Chemical Chemical ReactionsReactions

Atoms are the building blocks Atoms are the building blocks for everythingfor everything

Elements are made of atomsElements are made of atoms Compounds are made of Compounds are made of

elementselements

Chemical ReactionsChemical Reactions

Let's start with the idea of a Let's start with the idea of a reaction. In chemistry, a reaction. In chemistry, a reactionreaction happens when two or happens when two or more molecules more molecules interactinteract and and something happens. something happens.

There are a few key points you There are a few key points you should know about should know about chemical chemical reactionsreactions.. 1. A 1. A chemical changechemical change must must

occur. You start with one occur. You start with one compound and turn it into another. compound and turn it into another.

2. A reaction could include ions, 2. A reaction could include ions, molecules, or pure atoms. A molecules, or pure atoms. A reaction can happen with reaction can happen with anything, just as long as a anything, just as long as a chemical change occurs (not a chemical change occurs (not a physical one).physical one).

CompoundsCompounds

A substance formed from A substance formed from elements, but it does not elements, but it does not have the same characteristics have the same characteristics as the individual elementsas the individual elementsEx. Iron oxide (rust)Ex. Iron oxide (rust)

ReviewReview

Chemical FormulasChemical Formulas

Chemists us chemical formulas Chemists us chemical formulas to represent the composition to represent the composition (make-up) of the elements in (make-up) of the elements in compoundscompounds

A short-hand (text message) way A short-hand (text message) way of writing a chemical compoundof writing a chemical compoundNaCl- salt or Sodium ClorideNaCl- salt or Sodium ClorideHH220- water 0- water

Electron shellsElectron shells

a)a) Atomic number = number of Atomic number = number of ElectronsElectrons

b)b) Electrons vary in the amount of Electrons vary in the amount of energy they possess, and they energy they possess, and they occur at certain energy levels occur at certain energy levels or or electron shells.electron shells.

c)c) Electron shellsElectron shells determine determine how an atom behaves when how an atom behaves when it encounters other atomsit encounters other atoms

Electrons are placed in Electrons are placed in shells according to rules:shells according to rules:

1)1) The 1st shell can hold up to The 1st shell can hold up to two electrons, two electrons,

2)2) and each shell thereafter and each shell thereafter can hold up to 8 electrons. can hold up to 8 electrons.

ValenceValence

An atom is stable when it has An atom is stable when it has 8 electrons in its outer shell. 8 electrons in its outer shell. This makes them “fat and This makes them “fat and happy”happy”

Electron Dot StructuresElectron Dot Structures

Symbols of atoms with dots to represent the Symbols of atoms with dots to represent the valence-shell electrons valence-shell electrons

1 2 13 14 15 16 17 1 2 13 14 15 16 17 18 18

HH He: He:

LiLi BeBe B B C C N N O O :: F F ::Ne Ne ::

NaNa Mg Mg Al Al SiSi PP SS ::Cl Cl ::Ar Ar ::

Why are electrons Why are electrons important?important?

Elements have different Elements have different electron configurationselectron configurations different electron different electron

configurations mean configurations mean different levels of bondingdifferent levels of bonding

The configuration The configuration determines how it bonds determines how it bonds with other elementswith other elements

Chemical BondChemical Bond

When an element comes When an element comes together or combines with together or combines with another element to form a another element to form a compoundcompound

An attempt to fill outer shell An attempt to fill outer shell (make it fat and happy) with (make it fat and happy) with 8 electrons8 electrons

Types of BondsTypes of Bonds

IonicIonic- giving or receiving of - giving or receiving of electrons to another elementelectrons to another element

CovalentCovalent- sharing of - sharing of electrons in the outer shell electrons in the outer shell (valence). Covalent bonds (valence). Covalent bonds form moleculesform molecules

IONIC BONDIONIC BONDbond formed bond formed

between between two ions by the two ions by the

transfer transfer of of electrons- electrons- metals metals

combine with combine with nonmetalsnonmetals

IonsIons

Formed when electrons (-) are Formed when electrons (-) are given away from element given away from element resulting in a positive charge, resulting in a positive charge, because the number of protons because the number of protons (+) is greater than the number (+) is greater than the number of electrons (-) in the atomof electrons (-) in the atom

Positive ions are called Positive ions are called cationscations

IonsIons

Formed when electrons (-) are Formed when electrons (-) are received from an element received from an element resulting in a negative charge, resulting in a negative charge, because the number of protons because the number of protons (+) is less than the number of (+) is less than the number of electrons (-) in the atom electrons (-) in the atom

Negative ions are called Negative ions are called anions.anions.

Formation of Ions from Formation of Ions from MetalsMetals

Ionic compoundsIonic compounds result when metals react result when metals react with nonmetals with nonmetals

Metals Metals loselose electrons to match the electrons to match the number of number of

valence electrons valence electrons of their nearest noble gasof their nearest noble gas Positive ionsPositive ions formform when when the number of the number of

electrons are less than the number of electrons are less than the number of

protons protons

Group 1 Group 1 metalsmetals ion ion 1+1+

Group 2 Group 2 metalsmetals ion ion 2+2+

Group 3A (13) Group 3A (13) metalsmetals ion ion 3+3+

Ions from Nonmetal IonsIons from Nonmetal Ions

In ionic compounds, In ionic compounds, nonmetalsnonmetals in 15, 16, in 15, 16,

and 17 gain electrons from and 17 gain electrons from metalsmetals

Nonmetals add electrons to achieve the Nonmetals add electrons to achieve the

octet (8) arrangement octet (8) arrangement

Negative ionsNegative ions formform when when the number of the number of

electrons are more than the number of electrons are more than the number of

protons protons

Group 5(15) Group 5(15) nonmetalsnonmetals ion ion 1-1-

Group 6 (16) Group 6 (16) nonmetalsnonmetals ion ion 2-2-

Group 7 (17) Group 7 (17) nonmetalsnonmetals ion ion 3-3-

Learning CheckLearning Check

Give the ionic charge for each of the Give the ionic charge for each of the following:following:A. 12 pA. 12 p+ + and 10 e and 10 e--

