Chemical Bonds & Naming Compounds

Chemical Bonds & Naming CompoundsAn assessment review

Chemical Bonds and Naming Compounds AssessmentMONDAY!!• 27 questions

• 12 Level 2 questions • All multiple choice, includes naming compounds & acids• Level 2 = approaching standard, equivalent to a C, or 2.0

• 14 Level 3 questions • 13 multiple choice includes naming compounds & acids• 1 short answer on solubility & conductivity of ionic bonds• Level 3 = meets standard, equivalent to a B, or 3.0

• 1 Level 4 question • Ionic vs. atomic radius• Level 4 = exemplary, equivalent to an A, or 3.75 & above• Must be answered to reach 4.0, “A”

• Periodic tables, flow charts, & bond table summary provided

Instructions1. These notes are organized into 3 sections

i. Part I: Chemical Bondsii. Part II: Naming Compounds and Acidsiii. Part III: Level 4 “challenge” question for students working

towards the 4.0 (A) exemplary standard2. Read through & highlight these notes. 3. Follow any instructions or internet links or practice

problems4. Come to class on Wednesday/Thursday prepared with

questions and to review

PART I- Chemical BondsThree students were discussing their ideas about chemical bonds. This is what they said:

Jane: I think a chemical bond is produced by a molecule. It is a substance made up of matter that holds atoms together, like in a ball & stick molecular model

Chemical BondsWill: I think a chemical bond is an attraction between atoms. It’s caused by electromagnetic forces, and is not made of matter.

Chemical BondsLeta: I think a chemical bond is a structural part of an atom that connects it to other atoms, like the hook & loop system in velcro.

Which student do you most agree with and why?

Chemical BondsWhich student do you most agree with and why?

• The best response is Will’s. • A chemical bond is an attraction between atoms; it is not made up of

matter that holds atoms together, and it is not a structural part of an atom.

• Two or more atoms are linked together by chemical bonds.• There two general types of chemical bonds:

• Intramolecular forces - bonds between atoms• The four types are nonpolar covalent, polar covalent, & ionic, and metallic.

• Intermolecular forces -bonds between molecules already bonded by intramolecular forces

• One example is hydrogen bonds

• Chemical bonds are formed between atoms & molecules as a result of forces of attraction between electrons & protons.

Intramolecular forcesBonds between atoms

(in this case polar covalent)

Chemical Bonds

Intermolecular forcesBonds between

molecules

Bond SummaryType of Bond

Types of ElementInvolved

What’s Holding the

Bonds Together?

Electronegativity Difference

Relative Melting

Point

Relative Bond

Strength

Relative Bond

Length

Misc.

Ionic(ionic

compounds)

Metal (cation) & Non Metal

(anion)

Transfer of electrons

between (-)anion & (+)

cation

≥ ~1.7 High Weak RelativelyLong

Many are soluble in

water allowing for electrical conductivity

Polar Covalent(covalent

molecules)

Non Metal& Non Metal

Unequalsharing of electrons

~0.4 to ~1.7 Low Strong RelativelyShort

Strong intermolecular forces b/c unequal sharing of electronsresults in some atoms having –or + “poles”

Non polarCovalent(covalent

molecules)

Non Metal & Non Metal

Sharing of electrons ≤ 0.4 Extremely

lowStrongest Very short

(relatively)

Weak intermolecular

forces

Metallic Metals & Metals

“Sea of Electrons”

n/a Very high Weakest

Intermolecular Forces

(Hydrogenbonds)

CovalentMolecules

Attraction between (+)

charged atoms on molecule w/(-)

charged atoms on another

n/aRelatively low

(but depends on the

molecule/compound)

Ionic Compounds• TERMS TO KNOW If you can’t look at these and know their

definition, take some time during class today and define them in your lab journal!• Ion• Cation• Anion• Polyatomic ion• Ionic Compound• Oxidation number (a.k.a. ionic charge number)• Rule of Zero Charge

