Chapter 19 Chemical BondsChapter 19 Chemical Bonds

How does the nucleus of an atom How does the nucleus of an atom stay together???stay together???

Forces act on itForces act on it

1. electromagnetic force – 1. electromagnetic force – opposites attract and like charges opposites attract and like charges repelrepelHelps explain electrons are Helps explain electrons are

attracted to the atom’s center attracted to the atom’s center

So why do protons stick together?So why do protons stick together?

A special force acts between A special force acts between protons and neutrons called the protons and neutrons called the strong forcestrong force

It is stronger than the It is stronger than the electromagnetic force acting on electromagnetic force acting on an atoman atom

Chemical Formula VS Chemical SymbolChemical Formula VS Chemical Symbol

Chemical Formula-Chemical Formula- tells which elements tells which elements are in a compound are in a compound and their ratiosand their ratios

ExampleExample NaClNaCl HH22OO

Chemical Symbol-Chemical Symbol- short hand way of short hand way of writing an element’s writing an element’s namename

ExampleExample CC OO NaNa

Chemical FormulaChemical Formula

Try These: list the element and number of Try These: list the element and number of atomsatomsHydrochloric Acid: HClHydrochloric Acid: HClMethanol: CHMethanol: CH44OO

Ethanol: CEthanol: C22HH66OO

Nitroglycerin: CNitroglycerin: C33HH55NN33OO99

ActivityActivity

Your teacher will assign to you an Your teacher will assign to you an element.element.

For that element complete the following on For that element complete the following on a sheet of white papera sheet of white paper

Name and symbolName and symbolDraw an electron configuration Draw an electron configuration Draw an electron dot diagramDraw an electron dot diagramList the group number and period numberList the group number and period number

NextNext

On the board place your element in the On the board place your element in the appropriate space on the PTOEappropriate space on the PTOE

Why do atoms form Compounds?Why do atoms form Compounds?

To become stableTo become stable In order to be stable an atom needs 8 In order to be stable an atom needs 8

outer electrons aka valence electronsouter electrons aka valence electrons In order to become stable atoms form In order to become stable atoms form

bonds to become a compoundbonds to become a compoundNoble Gases/ group 18 are stable Noble Gases/ group 18 are stable

because they have a full outer orbital (8 because they have a full outer orbital (8 outer electrons)outer electrons)

Types of bondsTypes of bonds

IonicIonic

Gains or Gains or loses loses electronselectrons

CovalentCovalent

Shares Shares electronselectrons

Let’s talk more about ionic bonds..Let’s talk more about ionic bonds..

What you already know… gains or loses What you already know… gains or loses electronselectrons

But you don’t know… elements that are far But you don’t know… elements that are far away from each other on the PTOE will away from each other on the PTOE will form ionic bondsform ionic bonds

Metals form ionic bonds with nonmetalsMetals form ionic bonds with nonmetalsMetals lend electrons and nonmetals gain Metals lend electrons and nonmetals gain

themthem

Ionic Bond ExamplesIonic Bond Examples

Potassium and IodinePotassium and Iodine

Magnesium and SulfurMagnesium and Sulfur

An atom that loses or gains electrons = An atom that loses or gains electrons = IONION

When an atom loses one or more When an atom loses one or more electrons it is losing negative charges so it electrons it is losing negative charges so it becomes a becomes a positive ionpositive ion

When an atom gains one or more electrons it is gaining negative charges so it becomes a negative ionnegative ion

Let’s talk more about covalent Let’s talk more about covalent bonds..bonds..

What you already know… share electronsWhat you already know… share electronsBut you don’t know… elements with larger But you don’t know… elements with larger

number of electrons (4) need a lot of number of electrons (4) need a lot of energy to lose them so the electrons are energy to lose them so the electrons are shared insteadshared instead

The compound formed by sharing The compound formed by sharing electrons is called a electrons is called a moleculemolecule

Elements close to each other on the PTOE Elements close to each other on the PTOE will form covalent bonds will form covalent bonds (usually nonmetals)(usually nonmetals)

Covalent BondingCovalent BondingCovalent Bonding- Electrons are Covalent Bonding- Electrons are

sharedsharedNonpolar bonds- Electrons are Nonpolar bonds- Electrons are

shared equallyshared equallyPolar Bonds- Electrons are not Polar Bonds- Electrons are not

shared equallyshared equally

Covalent Bond ExamplesCovalent Bond Examples

Hydrogen and OxygenHydrogen and Oxygen

Hydrogen and ChlorineHydrogen and Chlorine

Hydrogen and FluorineHydrogen and Fluorine

Which type of bond will these Which type of bond will these elements form?elements form?

1.1. Carbon and oxygenCarbon and oxygen

2.2. Sodium and oxygenSodium and oxygen

3.3. P and oxygenP and oxygen

4.4. Mg and oxygenMg and oxygen

5.5. Al and oxygenAl and oxygen

6.6. Cl and oxygenCl and oxygen

7.7. Sulfur and oxygenSulfur and oxygen

Ionic Covalent Why?Ionic Covalent Why?

Oxidation numberOxidation number

Positive or negative number that indicates Positive or negative number that indicates how many electrons an atom has gained, how many electrons an atom has gained, lost or shared to become stablelost or shared to become stable

The oxidation number is the same as the The oxidation number is the same as the charge on an ionic compoundcharge on an ionic compound

Used to write formulasUsed to write formulasExampleExample

Na ion has a charge of 1+ so its oxidation Na ion has a charge of 1+ so its oxidation number is 1 +number is 1 +

PToE and Oxidation NumbersPToE and Oxidation Numbers

Open books to page 588 and take out your Open books to page 588 and take out your PToE from your bindersPToE from your binders

Oxidation Numbers Practice on board/in Oxidation Numbers Practice on board/in student notesstudent notes

Writing FormulasWriting Formulas

Remember:Remember:Compound are neutralCompound are neutralSometimes you need to simplifySometimes you need to simplify

Use Worksheet titled: Crisscross method for Use Worksheet titled: Crisscross method for instructions for formula writinginstructions for formula writing

Binary IonicBinary Ionic CompoundsCompounds==

composed of 2 composed of 2 elementselements

Polyatomic ionsPolyatomic ions = =

positive or negative positive or negative group of covalently group of covalently bonded atoms that bonded atoms that bond to another bond to another elementelement

Has more than 2 Has more than 2 elementselements

Naming Binary Ionic CompoundsNaming Binary Ionic Compounds

First write name of positive ionFirst write name of positive ionNext the root of the negative ion and add –Next the root of the negative ion and add –

ide to the end of itide to the end of itExamples:Examples:

oxygen = oxideoxygen = oxide

nitrogen = nitridenitrogen = nitride

Naming Polyatomic CompoundsNaming Polyatomic Compounds

Same as binary but the negative ion ends Same as binary but the negative ion ends in -atein -ate

Naming Binary Covalent Naming Binary Covalent CompoundsCompounds

Formed between nonmetalsFormed between nonmetalsUses prefixes to identify how many atoms Uses prefixes to identify how many atoms

of each element there areof each element there areLook at page 593 and learn these prefixesLook at page 593 and learn these prefixesExamples:Examples:

NN22O dinitrogen oxideO dinitrogen oxide