  24. Bell ringer • Is HCl polar or nonpolar?

  25. Intermolecular Forces • Forces that occur between molecules- require more than one molecule to occur • There are four types: • 1. Dipole-dipole forces • 2. Induced dipole forces • 3. Dispersion forces • 4. Hydrogen bonding

  26. To recap… • Dipole-dipole: 2 polar molecules have opposite sides facing each other. Opposites attract. • Induced dipole forces: 1 polar molecule causes a neighboring nonpolar molecule to become polar by shifting electrons. Opposite sides are facing each other. Opposites attract. • Dispersion forces: Temporary dipole formed by random movement of electrons. Induces dipoles. Opposites attract. • Hydrogen bonding: Positive hydrogen from 1 molecule is attracted to negative end of neighboring molecule. VERY STRONG!!

  27. Chemical Bonding • Chemical Formulas • Represent a compound without having to write the name • Show the number of atoms in the compound • There are two types: • Ionic- metals with nonmetals • Covalent- nonmetals with nonmetals

  28. Chemical Bonding • Ionic Formulas • Naming Ionic Compounds 1. Write the name of the first element 2. Write the name of the second element but add –ide to the end of the name. Examples: MgS magnesium sulfide ZnCl2 zinc chloride

  29. Chemical Bonding • Ionic Formulas • Charge numbers • Each group is assigned a charge number based on how many electrons are gained or lost by the elements in that group. Group 1 1 Group 14 4 Group 2 2 Group 15 3 Group 13 3 Group 16 2 Group 17 1

  30. Chemical Bonding • Ionic Formulas • Charge numbers • Tansition elements have individual charge numbers Cr 2 Cu 1 Sn 2 Mn 2 Zn 2 Au 3 Fe 3 Zr 2 Hg 1 Co 2 Ag 1 Pb 2 Ni 2 Cd 2 Bi 3 U 6

  31. Chemical Bonding • Writing Ionic Formulas 1. Write the symbols for the elements in the compound. 2. Look up the charges for each element and write them as superscripts behind the elements. 3. Cross the numbers in an “X” until they are behind the other element.

  32. Chemical Bonding • Examples: Aluminum fluoride Al F Al3 F1 AlF3 Calcium oxide Ca O Ca2 O2 CaO

  33. Chemical Bonding • Covalent Formulas • Naming Covalent Compounds 1. Write the name of the first element. 2. Write the name of the second element but add –ide to the end of the name. 3. Find the prefix that matches the subscript in the formula. 4. Write the prefix in front of the element’s name.

  34. Chemical Bonding • Examples: NO3 Nitrogen oxide 3 = tri Nitrogen trioxide As2S3 Arsenic sulfide 2 = di 3 = tri Diarsenic trisulfide

  35. Chemical Bonding • Writing Covalent Formulas 1. Write the symbols for the elements. 2. Find the number that matches the prefix in the name. 3. Write the number as a subscript behind the appropriate element.

  36. Chemical Bonding • Examples: Carbon monosulfide C S mono = 1 CS Dinitrogen pentachloride N Cl Di = 2 penta = 5 N2Cl5

  37. Chemical Bonding • Polyatomic Ions • Groups of elements that act as one element in a compound • Polyatomic ions are given special names

  38. Chemical Bonding • Naming compounds with polyatomic ions 1. Write the name of the first element. 2. Find the polyatomic ion on your sheet. Write its name as it appears on the sheet. • Examples: Na3PO4 Sodium phosphate KMnO4 Potassium permanganate

  39. Chemical Bonding • Writing Formulas with Polyatomic Ions 1. Write the symbols for the element and the polyatomic ion. 2. Find the charge number for the element and the polyatomic ion. Write them as superscripts. 3. Cross the charge numbers over.

  40. Chemical Bonding • Examples: Sodium hydroxide Na OH Na1 OH1 NaOH Boron nitrate B NO3 B3 NO31 B(NO3)3

  41. Molar Mass • Mass in 1 mole of a compound • Add all of the atomic masses to find the total with significant figures!! NaF Na- 22.98977 AlCl3 Al- 26.98154 + F – 18.998403+ 3 Cl- 3(35.453) 41.988173 133.34054 Rounded: 41. 98817 g/mol 133.341 g/mol Now… you do Ba(ClO3)2

  42. Molar Conversions 1 mole = 6.02 x 10 ^23 atoms The Mole A quantity that represents the number of atoms in 12 g of C-12 Avogadro’s number For a compound, it is 6.02 X 1023 molecules in one mole.

  43. Molar Conversions 0.25 mol WO3 = _____ g WO3 15.79 g MgS= _____ mol MgS 3 mol HCl= _____ molec. HCl 4.17 x 1025molec. CH4 = _____ g CH4 Q: If a mole of moles is digging a mole of holes, what do you see? A: A mole of molasses

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