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Covalent Bonding

Covalent Bonding. Quick Review. Covalent bond – two atoms held together by sharing electrons -- Usually occurs between nonmetals. Octet Rule – chemical compounds tend to form so that each atom, by gaining, losing, or sharing electrons, has an octet of electrons in its highest energy level.

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Covalent Bonding

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  1. Covalent Bonding

  2. Quick Review • Covalent bond – two atoms held together by sharing electrons -- Usually occurs between nonmetals. • Octet Rule – chemical compounds tend to form so that each atom, by gaining, losing, or sharing electrons, has an octet of electrons in its highest energy level. • Valence electrons – the electrons in an atom’s outer energy level

  3. Electron-dot diagrams • shows an atom’s valence electrons • Draw electron-dot diagrams for: N F Na O

  4. New Terms • Molecule – a neutral group of atoms held together by covalent bonds • Molecular formula – shows the types and numbers of atoms combined in a single molecule (ex: H2O, CO2, H2SO4) • Diatomic molecule – molecule containing two atoms (Examples: H2, N2, O2, F2, Cl2, Br2, I2, HCl, NO)

  5. · · · · Using Electron Dot Notation diagrams H2 molecule (nonpolar covalent = EQUAL sharing) • H· ·H H : H • Structural formula: H-H (Use single line for e- pair) the hydrogen orbitals overlap

  6. F2 molecule ·· ·· ·· ·· : F· ·F :: F : F : ·· ·· ·· ·· • Structural formula: F-F • Each fluorine atom has 8 electrons in the outer energy level.

  7. HCl molecule • H Cl H Cl • H – Cl • Each atom now has a filled outer energy level.

  8. Usually there will be more than two atoms bonding together. • Water H2O • Each hydrogen atom is bonded to oxygen atom H O H O H H • Structural formula H O H

  9. Try these molecules: NH3, ClI, H2O2 • NH3 molecule • Each hydrogen atom is bonded to the nitrogen atom. H N H H

  10. ClI molecule (chlorine and iodine) Cl I Cl I Structural formula Cl – I

  11. H2O2 molecule • H O H O O H O H Structural Formula H O O H

  12. Bond Length and Energy • Bond length – the average distance between bonded atoms • Bond energy – energy required to break a chemical bond and form neutral isolated atoms.

  13. Single Bonds • Single bonds – a covalent bond produced by the sharing of one pair of electrons between two atoms. • All of the examples so far have been of single bonds.

  14. Double Bonds • Double bonds – a covalent bond produced by the sharing of two pairs of electrons between two atoms. • O2 molecule O O Structural formula O=O

  15. Triple Bonds • Triple bonds – a covalent bond produced by the sharing of three pairs of electrons between two atoms. • N2 molecule N N Structural formula N≡N

  16. Relationships • Between bond length and # of bonds: As the number of bonds INCREASES, the bond length DECREASES • Between bond energy and # of bonds: As the number of bonds INCREASES, the energy required to break those bonds INCREASES

  17. How to draw Lewis Structures (AKA electron dot diagrams) Two Types of Electron Pairs: • Shared Pair – a bonded pair; exists between 2 atoms in the same molecule. Represented by a straight line between the bonded atoms. • Unshared Pair – a lone pair; belongs entirely to one atom. Represented by a pair of dots on that atom.

  18. Rules for Drawing Lewis Structures: • 1) Draw a skeleton structure for the compound by joining the atoms with single bonds (single straight lines). • The central atom is usually: • a) The one with the highest number of valence electrons • b) The largest atom • c) The least electronegative atom

  19. Rules for Drawing Lewis Structures: • d) Hydrogen will NEVER be a central atom • e) Oxygen will only be central if bonded to H or F

  20. Rules for Drawing Lewis Structures: • 2) Count/Tally the number of total valence electrons • 3) Determine the number of electron pairs by dividing the total number of valence electrons (step #2) by 2 • 4) Determine the number of available electron pairs by subtracting the number of pairs already used in the skeleton structure

  21. Rules for Drawing Lewis Structures: • 5) Place LONE PAIRS around the terminal/end atoms. If any pairs are left, put them as lone pairs on the central atom • 6) Check the OCTET RULE. If the central atom is not yet surrounded by 8 electrons, form multiple bonds.

  22. Rules for Drawing Lewis Structures: • Example: draw the Lewis Structure for Carbon Dioxide

  23. Rules for Drawing Lewis Structures: • Draw the Lewis Structure for Methanal (Formaldehyde) CH2O

  24. Rules for Drawing Lewis Structures: • CF4PCl3 • OCl2O2

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