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Covalent Bonds

Covalent Bonds. Atoms can form molecules by sharing electrons in the covalent bond. This is done only among non-metal atoms. Molecules. Some elements in nature are found in the form of molecules Diatomic = 2 atoms BrINClHOF Compound composed Of molecules is called a Molecular compound.

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Covalent Bonds

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  1. Covalent Bonds Atoms can form molecules by sharing electrons in the covalent bond. This is done only among non-metal atoms.

  2. Molecules • Some elements in nature are found in the form of molecules • Diatomic = 2 atoms BrINClHOF • Compound composed Of molecules is called a Molecular compound

  3. PROPERTIES • Relatively low melting points and boiling points • Many are gases and liquids at room temperature • Composed of atoms of 2 or more nonmetals

  4. Molecular Formulas • Show how many atoms of each element a molecule contains • Ex. H2O has 2 hydrogen atoms and 1 oxygen atom • Doesn’t show shape of molecule or which atoms are covalently bonded and how

  5. Dot Structures-Octet Rule(All atoms want 8 electrons around them.) Valence electrons are those in the outermost orbitals. They are the ones that can form bonds. Electron sharing occurs in such a way so that atoms attain the electron configuration of the noble gases.

  6. SINGLE COVALENT BONDS • Two atoms held together by sharing a pair of electrons. Can be shown by lewis dot or a dash H H

  7. UNSHARED PAIRS In F2 each flourine contributes one electron The electrons that are not shared are called Unshared pairs, lone pairs or nonbonding pairs

  8. Draw Lewis structures • NH3 • PCl3 • Cl2 • SBr2

  9. DOUBLE AND TRIPLE COVALENT BONDS Occurs when three pairs of electrons Are shared Occurs when two pairs of electrons are shared

  10. NASL Method for Lewis Dot Structures • Helps to determine how to place electrons around an atom ( double/triple bonds + lone pairs) • Exceptions to octet = H = 2, Be = 4, B= 6 STEPS • Write a skeleton molecule with the lone atom in the middle (Hydrogen can never be in the middle) • Calculate (N) Needed which is the sum of electrons needed for all atoms to obey the octet rule.

  11. NASL MethodShow structure for CO2 • O C O skeleton 2. Needed electrons C = 1 x 8 = 8 O = 2 x 8 = 16 N = 24

  12. NASL METHOD • Step 3; Calculate A (Available) = sum of all valence electrons. For anions and cations you need to subtract or add electrons here. • Step 4; Calculate S ( Shared) = Difference between N and A

  13. CO2 1 x 4 = 4 for Carbon 2 x 6 = 12 for Oxygen 16 A (available) Shared Needed – Available = 24-16= 8

  14. NASL Method • Divide S by 2 to obtain the number of bonds to be extended from the central atoms. 8 / 2 = 4 O::C::O • Calculate L ( Lone-pair electrons ) the difference between A and S 16 – 8 = 8 .. .. O::C::O ●● ●●

  15. Let's Try it! H O H Water H2O 2 x 2 = 4 for Hydrogen1 x 8 = 8 for Oxygen4+8=12 needed electrons 12 N - 8 H 2 x 1 = 2 for Hydrogen1 x 6 = 6 for Oxygen You have 8 available electrons 4 B - 4 NB 12 – 8 = 4/2 = Bonding S N A S L E H:O:H 8 – 4 = 4 non-bonding electrons .. H:O:H●● .. H:O:H●●

  16. Let's Try it! HH N H Ammonia NH3 3 x 2 = 6 for Hydrogen1 x 8 = 8 for Nitrogen6+8=14 needed electrons 14 N - 8 H 3 x 1 = 3 for Hydrogen1 x 5 = 5 for Nitrogen You have 8 available electrons 6 B - 2 NB 14 – 8 = 6/2 = 3 bonding pairs S N A S L E H ..H:N:H 8-6 = 2 lone electrons H .. H:N:H●● H .. H:N:H●●

  17. REVIEW • Draw lewis dot structures for the following • PCL3 • CH4

  18. Review Quiz #2 • Using NASL Show covalent bonding for the following compounds. Show all work for credit. ( 6 points ) SO2

  19. NomenclatureNaming of Binary Molecular Compounds Binary Compounds: Composed of two different elements that are nonmetals. Ex. CO and CO2 (not carbon Oxide) CO = Carbon monoxide = poisonous gas CO2 = carbon dioxide waste product of breathing Need to differentiate different types of compounds by using prefixes. Tells you how many of each element are present Mono = 1 Penta = 5 Di = 2 Hexa = 6 Tri = 3 Hepta = 7 Tetra = 4 Octa = 8

  20. Naming Guidelines • 1. make sure you have a binary molecular compound composed of two nonmetals • 2. Name must identify the elements and how many are present • 3. Name the elements in the order listed • 4. Omit the prefix – mono when the first element only has one • Ex. SF6 is sulfur hexaflouride NOT monosulfurhexaflouride • 5. The suffix for the second element is -ide

  21. Writing Formulas • Use the prefixes in the name to determine the correct subscripts for the formula. • Ex. Silicon Carbide ( no prefixes so must contain one of each) SiC • DinitrogenTetroxide = N2O4

  22. Let’s Practice! • Phosphorus Pentachloride • Iodine Heptaflouride • Chlorine triflouride OF2 SO2 N2O4

  23. Using a few sentences discuss what the cartoon might mean in terms of how Cl and H bond

  24. POLARITY • Covalent bonds involve atoms sharing electrons (pulled in a tug of war) • When electrons are pulled equally = nonpolar Covalent bond • When electrons are pulled unequally = polar covalent bond

  25. Electronegativity • The magnitude of attraction for electrons is called “Electronegativity”. The more electronegative an atom is, the more it wants the electrons.

  26. The higher the electronegativity Value the greater the ability to attract electrons

  27. Bond types WATER IS A POLAR MOLECULE O = 3.5 ELECTRONEGATIVE H = 2.1 ELECTRONEGATIVE DIFFERENCE = 1.4 = POLAR COVALENT OXYGEN PULLS HYDROGENS ELECTRONS CLOSER THAN HYDROGEN CAN PULL OXYGENS ELECTRONS. OXYGEN GETS AN OVERALL PARTIAL NEGATIVE CHARGE AND HYDROGEN GETS AN OVERALL PARTIAL POSTITIVE CHARGE DESIGNATED BY A GREEK DELTA SIGN

  28. VSEPR Theory • Electron dot structures fail to reflect the 3-dimensional shape of molecules Molecules in reality are 3 dimensional and can be explained by the VSEPR theory

  29. VSEPR Theory • Explains 3-D shape of molecules • Based on the theory that repulsion occurs between electron pairs and causes a variety of molecular shapes. • Electrons want to stay as far apart as possible • Can be determined by first looking at the lewis dot structure • Counting how many electron clouds (pairs) are radiating

  30. LINEAR MOLECULES The simplest structure has two groups around the central atom. Carbon monoxide, CO2, is an example of this kind of shape. The two groups of electrons in the two double bonds repel each other and assume a shape with an angle of 180 degrees.

  31. MOLECULAR SHAPES

  32. Review Pyramidal = 3 bonding pairs And a lone pair Trigonal planar = 3 bonding No lone pairs

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