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Bonding Honors Chemistry Unit 6 Bond Types Ionic: transfer of electrons Ionic: transfer of electrons Covalent: sharing electron pair(s) Covalent: sharing.

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Presentation on theme: "Bonding Honors Chemistry Unit 6 Bond Types Ionic: transfer of electrons Ionic: transfer of electrons Covalent: sharing electron pair(s) Covalent: sharing."— Presentation transcript:

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2 Bonding Honors Chemistry Unit 6

3 Bond Types Ionic: transfer of electrons Ionic: transfer of electrons Covalent: sharing electron pair(s) Covalent: sharing electron pair(s) Metallic: delocalized electrons Metallic: delocalized electrons

4 Covalent Bonds Characteristics Characteristics Low melting points Low melting points Dont conduct electricity Dont conduct electricity Most are brittle if solid, but usually gas or liquid Most are brittle if solid, but usually gas or liquid Particle of a covalent compound is called a molecule (most are between nonmetals) Particle of a covalent compound is called a molecule (most are between nonmetals)

5 Covalent Bonds Two types: Two types: Polar covalent – one atom attracts shared pair of electrons more strongly (most) sides of bond appear to be partially charged Polar covalent – one atom attracts shared pair of electrons more strongly (most) sides of bond appear to be partially charged Nonpolar covalent – electrons are being shared equally, no charge difference (no electronegativity difference) Nonpolar covalent – electrons are being shared equally, no charge difference (no electronegativity difference) usually between two atoms usually between two atoms of same element of same element

6 Terms to Know Bond axis: line joining nuclei Bond axis: line joining nuclei Bond angle: angle between 2 axes Bond angle: angle between 2 axes Bond length: distance between nuclei Bond length: distance between nuclei Bond energy: energy to break bond Bond energy: energy to break bond Bonds are not fixed Bonds are not fixed More like a stiff spring More like a stiff spring Average position is given as bond length or bond angle Average position is given as bond length or bond angle

7 Molecules Covalently bonded compounds Covalently bonded compounds Diatomic molecules: always as 2 atoms when in element form (like O 2 ) Diatomic molecules: always as 2 atoms when in element form (like O 2 ) 7 elements, make a 7 in the periodic table (begin with N) and most are in group 17 7 elements, make a 7 in the periodic table (begin with N) and most are in group 17 Elements: Elements: Br, I, N, Cl, H, O, F

8 Naming a compound with two non-metals Use the prefixes: Use the prefixes: (1) mono-, (2) di-, (3) tri-, (4) tetra-, (5) penta, (6) hexa-, (7) hepta-, (8) octa-, (9) nona-, (10) deca (1) mono-, (2) di-, (3) tri-, (4) tetra-, (5) penta, (6) hexa-, (7) hepta-, (8) octa-, (9) nona-, (10) deca If the first element listed has a quantity of just one then you dont use mono- as a prefix. If the first element listed has a quantity of just one then you dont use mono- as a prefix. Put the appropriate prefix in front of the name of each element change the ending to –ide. Put the appropriate prefix in front of the name of each element change the ending to –ide. Example: Example: N 2 O 5 N 2 O 5 Dinitrogen pentaoxide Dinitrogen pentaoxide

9 Lewis Dot Structures Find the total number of valence electrons using group numbers for each element Find the total number of valence electrons using group numbers for each element Arrange atoms to form skeleton structure with lines connecting the atoms. If carbon is present, it is central. Arrange atoms to form skeleton structure with lines connecting the atoms. If carbon is present, it is central. Otherwise, the least Otherwise, the least electronegative element is electronegative element is central. H is NEVER central. central. H is NEVER central.