Ionic CompoundsTERMS TO KNOW • Ion- an atom that has an uneven number of electrons because it has lost of

gained electrons • Cation- ions with a positive charge because they have lost electrons (remember

CATions are “pawsitive”). • Metals form cations

• Anion- ions with a negative charge because they have gained electrons• Non metals form anions

• Polyatomic Ion (a.k.a. molecular ion)- a group of covalently bonded nonmetals with an uneven number of electrons (so they carry a charge)• The table of polyatomic ions are found on the back of your class periodic table, or

you can download one from my class webpage.• Most are anions, but a key polyatomic cation is ammonium (NH4

+1)• Ionic Compound-a compound composed of positive and negative ions, formed

when metal and nonmetal atoms combine.• Oxidation number (a.k.a. charge number)- the number of electrons an element

will gain or lose when it forms an ion• Oxidation number is associated with the number of valence electrons an elements

gains or looses to form an electron configuration like is nearest noble gas neighbor (a.k.a. the “octet rule”)

• Rule of Zero Charge- in an ionic compound, the positive charges on the metal cations and the negative charges on the nonmetal anions must add up to 0

https://www.youtube.com/watch?v=MJZeZvDxcx8

Properties of Ionic Compounds• Formed by the attraction between the positive cation

(metals) and negative anions (nonmetals/polyatomic ions).

• Electrons are transferred• Electronegativity difference between atoms in an ionic

bond is ≥ ~1.7 • Melting points of ionic compounds are relatively high

• But ionic bonds are relatively weak• High melting point due to the large number of attractions and

the crystal structure form between the ions• Crystal structure of ion compounds is formed by alternating

structure of positive & negative ions• Their atoms are relatively far apart; bond length is

relatively long• Recall: what’s the greatest influence on force of attraction

(Coulombic attraction)? Distance between charged particles! • Many ionic compounds are soluble (dissolved in

solution)• When dissolved, ionic compounds breakdown into their

component ions and can conduct electricity

https://www.youtube.com/watch?v=aKTmn2YLP2A

Electronegativity & Bonding

One way to tell the difference between ionic and covalent bonds is to compare their electronegativity

Electronegativity & Bonding1. What does electronegativity tell you about

an element?

Measure of an atom’s ability to gain an electron FROM ANOTHER ATOM

a. If an element has a high electronegativity, the element is good at…

Gaining electrons

a. If an element has a low electronegativity, the element…

Losing electrons

Electronegativity & Bonding2. Do you notice a pattern between metals

and non-metals in Model 1? Metals relatively low, non-metals relatively high electronegativity

3. As you move down a group on the periodic table what typically happens to electronegativity? Electronegativity decreases

4. As you move from left to right across a period what typically happens to electronegativity? Electronegativity increases

5. Which corner of the periodic table are the elements that are the best at attracting electrons? Top right

6. Which corner of the periodic table are the elements that have difficulty holding onto to their electrons? Bottom left

Electronegativity & Bonding7. Make a prediction: if two atoms with

very different electronegativitiesget close together, the atoms are likely to (share electrons / transfer electrons / bounce off without reacting). Explain your reasoning below.

7. Make a prediction: if two atoms with similar electronegativities get close together, the atoms are likely to (share electrons / transfer electrons / bounce off without reacting). Explain your reasoning below.

Electronegativity & Bonding

~1.7 or greater

~1.7 or less

NaCl3.16 (chlorine)

- 0.93 (sodium)2.23 CO2

3.44 (oxygen)- 2.55 (carbon)0.89

Which pair represents ionic

and which represent covalent?

~1.7 or greater

~1.7 or less

NaCl3.16 (chlorine)

- 0.93 (sodium)2.23 CO2

3.44 (oxygen)- 2.55 (carbon)0.89

• An easy analogy to use when it comes to chemical bonds is to think of it as dogs sharing or transferring a bone.

