Chapter 15 & 16: Bonding Why Atoms Combine Most of the matter you see around you is formed by compounds and mixtures. Most of the matter you see around you is formed by compounds and mixtures. There is some matter that is in the form of elements. Can you name some? There is some matter that is in the form of elements. Can you name some? Oxygen: present in the air Iron: found in dirt and sand as iron fillings Compounds have properties that are different than their elements. Compounds have properties that are different than their elements. Ex: what are the properties of Sodium? it is a metal, solid, soft, very reactive Ex: what are properties of Chlorine? it is a gas, green, nonmetal, and poisonous Ex: what are the properties of Sodium Chloride? white to clear in color, hard, solid, not very reactive, not poisonous Examples of Elements and Their Compounds Sugar CFCs Sodium chloride Can you name the different elements and their properties? Now name the compounds properties. Chemically Stable Atoms An atom is chemically stable if its outer energy level is completely filled with e- An atom is chemically stable if its outer energy level is completely filled with e- Which group of the periodic table is the only group with all chemically stable atoms? Which group of the periodic table is the only group with all chemically stable atoms? Group 8A: The Noble Gases Ex: Each Noble gas has 8 e- in their outer shell. This is called the Octet Rule. Octet Rule says that all elements would like to have 8 e- in their outer shell. Valence Electrons: the e- in the highest occupied energy level of an elements atoms. Valence Electrons: the e- in the highest occupied energy level of an elements atoms. You can find the number of valence e- by the group number. You can find the number of valence e- by the group number. Ex: group 3A = 3 valence e- Ex: group 5A = 5 valence e- Below is an example of a Carbon atom. Below is an example of a Carbon atom. It has 4 valence e- in its outermost energy level It has 4 valence e- in its outermost energy level Electron Dot Diagram Diagrams that show valence e- as dots. Diagrams that show valence e- as dots. The element symbol is written with the number of valence e- drawn around it. The element symbol is written with the number of valence e- drawn around it. The first dot should be placed on the right side of the symbol and then add 1 dot at a time in a clockwise fashion. The first dot should be placed on the right side of the symbol and then add 1 dot at a time in a clockwise fashion. If there is 1 e- place it on the right side of the symbol. If there is 1 e- place it on the right side of the symbol. If there are only 2 e- place them on the right and left sides of symbol. If there are only 2 e- place them on the right and left sides of symbol. Any single electrons are unpaired electrons. Two electrons in one area is said to be paired Any single electrons are unpaired electrons. Two electrons in one area is said to be paired These unpaired e- might make 2 single covalent bonds, as in the case of H 2 O. Or they might make 1 double covalent bond, as in the case of CO 2. These unpaired e- might make 2 single covalent bonds, as in the case of H 2 O. Or they might make 1 double covalent bond, as in the case of CO 2. When Lewis dot diagrams are used for compounds, "x" are often used to substitute for the dots of 1 or more elements in order to show which e- came from which element. When Lewis dot diagrams are used for compounds, "x" are often used to substitute for the dots of 1 or more elements in order to show which e- came from which element. Hydrogen and Oxygen to form Water Transition Metals are variable Electron Configurations for Cations Remember a cation loses e- and becomes more positive. Remember a cation loses e- and becomes more positive. Normal config for Na: 1s 2 2s 2 2p 6 3s 1 Normal config for Na: 1s 2 2s 2 2p 6 3s 1 Cation config: 1s 2 2s 2 2p 6 Cation config: 1s 2 2s 2 2p 6 Note 1 electron missing ! The 3s orbital is gone!!! Electron Configurations for Anions Remember to form an anion an atom gains electrons! Remember to form an anion an atom gains electrons! Electron config of Cl: Electron config of Cl: 1s 2 2s 2 2p 6 3s 2 3p 5 Anion config: 1s 2 2s 2 2p 6 3s 2 3p 6 Note change in number of P electrons Review of Bonding Types Ionic Bonding Ionic Bonding Covalent Bonding Covalent Bonding Nonpolar Covalent Bonding Nonpolar Covalent Bonding Polar Covalent Bonding Polar Covalent Bonding Metallic Bonding Metallic Bonding Ionic Bond: One big greedy thief dog! Ionic bonding can be best imagined as a big dog stealing another dog's bone. If the bone represents the e- that is up for grabs, then when the big dog gains an e- he becomes negatively charged and the little dog who lost the e- becomes positively charged. The 2 ions are attracted very strongly to each other as a result of the opposite charges.Ionic Bond: One big greedy thief dog! Ionic bonding can be best imagined as a big dog stealing another dog's bone. If the bone represents the e- that is up for grabs, then when the big dog gains an e- he becomes negatively charged and the little dog who lost the e- becomes positively charged. The 2 ions are attracted very strongly to each other as a result of the opposite charges. Formation of Ionic Compounds Anions (-) and cations (+) have opposite charges. Anions (-) and cations (+) have opposite charges. They attract one another by electrostatic forces. They attract one another by electrostatic forces. The attraction that bind these oppositely charged ions are called ionic bonds. The attraction that bind these oppositely charged ions are called ionic bonds. The metal gives its electron(s) to the nonmetal. The metal gives its electron(s) to the nonmetal. Covalent Bonds: Dogs of equal strength. Covalent bonds can be thought of as 2 dogs with equal attraction to the bone. Since the dogs (atoms) are identical, then the dogs share the pairs of available bones evenly. Since 1 dog does not have more of the bone than the other dog, the charge is evenly distributed among both dogs. The molecule is not "polar" meaning one side does not have more charge than the other.Covalent Bonds: Dogs of equal strength. Covalent bonds can be thought of as 2 dogs with equal attraction to the