NOTES: UNIT 6: Bonding

Transcription

1 Name: Regents Chemistry: Mr. Palermo NOTES: UNIT 6: Bonding

2 Name: Key Ideas Compounds can be differentiated by their chemical and physical properties. (3.1dd) Two major categories of compounds are ionic and molecular (covalent) compounds. (5.2g) Chemical bonds are formed when valence electrons are transferred from one atom to another (ionic), shared between atoms (covalent), mobile within a metal (metallic). (5.2a) In a multiple covalent bond, more than one pair of electrons are shared between two atoms. (5.2e) Molecular polarity can be determined by the shape of the molecule and the distribution of charge. Symmetrical (nonpolar) molecules include CO2, CH4, and diatomic elements. Asymmetrical (polar) molecules include HCl, NH3, and H2O. (5.2l) When an atom gains one or more electrons, it becomes a negative ion and its radius increases. When an atom loses one or more electrons, it becomes a positive ion and its radius decreases. (5.2c) When a bond is broken, energy is absorbed. When a bond is formed, energy is released. (5.2i) Atoms attain a stable valence electron configuration by bonding with other atoms. Noble gases have stable valence configurations and tend not to bond. (5.2b) Physical properties of substances can be explained in terms of chemical bonds and intermolecular forces. These properties include conductivity, malleability, solubility, hardness, melting point, and boiling point. (5.2n) Electron-dot diagrams (Lewis structures) can represent the valence electron arrangement in elements, compounds, and ions. (5.2d) Electronegativity indicates how strongly an atom of an element attracts electrons in a chemical bond. Electronegativity values are assigned according to arbitrary scales. (5.2j) The electronegativity difference between two bonded atoms is used to assess the degree of polarity in a bond. (5.2k) Metals tend to react with nonmetals to form ionic compounds. Nonmetals tend to react with other nonmetals to form molecular (covalent) compounds. Ionic compounds contain polyatomic ions have both ionic and covalent bonding. (5.2h)

3 UNIT 6 BONDING AL ERMO.C O M LESSON 6.1 TYPES OF BONDS AL ERMO.C O M Objective: By the end of this video you will be able to: Identify whether a bond is being broken or formed based upon energy being absorbed or released Distinguish between the three types of bonds and Decide which type of bond is present based upon the atoms involved Classify a substance as Ionic, Covalent or Metallic based upon its properties What is a Bond? Force of attraction between two atoms The energy stored in a bond is potential energy Why do atoms Bond? Atoms bond together to get a full valence shell of electrons (8) to become STABLE (Stable Octet) Forming a Bond Energy is RELEASED (EXOTHERMIC) spontaneously Forms a STABLE compound Exception: Hydrogen can only have 2 (stable duet) 1

4 Breaking a Bond Energy is ABSORBED (ENDOTHERMIC) Stability decreases Ex. Ripping two atoms apart requires ENERGY Remember BARF Breaking bonds Absorbs (requires) energy Release of energy when bonds are Formed Check your understanding Identify whether a bond is being broken or formed based upon energy being absorbed or released 1. Ionic 2. Covalent 3. Metallic Three Types of Bonds Ionic Bonds Example: sodium reacts with chlorine Occur between: - METALS and NON-METALS - TRANSFER of ELECTRONS from metal to nonmetal to form a bond. electrostatic attraction 2

5 Properties of Ionic Compounds Hard Crystalline structure HIGH Melt/Boiling Pt SOLUBLE in water Conduct ELECTRICITY only in solution (aq) Electrolyte Compound that separates into ions in solution and is able to conduct electricity Check your understanding Distinguish between the three types of bonds and Decide which type of bond is present based upon the atoms involved Classify a substance as Ionic, Covalent or Metallic based upon its properties Covalent Bonds Occur between: - NONMETALS and NONMETALS - SHARING of ELECTRONS to obtain a full valence shell (stable) - Form MOLECULAR substances Why do they share instead of transfer? Each element is not strong enough to remove ( steal ) an electron from the other. **Trick to remember: SHARING is CARING 3

6 Properties of Covalent Compounds Soft Low melting and boiling pts (due to weak attraction between molecules) Do not conduct electricity due to lack of charged particles (ions) Metallic Bonds Between METAL atoms of the SAME element Ex. Au atoms in a gold ring Properties of Metals High MP and high BP because bonds are strong. Always capable of conducting electricity because of mobile electrons (freely flowing delocalized electrons) Sea of mobile electrons Example: Check your understanding What type of bond is created in following: a. KBr b. HI c. NO d. LiCl Distinguish between the three types of bonds and Decide which type of bond is present based upon the atoms involved Classify a substance as Ionic, Covalent or Metallic based upon its properties 4

