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Unit 4: Chemical Bonding

Unit 4: Chemical Bonding. -How Elements Get Together- 3 types of bonding. What is Chemical Bonding?. The joining of atoms to form new substances The properties of these “ substances ” are completely different from the properties of the original elements

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Unit 4: Chemical Bonding

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  1. Unit 4: Chemical Bonding -How Elements Get Together- 3 types of bonding

  2. What is Chemical Bonding? • The joining of atoms to form new substances • The properties of these “substances” are completely different from the properties of the original elements • An interaction that holds 2 atoms together is called a chemical bond

  3. Why revisit the Bohr Model? • Scientists and their theories are best explained with models • Remember: we use models to explain what we can not see or directly observe • Based on theories

  4. Do Atoms Bond Only through their Electrons? • Yes and where are the electrons? • The electrons are located around the nucleus in various energy levels • Remember: • The atomic number is the number of protons in an atom • the atomic number also represents the number of electrons in the atom.

  5. What are the energy levels of an atom? p.311

  6. What are the outer Electrons called?p.311 • Valence Electrons are the outer most orbital or “ring” of an atom • ALL bonding occurs at this energy level • This energy level is the highest

  7. How do you know how many Valance Electrons an atom has? p.312 2 3 4 5 6 7 8

  8. What is the “Octet Rule”? • The octet rule refers to the tendency of atoms to prefer to have eight electrons in the valence shell. • When atoms have fewer than eight electrons, they tend to react and form more stable compounds • The exceptions are with Hydrogen (H) & Helium (He) that need only 2 in their outer shell.

  9. Do All Atoms Bond? • Not necessarily • Group 18 atoms VERY rarely form bonds • The Noble Gases have a full outer electron shell - a full octet • 8 valence electrons = stable; no bonding

  10. How do Atoms fill their Outermost level? • All Atoms are LAZY! • Some atoms accept or take electrons • If they have 4 or more valence they accept more to reach 8 • Some atoms give up electrons • If they have 1, 2 or 3 they give them up and drop down to their lower energy level Sulfur Magnesium

  11. What are the Rules for determining what type of bond is occurring? • Ionic Bonds • ONLY with groups 1, 2 & sometimes 3 bonding with any nonmetal (groups 15-17) • Covalent Bonds • ONLY between nonmetals • Metallic Bonds • ONLY between metals

  12. What are Ionic Bonds? • A bond that forms when electrons are transferred from one atom to another atom. • What is an Ion? • Charged particles that form when atoms gain or lose electrons. • Can be a positive ion (+) or negative ion (-) • Positive ion = more protons (+) than electrons (-) • Negative ion = more electrons (-) than protons (+)

  13. How are Positive Ions Formed? • Metal atoms tend to lose their valence electrons • Sodium loses its 1 valence electron and drops to the second energy level • Groups 1 & 2 lose their electrons very easily Before After

  14. How are Negative Ions Formed? • Nonmetal atoms tend to accept electrons easily • Chlorine accepts a single electron to complete its octet or outer energy level • Group 17 atoms give off the most energy when they bond Before After

  15. Sodium + Chlorine = Salt

  16. What are Salts? • An ionic compound formed from the positive ion of Groups 1 or 2 and the negative ion of Groups 15 - 17. • Not necessarily NaCl (table salt).

  17. What are some uses of Salts? • NaCl • sodium chloride or table salt • NaOH • sodium hydroxide or lye • CaSO4 • calcium sulfate or wallboard • NaNO3 • sodium nitrate or food preservative

  18. 1+ 0 Oxidation States of the Groups 2+ 3+ 4+/- 3- 2- 1-

  19. Elements That Form Ionic Bonds Groups 1,2 or 3 with Groups 15 - 17

  20. What are Properties of Ionic Compounds? • The + or - charges that are exchanged results in a neutral compound • They form a crystal lattice • A 3-dimensional pattern • Brittle, with high melting & boiling points

  21. What are Lewis Dot Structures? • Models that focus only on valence electrons • The element symbol is centered among the dots representing the element’s valence electrons as shown below Cl Na

  22. What are Lewis Dot Structures? • Models that focus only on valence electrons • The element symbol is centered among the dots representing the element’s valence electrons as shown below Na Cl

  23. Draw the element symbol Determine the number of valence electrons Arrange the “dots” around the symbol as follows… O Be Ne

  24. A Quick Assignment • You need the small dry-erase board at your table & a dry-erase marker • Turn to your book’s Periodic table • Draw the Lewis-dot structures for the following Elements: • Hold your board up when finished

  25. Potassium Strontium Phosphorous Tin Gallium Selenium Xenon Silicon Beryllium Lead

  26. What are Covalent Bonds? • When atoms share electrons • Mostly happen between nonmetals on the periodic table • Properties include • Low melting & boiling points • Brittle only in a solid state • Examples: water, sugar, oxygen, wood, etc…

  27. What are Covalent Bonds?p.318 What Compound is this? H2

  28. What does a Covalent bond of water look like? The Lewis Dot model of water looks like….

  29. The Lewis Dot Model looks like….

  30. What are the Diatomic Molecules? F2 • The simplest molecule • Made up of two bonded atoms • Elements found in nature as diatomic molecules are called diatomic elements • H2, O2, N2, & the Halogens - F2, Cl2, Br2 & I2 are diatomic elements What Compound is this?

  31. What are the More-Complex Molecules? • Typically have Carbon involved in some way • Each carbon atom needs to make 4 covalent bonds to reach the octet (8 valence electrons) • Hydrocarbons are good examples Molecule of Propane

  32. Naming Covalent Compounds • Using number pre-fixes to indicate the number of elements: • Mono = 1 • Di or bi = 2 • Tri = 3 • Tetra = 4 • Penta = 5 • Hexa = 6 • Hepta = 7 • Octa = 8 • Non = 9 • Deca = 10

  33. Examples… • Dihydrogen monoxide – chemical responsible for the death of thousands year after year & hundreds daily! • The formula for Dihydrogen monoxide is: • H2O

  34. What are Metallic Bonds? • A bond formed by the attraction between positively charged metal ions and the electrons in the metal • When metal atoms are close enough their valence electrons overlap • The result is a solid (mostly) with electrons that flow freely around the material

  35. What are the properties of Metallic Bonds? • It is these bonds that give all metals their particular characteristics • Electrical conductivity • Electricity means negative charges (electrons) moving through the metal • Malleability & ductility

  36. Malleability & Ductility? • Because the electrons (-) move freely atoms can easily be rearranged • Bent, hammered into sheets = malleability • Pulled into wire = ductility

  37. Bending without breaking? • Because the electrons (-) move about fixed positive ions (+) • The compounds can bend instead of break • All metals have this property

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