1 / 13

Ch 6 Covalent bonds

Ch 6 Covalent bonds. Share electrons (between nonmetal/metaliods): to reach a stable octet of atoms in a chemical bond. Forming molecular orbital. Simplest: diatomic molecules. Attraction & repulsion between atoms balanced and at lowest energy.

loos
Download Presentation

Ch 6 Covalent bonds

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Ch 6Covalent bonds Share electrons (between nonmetal/metaliods): to reach a stable octet of atoms in a chemical bond

  2. Forming molecular orbital • Simplest: diatomic molecules. Attraction & repulsion between atoms balanced and at lowest energy. • Shared pair of electrons to form a covalent bond. • Covalent bond: atoms share one or more pairs of electrons. • Molecular orbital: overlap of two atomic orbits • Energy and stability: • Unbonded atoms have high potential energy • Bonded atoms have lower PE & high stability

  3. P.E. & bond length (pg 192 figure 4) • When P.E. between two atoms are at a minimum --> bond length • Covalent bonds are flexible, nuclei vibrate back and forth --> bond length is an average. • Bond energy: energy released when bonds are formed & the energy required to break bonds • Bond E & length (pg 193, table 1) units kJ/mol & pm. • Trend: increase bond strength decrease bond length.

  4. Electro negativity & covalent bonding • E.N. useful to predict type of bond(pg194, figure 6) either ionic or covalent. • Covalent bonds: • Electrons shared equally or unequally • Nonpolar covalent bond: • Bonded electrons are equally attached to both atoms. Electro negativity value the same • Polar covalent bond: • Bonded electrons is held more closely by one atom more. Electro negativity value higher than the other atom.

  5. Electro negativity and bond type • E.N. • 0-.5 nonpolar bond, .5-2.1 polar, 2.1-3.3 ionic bond • Polar molecules: • Opposite charges between atoms in a molecule • + more positive, lower E.N. • - more negative, higher E.N. • Pair of electrons attracted to the atom with higher E.N. • ==> form dipole, molecules contains both positive and negative charged region. • Greater E.N., greater polarity and bond strength. (pg 196, table 2) - O H H Water molecule +

  6. Bond character • Greater the EN the greater (higher %) of ionic character • Properties depended on bond type (pg 197 table 3) • Metallic bond: • Good electrical/heat conductor, solid rm temp. valence e- attracted to all atoms, e- move freely • Ionic substance: • Attraction between cation & anion. Conductor as liquid or aqueous solution. • Molecular: • Shared electrons, non conductor.

  7. Drawing and naming molecules • Lewis electron dot structure: • Valance electrons (outer electrons) used to form chemical bonds & determine chemical properties. • Lewis structure (electron dot diagram) • Structural formula, electrons represented with dots between two atomic symbols representing pairs of electrons in a bond. • Only show valance electrons, symbol of atom represents kernel electrons (inner electrons) • Mirror s&p orbital notation. s p X p X = symbol of element p

  8. Chemical bonds/Lewis struct. • Unshared electrons: • Nonbonding pair of electrons in the valance shell (lone pair) • Single bond: • Covalent bond in which two atoms share one pair of electrons. • Drawing Lewis structure: • 1. Determine total valance electrons. • 2. Determine total electrons need for octet • 3. Determine # of shared pair of electrons (bonds) • #in step 2 - # in step 1 divided by 2 (1 bond = 2 electrons) • 4 place bonds & lone pairs in structure. • Draw the following: SCl2, AsF3, SiH4, CHF3

  9. Lewis struct./polyatomic ions • Same as before with the addition of adding or subtracting valence electrons due to charge • Place brackets, [ ], around ion with charge on the outside. • Draw the following: HS-, NF4+, IO-, PCl4+, CH3+ • Multi bonds: • More than one shared pair of electrons between 2 atoms. • Double bond: • Covalent bond, 2 atoms share 2 pair of electrons. • Triple bond: • Share 3 pair of electron between 2 atoms (covalent) • Draw the following: CO2, HCN, HC2Cl, N2F2, NO2-

  10. Resonance structure • Molecules that can not be represented by a single Lewis structure. • Compounds have identical geometry but different arrangement of of electrons/bonds. • Compounds with multi bonds. • Draw all possible Lewis structures with double headed arrows between each. • Draw the following: NO2, O3, SO2

  11. Naming covalent cpds • Binary cpds (pg 207 table 5) • Just two nonmetal/metaliods covalently bonded • 1. Use prefixes to indicate # of atoms of each element (no mono for first element) • 1-mono, 2-di, 3-tri, 4-tetra, 5-penta, 6-hexa, 7-hepta, 8-octa, 9-nona, 10-deca. • 2. Name 1st element as is 2nd element end in ide • 3. Drop vowel in prefix if element begins with a vowel (not always) • Name or write the following: CO2, N2O5, diphosphorus tetroxide, sulfur hexafluoride

  12. Molecular shape • 3-d shape of a molecule • Help determine properties of the molecule. • Lewis structure predicts molecular shape. • VSEPR theory: • Valence shell electron pair repulsion theory • Valence electrons surrounding an atom repel each other --> spread out to maximize space between electron pairs. • Lone (unbonded) electrons contort molecular shape.

  13. Molecular geometry • Formula shape bond angle(o) • AB2 linear 180 • AB3 trigonal planar 120 • AB2E1 bent >120 • AB4 tetrahedral 109.5 • AB3E1 pyramidal >109.5 • AB2E2 bent >109.5 • AB5 trigonal bipyramidal 90 & 120 • ** symmetrical molecules are nonpolar**

More Related