1. chemical bond= an interaction between atoms that holds them together by reducing the potential energy of their electrons

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2 1. chemical bond= an interaction between atoms that holds them together by reducing the potential energy of their electrons 2. chemical formula= a shorthand representation of the composition of a substance using atomic symbols and numeric subscripts (Ex: NaCl, MgCl 2, H 2 O, C 6 H 12 O 6 )

3 3. Chemical bonding involves the valence electrons of the atoms involved in a chemical bond.

4 4. valence electrons= the electrons available to be lost, gained, or shared in the formation of chemical bonds For atoms of main group elements, valance electrons are electrons in the outermost main energy level.

5 Use of the periodic table to determine the number of valence electrons for atoms of the main group elements: Exception = a helium atom has two valence electrons Group Number of valance electrons

6 Electron Configuration of oxygen:

7 5. In the Lewis electron-dot formulas for atoms of main group elements, valence electrons are represented by dotsthat surround an element s symbol.

9 Examples of electron-dot formulas for atoms of the main group elements:

10 Yes or No? 1. Valence electrons are in the outermost energy level. YES 2. Elements in group 16 of the P.T. have 7 valence electrons. NO-6 3. Helium only has 2 valence electrons even though it is in group 18. YES

11 1. ionic bond= a chemical bond resulting from electrostatic attractionbetween positive and negative ions a) In a purely ionic bond, one or more electrons are transferred from one atom to another

13 2. covalent bond= a chemical bond resulting from the sharingof electrons between two atoms a) nonpolar-covalent bond= a covalent bond in which the bonding electrons are shared equallyby the bonded atoms b) polar-covalent bond= a covalent bond in which the bonding electrons are shared unequally by the bonded atoms

15 δ+ δ-

16 3. Chemical bonds between two unlike atoms are NEVER completely ionic and RARELY completely covalent. Bonds can be anywhere in the range between these two extremes, depending upon how strongly the bonded atoms attract electrons.

17 4. electronegativity = a measure of the ability of an atom in a chemical compound to attract electrons 5. The degree to which bonds are ionic or covalent can be estimatedby comparing the electronegativities of the bonded atoms.

18 6. The electronegativity difference of two atoms can be used to determine the ionic character of a bond. Only positivevalues are used for the final electronegativity

19 7. The scale below can be used to classify the probable bond type between two atoms. a) If the electronegativity difference between two atoms is: 0 to 0.3the probable bond type is usually classified as nonpolar covalent. 0.3 to 1.7the probable bond type is usually classified as polar covalent. 1.7 or abovethe probable bond type is usually classified as ionic.

21 8. Polar covalent bonds, a closer look: a) In a polar covalent bond electrons are shared unequally. b) Shared electrons spend MOREof their time near the atom with the higherelectronegativity.

22 c) Partial charges(δ + or δ - ) result. A δ - is assigned to the atom with the HIGHEST electronegativity A δ + is assigned to the atom with the LOWEST electronegativity

23 d) Ex: An H atom and a Clatom form a polar-covalent bond resulting in partial charges.

Nonpolar-covalent bond result when electrons are shared

24 Yes or No? 1.An ionic bond results from an electrostatic repulsion between positive and negative ions. NO- attraction between ions! 2. Nonpolar-covalent bond result when electrons are shared unequally by the bonded atoms NO- e- shared equally 3. Polar-covalent bond result when electrons are shared unequally by the bonded atoms. YES

25 9. Determine the electronegativity difference and probable bond type with respect to bonds formed between the following pairs of atoms. Assign partial charges if the probable bond type is polar-covalent.

26 Pair of Atoms Electronegativity Difference Probable Bond Type Partial Charges S and H S and Cs I and I Cl and Br S and Cl Br and F

28 1. Characteristics of ionic compounds: a) Ionic compounds are held together by ionic bonding. b) Ionic compounds usually involve metals and nonmetals. c) Ionic compounds are solids under normal conditions.

29 d) Ionic compounds consist of a very large number of positive and negative ions (anions and cations) that are combined so that the numbers of positive and negative charges are equal. e) The chemical formula for an ionic compound represents a formula unit, NOT a molecule.

