Chapter 4 Compounds and Their Bonds Octet Rule

Chapter 4 Compounds and Their Bonds  Octet Rule

Chapter 4 Compounds and Their Bonds Octet Rule and Ions Ionic Compounds Naming and Writing Ionic Formulas Polyatomic Ions Covalent Compounds Electronegativity and Bond Polarity Shapes and Polarity of Molecules Attractive Forces in Compounds 03/02/2020 1

Evidence for the Octet Rule Each filled shell (group 8A, noble gases) has eight valence electrons. Noble gases tend not to react. Stability of atom due to these eight electrons. Atoms like sodium tend to always lose one electron. Atoms like chlorine tend to always gain one electron. 03/02/2020

2 Octet Rule Atoms in a compound will lose, gain, or share eight electrons. Two types of compounds: Ionic and Covalent Ionic atoms gain or lose electrons to form ions. Covalent atoms share electrons 03/02/2020

3 Octet Rule 03/02/2020 4 Ionic Compounds Metals will always lose electrons. Group 1A metals will always lose one electron. What is its charge (valence)?

Group 2A metals will always lose two electrons. What is its valence? 03/02/2020 5 Ionic Compounds 03/02/2020

6 Ionic Compounds 03/02/2020 7 Ionic Compounds Non-metals (in an ionic compound) will always gain electrons. Group 7A will always gain one electron. What is the valence of this group?

Group 6A (Oxygen and Sulfur) will always gain two electrons What are their valences? 03/02/2020 8 Ionic Compounds 03/02/2020

9 Learning Check Predicting charges What valence will Barium have? What valence will Bromine have? What valence will Aluminum have? What valence will Nitrogen have? 03/02/2020 10

Common Valences 03/02/2020 11 Learning Check Potassium (K) in a compound will a) gain one electron b) lose one electron Potassium will have a valence of a) 1 b) +1

03/02/2020 12 Learning Check Sulfur (S) in an ionic compound will a) gain two electrons b) lose two electrons Sulfur will have a valence of a) 2 b) +2 03/02/2020

13 Ionic Compounds All ionic compounds consist of both positive ions (cations) and negative ions (anions). Why both? Ionic compounds are always solids at room temperature with high melting points. MP of NaCl = 801oC 03/02/2020

14 Ionic Compounds An ionic formula is always written with the cation first followed by the anion. always electrically neutral that means the total positive charges must equal the total negative charges. always empirical lowest whole number subscripts. 03/02/2020

15 Ionic Compounds A subscript of 1 is always understood and never written. ex) NaCl, consists of one sodium cation and one chlorine anion. Subscripts of 2, 3, 4, etc. are added after each symbol when needed.

ex) Al2O3 consists of two aluminum cations and three oxygen anions. 03/02/2020 16 Ionic Compounds Formation of an Ionic Compound using Lewis Dot symbols 03/02/2020

17 Learning Check Show the formation of CaF2 and Li2S using Lewis Dot symbols. 03/02/2020 18 Ionic Compounds Writing ionic formulas requires that all

charges balance to make it neutral. Ex) Al+3 +3 , Cl-1 -1

-1 -1 +3 + -3 = 0 AlCl 3 03/02/2020 19 Learning Check

Write formulas between each of the following ions. Mg+2 , O-2 Li+1 , N-3 Sr+2 , Br-1 Al+3 , S-2 03/02/2020 20 Nomenclature Naming ionic compounds requires that you

determine whether the cation (metal) has a fixed or a variable charge. Main group metals have fixed charges. Exception: Sn and Pb 03/02/2020 21 Nomenclature Transition group metals have variable charges.

Exception: Ag and Zn Naming an ionic compound whose cation has a fixed charge: Name the metal (cation) first. 2. Name the non-metal (anion) second, but change its suffix to ide. 1. 03/02/2020

22 Nomenclature Naming an ionic compound whose cation has a variable charge: Determine the charge of the cation by deduction. 2. Name the metal (cation) first followed by its charge in (roman numerals). 3. Name the non-metal (anion) second, but change its suffix to ide. 1.

