CHEMICAL REACTIONS

All chemical reactions involve change. Burning is one way of converting chemicals such as coal or oil into energy that can be used to power engines or provide heat. A chemical reaction is any process that changes one substance into another. Reactions involve the interaction between two basic components of the universe – matter and energy. Any substance that takes up space is matter. Heat, light and electricity are types of energy. During a chemical reaction energy works to reorganize matter.

I. Inside Matter:

a. All matter is made up of elements.

b. All elements are made up of atoms.

i. Elements are found in combinations called molecules

ii. Pure substances have one type of molecule.

1. ex: water which is two hydrogen atoms are connected to one oxygen (H2O)

c. Atoms are made up of a proton, neutron, and electron.

II. Chemical Reaction Ingredients:

a. The substance that you start with in a chemical reaction is called the reactant.

b. The new substance formed is called the product.

c. This process is written as a chemical equation

i. Reactants ® Products

ii. Numbers are used in equations to indicate how much of each substance is needed.

iii. C + O2 ® CO2 This equation is balanced on both sides.

III. Subatomic Particles:

a. Nucleus is at the center of an atom

b. Protons are packed in the nucleus.

c. Neutrons are in the nucleus.

d. Electrons are on the outside of the atom.

i. Opposite charges attract (like a magnet)

ii. Like charges repel (like a magnet)

IV. Inside Energy:

a. Energy is necessary for a chemical reaction.

b. Energy is required to break a chemical bond and to form new bonds.

c. Heat is one type of energy involved in chemical reactions.

i. Some reactions take in heat.

ii. Some reactions will give off heat – burning of fuel.

V. Putting It All Together:

a. Compounds that undergo chemical reactions rearrange bonds:

i. AB + C ® A + BC

ii. Elements A and B form a compound. C is a reactant. During the reaction A and B break apart and B and C become a compound.

b. In this reaction one bond broke and new bond formed. The atoms did not change only the elements joined differently.

VI. Chemical Bonds:

a. Chemical bonds are created when atoms give, take, or share electrons.

b. The types of bonds formed between atoms depends on how many electrons they have in an atom and how they are arranged.

VII. Electron Locations:

a. The location of electrons is one factor that determines how that atom will form bonds.

b. The Bohr model states that electrons orbit or circle the nucleus of an atom.

i. As electrons circle they are held in place by the pull of the nucleus.

ii. The nucleus has positive charges that attract the negative charges.

VIII. Energy Levels:

a. Electrons sit at different energy levels.

b. Electrons in energy levels farthest from the nucleus become involved in reaction because the are held weakly by the nucleus – due to distance from the center of the atom – less ‘pull’ by the protons. Ex: Put opposites ends of a magnet farther away from each other and there is less pull to join together.

c. Energy levels are sometimes called orbitals.

d. Chemists also called them electron shells.

IX. Electron Numbers:

a. The number of electrons in an atom determines how that atom will react and form bonds.

i. If the shell is full of electrons it is most stable and unreactive.

ii. If the shell is not full of electrons it is not stable and reactive.

b. When atoms give, take, or share electrons they create bonds.

c. Electrons fill in the inner shells first.

i. The lowest energy shell has space for just two electrons.

ii. This is a stable atom because it is filled to its capacity. It does not give, take or share electrons because the shell is full.

d. larger atoms have two or more electron shells.

e. Extra shells need eight electrons to become stable.

f. Stable atoms are unreactive.

g. Atoms with incomplete outer shells will give, take or share electrons to fill the energy levels.

h. When atoms give, take or share electrons they create bonds.

X. Ionic Bonds:

a. An ionic bond occurs when a metal atom gives an electron to a nonmetal atom.

b. A positively charged ion is a cation.

c. An atom that takes an extra negative charge becomes an ion or anion.

d. Common ionic compound is table salt Na bonds with Cl.

XI. Covalent Bonds:

a. A covalent bond forms when two nonmetal atoms share their electrons to become stable.

b. Shells overlap to share an electron

c. Covalent compounds tend to have similar properties.

XII. Metallic Bonds:

a. Metallic bonds occur when metal atoms share a pool of electrons.

b. Metallic bonds make most metals hard solids.

XIII. Types of Reactions:

a. Combination reactions: two or more reactants combine to form one product: A + B ® AB.

b. Decomposition reactions occurs when a single compound breaks down into two or more simpler substances: AB ® A + B.

XIV. Energy Changes:

a.