Name: Mr. Dolgos Regents Chemistry NOTE PACKET. Unit 4: Bonding & Naming

Transcription

1 Name: Mr. Dolgos Regents Chemistry NOTE PACKET Unit 4: Bonding & Naming 1

2 UNIT 4 BON::DING & Naming Compounds Vocabulary: 1. Molecule 2. Compound 3. Bond 4. Octet Rule 5. Exothermic 6. Endothermic 7. Ionic Bond 8. Covalent Bond 9. Oxidation number 10. Polyatomic ions 11. Stock system 12. Binary compound 13. Ternary compound 14. Polar molecule 15. Nonpolar molecules 16. Intermolecular forces (IMF s) 2

3 UNIT OBJECTIVES: Compounds can be differentiated by their chemical and physical properties Two major categories of compounds are ionic and molecular (covalent) compounds. Chemical bonds are formed when valence electrons are: transferred from one atom to another (ionic); shared between atoms (covalent); mobile within a metal (metallic). In a multiple covalent bond, more than one pair of electrons is shared between two atoms. Unsaturated organic compounds contain at least one double or triple bond. Molecular polarity can be determined by the shape and distribution of that charge. Symmetrical (nonpolar) molecules include CO 2, CH 4, and diatomic elements. Asymmetrical (polar) molecules include HCl, NH 3, and H 2 O. 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. When a bond is broken, energy is absorbed. When a bond is formed, energy is released. Atoms attain a stable valence electron configuration by bonding with other atoms. Noble gases have stable valence electron configurations and tend not to bond. 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. Electron-dot diagrams (Lewis structures) can represent the valence electron arrangement in elements, compounds, and ions. Electronegativity indicates how strongly an atom of an element attracts electrons in a chemical bond. Electronegativity values are assigned according to an arbitrary scale. The electronegativity difference between two bonded atoms is used to assess the degree of polarity in the bond. Metals tend to react with nonmetals to form ionic compounds. Nonmetals tend to react with other nonmetals to form molecular (covalent) compounds. Ionic compounds containing polyatomic ions have both ionic and covalent bonding. Determine the noble gas configuration an atom will achieve when bonding. Demonstrate bonding concepts, using Lewis dot structures, representing valence electrons: transferred (ionic bonding); shared (covalent bonding); in a stable octet. Distinguish between nonpolar and covalent bonds (two of the same nonmetals) and polar covalent bonds. 3

4 Lesson 1 Review What is a compound? A substance that has atoms of 2 or more chemically bonded together (Ex: NaCl) BOND = forces of between the protons (nucleus) of one atom and the electrons of another atom Only electrons participate in bonding Bonds are formed as a result of a LAW of CONSERVATION of ENERGY/MASS/CHARGE = during a chemical reaction, energy, mass, and charge can be created or destroyed (That means that all three are ). OCTET RULE à atoms bond together to get valence electrons around them Recall: Noble gases already have 8 valence electrons this is why they don t react/bond with other elements. Considering that radon is radioactive and doesn t hang around long enough to be converted into chemical compounds, answer the following questions: Which noble gas would be most likely to form a bond with another element, and how can you tell by looking at your PT? What do you think causes the noble gases to be more reactive as you move down the group? Which element Na, O, F, P, or S would be most likely to form a bond with this noble gas? Why do you think that is? 4

5 ENERGY & BONDING Energy associated with bonding: Bond formation = Energy is go from energy (unhappy atoms) to energy (happy atoms) creating a bond creates B A R F r b e o e s l r a o e m k r a b s e EXOTHERMIC = when energy is as a product A + B C + energy *NOTE: energy on side of arrow Ex: CaCl 2 + NaHCO 3 + H 2 O CaCO 3 + CO 2 + Breaking Bonds (NOT spontaneous) = Energy is go from energy (happy atoms) to energy (unhappy atoms) ripping two atoms apart takes ENDOTHERMIC = when energy is or needed as an ingredient to fuel the process A + energy B + C *NOTE: energy on side of arrow Ex: an ice pack chemicals combine, bonds are broken, and energy is consumed you feel cold because you re losing heat to the ice pack 5

