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Chapter 6 Section 2

Chapter 6 Section 2. Covalent Bonding and Molecular Compounds. Molecule. Neutral group of atoms Held together by covalent bond Individual unit Able to exists on its own May be same element joined together Could be two or more elements joined together. Molecular Compound.

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Chapter 6 Section 2

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  1. Chapter 6 Section 2 Covalent Bonding and Molecular Compounds

  2. Molecule • Neutral group of atoms • Held together by covalent bond • Individual unit • Able to exists on its own • May be same element joined together • Could be two or more elements joined together

  3. Molecular Compound • Chemical compound • Simplest units are molecules Water Molecule from en.wikipedia.org Water Molecule from en.wikipedia.org dreamstime.com dreamstime.com

  4. Chemical Formula • Tells the number of atoms of each kind in a chemical compound • Uses the symbols for the atoms from the periodic table • Uses subscripts to tell how many of each element are needed • Diatomic molecules have only two atoms

  5. Molecular Formula • Shows the types of atoms • Shows the number of atoms in a single molecule • C12H22O11 • What is this formula for? • Sucrose AKA table sugar

  6. Formation of a Covalent Bond • Two atoms are far apart • Overall potential energy is zero • Atoms approach each other • Charged parts of the atoms begin to interact • Nuclei and electrons attract each other • Total potential energy drops

  7. Formation of a Covalent Bond Continued • At the same time the attraction is happening • The positive part of the nuclei repel each other • The negative electrons repel each other • This increases the potential energy • Strength of attraction depends on repulsion and distance

  8. Formation of a Covalent Bond continued again • Forces continue to change until the attractive force balances the repulsive force • Potential energy is at a minimum pegasus.cc.ucf.edu

  9. Characteristics of the Covalent Bond • Bond length-distance between the nuclei of two bonded atoms • Bond energy-energy required to break a chemical bond and form neutral isolated atoms

  10. The Octet Rule • Noble-gas atoms exist unbonded in nature • Stable because of their completely filled outer shell • S and p are completely filled totaling 8 electrons • Other main group elements share, lose or get electrons to make a full octet

  11. Exceptions to the Octet Rule • Boron has just 3 valence electrons • Tends to form compounds that give it just 6 total valance electrons • Other elements might exceed the 8 electrons • Phosphorous in PF5 • Sulfur in SF6 • Usually when bonded to highly electronegative elements

  12. Electron Dot Notation • Only need to use the outermost energy level electrons • Need a way to keep track of these electrons • Electron-dot notation is that way • It is yet another electron notation • It is okay to scream, I understand

  13. Electron Dot Notation • Only valence electrons of an atom are shown • Dots are used to represent electrons • Placed around elements symbol • Number of valence electrons can be found from the periodic table • The column is the same as the valence electrons • Start on the left first column has 1, second column has 2 • Skip the transitions • Continue to count across

  14. Example 3 • Write the electron dot notation for hydrogen. middleschoolchemistry.com

  15. Example 4 • Write the electron dot notation for nitrogen.

  16. Lewis Structures • Formulas in which atomic symbols represent nuclei and inner shell electrons • Dot pairs of dashes between atoms are electrons • Dots singles are unshared electrons

  17. Lewis Structures thenakedscientists.com

  18. Lewis Structures classes.lt.unt.edu

  19. Structural Formula • Show number,kind, arrangements,and bonds • Does NOT show unshared pairs of atoms • Single bond is one shared pair of electrons • Represented by one line

  20. Example 6 • Draw the Lewis structure for iodomenthane.

  21. Lewis Structure hyperphysics.phy-astr.gsu.edu

  22. Example 7 • Draw the Lewis structure for each of the following • H2O • CH4 • CH4O • HCl

  23. Multiple Covalent Bonds • Some a • toms can share more than one pair of electrons • Carbon, Nitrogen, and Oxygen • Double bond-two pairs of electrons shared • Represented by two parallel lines • Triple bond-three pairs of electrons shared • Represented by three parallel lines • These are called multiple bonds

  24. Multiple Covalent Bond Carbon dioxide molecule from thestephenation.blogspot.com Carbon dioxide molecule from thestephenation.blogspot.com Ethane from chemistry.mcmaster.ca

  25. Example 8 • Draw the Lewis structure for methanol, CH2O, which is also known as formaldehyde.

  26. Example 9 • Determine the Lewis structure for each of the following molecules • O2 • C2H4 • C2H2

  27. Resonance Structures • Some molecules may take more than one structure • That is there is more than one way the molecule might be put together • Chemist think of compounds as bouncing between the possibilities aka resonating • Resonance-bonding that cannot be correctly represented by a single Lewis structure

  28. Covalent Network Bonding • These are not the individual units we have been dealing with • We will work with them more in chapter 7

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