Chemical Bonds & Reactions+-

+-

Chemical BondA force of attraction that holds two atoms togetherHas a significant effect on chemical and physical properties of compoundsinvolves the valence electrons

Valence Electrons the electrons in the outermost energy level of an atomThis Lithium Atom has onevalence electron

Carbon 4 valence electronsOxygen

6 valence electronsBeryllium

2 valence electronsCounting Valence Electrons

Determining the Number of Valence Electrons by Using the Periodic Table

*Atoms of elements in Groups 1 and 2 have the same number of valence electrons as their group number.

*Atoms of elements in Group 3-12 do not have a general rule relating their valence electrons to their group number. However, they typically have between 1 or 2 valence electrons.

*Atoms of elements in Groups 13-18 have 10 fewer valence electrons than their group number. (Exception - helium atoms have only 2 valence electrons, even though they are in group 18)

How Many Valence Electrons?Hydrogen

Lead

Xenon

Sulfur

Rubidium

1 Valence Electron4 Valence Electrons8 Valence Electrons6 Valence Electrons1 Valence Electron

The Octet RuleAtoms will combine to form compounds in order to reach eight electrons in their outer energy level.Atoms with less than 4 electrons tend to lose electrons. Atoms with more than 4 electrons tend to gain electrons. Be aware that there are some exceptions!

CONSIDER EIGHT A HAPPY NUMBER FOR ATOMS!

The Octet Rule In ActionNotice how the sodium atom has one valence electron. It is this electron that it will try to get rid of according to the Octet Rule.Notice how this chlorine atom has seven valence electrons, one away from eight. It will try to gain one more according to the Octet Rule.12345671

Where do you think Chlorine finds that one electron that it needs?

Lewis Structure(Electron Dot Diagram)a way of drawing the outer energy level electrons (valence) of an atom The symbol for the element surrounded by as many dots as there are electrons in its outer energy level (valence)Examples

How many valence electrons do each of these atoms have?

Making an Electron Dot DiagramElement X has 8 valence electrons1234567Write down the elements symbol and place the first two dots on any side of the symbol. Place the rest of the dots in either a clockwise or counter clockwise manner around the symbol, with no side receiving two dots until each side gets one. If this were an atom of an elementfrom group 1, you would just place theone dot on any side of the element.

What Would the Electron Dot Diagram Look Like? HSrONe

How many valence electrons does each atom have?1 Valence Electron6 Valence Electrons8 Valence Electrons2 Valence Electrons

Oxidation NumberThe charge that an atom would have if it lost or gained electrons; ionic chargeCan be helpful in determining which atoms will interact or bond with each otherExample:

According to electron dot diagram for Magnesium, it has two valence electrons. Because Magnesium is unhappy with two, it will typically lose them. If this happens it will turn into a Magnesium ion. At this point it will have an oxidation number of +2. Mg2+

What Could the Oxidation Number Be? +1 or -1 because it can gain or lose one electron-2 because it will gain two electrons0 because it will notgain or lose electrons+2 because it will lose two electrons

3 Types of Chemical BondsIonicCovalentMetallic

What can you describe about each of thesebonds just by looking at the name?

Which different groups or familiesof elements will most-likelyinteract to create these typesof bonds?IONIC BONDS-The force of attraction between oppositely charged ions.Occurs after a transfer or loss/gain of electronsUsually form between atoms of metals and atoms of non-metalsResulting compounds have a name that usually ends in ide

Example - Sodium Chloride (NaCl)ClNa1-1+

COVALENT BONDA force that bonds two atoms together by a sharing of electronsEach pair of shared electrons creates a bondUsually occurs between atoms of non-metals

++Example Water (H2O)

----------

Types of Covalent BondsDifferent covalent bond types share a different number of electrons

Single Bonds Share 2 ElectronsDouble Bonds Share 4 ElectronsTriple Bonds Share 6 ElectronsWater (H2O)

Carbon Dioxide (CO2)Nitrogen (N2)

Unequal Sharing (Polar Covalent Bond)Why do you think the two Hydrogen atoms shareequally, but the Hydrogen and fluorine do not?++

+

Bonded hydrogen atoms showing equal sharing ofelectronsHydrogen and fluorine bond with an unequal sharing of electrons

The unequal sharing of electrons between two atoms that gives rise to negative and positive regions of electric charge Results from an atoms electronegativity the ability to attract electrons to itself

