Move salts to after ionic

Transcription

1 Move salts to after ionic BNDING Ahem-I mean, Chemical Bonding n 1. Chemical bond attraction between atoms in a compound or a molecule Forming a bond n a. When a chemical bond is formed, ENERGY is. RELEASED n This is a exothermic reaction. 2 Mg (s) + 2 (g)à 2Mg (s) attraction 1

2 Breaking a bond n b. When a chemical bond is broken, ENERGY is. ABSRBED n This is a endothermic reaction. 2. Chemical Energy n a. Stored in CEMICAL. BNDS n b. Form of PTENTIAL energy. electricity 2 2 (l) 2 2 (g) + 2 (g) (Electrolysis) 3. Bond Formation n Valence e- play a major role in chemical bonding 3. Bond Formation (cont.) n b. When forming chemical bonds, atoms take on e- configuration of the nearest noble gas (octet rule). 2

3 The ctet Rule n Atoms try to achieve a noble gas e- configuration n For most atoms this means a total of 8 valence e- n Atoms will gain, lose or share to get that magic number. Ionic Bonds n 1.e- are TRANSFERRED from outer shell of one atom to the outer shell of another atom TRANSFER What s an ion?! Ionic Bonds n 2. Bond is formed when the positive ion is attracted to the negative ion. Ions n 1. cation is a PSITIVE ion. cation n 2. anion is a NEGATIVE ion. anion negative 3

4 3. Best examples of ionic bonding n a. Between groups 1A and 2A with groups 6A and 7A When is a bond ionic? n 1. Metal combined with a nonmetal n Ex: Mg, Na n 2. Positive ion with a negative ion n 3. Electronegativity difference 1.7 or greater Let s look at that electronegativity deal. Ions cont. n 3. Positive ions (metallic ions) are smaller than their atoms 1s 2 2s 2 2p 6 3s 1 1s 2 2s 2 2p 6 Na Na +1 Na Na = 0.9 = 3.0 Difference = 2.1 Li 2 Li = 1.0 = 3.5 Difference= 2.5 CaF 2 Ca = 1.0 F = 4.0 Difference = 3.0 *Greatest ionic character n a. Why? n 1. outer energy level was removed n 2. Unbalanced positive charge draws e- closer to nucleus 4

5 Ions cont. if you can t read this see the next slide n 4. Negative ions (nonmetallic ions) are larger X than their + atoms -1 X n a. Why? n 1. Excess negative charge weakens pull of nucleus on e- cloud F F -1 1s 2 2s 7 e- 2 2p 5 1s 2 8 e- 2s 2 2p 6 Ions cont. n 4. Negative ions (nonmetallic ions) are larger than their atoms n a. Why? n 1. Excess negative charge weakens pull of nucleus on e- cloud F 1s 2 2s 2 2p 5 F -1 1s 2 2s 2 2p 6 Chemical Formulas n 1. Empirical formula n a. Shows only lowest ratio of atoms or ions in the compound n b. represents all ionic compounds Ex: Na, Mg 2, Al 2 3, Ba 2 Chemical Formula cont. n 2. Molecular formula n a. Shows number & kind of atoms in one molecule n b. not necessarily in lowest ratio n c. represents covalent compounds only Ex: C , 2 2, C 2, 2 5

6 Electron Dot Structures again! (Lewis Dot Structures) n Represents the valence e - Wooohooo! n B s e- configuration is 1s ; 2 2s 2 2p 1 so the outer energy level is, 2 and there are 2+1 = 3 electrons in level 2. These are the valence electrons!" Try another one n Br is [Ar] 3d 10 4s 2 4p 5 n ow many valence electrons are present? 7 Represents valence e- Represents nucleus and core e- Lewis Dot and Ionic Bonding Let s take a closer look Na ow many does Na want to give away? 1 ow many does want to take? 1 ow many valence e-? Does it want to give away or take to make 8 (octet rule)? ow many valence e-? Does it want to give away or take to make 8 (octet rule)? So what is the charge? +1 Na +1 So what is the charge?