10 Lewis Structures (continued) Each line counts as 2 electrons. Subtract these from total valence electrons. Each line counts as 2 electrons. Subtract these from total valence electrons. Compare the electrons left to what each needs to be full. If they are the same, add unshared pairs to give each nonmetal or metalloid a full octet (except H). Add all electrons to see if they equal the valence electrons. (Gr2 and 13 just double their electrons dont get a full octet, Gr. 2 gets 4, Gr. 13 gets 6) Compare the electrons left to what each needs to be full. If they are the same, add unshared pairs to give each nonmetal or metalloid a full octet (except H). Add all electrons to see if they equal the valence electrons. (Gr2 and 13 just double their electrons dont get a full octet, Gr. 2 gets 4, Gr. 13 gets 6) If there are not enough electrons to give each its own dots, one more line needs to be drawn for each 2 electrons you are short (2 atoms share). Recalculate from the valence electrons and dots can be given. If there are not enough electrons to give each its own dots, one more line needs to be drawn for each 2 electrons you are short (2 atoms share). Recalculate from the valence electrons and dots can be given.

11 Example 1 H 2 O H 2 O 2(1) + 6 = 8 valence electrons 2(1) + 6 = 8 valence electrons Skeleton: Skeleton:....H-O-H Subtract 2 for each line 8-4 = 4 e - left Put dots to complete octet for oxygen

12 Example 2 CH 3 I CH 3 I 4+3(1)+7 = 14 valence electrons 4+3(1)+7 = 14 valence electrons Skeleton: H Skeleton: H | H – C – H H – C – H | : I : : I :.... Subtract 2 for each line 14-8 = 6 e - left Subtract 2 for each line 14-8 = 6 e - left Add dots to I to complete the octet. Add dots to I to complete the octet. Other Examples: NH 3, AlI 3, SeO 2, CO 2, SO 3

13 Resonance Using more than one Lewis structure to explain when bonds are in between drawn structures (from lab measurements) Using more than one Lewis structure to explain when bonds are in between drawn structures (from lab measurements)

14 Molecular Shape Based on VSEPR theory: valence-shell electron-pair repulsion theory Based on VSEPR theory: valence-shell electron-pair repulsion theory Electrons want to be as far apart as possible (like charges repel) Electrons want to be as far apart as possible (like charges repel) Pairs around central atom will give angles Pairs around central atom will give angles 2 pairs: linear 180 o angle 2 pairs: linear 180 o angle 3 pairs: trigonal planar 120 o angle 3 pairs: trigonal planar 120 o angle 4 pairs: tetrahedral o angle 4 pairs: tetrahedral o angle Repulsion is greater for unshared pairs: they push harder on shared pairs, decreasing the expected bond angle 2 unshared>1 shared with one unshared>2 shared Repulsion is greater for unshared pairs: they push harder on shared pairs, decreasing the expected bond angle 2 unshared>1 shared with one unshared>2 shared

15 VSEPR Oklahoma State Link Oklahoma State Link Possible Shapes: p. 186 of book Possible Shapes: p. 186 of book Linear: 2 shared (bonded pairs) 180 o angle Linear: 2 shared (bonded pairs) 180 o angle Trigonal planar: 3 shared pairs 120 o angle Trigonal planar: 3 shared pairs 120 o angle Tetrahedral: 4 shared pairs o angle Tetrahedral: 4 shared pairs o angle Trigonal pyramidal: 3 shared, 1 unshared (lone) <109.5 o angle (107 o angle) Trigonal pyramidal: 3 shared, 1 unshared (lone) <109.5 o angle (107 o angle) Bent: 2 shared, 2 unshared (lone) <109.5 o angle (104.5 o angle) Bent: 2 shared, 2 unshared (lone) <109.5 o angle (104.5 o angle)

16 Determining Shape Draw Lewis structure Draw Lewis structure Count shared and lone pairs on central atom (ONLY!) to determine shape Count shared and lone pairs on central atom (ONLY!) to determine shape Example: H 2 O Example: H 2 O Lewis structure: Lewis structure:....H-O-H 2 shared (lines), 2 unshared (dot pairs) 2 shared (lines), 2 unshared (dot pairs) Shape: bent, Angles: <109.5 o angle (104.5 o angle) Shape: bent, Angles: <109.5 o angle (104.5 o angle) Other Examples: NH 3, AlI 3, CH 4, HF, SO 3 Other Examples: NH 3, AlI 3, CH 4, HF, SO 3