bone. Since the dogs (atoms) are identical, then the dogs share the pairs of available bones evenly. Since 1 dog does not have more of the bone than the other dog, the charge is evenly distributed among both dogs. The molecule is not "polar" meaning one side does not have more charge than the other. Molecules and Covalent Bonds:Molecules and Covalent Bonds: Most atoms become more chemically stable by sharing e-, rather than by losing or gaining e- Neutral particles formed as a result of electron sharing are called molecules A bond that forms between atoms when they share electrons is known as a COVALENT BOND. Polar Covalent Bonds: Unevenly matched, but willing to share. These bonds can be thought of as 2 dogs that have different desire for bones. The bigger dog has more strength to possess a larger portion of the bones. Sharing still takes place, but is an uneven sharing. In the case of the atoms, the e- spend more time on the end of the molecule near the atom with the greater electronegativity (desire for the e-) making it seem more negative and the other end of the molecule seem more positive.Polar Covalent Bonds: Unevenly matched, but willing to share. These bonds can be thought of as 2 dogs that have different desire for bones. The bigger dog has more strength to possess a larger portion of the bones. Sharing still takes place, but is an uneven sharing. In the case of the atoms, the e- spend more time on the end of the molecule near the atom with the greater electronegativity (desire for the e-) making it seem more negative and the other end of the molecule seem more positive. Polar and Nonpolar MoleculesPolar and Nonpolar Molecules Polar Molecule: one that has a positive end and a negative end Note the picture below: one end of the molecule SEEMS to have a negative (red) and the other end seems to be positive (blue)Note the picture below: one end of the molecule SEEMS to have a negative (red) and the other end seems to be positive (blue) Here is an animation of a polar molecule forming. Notice that at one end of the molecule it is + and the other end of the molecule is -Here is an animation of a polar molecule forming. Notice that at one end of the molecule it is + and the other end of the molecule is - Non-polar molecules: a molecule that does not have oppositely charged ends. Both ends are either +, or, -Non-polar molecules: a molecule that does not have oppositely charged ends. Both ends are either +, or, - Note in the diagram the molecules are the same. They come together and form a non-polar compound. E: N 2 nitrogen gas occurs as 2 nitrogen atoms bonded together forming a non-polar molecule. This is an example of atoms coming together and forming a POLAR MOLECULE. Watch the interactions between the + atoms and the atoms.This is an example of atoms coming together and forming a POLAR MOLECULE. Watch the interactions between the + atoms and the atoms. Metallic Bonds: formed by the attraction between positively charged metal ions and the electrons around them.Metallic Bonds: formed by the attraction between positively charged metal ions and the electrons around them. Metallic Bonds: Mellow dogs with plenty of bones to go around. These bonds are best imagined as a room full of puppies who have plenty of bones to go around and are not possessive of any one particular bone. This allows the e- to move through the substance with little restriction. The model is often described as the "kernels of atoms in a sea of e-" Metallic Bonds & Properties Metals are made of closely packed cations rather than neutral atoms. Metals are made of closely packed cations rather than neutral atoms. The cations are surrounded by mobile valence e- which can drift freely from one atom to the next. The cations are surrounded by mobile valence e- which can drift freely from one atom to the next. Bond Dissociation Energies The total energy required to break the bond between two covalently bonded atoms. The total energy required to break the bond between two covalently bonded atoms. See table16.3 pg. 448 See table16.3 pg. 448 Lewis Structures Again! Resonance Structures: structures that occur when it is possible to write two or more valid electron dot formulas that have the same number of electrons pairs for a molecule or ion. Resonance Structures: structures that occur when it is possible to write two or more valid electron dot formulas that have the same number of electrons pairs for a molecule or ion. Exceptions to the Octet Rule Exceptions occur whenever the total number of valence electrons is an odd number. Exceptions occur whenever the total number of valence electrons is an odd number. Exceptions can also occur for an expanded octet (more than 8) or a deficient octet (less than 8). Exceptions can also occur for an expanded octet (more than 8) or a deficient octet (less than 8). Deficient Octet Expanded Octet VSEPR Theory Because e- pairs repel, molecular shape adjusts so the valence e- pairs are as far apart as possible! Because e- pairs repel, molecular shape adjusts so the valence e- pairs are as far apart as possible! THE E- HATE EACH OTHER!! THE E- HATE EACH OTHER!! Trigonal Planar BENT BENT PYRAMIDAL Unpaired electrons VSEPR Box Idea! Put your molecule in a box and use it to get the electrons as far away from each other as possible!! Get the electrons as far away from each other as possible!!! Polar Molecules One end of the molecule is slightly negative and the other end is slightly positive. One end of the molecule is slightly negative and the other end is slightly positive. A molecule with 2 such poles is dipolar or a dipole. A molecule with 2 such poles is dipolar or a dipole. The element with the higher electronegativity value (or the most dots) will attract the shared e- for the majority of the time. This makes that end of the molecule the NEGATIVE end! The element with the higher electronegativity value (or the most dots) will attract the shared e- for the majority of the time. This makes that end of the molecule the NEGATIVE end! Polar Bonds A molecule can be covalent but have polar bonds in which one end of the bond is (+) and the other end is () A molecule can be covalent but have polar bonds in which one end of the bond is (+) and the other end is () Polar Covalent Bond ++++ ----