Balancing Chemical Balancing Chemical EquationsEquations

Chemical Bonds & Chemical Bonds & ReactionsReactions

Let’s BondLet’s Bond

H2

A moleculemolecule is formed when two or more atoms are bonded together.

Chemical Bonds are formed Chemical Bonds are formed when atoms when atoms gaingain, , loselose or or shareshare

valence electrons.valence electrons.

Valence electrons are like the outer level of skydivers in this formation… it’s much easier for them to pull away than it is for the skydivers in the middle. It’s also easier for a new skydiver (electron) to join the outer levelouter level of the formation than it is to move into the middle middle of the formation.

When atoms come together by sharing sharing electronselectrons, the bond is a covalent bondcovalent bond.

Water - A Most Important MoleculeWater - A Most Important Molecule

Note how covalent bondingcovalent bonding fills all outer electron levels; oxygen has 8 valence electrons, and the hydrogens both have 2. By sharing their electrons, everybody is happy! Water is one of the most stable molecules around.

The electron dot diagrams on the right show molecules with covalent bonds.covalent bonds.

Ion FormationIon Formation: one atom gives electrons, one atom takes electrons

Sodium gives a single electron to chlorine to complete its outer electron shell. Chlorine is happy to take it.

An ionion is an atom or molecule with a positive or negative atom or molecule with a positive or negative chargecharge. Since sodiumsodium loses one electron, it has a positive charge of +1, written as Na+.Na+. Since chlorinechlorine gains one electron, it has a negative charge of -1, written as Cl-Cl-..The type of chemical bond formed in this way is called an ionic bond.ionic bond.

The result is ion formationion formation.

Ions and Ion Formation

Ionic BondsIonic BondsTwo oppositely charged ions are attracted to each other, and bond together.

This type of chemical bond is an ionic bondionic bond.

SaltsSalts are solids held together by ionic bonds.

Elements in Group 1Group 1 (Alkali metals)(Alkali metals) all have 1 valence 1 valence electronelectron, so they bond easily with elements in Group 17Group 17 (Halogens)(Halogens),, which are short 1 valence short 1 valence electronelectron.

Why do Group 1 and Group 17 react so easily with one another?

The answer lies in the valence electrons. The Alkali metalsAlkali metals in Group 1 all have 1 valence electron they want to 1 valence electron they want to get rid ofget rid of.. The HalogensHalogens in Group 17 are all short 1 valence electron, and want all short 1 valence electron, and want to to gaingain one one to fill their outer electron level. Each group has what the other needs. Result: 2 happy atoms.

Sodium mixing with chlorine

http://www.youtube

.com/watch?v=2mzDwgyk6QM&NR=

1

The Parts of a Chemical ReactionThe Parts of a Chemical Reaction

ReactantsReactants: ingredients in a chemical reaction; ingredients in a chemical reaction; substances that you substances that you startstart with with

ProductsProducts: new substances formed in a chemical new substances formed in a chemical reaction (what you reaction (what you end upend up with) with)

ExampleExample: : PhotosynthesisPhotosynthesis

carbon dioxide + water sugar + oxygen

reactantsreactants productsproducts

sunlight

The arrow stands for “becomes”

There are 4 types of chemical reactions:There are 4 types of chemical reactions:

1. SYNTHESIS : A + B ---> AB1. SYNTHESIS : A + B ---> ABTwo elements combine to form a compound.Two elements combine to form a compound.

2. DECOMPOSITION : AB ---> A + B2. DECOMPOSITION : AB ---> A + BA compound breaks down to form simpler A compound breaks down to form simpler

substances.substances.

3. SINGLE REPLACEMENTSINGLE REPLACEMENT A + BC ---> AC + BA + BC ---> AC + BOne element replaces another in a compound.One element replaces another in a compound.

4. DOUBLE REPLACEMENT4. DOUBLE REPLACEMENT AB + CD ---> AC + BDAB + CD ---> AC + BDTwo elements replace each other, forming two new Two elements replace each other, forming two new

compounds.compounds.

CHEMICAL REACTIONSCHEMICAL REACTIONS

Let’s look at the 4 types of chemical reactions Let’s look at the 4 types of chemical reactions in another way…in another way…

1.1. Synthesis reaction Synthesis reaction (putting together a compound)(putting together a compound)

+

2. Decomposition Reaction 2. Decomposition Reaction (breaking down a compound)(breaking down a compound)

+

3. Single Replacement Reaction 3. Single Replacement Reaction (1 atom switches places)(1 atom switches places)

+ +

4. Double Replacement Reaction 4. Double Replacement Reaction (2 atoms switch places)(2 atoms switch places)

+ +

4 types of chemical reactions

Or, we could use relationships to visualize the 4 Or, we could use relationships to visualize the 4 types of reactions….types of reactions….

1. Synthesis 1. Synthesis (Hook-up)(Hook-up)

++

2. Decomposition 2. Decomposition (Break-up)(Break-up)

++

3. Single Replacement 3. Single Replacement (change 1 partner)(change 1 partner) ++ ++

4. Double 4. Double Replacement Replacement (change 2 (change 2 partners)partners)

++ ++

relationships

The The Law of Law of Conservation Conservation of Massof Mass states: ““During a During a physical or physical or chemical chemical change, change, matter is matter is neither neither created nor created nor destroyeddestroyed.”.”

This means that during a during a chemical chemical reactionreaction, the atoms on the atoms on the leftleft side of the arrow must balance or equal the equal the atoms on the atoms on the rightright side of the arrow.

4 H atoms4 H atoms

2 O atoms2 O atoms

4 H atoms4 H atoms

2 O atoms2 O atoms

WRONGWRONG

WRONGWRONG

This one is This one is CORRECT!CORRECT!

Balancing Chemical EquationsBalancing Chemical Equations

_____H_____H33POPO44 + _____KOH => _____K + _____KOH => _____K33POPO44 + _____H + _____H22OO

_____K + _____B_____K + _____B22OO33 => _____K => _____K22O + ____BO + ____B

_____HCl + _______NaOH =>_______NaCl + _______H_____HCl + _______NaOH =>_______NaCl + _______H22

______Na + _______NaNO______Na + _______NaNO33 => _______Na => _______Na22O + ______NO + ______N22

_____C + _____S_____C + _____S88 => _____CS => _____CS22

Practice Balancing These EquationsPractice Balancing These Equations

______22__H__H33POPO44 + __ + __66__KOH => _____KOH => ___22__K__K33POPO44 + ___ + ___66__H__H22OO

____66___K + _____B___K + _____B22OO33 => ___ => ___33__K__K22O + __O + __22__B__B

_____HCl + _____NaOH =>_______NaCl + ______H_____HCl + _____NaOH =>_______NaCl + ______H22OO

Already balancedAlready balanced

______1010__Na + _____Na + ___22__NaNO__NaNO33 => ___ => ___66___Na___Na22O + ______NO + ______N22

____44___C + _____S___C + _____S88 => ___ => ___44__CS__CS22

ANSWERSANSWERS

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.