• The diagrams to the right illustrate the differences in ionic, polar covalent, and nonpolar covalent bonds

• Note the electronegativity differences, too

Covalent Molecules• So far we have talked about

bonds that form between metals and non-metals, which result in the complete transferof e- and an ionic bond

• Covalent molecules form between non-metals when electrons are shared

Covalent Molecules• Molecular compounds form when the

electronegativity difference is small• Because atoms are attracting e- to

the same extent, the e- will be shared rather than transferred

• Anytime a non-metal reacts with a non-metal, e- are shared

• This results in a covalent bond• The overlapping of the electron

clouds and sharing of e- holds the atoms together very strongly

• Atoms that are held together by a covalent bond are called molecules

Comparing Ionic & Molecular Compounds

- + -

+ - +

- + -

+ - +

+

-

+

-

Ionic Compound (NaCl) Covalent Molecule (H2O)

• All bonds are equivalent, if one breaks they all break

• Ions exist independently, the formula represents the ratio of cations to anions

• During melting or dissolving the ions separate completely (intramolecular forces break)

• Molecules exist as tiny units bound by strong covalent bonds

• During melting or boiling molecules remain intact as tiny units of matter; the covalent bonds are not broken

Intermolecular forces are broken, intramolecular are not

Bond StrengthWhen comparing the relative strength of chemical bonds, it’s best to ask yourself: how much energy would be required to separate (“break”) the bonds?

Comparing Ionic & Molecular Compounds

- + -

+ - +

- + -

+ - +

+

-

+

-

Ionic Compound (NaCl) Covalent Molecule (H2O)

• During melting or dissolving the ionic compounds “break apart”

• Intramolecular forces of ionic bonds break

• Ions separate completely

• During melting or boiling molecular compounds stay together as tiny units of matter

• Intramolecular forces of the covalent bonds are not broken

• Weaker Intermolecular forces are broken,

Bond Strength

Bond Strength & Melting Point

• Why do the strongest bonds (covalent) have the lowest melting points?• Because when covalent molecules

molecules melt, the intermolecular forces break, not the intramolecular

• Metallic bonds are held together by a “sea of electrons”• The valence electrons of the interacting

metal atoms delocalize. That is to say, instead of orbiting their respective metal atoms, they form a “sea” of electrons that surrounds the positively charged atomic nuclei of the interacting metal ions

• These electrons move freely between the nuclei, “flowing” like a sea

• This explains why metals are such good conductors of electricity as a solid an electric current can move freely through them

• In the diagram at right, the small purple dots represent the electrons. Note how they are not “attached” to any one particular nucleus?

Metallic Bonds

Using the dog & bond analogy, propose a diagram for metallic bonds’ “sea of electrons”

Metallic Bonds

What’s in the Bottle?In this lab, we examined the physical properties of ten compounds to determine their identity

• Physical property- any property of a compound that is observable or measurable

• The premise of the lab are summarized on the following 8 slides

What’s in the Bottle?Introduction:There is a problem in the chemical storeroom. The high humidity in thestoreroom caused the labels on some of the chemical bottles to fall off. Thelabels are lying all over the shelves and it’s your job to design a method thatwill help identify the chemicals so the labels can be put onto the correctbottles. There are ten unlabeled bottles that represent at least one of eachtype of bond. The unlabeled chemicals are all solids but may be ioniccompounds, nonpolar covalent compounds, polar covalent compounds, ormetals. As a group you will have to determine the data you need to collect inorder to identify all ten compounds. Do not settle for just one piece of datafor any of the compounds; try instead to develop several pieces of identifyingdata. Best of luck!

Safety goggles should be worn at all times in the laboratory. Be cautious ofacidic and basic solutions since they can cause skin burns and eye damage.Liquids and solids are to be disposed of in properly labeled waste containers. Itis recommended that the lab be done on a small scale to minimize solvent andchemical exposure.