6 Lesson 2:The Two Most Common Types of Compounds: 1. IONIC compounds formed by the TRANSFER of ELECTRONS from one atom (or polyatom) to another * * a. METAL LOSES e - to a NONMETAL Ex: Na x Cl b. METAL combines with a POLYATOMIC ION + [Na] _ c. POLYATOMIC ION combines with a NONMETAL d. POLYATOMIC ION combines with another POLYATOMIC ION 6

7 * 2. COVALENT compounds formed when 2 or more nonmetals SHARE ELECTRONS IONIC vs. COVALENT SUMMARY: NATURE of the ELEMENTS Metal + Nonmetal CLASSIFICATION Metal + Polyatomic Ion Nonmetal + Polyatomic Ion Polyatomic Ion + Polyatomic Ion Nonmetal + Nonmetal METALS = pure substances found to the left of the staircase atoms of a metal do not bond w/ other metal atoms metals share a sea of valence electrons allows metals to conduct electric (WAVE energy) Click here to see animation: 7

8 Lesson 3: Types of Bonds(con't) ( IONIC COVALENT Electron(s) Electrons Na x Cl H x H x O (click the link below for the animation) ( (click the link below for the animation) Physical Properties: High m.p./b.p (melting point/ boiling point) due to strong BONDS Electrolyte (conducts electric current in solution) ( Hard Electronegativity Difference = 2.3 Physical Properties: Low m.p./b.p. (melting point/ boiling point) due to weak IMF s Nonelectrolyte (does not conduct elec. current in solution) Soft Electronegativity Difference = 1.4 Na x Cl (3.5) (0.9) (3.2) (2.1) (2.1) The greater the difference between two elements the greater the percent The closer the difference is to zero, the greater the percent Electronegativity Scale

9 Click here to view vodca: ** We can classify a compound as ionic or covalent in one of two ways: 1) Look at the elements in the compound (TRUMP CARD): METAL and a NONMETAL = Two NONMETALS = 2) Do the math: Use Reference Table S for Electronegativity values The GREATER the electronegativity difference between the elements, the GREATER the ionic character The CLOSER the electronegativity difference between the elements, the GREATER the covalent character Practice: Find the electronegativity difference for each of the following compounds and then state whether each is ionic or covalent. Compound Electronegativity difference Ionic or covalent? 1. H 2 O 2. CaO 3. NaCl 4. FeCl 3 5. H 2 O 2 6. P 2 O 6 7. LiH 8. CH 4 9

10 Lesson 5: NAMING AND WRITING CHEMICAL FORMULAS: Each element within a compound has its own charge. We call these charges. Most common oxidation # s A. Rules for assigning OXIDATION STATES (numbers): 1) (elements not bonded to any other type of element) have an oxidation number of. This includes any formula that has only one chemical symbol in it (single elements & diatomic elements). Examples: 2) In (remember, they are neutral and have 2+ different elements bonded together), the sum of the must add up to so the ions within a compound have oxidation numbers equal to their oxidation # found on periodic table/individual charges. Ex: NaCl Ex: Mg 3 N 2 Ex: HNO 3 10

11 *We almost always write the (+) element first and the (-) element last in a compound formula. EXAMPLE: EXCEPTION to this rule: 3) GROUP 1 METALS always have an oxidation number of when in a compound (bonded to another species). GROUP 2 METALS always therefore have a oxidation number when located within a compound. Ex: Na Cl Ca Cl 2 4) FLUORINE is always a in compounds. The other HALOGENS (ex: Cl, Br) are also as long as they are the most electronegative element in the compound. Ex: Cu F Ni F 3 Cr Cl 2 Fe Br 3 5) HYDROGEN is a in compounds unless it is combined with a metal (and is at the end of the formula), then it is. Ex: H Cl H 2 S Li H Ca H 2 6) OXYGEN is USUALLY in compounds. Ex: Fe 2 O 3 C O 2 H 2 O When combined with FLUORINE (F), which is more electronegative, oxygen is. Ex: O F 2 When in a PEROXIDE oxygen is. A peroxide is a compound that has a formula of. Ex: H 2 O 2 Na 2 O 2 Li 2 O 2 Click here to view vodcast: 11