03/02/2020 23 Learning Check Name the following compounds with FIXED charges. NaBr CaO MgCl2 Al2O3 ZnF2

03/02/2020 24 Learning Check Name the following compounds with VARIABLE charges. FeCl2 Cu2S MnO2 Cr2S3 SnBr2

03/02/2020 25 Nomenclature Writing formulas from a name. Once again, an ionic compound is electrically neutral. Must figure out how many of each ion is needed to make it neutral. Roman numeral (if present) is that metals valence. 03/02/2020

26 Nomenclature Rules: 1. Write the symbol for each element, including its charge. 2. Determine the number(s) of each ion required to produce a neutral compound. 3. Write the formula with the cation first and the anion second, including their subscripts. 03/02/2020

27 Learning Check Write the formulas for: sodium oxide aluminum iodide lead(II) sulfide iron(III) fluoride magnesium nitride 03/02/2020 28

Polyatomic Ions A group of atoms bonded together with a net charge. Most common: P, N, S, and C bonded from one to four oxygen atoms. Less common: transition metals like Cr and Mn bonded to oxygen atoms. Less common: Cl, Br, and I bonded to oxygen atoms. 03/02/2020

29 Polyatomic Ions Do not need to memorize these! But being able to recognize them is ciritical! NO3-1 = nitrate CO3-2 = carbonate NO2-1 = nitrite

OH-1 = hydroxide SO4-2 = sulfate HCO3-1 = bicarbonate CrO4-2 = chromate ClO3-1 = chlorate PO4-3 = phosphate ClO4-1 = perchlorate

NH4+1 = ammonium SO3-2 = sulfite MnO4-1 = permanganate 03/02/2020 30 Polyatomic Ions These ions ALWAYS keep there name. Changing the name alters the meaning! Ex) Na2SO4 = sodium sulfate

If you called this sodium sulfide, then the formula is: Na2S. 03/02/2020 31 Naming Compounds with polyatomic ions Note: if the ammonium ion is present, then name it first followed by the name of the anion with the ide suffix. 1. Identify the metal present as having a fixed

or variable charge. If fixed, name the metal. b) If variable, name the metal followed by its charge in roman numerals. a) 03/02/2020 32 Naming Compounds with polyatomic ions 2. Name the polyatomic ion present keeping

its name EXACTLY the same as on the handout. Ex) K2CO3 = Ex) FeSO4 = 03/02/2020 33 Writing Formulas Once again, all ionic formulas must have an equal number of positive and negative charges.

If more than one polyatomic ion is required, then it is put in parenthesis with a subscript outside of these. 03/02/2020 34 03/02/2020 35 Learning Check Name each compound.

Na3PO4 Zn(OH)2 = V(NO3)3 = 03/02/2020 36 Learning Check Write the formulas for: lithium nitrite nickel(II) chlorate aluminum sulfate

03/02/2020 37 Covalent Compounds Covalent bonds form when two atoms share electrons to achieve an octet. Simplest case is when two Hydrogen atoms form an H2 molecule. Each atom has one electron. Note that an octet for Hydrogen is two

electrons. 03/02/2020 38 03/02/2020 39 Formation of F2 In F2 each F atom has seven valence electrons.

The odd electrons can pair up to form a bond. 03/02/2020 40 Formation of CH4, Methane C has four valence electrons and each H has one. These pair up to form four bonds.

03/02/2020 41 Multiple Bonds In some cases, a multiple bond may be needed to satisfy the octet rule. Ex) N2 03/02/2020 42

Making a Lewis Structure In general, a Lewis Structure can be set up as follows. Determine the total number of valence electrons from all atoms in the formula. 2. Set up a skeleton structure by putting the first element in formula in the middle. Place all the others around this central atom. 1. 03/02/2020

43 Making a Lewis Structure Draw a bond from the central atom to each external atom, then fill in the external atoms until each has an octet. 4. Count up all electrons and compare to the total in step #1. 3. a) b)

03/02/2020 If all are used, go to step #5. If some are left, then place on central atom as lone pairs to complete its octet. 44 Making a Lewis Structure 5. Check the central atom for an octet. a) b)

If yes, then you are finished. If no, then you need to have some multiple bonds. Do Lewis Structures for: 03/02/2020 CF4, NCl3, SBr2, H2O, and CO2

45 Naming Covalent Compounds Covalent compounds use prefixes to indicate the number of atoms of each type. one = mono (used only for second element!) two = di three = tri four = tetra five = penta six = hexa 03/02/2020

46 Naming Covalent Compounds Name the first element in the formula add the appropriate prefix if there is more than one. Name the second element in the formula change the suffix to ide include a prefix to indicate the subscript even if it is 1. 03/02/2020

47 Learning Check Name: CO2 NO NCl3 PCl5 03/02/2020 48 Writing a Covalent Formula

Since electrons are shared, charges do NOT apply. Simply look at the prefixes and apply them. Ex) sulfur trioxide = Ex) dinitrogen tetroxide = 03/02/2020 49 The Big Picture A compound is IONIC if: The first element in the formula or name is a

metal or the NH4+1 ion. A compound is COVALENT if: The first element in the formula or name is a non-metal or metalloid. 03/02/2020 50 Learning Check Decide if the compound is IONIC or COVALENT, then name it.