What’s in the Bottle?Objective

• Identify the compounds in the 10 bottles labeled A-J• Think about it…you’ve got 19 labels and 10 bottles• Note the information on the labels. How can they help you meet your

objective?• Not all the labels will “fit”• Design a series of experiments to determine “What’s in the Bottle?”

?

What’s in the Bottle

CompoundConducts Electricity MP

(˚C)Solubility in… Type of

CompoundSolid Solution Water EtherSodium carbonate

(NaCO3) No Yes 851 Yes No Ionic & Covalent

Potassium chloride (KCl) No Yes 993 Yes No Ionic

Sucrose(C12H22O11) No No 186 Yes No Polar

covalentIodine

(I2) No No 114 Slightly Yes Nonpolar covalent

Paraffin Wax(C31H64) No No 37 No Yes Nonpolar

covalentZinc(Zn) Yes NA 1535 No No Metallic

Prelab - a series of questions designed to get you thinking about how you could test the physical properties of unknown compounds to determine their identity (15 minutes) • Look over the data in the table and answer the question that follows.

Polar covalent Nonpolar covalent

What’s in the Bottle Prelab

KCl only conducts electricity when it’s dissolved

Soluble means a substance can dissolved. “Dissolvable”

Paraffin wax is a nonpolar covalent compound

Paraffin wax would dissolve in ether

Guaranteed test question: Metals & non-metals = ionic, nonmetals & nonmetals = covalent, metal & metal = metallic


• When ionic compounds melt, the ionic bonds break (intramolecular forces).

• When covalent molecules melt, intermolecular forces break, NOT the covalent bonds (intramolecular forces)


Ionic & metallic are conductive, covalent are not

Think about our answer to #4a---

When ionic compounds dissolve, the ionic bonds break, and ions are “free” to move in the solution


• Think about our warm-up question today…what holds metals together?

• A “sea of electrons”• “Sea of Electrons” means electrons are are “free flowing”


Other polar molecules and ionic compounds

Other nonpolar compounds

“Likes like Likes”or“Like dissolves like”

PART IINaming Compounds and Acids• Learning to write the names and formulae of compounds,

molecules and acids is a key skill for all chemistry students. • We spent nearly a month practicing• The following slides summarize the key ideas and steps to

successfully write the names of compounds, molecules, and acids from their formula and vice verse

• The next slide shows where on my school website students can go to get help if they are stuck on any particular naming convention

Practice, practice, practice!

Need help?1) Tutorial2) Class TA

list3) Tyler

DeWitt vlogs

There are 3 “Must Knows” for successfully naming compounds, molecules, and acids

Must Know #1Where to find the nonmetals

• Nonmetals outlined in red!

• Why is that important?• Gives you a clue to the

type of bond and therefore how to write its name/formula

• Ionic bonds metals & nonmetals

• Covalent bonds nonmetals & nonmetals

Must Know #2Where to find the oxidation numbers

• Why is that important?• Indicates number of electrons an

element will gain/lose when forming an ION

• (For our purposes) Used ONLY when writing name/formula for Ionic compounds

• Some transition metals have more than one oxidation number

• Non metals use first oxidation number listed

• Why? Octet Rule

Must Know #3Rule of Zero Charge

• When forming an ionic compounds & acids, charges (oxidation numbers) of cations and anions must add up to zero!

• The subscripts indicate how many elements are in the compound

• We don’t worry about this rule as much when naming covalent molecules because we use prefixes to establish the subscripts

Practice• Use the flowcharts• Answer key is on my webpage• If you need additional help, see the last series of slides after

these 4 practice slides OR my webpage

Formula to Name

Formula to Name

Name to Formula

Name to Formula

Additional Help for Naming Ionic Compounds• These are the trickiest, so the following slides will attempt to

walk you through them

How to Write the Formula of Simple Ionic Compounds• Example: Magnesium chloride

• Magnesium loses its 2 valence electrons, taking on the electron configuration of its closest Noble gas Neon that has 8, so it has a 2+ charge

• Chlorine gains 1 electron to add to its 7 valence electron, thus taking on the electron configuration of its closest Noble gas Argon that has 8. It adopts a 1- charge.