30 2. An ionic compound is NOTcomposed of independent, neutral units that can be isolated and examined. 3. ionic compound= a compound of positive and negative ions (anions and cations) that are combined so that the numbers of positive and negative charges are equal

31 4. The chemical formula of an ionic compound shows the ratioof ions present in a sample of any size. a) Ex: magnesium chloride has the following chemical formula: MgCl 2 For every one Mg +2 ion present, two Cl ions are present. If 13 mol Mg +2 ions are present in a sample, then 26 mol Cl ions are present in the sample.

32 5. The chemical formula for an ionic compound represents a formula unit, NOT a molecule. 6. formula unit= the simplest collection of ions from which an ionic compound s formula can be established

33 7. octet rule= chemical compounds tend to form so that each atom (by gaining, losing, or sharing electrons) contains eight electrons in its outermost occupied main energy level (valence electrons) 8. Electron-dot formulas can be used to illustrate the formation of ionic bonds.

34 a) Use electron-dot formulas to illustrate the formation of ionic bonds involving Na and Cl.

35 b) Use electron-dot formulas to illustrate the formation of ionic bonds involving Ca and F.

36 c) Use electron-dot formulas to illustrate the formation of ionic bonds involving K and O.

37 1. Characteristics of molecular substances: a) Molecular substances are held together by covalent bonding. b) Molecular substances usually involve ONLY nonmetals.

38 1. Characteristics of molecular substances: c) Molecular substances may be solids, liquids, or gasesunder normal conditions. d) Molecular substances consist of molecules. The size of different molecules varies greatly.

39 2. molecular compound= a chemical compound whose simplest units are molecules 3. molecule= a neutral group of atoms held to together by covalent bonds a) A single molecule is an individual unit capable of existing on its own.

41 4. The chemical formula for a molecular compound is called a molecular formula. 5. molecular formula= a shorthand representation showing the types and numbers of atoms combined in a single molecule a) Ex: hydrogen peroxide; H 2 O 2 ; twoatoms of hydrogen and two atoms of oxygen are held together by covalent bonds b) Ex: glucose; C 6 H 12 O 6 ; 6 atoms of carbon, 12 atoms of hydrogen, and 6 atoms of oxygen are held together by covalent bonds

42 6. diatomic molecule= a molecule containing only two atoms a) Ex: HCl, O 2 7. Certain elements occur naturally as diatomic molecules (you need to know these elements!!) a) They are: H 2, O 2, N 2, Cl 2, Br 2, I 2, and F 2

43 1.) Intermolecular forces (IM Forces)= forces of attraction between adjacent particles (molecules, atoms, or ions) a.) Generally much weakerthan ionic or covalent bonds

44 b.) The example below shows two HCl molecules. The force of attraction that exists between the two molecules is an intermolecular force.

45 c.) IM forces are moresignificant in solids and liquids than in gases because the particles are much closer together in solids and liquids.

46 d.) IM forcesare responsible for many properties of compounds such as melting point and boiling point, surface tension, and viscosity.

47 Strong IM forces = Highmelting points & boiling points oex: Ionic compounds orequires MOREenergy (higher temp.) to break strong IM forces between particles

48 Weaker IM forces = Lowmelting points & boiling points oex: Molecular compounds orequires LESS energy (lower temp.) to break weak IM forces between particles

49 Yes or No? 1.Ionic compounds are usually solids. YES 2. Ionic compounds usually involve metals and nonmetals. YES 3. Molecular compounds have weaker IM forces so will melt at lower temperatures. YES

50 Yes or No? 4. A molecule is a neutral group of atoms held to together by ionic bonds. NO- covalent bonds 5. A diatomic molecule is a molecule containing onlyone atom. NO- 2 atoms 6. Molecules can exist on their own. YES

51 IONIC COMPOUNDS VS. MOLECULAR COMPOUNDS Turn to page 32

Solids Solids, Liquids, Gases 3. This type of compound can be described as a collection of? 4. What type of bond is holding the atoms together?