12 7) The sum of the oxidation numbers in polyatomic ions must equal the charge on the (see Table E). -2 Ex: (Cr 2 O 7 ) *Compounds containing have and bonds. Practice: Identify and list the polyatomic ions in the following compounds (use Table E). We ll do the first one together as an example. (NH 4 ) 3 PO 4 NaHCO 3 NH 4 NO 3 H 2 SO 4 KNO 3 Ex 1: OH - Oxidation number of Oxygen is ALWAYS (except in peroxides) Therefore H must have a charge of **Note: Must add up to 1 (that is the charge on OH - ) Ex 2: PO 4 3- Oxidation number of O = (4 x ( ) = -8 total) Oxidation number of P = (is that one of the choices on the table?) 12

13 Lesson 6:IUPAC NAMING RULES for IONIC COMPOUNDS: IUPAC = UNIVERSAL way of naming compounds; stands for International Union of Pure and Applied Chemistry Compounds have a COMMON name and a CHEMICAL name There is a SYSTEMATIC method for naming ionic compounds FORMULA CHEMICAL NAME 1. Name the element (or the METAL) 2. Name the element (or the NONMETAL) Replace the ending of the negative element with IDE Ex: fluorine à oxygen à Examples: NaCl (table salt) K 2 O CaBr 2 Al 2 S 3 LiI CHEMICAL NAME FORMULA Examples lithium bromide Sodium fluoride Magnesium chloride Potassium iodide 3. POLYATOMIC IONS are named exactly as they are seen on TABLE E Examples: NaOH KNO 3 Ammonium hydroxide Calcium phosphate 13

14 4. TRANSITION METALS tend to have more than one oxidation number so you must use a to indicate their oxidation number within a compound. The roman numeral appears in parentheses the element symbol (STOCK SYSTEM) Example: Cobalt chloride could have a formula of CoCl 2 or CoCl 3 since cobalt can have an oxidation number of +2 or +3. CoCl 2 CoCl 3 Name: Name: Write the formula for the following 1) zinc oxide = 2) iron(ii) chloride = 3) mercury(i) sulfide = 14

15 Lesson 7: IUPAC NAMING RULES for COVALENT COMPOUNDS: Recall: Covalent(molecular) = + 15

16 Name the following covalent compounds: Chemical Formula Chemical Name CO CO 2 N 2 O N 2 O 5 CCl 4 SF 6 Give the formulas for the following compounds: Chemical Name Chemical Formula Nitrogen monoxide Carbon(IV) fluoride Bromine pentachloride nitrogen(v) sulfide Sulfur tetrabromide 16

17 Lesson 8: LEWIS DOT DIAGRAMS for IONIC COMPOUNDS Gives us a PICTURE of the compound Shows us the ARRANGEMENT of atoms in the compound *Within IONIC COMPOUNDS there is a TRANSFER or DONATION of electrons from the METAL to the NONMETAL Steps for Drawing Ionic Bonding Lewis Dot Diagrams: 1) Draw all elements (of the given compound) and their individual Lewis Dot Diagrams. Then draw an arrow indicating the transfer of electrons from metal to nonmetal. Example: NaCl 2) Redraw your now bonded compound with dots and appropriate new CHARGES. Draw the Lewis Dot Diagram for the following ionic compounds: 1. KF 2. BaS 3. AlBr 3 17

18 Lesson 9: LEWIS DOT DIAGRAMS FOR COVALENT COMPOUNDS - Atoms that are bonded share valence electrons. - Sharing is what creates covalent bond. - When atoms bond covalently, new entity termed molecule is formed. - Nuclei are bound together by their mutual attraction toward the shared electrons. Bonding in Diatomic Molecules Hydrogen H + H H H or H H - each atom contributes e - to the bond - e - in bond belongs to both atoms (e - are shared) - now each atom has full shell (like He) - note hydrogen is first exception to octet rule Fluorine F + F F F or F F - Since both atoms share electrons in bond, both atoms have 8 valence electrons, octet rule is satisfied. Hydrogen fluoride H + F H F or H F Oxygen O + O O O or O = O - note that a molecule can have more than one covalent bond Nitrogen N + N N N or N N 18

19 Lesson 10:Polar and nonpolar covalent bonding There are two types of covalent bonds. The F 2 molecule is a good example of the first type of covalent bond, the nonpolar bond. Because both atoms in the F 2 molecule have an equal attraction (or affinity) for electrons, the bonding electrons are by the two atoms, and a nonpolar covalent bond is formed. Whenever two atoms of the same element bond together, a nonpolar bond is formed. A polar bond is formed when electrons are between two atoms. Polar covalent bonding occurs because one atom has a stronger affinity for electrons than the other (yet not enough to pull the electrons away completely and form an ion). In a polar covalent bond, the bonding electrons will spend a greater amount of time around the atom that has the stronger attraction for electrons. A good example of a polar covalent bond is the hydrogen-fluorine bond below. 19