7 Check your understanding: You should be able to: Distinguish between the three types of bonds and Decide which type of bond is present based upon the atoms involved Classify a substance as Ionic, Covalent or Metallic based upon its properties Identify whether a bond is being broken or formed based upon energy being absorbed or released Distinguish between the three types of bonds and Decide which type of bond is present based upon the atoms involved Classify a substance as Ionic, Covalent or Metallic based upon its properties Objective: By the end of this video you will be able to: LESSON 6.2 BOND POLARITY AL ERMO.C O M Determine how strongly an atom of an element attracts electrons in a chemical bond using electronegativity values from Table S. Determine the degree of polarity in a bond based upon the electronegativity difference between two bonded atoms. Bond Polarity Earth has 2 poles (north & south) Magnets also have 2 poles Bonds may also have 2 poles (dipole) depending upon their electronegativities TYPES OF COVALENT BONDS 5

8 Non-polar covalent bond Polar Covalent Bond Equal sharing of electrons Electronegativity difference (E.N.D.) between atoms Usually between identical atoms Ex. H 2 E neg 2.2 E neg 2.2 Unequal sharing of electrons E.N.D. between atoms (can be higher than 1.7) One atom is slightly negative and one atom is slightly positive. This is known as a dipole. Ex: HF Comparing Ionic and Covalent Bonds How to determine type of bond Nonpolar Metal & Nonmetal Type of Bond Non metal & non metal Polar Ionic Bond Covalent Bond E.N.D. 0.4 Non polar covalent E.N.D. > 0.4 Polar covalent Ionic Summary of Bond Types Example: Ionic, Polar or NP Covalent Nonpolar Polar Ionic Na-S C-Br C-C H-O F-F K-O 6

9 Check your understanding You should be able to: Determine how strongly an atom of an element attracts electrons in a chemical bond using electronegativity values from Table S. Determine the degree of polarity in a bond based upon the electronegativity difference between two bonded atoms. Determine how strongly an atom of an element attracts electrons in a chemical bond using electronegativity values from Table S. Determine the degree of polarity in a bond based upon the electronegativity difference between two bonded atoms. Objective: By the end of this video you will be able to: Construct Lewis dot diagrams for ionic compounds LESSON 6.3 LEWIS DIAGRAMS FOR IONIC COMPOUNDS AL ERMO.C O M Lewis Dot Diagram: Ionic Compounds Draw ion dot diagrams next to each other making sure that: - The ion charges cancel out (add up to zero) - The opposite charged ions are next to each other, and the like charged ions are as far away from each other as they can be. Recall Dot diagrams for positive ions (metals) x Dot diagrams for negative ions (nonmetals) 7

10 Example: Dot diagram of NaCl Example: Barium Sulfide Dot diagram of CaCl 2 Example: Aluminum Oxide Check your understanding: Can you construct Lewis dot diagrams for ionic compounds You should be able to: Construct Lewis dot diagrams for ionic compounds LESSON 6.4 LEWIS DIAGRAMS FOR COVALENT COMPOUNDS AL ERMO.C O M 8

11 Objective: By the end of this video you will be able to: Construct lewis dot diagrams for covalent compounds Determine the number of electrons shared in a covalent bond Lewis Dot diagrams: Covalent Compounds 1. Write the element symbols next to each other (if more than two symbols write the UNIQUE symbol in the center) 2. Count up the total number of valence electrons for all the elements 3. Put 8 electrons around the central atom (if only two atoms pick one to place them around) 4. Distribute the remaining valence electrons to the other atoms equally until you run out 5. Check to see if each atom has a complete valence shell (8 electrons except Hydrogen which has 2) Example H 2 O: Total # of valence electrons for H 2 O = 2(1) + 6 = 8 Total # of valence electrons for 2 chlorine atoms 7 x 2 = 14 Cl Cl **A shared pair of electrons counts for both atoms **Each atom of Fluorine now has 8 electrons. Example F 2 : Example: Draw dot diagram for HBr Total # of valence electrons for F 2 = 7 + 7= 14 9