52 IONIC COMPOUNDS vs. MOLECULAR COMPOUNDS 1. What type(s) of elements are usually contained in this type of compound? IONIC COMPOUNDS Metals & Nonmetals MOLECULAR COMPOUNDS ONLY Nonmetals 2. Under ordinary conditions, in what state of matter would you find this compound? Solids Solids, Liquids, Gases 3. This type of compound can be described as a collection of? 4. What type of bond is holding the atoms together? Explain how atoms are held together by this type of bonding? Formula Units Ionic bonding = an electrostatic attraction between cations(+ ions) & anions ( -ions) Molecules Covalent bonding = atoms share valance electrons Polar-Covalent-unequal sharing of e- Nonpolar-covalent equal sharing of e-

53 IONIC COMPOUNDS vs. MOLECULAR COMPOUNDS 5. Describe the melting points and boiling points. 6. Describe the IM forces. IONIC COMPOUNDS High Melting & Boiling points Strong IM forces so MORE energy (higher temp.) to break strong IM forces between particles MOLECULAR COMPOUNDS Low Melting & Boiling points Weak IM forces so requires LESS energy (lower temp.) to break weak IM forces between particles

55 1. Electron-dot formulas illustrate the sharing of valence electronsbetween atoms.

56 2. Electron pairs: a) lone pair= an electron pair NOT involved in bonding b) bond pair= an electron pair shared between two atoms

57 a) single bond= a covalent bond produced by the sharing of one pair of electrons between two atoms Ex: H H or H : H

58 b.) double bond= a covalent bond produced by the sharing of two pairs of electrons between two atoms a) Ex: O 2

59 With six valence electrons each, two oxygen atoms can use twelve electrons to satisfy both octets. By sharing one electron from each oxygen, we can't have more than one oxygen's octet satisfied. We'll need to try a different sharing pattern; a double bond will work.

60 c.) triple bond= a covalent bond produced by the sharing of three pairs of electrons between two atoms a) Ex: N 2

61 With five valence electrons each, two nitrogen atoms can use ten electrons to satisfy both octets. By sharing one electron from each nitrogen, we can't have either nitrogen's octet satisfied. We'll need to try a different sharing pattern; a triple bond will work.

62 d) In general, double bonds are shorter and strongerthan single bonds. e) In general, triple bondsare shorter and stronger than double bonds.

63 a) Count the totalnumber of valence electrons in the molecule. THESE ARE ALL THE ELECTRONS YOU MAY USE! b) Identify the central atom and terminal atoms: His always a terminal atom C, if present is usually the centralatom Molecules tend to be somewhat symmetrical (if one atom is different than the others it is usually the central atom)

64 c) Place one pairof electrons between each pair of bonded atoms to form a single bond. d) Add electron pairs around the terminal atomsto satisfy the octet rule for the terminal atoms. THERE ARE EXCEPTIONS TO THE OCTET RULE! (see below)

65 e) Assign left over electron pairs to the central atom. f) Orient atoms so there is minimalelectron pair repulsions around the central atom. (arrange electron pairs as far apart as you can)

66 g) If the central atom has LESSthan an octet of electrons, then move one or more lone pairs from the terminal atoms to form multiple bonds (double and triple bonds). oxygen, nitrogen and carbon CANform double bonds

67 h) DO THE FOLLOWING FINAL CHECKS: Check that the total number of valence electrons in the molecule is correct. Check that the octet rule is satisfied for all atoms. DON T FORGET ABOUT THE EXCEPTIONS.

68 6. EXCEPTIONS to the octet rule: a) Hydrogenis an exception to the octet rule. In a molecule, hydrogen contains two electrons in its outermost occupied main energy level. HYDROGEN CAN FORM ONLY A SINGLE BOND AND WILL CONTAIN NO LONE PAIRS!

These atoms sometimes contain less than eight electrons in their outermost

69 6. EXCEPTIONS to the octet rule: b) Beryllium and boron are SOMETIMES exceptions to the octet rule. These atoms sometimes contain less than eight electrons in their outermost occupied main energy level. Remembering that these atoms DO NOTform double and triple bondswill be helpful when determining if they break the octet rule.