• Cations are always written first, the anion second

• Mg2+ + Cl -MgCl2

How to Write the Name of Simple Ionic Compounds• Example: Li3P

• Name of the cation stays the same as its metal, and the anion adopts an –ide suffix.

• Lithium phosphide

What About Metals with More Than One Oxidation Number?• Examine your periodic

table• Notice the numbers in

the top right hand corner or each panel

• Oxidation number- the number of electrons an element will gain or lose when it forms an ion

Writing the formula for ionic compounds with more than one oxidation number

• How many possible compounds could be formed between Calcium and chlorine? • One

• CaCl2• How many possible

compounds could be formed between iron and chlorine?• Two

• FeCl2• FeCl3

Writing the name for ionic compounds with more than one oxidation number

• How many ionic compounds could chromium make?• How many

oxidation numbers does it have?

• Three• So when it

combines with chlorine, it will form• CrCl2• CrCl3• CrCl6


• So when Chromium combines with chlorine, it will form• CrCl2• CrCl3• CrCl6

• But we can’t call them all chromium chloride. How will we be able to write the correct formula from the name?

• So we use a Roman Numeral between the cation and anion to indicate the oxidation number we use to write the formula!• CrCl2 becomes Chromium (II) chloride• CrCl3 becomes Chromium (III) chloride• CrCl6 becomes Chromium (VI) chloride

• Note: multiple oxidation numbers for ionic compounds apply ONLY to cations!

• We always use the first listed oxidation number for anions


Cation(s) Anion Formula Name

K+ Cl-

Calcium Sulfide

Fe 2+ O 2- FeO Iron (II) Oxide

Iron (III) Oxide

Ni 2+ Nickel (II) Bromide

Ni 3+ Br 1-

Rhodium (II) Flouride

RhF3

Rh 4+ F 1-

V 2+ I 1-

V 3+ I 1-

V 4+ I 1-

Vanadium (V) Iodide

W 2+ O 2-

W2O3

W 4+ O 2-

Terms to KnowAnions- use the FIRST listed oxidation number!

Cation(s) Anion Formula Name

K+ Cl- KCl Potassium Chloride

Ca 2+ S 2- CaS Calcium Sulfide

Fe 2+ O 2- FeO Iron (II) Oxide

Fe 3+ O 2- Fe2O3 Iron (III) Oxide

Ni 2+ Br 1- Ni Br2 Nickel (II) Bromide

Ni 3+ Br 1- Ni Br3 Nickel (III) Bromide

Rh 2+ F 1- Rh F2 Rhodium (II) Fluoride

Rh 3+ F 1- RhF3 Rhodium (III) Fluoride

Rh 4+ F 1- RhF4 Rhodium (IV) Fluoride

V 2+ I 1- VI2 Vanadium (II) Iodide

V 3+ I 1- VI3 Vanadium (III) Iodide

V 4+ I 1- VI4 Vanadium (IV) Iodide

V5+ I 1- VI5 Vanadium (V) Iodide

W 2+ O 2- WO Tungsten (II) Oxide

W 3+ O 2- W2O3 Tungsten (III) Oxide

W 4+ O 2- WO2 Tungsten (IV) Oxide

Naming Ionic Compounds with Polyatomic Ions

• We use the same method for naming ionic compounds with polyatomic ions as we do for the elements.

• Examples:• Sodium sulfate

• Na+1 + SO4-1 NaSO4

• Potassium carbonate• K+1 + CO3

-2 K2CO3

• Copper (II) Phosphate• Cu+2 + PO4

-3 Cu3(PO4)2

PART III-Level 4 question

1. Use any resource you’d like to research this topic

2. Come prepared to answer this question when you take your assessment

3. While you may research your question ahead of time, and prepare to answer it, in order to maintain academic integrity you may not bring a prewritten answer to the assessment

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Chemical Bonds & Naming Compounds