20 Lesson 11: MOLECULAR POLARITY How can you tell if a molecule is polar or nonpolar? The polarity of the molecule is different than the polarity of the bond. The polarity of the molecule is determined the polarity and positioning of all the bonds in the molecule. Why is it important to know the polarity of a molecule? The polarity can tell you many things: 1) How high or low the melting and boiling point of the substance is 2) How easily the liquid form of the substance evaporates 3) Whether the substance will dissolve in water, or in some other solvent Molecular polarity causes intermolecular attractive forces, which is what allows certain adhesives (tapes, glues) to hold things together. Attractive forces also hold the two twisted strands of RNA together to form DNA. Attractive forces allow insects and geckos to walk up walls, even glass walls. Think of attractive forces as molecular Velcro you can attach and detach the molecules from each other without doing any damage to the molecules themselves. Some molecules have stronger Velcro than others. How do you know which ones these are? Read on! First thing you need to know is what is the shape of the molecule? Its shape determines its properties. 20

21 Lesson 12: Determining Molecular Polarity POLAR MOLECULES: Nonmetals in a molecule share electrons, sometimes equally (nonpolar bond) or unequally (polar covalent bond) when forming molecules. If the molecule does not have a symmetrical shape (asymmetrical), then there is a greater concentration of electrons on one side of the molecule compared to the other side. This makes one side charged partially negative and the other side partially positive. The oppositely charged ends of these molecules are poles, making the molecule polar or a dipole. Polar molecules can attract each other, δ+ end of one molecule attracting to the δ- end of the other molecule. If a molecule has polar bonds in an asymmetrical arrangement, the molecule as a whole will have a net polarity towards the more electronegative atom in the molecule. The net direction of electron pull towards the more electronegative atom can be diagrammed by determining the sole axis of symmetry and drawing an arrow towards the more electronegative atom. 21

22 S y m m e t r i c a l N o n p o l a r A s s y m m e t r i c a l P o l a r 22

23 Lesson 13 Intermolecular forces, A.K.A. IMF s ONLY IN COVALENT MOLECULES, NEVER IONIC COMPOUNDS! forces that act BETWEEN that hold molecules to EACH OTHER Only exist in GASEOUS & LIQUID states Called WEAK forces because they are much weaker than CHEMICAL BONDS *REMEMBER: IMF s occur BETWEEN(inter) molecules, whereas BONDING occurs WITHIN(intra) molecules Just Remember IMF s ARE NOT BONDS!!! 23

24 Type of IMF London dispersion forces (LDF s) Description/Example(s) Weakest of all the IMF s Only important for NONPOLAR molecules = Electron-electron repulsion creates BRIEF DIPOLES in atoms/molecules Dipole (dipole-dipole) Molecules such as HCl have both POSITIVE and a NEGATIVE ends, or POLES Two poles = Results from an UNEQUAL/ASYMMETRICAL sharing of electrons DIPOLE-DIPOLE = two molecules with permanent dipoles are attracted to one another TEMPORARILY DIPOLE MOMENT = measure of the STRENGTH of the dipole within a molecule (POLARITY) The GREATER the difference in ELECTRONEGATIVITY between atoms, the GREATER the POLARITY/DIPOLE MOMENT The HIGHER the dipole moment, the STRONGER the intermolecular forces (IMF s) The stronger the IMF s, the higher the m.p. and b.p. Hydrogen Bonds Specific type of DIPOLE interaction In a POLAR BOND, hydrogen is basically reduced to a BARE PROTON w/ almost no ATOMIC RADIUS of all IMF s by far Only occur in molecules containing AND,, or 24

25 SUMMING IT ALL UP: A FLOWCHART SNAP So, what should you be able to do now? 1) Identify whether a compound is molecular, ionic or metallic based on its properties 2) Draw dot diagrams of simple molecules 3) Draw structural formulas of simple molecules 4) Determine the shape of simple molecules 5) Determine if simple molecules are polar or nonpolar 6) If polar, identify the partially charged ends 7) Determine the attractive force type that attracts specific simple molecules to each other. 25

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