1) 01) 0 2) 2+2) 2+ 3) 2-3) 2-

B. 50pB. 50p++ and 46 e- and 46 e-

1) 2+1) 2+ 2) 4+2) 4+ 3) 4-3) 4-

C. 15 pC. 15 p++ and 18e- and 18e-

1) 3+ 1) 3+ 2) 3-2) 3- 3) 5-3) 5-

COVALENT BONDCOVALENT BONDbond formed by bond formed by the the sharing sharing of of

electronselectrons

Covalent BondCovalent Bond

Between Between nonmetallicnonmetallic elements of similar elements of similar electronegativity.electronegativity.

Formed by sharing electron Formed by sharing electron pairspairs

Examples; OExamples; O22, CO, CO22, C, C22HH66, H, H22O, O, SiCSiC

Chemical ChangeChemical Change

Change from one substance Change from one substance to anotherto anotherBurning paperBurning paper

Physical ChangePhysical Change

Change is physical or Change is physical or outward appearance. Does outward appearance. Does not change chemical make-upnot change chemical make-upWrinkled paperWrinkled paper

Reactants Reactants the elements or the elements or compounds that are put compounds that are put together to form a chemical together to form a chemical changechange

Na + ClNa + Cl NaCl NaClreactants

ProductsProducts- the end result of - the end result of reactants coming togetherreactants coming together

Na + ClNa + Cl NaCl NaClproducts

Chemical Reactions Chemical Reactions TypesTypes

Endothermic-energy Endothermic-energy absorbedabsorbed

Exothermic- energy is Exothermic- energy is releasedreleased

Rates of ReactionsRates of Reactions

CatalystCatalyst- speeds up a - speeds up a chemical reactionchemical reaction

InhibitorInhibitor- slows down a - slows down a chemical reaction (takes chemical reaction (takes longer)longer)

Law of Conservation of Law of Conservation of MassMass

““In an ordinary chemical reaction, matter In an ordinary chemical reaction, matter is neither created nor destroyed.”is neither created nor destroyed.”

This means that you have neither gained nor This means that you have neither gained nor lost any atoms during the reaction. They may lost any atoms during the reaction. They may be combined differently, but they’re still there. be combined differently, but they’re still there.

Law of Conservation of Law of Conservation of MassMass

The mass of the products must equal The mass of the products must equal the mass of the reactants (what I put the mass of the reactants (what I put into a reaction, I must get out)into a reaction, I must get out)

Mass is neither created or destroyedMass is neither created or destroyed..

If the product has a mass less If the product has a mass less than the reactants what than the reactants what happed? Was their a gas, happed? Was their a gas, smoke or other byproducts?smoke or other byproducts? Example Burning paper- does Example Burning paper- does

the burnt paper (ashes) weigh the burnt paper (ashes) weigh as much as the original piece? as much as the original piece? Why?Why?

Mass of Smoke =7 g

How to Balance How to Balance EquationsEquations

Draw boxes Draw boxes around all the around all the chemical chemical formulas.formulas.

Make a Chemical Make a Chemical InventoryInventory (Look at (Look at the subscripts next the subscripts next to each atom to find to each atom to find the number of the number of atoms in the atoms in the equation.)equation.)

Write numbers in Write numbers in front of each of front of each of the boxes the boxes (coefficient) until (coefficient) until the inventory for the inventory for each element is each element is the same both the same both before and after before and after the reaction.the reaction.

Multiply the coefficientMultiply the coefficient Never change subscriptsNever change subscripts Try to leave singleTry to leave single

elements for lastelements for last

Whenever you change a Whenever you change a number, make sure to number, make sure to update the inventory - update the inventory - otherwise, you run the otherwise, you run the risk of balancing it risk of balancing it incorrectly. When all incorrectly. When all the numbers in the the numbers in the inventory balance, then inventory balance, then the equation can balancethe equation can balance

FinishedFinished

Since both sides of Since both sides of the inventory the inventory match, the equation match, the equation is now balanced!  is now balanced!  All other equations All other equations will balance in will balance in exactly the same exactly the same way, though it way, though it might take a few might take a few more steps in some more steps in some cases. cases.

Some practice problems:

1.__NaCl + __BeF2 --> __NaF + __BeCl2

2. __FeCl3 + _Be3(PO4)2 --> _BeCl2 + _FePO4

3. __AgNO3 + _LiOH --> _AgOH +

__LiNO3

4. __CH4 + __O2 --> __CO2 + __H2O 5. __Mg + __Mn2O3 --> __MgO + __Mn

SolutionsSolutions

2 2 NaCl + NaCl + 11 BeF BeF22 --> --> 22 NaF + NaF + 11 BeCl BeCl2 2

22 FeCl FeCl33 + + 11 Be Be33(PO4)(PO4)22 --> --> 3 3 BeClBeCl22 + + 22 FePOFePO44

11 AgNO3 + AgNO3 + 11 LiOH --> LiOH --> 11 AgOH + AgOH + 11 LiNO LiNO33

1 1 CHCH44+ 2 O+ 2 O22 --> --> 11 CO CO22 + + 2 2 H H22O O

3 3 Mg + Mg + 1 1 MnMn22OO33 --> --> 33 MgO + MgO + 22 Mn Mn

Practice at homePractice at home

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