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Lets consider the compound Cesium Fluoride, CsF. –The electro-negativity value (EV) for Cs is 0.70; the EV for F is 4.00. –The difference between the.

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Presentation on theme: "Lets consider the compound Cesium Fluoride, CsF. –The electro-negativity value (EV) for Cs is 0.70; the EV for F is 4.00. –The difference between the."— Presentation transcript:

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3 Lets consider the compound Cesium Fluoride, CsF. –The electro-negativity value (EV) for Cs is 0.70; the EV for F is –The difference between the two is 3.30, which falls within the scale of ionic character. When the electro-negativity difference between two atoms is greater than 1.7 the bond is mostly ionic. Lets consider the compound Cesium Fluoride, CsF. –The electro-negativity value (EV) for Cs is 0.70; the EV for F is –The difference between the two is 3.30, which falls within the scale of ionic character. When the electro-negativity difference between two atoms is greater than 1.7 the bond is mostly ionic. Bonding

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5 Ionic Bonding

6 In an Ionic bond: –The electro-negativity difference is extreme, So the atom with the stronger pull doesnt really share the electron –Instead the electron is essentially transferred from the atom with the least attraction to the atom with the most attraction In an Ionic bond: –The electro-negativity difference is extreme, So the atom with the stronger pull doesnt really share the electron –Instead the electron is essentially transferred from the atom with the least attraction to the atom with the most attraction Ionic Bonding

7 When a metal bonds with a nonmetal an: Ionic bond is formed An ionic bond contains a positive and negative ion. A positive ion is called a cation. A negative ion is called an anion. An Ionic bonding always involves the transfer of an electron from the metal to the nonmetal. The cation and anion are held together by electrostatic attraction. When a metal bonds with a nonmetal an: Ionic bond is formed An ionic bond contains a positive and negative ion. A positive ion is called a cation. A negative ion is called an anion. An Ionic bonding always involves the transfer of an electron from the metal to the nonmetal. The cation and anion are held together by electrostatic attraction. Ionic Bonding

8 Ionic compounds do not consist of individual molecules. Instead there is a huge network of positive and negative ions that are packed together in a solid brittle crystal lattice. Because their bonds are strong, ionic compounds tend to have very high melting and boiling points -Ionic compounds are electrolytes, which means they can conduct electricity When forming ionic compounds the positive and negative charges must balance Ionic crystals cannot conduct electricity because the ions must be able to move. Ionic compounds do not consist of individual molecules. Instead there is a huge network of positive and negative ions that are packed together in a solid brittle crystal lattice. Because their bonds are strong, ionic compounds tend to have very high melting and boiling points -Ionic compounds are electrolytes, which means they can conduct electricity When forming ionic compounds the positive and negative charges must balance Ionic crystals cannot conduct electricity because the ions must be able to move. Characteristics of Ionic Compounds

9 Sea of Electrons

10 The take home lesson on electro-negativity and bonding is this: –The closer together the atoms are on the P.T., the more evenly their e - interact, and are therefore more likely to form a covalent bond –The farther apart they are on the P.T., the less evenly their e - interact, and are therefore more likely to form an ionic bond. The take home lesson on electro-negativity and bonding is this: –The closer together the atoms are on the P.T., the more evenly their e - interact, and are therefore more likely to form a covalent bond –The farther apart they are on the P.T., the less evenly their e - interact, and are therefore more likely to form an ionic bond. metal w/nonmetal = ionic nonmetal w/nonmetal = covalent Bonding

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13 In a covalent bond: –The electro-negativity difference between the atoms involved is not extreme –So the interaction between the involved electrons is more like a sharing relationship –It may not be an equal sharing relationship, but at least the electrons are being shared. In a covalent bond: –The electro-negativity difference between the atoms involved is not extreme –So the interaction between the involved electrons is more like a sharing relationship –It may not be an equal sharing relationship, but at least the electrons are being shared. Covalent Bonding

14 Covalent Bonding is between two or more non-metals. Covalent bonds are formed when electrons are shared between two atoms. If they share 2 electrons, the form a single bond; 4 electrons is a double bond; If two atoms share 6 electrons, they form a triple bond. Covalent Bonding is between two or more non-metals. Covalent bonds are formed when electrons are shared between two atoms. If they share 2 electrons, the form a single bond; 4 electrons is a double bond; If two atoms share 6 electrons, they form a triple bond. Covalent Bonding

15 Polar bonds usually involve nitrogen, oxygen or fluorine (NOF) Non-Polar bonds usually involve carbon- hydrogen bonds In polar bonds, the electrons are shared unequally In non-polar bonds, the electrons are shared equally. Covalent compounds can exist in any state (solid, liquid or gas). They have low melting and boiling points. Polar bonds usually involve nitrogen, oxygen or fluorine (NOF) Non-Polar bonds usually involve carbon- hydrogen bonds In polar bonds, the electrons are shared unequally In non-polar bonds, the electrons are shared equally. Covalent compounds can exist in any state (solid, liquid or gas). They have low melting and boiling points. Covalent Bonding

16 Lets look at the molecule Cl 2 Covalent Bonds Cl Shared Electrons Shared Electrons Cl

17 Shared electrons are counted with both atoms Cl Notice 8 e - in each valence shell!!!

18 Cl H H H H Covalent Bonds How about the molecule HCl? (Polar Covalent) shared, but not evenly

19 To be stable the two atoms involved in the covalent bond share their electrons in order to achieve the arrangement of a Noble Gas. So whats the bottom line?