Ca3(PO4)2 FeBr3 SCl2

Cl2O MnSO4 03/02/2020 51 Learning Check Decide if the compound is IONIC or COVALENT, then write the formula.

lithium nitride ammonium chloride carbon monoxide cobalt(II) carbonate boron trifluoride 03/02/2020 52 Bond Polarity In most covalent bonds, the electrons are not

shared equally. Rather, one element has a stronger desire for the electron pair. 03/02/2020 53 Electronegativity The ability of an atom to attract the electron pair in the bond is called its electronegativity. The element fluorine has the greatest desire

and is assigned the value of 4.0. All others are compared to fluorine. 03/02/2020 54 Electronegativities 03/02/2020 55 Covalent Bonds

Non-polar Covalent Occurs when the difference in electronegativity is zero. Ex) Cl-Cl, O-O, and N-Cl Polar Covalent All other covalent bonds Ex) H-I, N-F, O-H, H-F 03/02/2020 56 Ionic Bonds Always occur between metal and non-metal

regardless of difference in electronegativity. Ex) Na-Cl, Mg-S, Al-Br 03/02/2020 57 Polar Covalent Bonds Use a partial positive charge (d+) over the less electronegative atom. Use a partial negative charge (d-) over the more electronegative atom.

Ex) H Cl d+ 03/02/2020 d- 58 Shapes of Molecules VSEPR theory valence shell electron pair repulsion

States that bonding pairs of electrons will completely repel each other We will limit this to two, three, or four pairs of electrons. 03/02/2020 59 Shapes of Molecules Two pairs of electrons will point in opposite directions producing a linear geometry

03/02/2020 60 Shapes of Molecules Three pairs of electrons will point at the corners of an equilateral triangle, which is called trigonal planar 03/02/2020 61

Shapes of Molecules Four pairs of electrons will produce a three dimensional object known as tetrahedral 03/02/2020 62 Shapes of Molecules If one of the pairs in the tetrahedral shape is a lone pair, then the shape is called trigonal

pyramidal 03/02/2020 63 Shapes of Molecules If two of the pairs in the tetrahedral shape are lone pairs, then the shape is called bent 03/02/2020

64 Polarity of Molecules Molecules with polar bonds can produce non-polar molecules when they are symmetrical. While the bonds in carbon dioxide are polar, the molecule itself is non-polar. O 03/02/2020 C

O 65 Polarity of Molecules Similarly, in BF3 this molecule is also non- polar because the polar bonds cancel each other out. F B F

03/02/2020 F 66 Polarity of Molecules However, if you have different external atoms, then the molecule will be polar. H

C O H 03/02/2020 67 Polarity of Molecules The trigonal pyramidal and bent geometries will always be polar.

H H H N O H H 03/02/2020

68 Summary Molecules are non-polar when they have geometries of linear, trigonal planar, or tetrahedral AND all of the external atoms are the same. Molecules are polar when they have different external atoms or have geometries of trigonal pyramidal and bent. 03/02/2020

69 Attractive Forces Molecules that are polar have dipole-dipole intermolecular forces. 03/02/2020 70 Attractive Forces In a few cases, the dipole-dipole force is

exceptionally strong. This occurs when Hydrogen is bonded to either N, O, or F and the N, O, or F atom has one or more lone pairs. This interaction is called Hydrogen Bonding. 03/02/2020 71 Attractive Forces A hydrogen bond is a strong attraction

between a H atom on one molecule and a lone pair of electrons on another molecule. 03/02/2020 72 Attractive Forces Non-polar molecules have very weak London Dispersion forces. These forces are due to the fact that

electrons in our atoms are constantly moving and occasionally produce a brief dipole when they are not evenly distributed. 03/02/2020 73 Attractive Forces 03/02/2020 74

Importance of Forces The type and strength of forces determines many physical properties like melting and boiling points. 03/02/2020 75 Summary of Forces

03/02/2020 76 Learning Check What types of forces would each of the following substances have? Cl2 HF KF OF2

03/02/2020 77

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