70 a) Follow all guides from above except write a dashto indicate every bond pair. b) Dotsare still used to represent lone pairs.

71 We will practice as a class only the first 3 columns!

74 Electron Dot Formula Structural Formula

75 a) Follow the guide from above except: Add a bracket and chargeto the electron-dot and structural formulas Account for chargewhen counting valence electrons A POSITIVE CHARGEindicates you have to subtract electron(s)

76 Ex: H 3 O +1 has 8valence electrons: O= 6 valence e- H 3 = 3 valence e- So now there is 9 e-and you subtract 1e-since the ion has a +1charge to get the final total of 8 valence electrons

77 Ex: NH 4 +1 Electron Dot Formula Structural Formula

78 A NEGATIVE CHARGEindicates you have to add electron(s) Ex: CO 3-2 has24 valence electrons C= 4 valence e- O 3 = 18 valence e- So now there is 22 e-and you add 2esince the ion has a -2charge to get the final total of 24 valence electrons

79 We will practice as a class only the first 3 columns!

82 1. The VSEPR modelhas proven useful in predicting molecular geometry and bond angles. 2. The VSEPR model assumes that atoms will orient themselves so as to minimize electron pair repulsions around the central atom.

83 3. Steps to determine molecular geometry and bond angles: a) Draw an electron-dot formula. b) Arrange the electron pairs around the central atom in a way that minimizes repulsion. In other words, put the electron pairs as far apart as possible. c) Determine molecular geometry: d) Predict the bond angles from the molecular geometry.

85 Molecular Geometry Atoms Bonded to Central Atom Lone Pairs Around the Central Atom Predicted Bond Angles Example Linear BeF 2 Trigonal Planar BeF 3 Trigonal Pyramidal NH 3

86 Molecular Geometry Atoms Bonded to Central Atom Lone Pairs Around the Central Atom Predicted Bond Angles Example Bent SnCl 2 H 2 O Bent CH 4 Tetrahedral

87 e) Notice the bond angle distortion for molecules with a molecular geometry of trigonal pyramidal and bent (with two lone pairs).

88 Ex: O 3 is considered bent with a predicted bond angle of 120º since there is only 1 lone pair of electrons 120

89 Ex: H 2 O is considered bent with a predicted bond angle of 105 since there is 2 lone pairs of electrons O H 105 H

90 VSEPR model assumes that lone pairs require more room than bond pairs and tend to compress the angles between bond pairs. In general, bond angles of at least 120 degreesprovide enough room for lone pairs that significant bond angle distortion does NOT occur.

easily shows molecular geometry A wooden peg represents a single bond (one bond pair of electrons) Use longer pegs first, then if needed use smaller pegs A spring represents a multiple bond a

91 easily shows molecular geometry A wooden peg represents a single bond (one bond pair of electrons) Use longer pegs first, then if needed use smaller pegs A spring represents a multiple bond a colored wooden ball represents various atoms When writing dot formulas and structural formulas you still will have to account for lone pair(s) of electrons since models do not account for lone pair(s)

92 Modeling Kit Color Codes:

93 We will practice as a class and add the information to columns 4-5!

97 POLAR vs. NONPOLAR MOLECULES Use the following chart to determine if a molecule is polar or nonpolar. 1. Does the molecule have ANY polar bonds? YES NO 2. Is the electronegativity of all terminal atoms the same? The molecule is NONPOLAR NO YES Note: a 2 atom molecule w/ single bondstop after 1 st question The molecule is POLAR NO The molecule is POLAR Is the molecule symmetrical? 3. Is the molecule symmetrical? (Lone pairs on central atom means molecule is asymmetrical) YES The molecule is NONPOLAR

98 We will practice as a class and add the information to column 6!

100

101

BONDING REVIEW. You need a Periodic Table, Electronegativity table & Polarity chart!

BONDING REVIEW. You need a Periodic Table, Electronegativity table & Polarity chart! BONDING REVIEW You need a Periodic Table, Electronegativity table & Polarity chart! What is the correct bond angle for Bent with 2 lone pairs on the central atom? 105 What is the predicted bond angle for