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21 Lewis structures are representations of molecules showing all valence electrons, bonding and nonbonding.

22 The most important requirement for the formation of a stable compound is that the atoms achieve a noble gas electron configuration.

23 PCl 3 1.Find the sum of valence electrons of all atoms in the polyatomic ion or molecule. – If it is an anion, add one electron for each negative charge. – If it is a cation, subtract one electron for each positive charge (7) = 26

24 2.The central atom is the least electronegative element that isnt hydrogen. Connect the outer atoms to it by single bonds. Keep track of the electrons: = 20

25 3.Fill the octets of the outer atoms. Keep track of the electrons: = 20; = 2

26 4.Fill the octet of the central atom. Keep track of the electrons: = 20; = 2; = 0

27 5.If you run out of electrons before the central atom has an octet… …form multiple bonds until it does. Usually occurs with carbon, nitrogen, oxygen

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29 This is the Lewis structure we would draw for ozone, O 3. -

30 But this is at odds with the true, observed structure of ozone, in which… – …both O-O bonds are the same length. – …both outer oxygens have a charge of -1/2.

31 One Lewis structure cannot accurately depict a molecule like ozone. We use multiple structures, resonance structures, to describe the molecule.

32 Just as green is a synthesis of blue and yellow… …ozone is a synthesis of these two resonance structures.

33 In truth, the electrons that form the second C-O bond in the double bonds below do not always sit between that C and that O, but rather can move among the two oxygens and the carbon. They are not localized; they are delocalized.

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35 There are three types of ions or molecules that do not follow the octet rule: –Ions or molecules with an odd number of electrons –Ions or molecules with less than an octet –Ions or molecules with more than eight valence electrons (an expanded octet)

36 Though relatively rare and usually quite unstable and reactive, there are ions and molecules with an odd number of electrons.

37 Consider BF 3 : – Giving boron a filled octet places a negative charge on the boron and a positive charge on fluorine. – This would not be an accurate picture of the distribution of electrons in BF 3.

38 Therefore, structures that put a double bond between boron and fluorine are much less important than the one that leaves boron with only 6 valence electrons.

39 The lesson is: if filling the octet of the central atom results in a negative charge on the central atom and a positive charge on the more electronegative outer atom, dont fill the octet of the central atom.

40 The only way PCl 5 can exist is if phosphorus has 10 electrons around it. It is allowed to expand the octet of atoms on the 3rd row or below. – Presumably d orbitals in these atoms participate in bonding.

41 Even though we can draw a Lewis structure for the phosphate ion that has only 8 electrons around the central phosphorus, the better structure puts a double bond between the phosphorus and one of the oxygens.

42 This eliminates the charge on the phosphorus and the charge on one of the oxygens. The lesson is: when the central atom in on the 3rd row or below and expanding its octet eliminates some formal charges, do so.

43 In the construction of a crystal lattice, depending on the ions involved there can be small pores develop between ions in the ionic crystal. Some ionic compnds have enough space between the ions that water molecules can get trapped in between the ions Ionic compounds that absorb water into their pores form a special type of ionic compound called a hydrate. In the construction of a crystal lattice, depending on the ions involved there can be small pores develop between ions in the ionic crystal. Some ionic compnds have enough space between the ions that water molecules can get trapped in between the ions Ionic compounds that absorb water into their pores form a special type of ionic compound called a hydrate. Hydrate Formation

44 Trapped Water Molecules

45 Hydrates typically have different properties than their dry versions - A.K.A. anhydrides Anhydrous CuSO 4 is nearly colorless CuSO 4 5 H 2 O is a bright blue color When Copper (II) Sulfate is fully hydrated there are 5 water molecules present for every Copper ion. The hydrated name would be Copper (II) Sulfate Pentahydrate Hydrates typically have different properties than their dry versions - A.K.A. anhydrides Anhydrous CuSO 4 is nearly colorless CuSO 4 5 H 2 O is a bright blue color When Copper (II) Sulfate is fully hydrated there are 5 water molecules present for every Copper ion. The hydrated name would be Copper (II) Sulfate Pentahydrate Hydrate Formation

46 Have you ever bought a new purse or camera and found a small packet of crystals labeled – do not eat? These crystals are there to absorb water that might lead to mildew or mold The formula of a hydrate is X A Y B Z H 2 O (Z is a coefficient indicating how many waters are present per formula unit) Have you ever bought a new purse or camera and found a small packet of crystals labeled – do not eat? These crystals are there to absorb water that might lead to mildew or mold The formula of a hydrate is X A Y B Z H 2 O (Z is a coefficient indicating how many waters are present per formula unit) Hydrate Formation

47 Molecules will be polar if a)bonds are polar AND b)the molecule is NOT symmetric All above are NOT polar


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