12 Check your understanding: Construct lewis dot diagrams for covalent compounds 6. If all atoms do not have a full valence shell then you must ADD MULTIPLE BONDS (sharing of 2 or more PAIRS of electrons) Example: CO 2 How many electrons can be shared? Example: Draw the dot diagram for O 2 Single bond = sharing a pair (2) electrons Double bond = sharing 2 pair (4) electrons Triple bond = sharing 3 pair (6) electrons Stop and Think: Draw the dot diagram for N 2 Check your understanding: Construct lewis dot diagrams for covalent compounds Determine the number of electrons shared in a covalent bond 10

13 You should be able to: Construct lewis dot diagrams for covalent compounds Determine the number of electrons shared in a covalent bond LESSON 6.5 MOLECULAR POLARITY AL ERMO.C O M Objective: By the end of this video you will be able to: Determine the polarity of a molecule Determine the shape of a molecule Types of electron pairs Bonding pairs - form bonds Lone pairs - nonbonding e - Molecular Polarity depends on: 1. Bond Polarity 2. Shape of molecule (Symmetrical vs. nonsymmetrical) Shape caused by: VSEPR The Valence Shell Electron Pair Repulsion Valence electrons are arranged as far from one another as possible to minimize the repulsion between them (Like charges repel each other) 11

14 Polar Molecules A molecule is polar if it: - Contains POLAR BONDS - Is ASYMMETRICAL (not symmetrical) Non Polar Molecules A molecule is nonpolar if it: - Contains only NONPOLAR BONDS - Is SYMMETRICAL ****If there are LONE PAIRS on central atom then the molecule is automatically POLAR 1. LINEAR Must be asymmetrical SHAPES OF POLAR MOLECULES δ + δ - 2. BENT 2 pair of lone pair electrons on central atom 3. PYRAMIDAL 1 lone pair of electrons on central atom δ - δ + δ - δ + δ + δ + δ + 12

15 Check your understanding Determine the polarity of a molecule Determine the shape of a molecule SHAPES OF NONPOLAR MOLECULES 1. LINEAR Must be SYMMETRICAL δ + δ + δ - δ + δ - 2. TETRAHEDRAL Central atom bonded to 4 identical atoms Summary of Shapes and Polarity Example: Determine the molecular polarity and shape of CCl 4 If the central atom has... the shape is Bond type 1 or 2 bonds only linear Polar if asymmetrical Nonpolar if symmetrical 2 bonded pairs and 2 lone pairs bent polar 3 bonded pairs and 1 lone pair pyramidal polar Nonpolar because its symmetrical Tetrahedral 4 bonded pairs and 0 lone pairs tetrahedral Non-polar 13

16 Example: Determine the molecular polarity and shape of H 2 S Check your understanding: Determine the polarity of a molecule Determine the shape of a molecule Polar due to 2 pair of lone pair e- Bent You should be able to: Determine the polarity of a molecule Determine the shape of a molecule LESSON 6.6 INTERMOLECULAR FORCES AL ERMO.C O M Objective: By the end of this video you will be able to: Determine the type of intermolecular force that exists between covalent compounds Determine the effect of intermolecular forces on melting and boiling point WHAT TYPE OF FORCES HOLD MOLECULES TOGETHER? 14

17 Intermolecular Forces (IMF s) Weak forces of attraction BETWEEN molecules (covalent compounds) Types of Intermolecular Forces 1. Dispersion Forces 2. Dipole-Dipole 3. Hydrogen Bonding Dispersion Forces Weakest IMF Occurs between nonpolar molecules Explains how nonpolar molecules can exist in solid & liquid phase MORE ELECTRONS = GREATER FORCE Example: H 2 Dipole-Dipole Between polar covalent molecules Partial negative end of dipole attracted to partial positive end of another dipole The more polar the bond the greater the IMF between the molecules 15

18 Example: HCl Hydrogen Bonding Special case of dipole interaction. Strongest IMF Occurs between hydrogen of 1 molecule and F, O or N in another Remember H bonding is FON Example: NH 3 Practice: What type of IMF occurs between molecules of Cl 2 Dispersion force because Cl 2 is nonpolar Check your understanding: Recall Determine the type of intermolecular force that exists between covalent compounds The stronger the intermolecular force the greater the melting and boiling point of a substance 16

19 Example at STP Check your understanding: H 2 (g) H 2 O (l) Determine the effect of intermolecular forces on melting and boiling point You should be able to: Determine the type of intermolecular force that exists between covalent compounds Determine the effect of intermolecular forces on melting and boiling point 17