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Covalent Bonding

Covalent Bonding. Chemistry 5th Edition McMurry/Fay. Electronegativity. χ = (E i + E ea )/2 Usually converted to a unitless number between 0 and 4. Low χ → form cation High χ → form anion. Electronegativity. Bond polarity is due to electronegativity differences between atoms.

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Covalent Bonding

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  1. Covalent Bonding Chemistry 5th Edition McMurry/Fay

  2. Electronegativity χ = (Ei + Eea)/2 Usually converted to a unitless number between 0 and 4. Low χ → form cation High χ→ form anion

  3. Electronegativity • Bond polarity is due to electronegativity differences between atoms. • Pauling Electronegativity: is expressed on a scale where F = 4.0

  4. Electronegativity Pauling Electronegativities

  5. Electronegativity Predicting χ 1. Increases across periods 2. Decreases down groups 3. Very low for noble gases.

  6. Electronegativity • % Ionic Character: As a general rule for two atoms in a bond, we can calculate an electronegativity difference (∆EN ): ∆EN = EN(Y) – EN(X) for X–Y bond. If ∆EN < 0.5 the bond is covalent. If ∆EN < 2.0 the bond is polar covalent. If ∆EN > 2.0 the bond is ionic.

  7. The Covalent Bond • Covalent bonds are formed bysharingat least one pair of electrons.

  8. The Covalent Bond • Every covalent bond has a characteristic length that leads to maximum stability. • This is thebond length.

  9. The Covalent Bond • Every covalent bond has a characteristic length that leads to maximum stability. • This is thebond length.

  10. Polar Covalent Bonds • Using electronegativity values, predict whether the following compounds are nonpolar covalent, polar covalent, or ionic: • SiCl4 CsBr FeBr3 CH4 • HCl CCl4 NH3 H2O

  11. Electron-Dot Structures • Using electron-dot (Lewis) structures, the valence electrons in an element are represented by dots. • Valence electrons are those electrons with the highest principal quantum number (n). Valence electrons normally occupy s and p subshells

  12. Electron-Dot Structures • Use the chemical symbol of the element, and add dots for each valence electron. N → [He] 2s22p3 ↑↓ ↑ ↑ ↑ 2s 2p N

  13. Electron-Dot Structures • Octet: The s2p6 configuration. The complete octet is the most stable configuration. Ar → [Ne] 3s23p6 ↑↓ ↑↓ ↑↓ ↑↓ 3s 3p Ar

  14. Electron-Dot Structures Ion Formation Elements may form ions in order to complete their octets. s-block and the lower left p-block elements will lose electrons; elements on the right of the p-block will gain electrons.

  15. Electron-Dot Structures Ionic Bonds: Two atoms form octets for each by one donating electron(s) to the other. Covalent Bonds: A pair of electrons is shared between two atoms, giving both an octet. (predicted by electronegativity)

  16. Electron-Dot Structures • The electron-dot structures provide a simple, but useful, way of representing chemical reactions. • Ionic: • Covalent:

  17. Electron-Dot Structures Double Bond: Two atoms share two electron pairs, again forming octets for each. Triple Bond: Three electron pairs are shared.

  18. Electron-Dot Structures • Single Bonds: • Double Bonds: • Triple Bonds:

  19. Drawing Lewis Structures Lewis Structure: A diagram showing how electrons are shared between atoms in a molecule. Octet Rule: Atoms proceed as far as possible toward completing their octets by sharing electron pairs. H needs only 2 electrons (and can accept no more).

  20. Drawing Lewis Structures Exceptions to the Octet Rule: 1. Boron may form an incomplete octet with only 6 valence electrons. 2. Phosphorus may form an extended octet with 10 valence electrons. 3. Sulfur may form an extended octet with 12 valence electrons.

  21. Drawing Lewis Structures Lone Pair: A pair of electrons residing on a single element and thus not involved in bonding. Bonding Pair: A pair of electrons shared in a covalent bond. Often represented as a line between atoms. F F

  22. Drawing Lewis Structures Step 1: Determine the total number of valence electrons in the molecule. For anions add 1 electron for each negative charge. For cations subtract 1 electron for each positive charge. Step 2: Find the total number of electron pairs by dividing by 2.

  23. Drawing Lewis Structures Step 3: Identify the central atom(s) and arrange the other atoms around it (them). Central atoms are usually: C, N, B, P, S Step 4: Connect the atoms with single electron pairs first, then attempt to complete each octet by adding lone pairs or multiple bonds until all electrons are used.

  24. Drawing Lewis Structures

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