17 Hybridization Hybridized orbitals merge s and p orbitals by borrowing empty p orbitals to put one electron in each. This allows them to share that orbital with an electron from another atom in a covalent bond. Hybridized orbitals merge s and p orbitals by borrowing empty p orbitals to put one electron in each. This allows them to share that orbital with an electron from another atom in a covalent bond. The new hybrids have an energy that is in between that of s and p The new hybrids have an energy that is in between that of s and p Examples: Be, Al & B, C & Si (& others) Examples: Be, Al & B, C & Si (& others)

18 Hybrid Orbitals Hybrid Orbitals Count bonds to see how many orbitals are sp hybrids orbitals are sp hybrids needed. Start with s, then needed. Start with s, then add p orbitals to make enough. add p orbitals to make enough. This names the hybrids. This names the hybrids. sp 2 hybrids sp 3 hybrids

19 Predicting Bonds Based on electronegativity difference Based on electronegativity difference Examples of calculation: (use table on p. 151) Examples of calculation: (use table on p. 151) H-F 4.0 – 2.1 = 1.9 H-F 4.0 – 2.1 = 1.9 H-Br 2.8 – 2.1 =.7 H-Br 2.8 – 2.1 =.7 H-I 2.5 – 2.1 =.4 H-I 2.5 – 2.1 =.4 The greater the difference, the stronger the bond The greater the difference, the stronger the bond

20 Bond Character Large difference: ionic bond Large difference: ionic bond Small difference: covalent bond Small difference: covalent bond Dividing line is 1.7 Dividing line is 1.7 > 1.7 is ionic, 1.7 is ionic, < 1.7 is covalent, = 1.7 is 50% ionic and 50% covalent Unless bonded to the same type atom, the bond has both ionic and covalent character (use chart on back of per. table) Unless bonded to the same type atom, the bond has both ionic and covalent character (use chart on back of per. table)

21 Find the electronegativity difference in black in the chart Find the electronegativity difference in black in the chart The percent ionic character is underneath in red The percent ionic character is underneath in red Subtract from 100 to find the covalent character Subtract from 100 to find the covalent character Example: H-F difference was 1.9 Example: H-F difference was 1.9 Ionic character is listed as 59%, so covalent character is = 41% covalent Ionic character is listed as 59%, so covalent character is = 41% covalent H-Br, H-I H-Br, H-I

22 Bonding Demo Record color and intensity (brightness) as each bond forms in your journal, then calculate the % character for each bond Record color and intensity (brightness) as each bond forms in your journal, then calculate the % character for each bond S-O S-O 3.5 – 2.5 = 1.0 difference 3.5 – 2.5 = 1.0 difference 22% ionic, 78% covalent 22% ionic, 78% covalent Mg-O Mg-O 3.5 – 1.2 = 2.3 difference 3.5 – 1.2 = 2.3 difference 74% ionic,26% covalent 74% ionic,26% covalent

23 Polarity If charge of polar bonds is distributed If charge of polar bonds is distributed equally in all directions, the molecule is nonpolar nonpolar If charge of polar bonds is not equal in all directions, the molecule is polar If charge of polar bonds is not equal in all directions, the molecule is polar Look for something that makes the charge asymmetrical (either of these makes it polar) Look for something that makes the charge asymmetrical (either of these makes it polar) Bonded atoms are not all the same element attached to the central atom Bonded atoms are not all the same element attached to the central atom Unshared pairs of electrons on the central atom Unshared pairs of electrons on the central atom A polar molecule is called a dipole (has + and – poles) A polar molecule is called a dipole (has + and – poles) Polarity is measured as dipole moment Polarity is measured as dipole moment