7 Na &.perfect match Na +1-1 What would the empirical formula look like? Na 1 1 or just Na Try another Mg ow many valence e-? Does it want to give away or take to make 8 (octet rule)? Br ow many valence e-? Does it want to give away or take to make 8 (octet rule)? Let s take a closer look Mg & Br what a team! ow many does Mg want to give away? 2 So what is the charge? +2 Mg +2 ow many does Br want to take? 1 So what is the charge? -1 Br -1-1 Mg Br -1 Br +2 What would the empirical formula look like? Mg 1 Br 2 or just MgBr2 7

8 Formation of Salt verall: Na + ½ 2 à Na 1. Ionization of Na Na kcal/mol à Na +1 +1e 2. Splitting of 2 molecule Energy released? ½ kcal/mol à 3. Formation of Chloride Ion Energy taken in? + 1e à kcal/mol 4. Bond Formation Na à Na kcal/mol verall Energy Change? n Energy released: = 272 kcal n Energy taken in: = 145 kcal n verall energy released = 127 kcal/mol LATTICE ENERGY Lattice Structure Covalent bonding n 1. Form when 2 atoms share a pair of e- n 2. Between 2 nonmetals (C 2 ) n 3. Between & a Nonmetal ( 2, ) 8

9 Molecule n 1. Smallest particle of a substance formed by covalent bonding n 2. Can represent elements ( 2 ) or compounds (C 2 ) Two types of Covalent Bonding n 1. Nonpolar n e- are shared equally WY?! n 2. Polar n e- are shared unequally ; some atoms have a stronger attraction for e- Nonpolar Covalent Bonds (e- shared equally) n Between the same atoms n Can be diatomic elements : 2, N 2, 2, F 2, 2, Br 2, I 2 n Electronegativity difference is 0.3 or less Diatomic elements e- dot formula Molecular formula 2 2 Single covalent bond 9

10 More Diatomic Elements N N e- dot formula Molecular formula 2 Double covalent bond You try N N N 2 N 2 Triple covalent bond Polar Covalent Bonds (e- are shared unequally) n Between different atoms n Electronegativity difference 0.4à 1.6 Polar Covalent Bonding: Linear e- dot formula Molecular formula atoms in the bond.9 Polar Covalent Bonding: Bent e- dot formula Molecular formula 4 e- pairs 2 bonds

11 Polar Covalent Bonding: Pyramid N e- dot formula Molecular formula N N N.9 Pyramid 4 e- pairs 3 bonds Valence-Shell Electron Pair Repulsion Theory (VSEPR) n VSEPR states that e- pairs around an atom try to get as far apart from one another as possible n Shapes of molecules are based on this idea ybridization n Carbon forms 4 equivalent bonds n Why? 2s 2 2p 2 PRMTIN 2s 1 2p 3,, YBRIDIZATIN (sp 3 ) 4 ne s & three p orbitals combine to form four orbitals of equal energy (sp 3 orbital) 11

12 sp 3 hybrid orbital When bonding, the promotion to hybridization can occur Ex: Methane C 4 & C C Shape: tetrahedron sp 3 hybrid orbital C Nonpolar Covalent Bonding: Tetrahedron C e- dot formula 4 e-pairs, 4 bonds C C Another type of linear C 2 C C C *nonpolar Molecular formula : C 4 12

13 Recap: Shapes of Molecules n 1. Linear n 2. Bent n 3. Pyramid n 4. Tetrahedron Polar Molecules DIPLES (polar molecules) a. define: Molecule with a asymmetrical (uneven) distribution of electrical charge (e-) b. examples: F,, Br, N 3, attracts electrons more c. Polar covalent bonding usually results in polar molecules n Case 1: Polar covalent bond between 2 atoms gives a polar molecule Ex:, Br n Case 2: Molecule with unsymmetrical arrangement of polar bonds Ex: N 3 N 2 PYRAMID BENT 105 d. Nonpolar Molecules n Case 1: Can result from polar bonds if there is a symmetrical distribution of charge (bonds) Ex: C 4, C 4, C C C C C 13

14 Case 2: Nonpolar covalent bonds always produce nonpolar molecules Ex: 2, N 2, 2, F 2, 2, Br 2, I 2 Nonmetals + Nonmetals Nonmetals + MLECULE Molecular SARED TRANSFERRED Metals + Nonmetals INS Empirical 1.7 or > Diatomic Elements Bonds to form..3 or less.4à 1.6 NNPLAR Share e- equally Nonpolar 2, 2 PLAR Share e- unequally Polar 2, N 3 Symmetrical arrangement C 4, C 4, C 2 Main Properties of Salts Ionic! n igh melting points and boiling points n Very hard, very brittle (breaks on cleavage plane) n Conduct electricity when dissolved in water n STP! 14

15 CEMICAL BND CNCEPT MAP Nonmetals + Nonmetals Nonmetals + MLECULE Molecular SARED 0.3 or less 0.4à 1.6 NNPLAR Share e- equally PLAR Share e- unequally TRANSFERRED Metals + Nonmetals INS Empirical 1.7 or > Exceptions to the Rule n e n n Be n B Something could bond here! Something could bond here! Something could bond here! Something could bond here! e B Be Nonpolar 2, 2 Polar 2, N 3 Symmetrical arrangement C 4, C 4, C 2 15