ElectronCloud

Metallic BondA force of attraction between a positively charged metal ion and the electrons in a metalMany metal ions pass along many electronsMany properties of metals, such as conductivity, ductility, and malleability, result from the freely moving electrons in the metalUsually occurs between atoms of metals

Notice how the electrons do not just stay with one ion--------------

Results of BondingMolecule A neutral group of two or more non-metal atoms held together by covalent bonds Type:

Diatomic - molecules consisting of two atoms of the same element bonded togetherExamples:H2, F2, O2, N2 Compound A pure substance composed of two or more different elements (atoms) that are chemically combined

Examples:CO, NO2, NaClWhat would you call something that has characteristics of both?

Molecule, Compound, or Both?H2HydrogenNO2Nitrogen DioxideCl2ChlorineO2OxygenNONitric OxideCO2Carbon DioxideN2NitrogenH2OWater

CH4Methane

Chemical ReactionThe process by which a chemical change occurs Atoms are rearranged, and chemical bonds are broken and reformedOne or more substances change to produce one or more different substancesTypesSynthesis (creating)Decomposition (separating)Combustion (burning)Displacement/Replacement (switching)

O2H2What does H2 & O2 gascreate?Out of the four types of reactions, which would describe the chemical reaction taking place to the right?

Physical Changea change in shape, size, color, or statea change without a change in chemical compositiona change that is reversibleThe Mixtures Lab

Examplestearing papercutting your hairchange in statePhysical changes are not indicative of a chemical reaction

Chemical Changea change in which a substance becomes another substance having different propertiesa change that is not reversible using ordinary physical means Changes that usually cause, heat, sound, light, odor, fizzing/foaming, color changes

You usually need more than one of the above characteristics to be considered a chemical change!

Examplesmixing vinegar & baking sodaburning a piece of woodsoured milkA chemical analysis is the only 100% way to know a chemical change has occurred.

Chemical EquationShorthand form for writing what reactants are used and what products are formed in a chemical reaction Sometimes shows whether energy is produced or absorbedExamples:

2H2 + O2 2H2O

CH4+2O2 CO2+2H2O

C6H12O6 + 6O2 6CO2 + 6H2O + energy

Components of a Chemical Equation 2H2 + O22H2O(Reactants)(Products)(Yield)Chemical FormulasChemical FormulaSubscriptsCoefficientSometimes you will see a yields sign that looks like this. What do you think it means?

CoefficientSubscript

Energy and Chemical Reactions Exothermic Reaction A chemical reaction in which energy is released.The products have greater bond energy than the reactants

C6H12O6 + 6O2 6CO2 + 6H2O + energy(respiration) Endothermic Reaction A chemical reaction in which energy is absorbed.The products have lower bond energies than the reactants

6CO2 + 6H2O + energy C6H12O6 + 6O2 (photosynthesis)Chemistry Comes Alive! Sample MoviesTeacherTube - VideosChemistry Demonstration Videos Can you think of other reactions where energy is gained or released?

Rates of Chemical ReactionsTemperature a measure of the average kinetic energy of the particles in a sample of matter Ex. Increasing the temperature when cookingSurface area amount of material that comes into contact with the reactantsEx. Cutting a potato into smaller pieces when cookingConcentration amount of substance per volumeEx. Turning the valve on a gas stove to increase the concentration of methane molecules Catalysts (enzymes) organic substances that help speed up chemical reactions, but are not consumed in the reaction

The rates at which chemical reactions can take place arebased on the interaction (collisions) between the differentparticles. These rates can be impacted by the following:

Law of Conservation of MassProposed by Antoine LavoisierIn a chemical reaction, atoms are neither created nor destroyedAll atoms present in the reactants are also present in the productsChemical equations must account for/show the conservation of mass balancing equations

H2 + O2H2OIn its present form, does this chemical equation show a conservation of mass? How would you balance this equation to show the conservation of mass?22ReactantsH 2O 2Products42H 2O 142

Hints For Balancing EquationsCount the atomsList the number of atoms of each element to see which elements must be balancedUse a coefficient to add atoms to one side of the equationStart with the reactant or product that has the greatest number of different elementsAdd a coefficient to another reactant or productMake sure that the coefficients in your balanced equation are the smallest whole numbers possible (they should have no common factor other than one)

Tutorial on Balancing Equations