24 van der Waals Forces Intermolecular: Weak forces between molecules (van der Waals forces) Intermolecular: Weak forces between molecules (van der Waals forces) Intramolecular: strong forces inside a molecule holding atoms together (bonds) Intramolecular: strong forces inside a molecule holding atoms together (bonds) Types of van der Waals forces Types of van der Waals forces Dipole-dipole: between polar molecules Dipole-dipole: between polar molecules Dipole-induced dipole: between dipole and nonpolar (peer pressure model) Dipole-induced dipole: between dipole and nonpolar (peer pressure model) London Dispersion Forces: temporary dipoles that happen because of electron movement London Dispersion Forces: temporary dipoles that happen because of electron movement Induced by concentrations of electrons in nonpolar molecules Induced by concentrations of electrons in nonpolar molecules Only attractive force operating in nonpolar substances Only attractive force operating in nonpolar substances 85% of force in most polar molecules (exceptions: NH 3, H 2 O) 85% of force in most polar molecules (exceptions: NH 3, H 2 O)

25 Induced Dipole Peer pressure model Peer pressure model Electrons of nonpolar molecule are disturbed by presence of charged particle (ion or dipole)

26 Dipole-Induced Dipole

27 Temporary Dipole Movement of electrons may cause electron distribution to become asymmetrical for an instant Movement of electrons may cause electron distribution to become asymmetrical for an instant

28 Effects of IM Forces Properties are affected by IM forces Properties are affected by IM forces Boiling and melting points give an indication of how strong the IM forces are Boiling and melting points give an indication of how strong the IM forces are Nonpolar substances have the weakest IM forces: gases or lowboiling liquids (lower melting and boiling points) Nonpolar substances have the weakest IM forces: gases or lowboiling liquids (lower melting and boiling points) Polar substances have dipole forces that are stronger: liquid or solid at room temp (higher melting and boiling points) Polar substances have dipole forces that are stronger: liquid or solid at room temp (higher melting and boiling points)

29 Soaps and Detergents There are polar and nonpolar sides to a soap molecule There are polar and nonpolar sides to a soap molecule The nonpolar side embeds or dissolves in greasy dirt The nonpolar side embeds or dissolves in greasy dirt The polar side is attracted to water molecules (polar) The polar side is attracted to water molecules (polar) Agitation breaks globule up into small pieces which are then pulled away into the water and washed away. Agitation breaks globule up into small pieces which are then pulled away into the water and washed away. Detergents have an additive to keep soap scum from forming. Detergents have an additive to keep soap scum from forming.

30 Chromatography Fractionation (separation) based on polarity Fractionation (separation) based on polarity Two phases: Two phases: Mobile phase: mixture to be separated dissolved in liquid or gas Mobile phase: mixture to be separated dissolved in liquid or gas Stationary phase: solid or liquid adhering to a solid Stationary phase: solid or liquid adhering to a solid Types: column, paper, gas Types: column, paper, gas

31 Column Chromatography Stationary phase is in a column. Stationary phase is in a column. Used for delicate separations such as vitamins, hormones, and proteins. Used for delicate separations such as vitamins, hormones, and proteins. HPLC and ion are special kinds of column chromatography HPLC and ion are special kinds of column chromatography

32 Paper Chromatography Separation on paper into spots or lines on the strip Separation on paper into spots or lines on the strip Has limitations Has limitations

33 Gas Chromatography Used to analyze volatile liquids and gas or vapor mixtures. Used to analyze volatile liquids and gas or vapor mixtures. Mixed with inert gas (like He) in mobile phase Mixed with inert gas (like He) in mobile phase Interpreted by computer Interpreted by computer

34 Gas Chromatogram

35 Chromatography Applications Drug testing uses column and gas chromatography Drug testing uses column and gas chromatography Car emissions are done with gas chromatography Car emissions are done with gas chromatography


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