Eighth Grade Review Chemistry

Matter is anything that has mass and occupies space. All matter is made up of small particles called atoms.

Matter can exist as a solid, liquid, gas or plasma

Matter can be classified as elements, compounds, and mixtures The atoms of any element are alike but are different from atoms of other elements. Compounds consist of two or more elements that are chemically combined in a fixed ratio. Mixtures also consist of two or more substances, but the substances are not chemically combined.

Compounds Compounds can be classified in several ways, including: acids, bases, salts inorganic and organic compounds. (All organic compounds contain carbon).

Matter can be described by its physical properties that include, but are not limited to, shape, density solubility, odor, melting point, boiling point, and color

Acids make up an important group of compounds that contain hydrogen ions. When acids dissolve in water, hydrogen ions (H + ) are released into the resulting solution. A base is a substance that releases hydroxide ions (OH – ) into solution.

pH is a measure of the hydrogen ion concentration in a solution. The pH scale ranges from 0–14. Solutions with a pH lower than 7 are acidic; solutions with a pH greater than 7 are basic. A pH of 7 is neutral.

Neutralization Equation

To Calculate the density, measure the mass and volume of substances.

Kinetic Theory of Matter The kinetic theory of matter (particle theory) says that all matter consists of many, very small particles which are constantly moving or in a continual state of motion.

Equal volumes of different substances usually have different masses

Matter can be described by its chemical properties that include, but are not limited to, acidity, basicity, combustibility, and reactivity (including the ability to rust).

Matter can also be described by its chemical properties, which include acidity, basicity, combustibility, and reactivity. A chemical property indicates whether a substance can undergo a chemical change.

Atoms of the same element are alike

The atom is the basic building block of matter

Atoms and molecules are perpetually in motion

Protons are positively charged, found in the nucleus, and = the number of electrons Neutrons are neutral particles and are found in the nucleus

Electrons are negatively charged particles found spinning around the nucleus

Dalton Chemical elements are made from atoms

Thomson Electrons are around a positively charge pudding like substance.

Rutherford The atom is mostly space, there is a positively charged nucleus in the center.

Bohr The Bohr model is a model used to describe the atom but it does not depict the three dimensional aspect of an atom

The electron cloud model represents our current theory of the atom which shows that the electrons are not in a fixed orbit but an electron cloud Schrödinger

The periodic table of elements is an arrangement of elements according to atomic numbers and properties

Metals, nonmetals, and Metalloids

Periodic Table Basics: Essential Question: What are Horizontal Rows called? Answer: PERIODS

Electron Configuration The “Period” number is equal to the number of energy levels in an atom Remember: The number of electrons are equal to the number of protons in a neutral atom

What are Groups on the Periodic Table? Essential Question: Groups are also known as Families of Elements. They share chemical properties. WHY? Answer: They have the same number of valence electrons.

Electron Configuration For Groups IA – VIII the group numbers are equal to the number of outer shell electrons or valence electrons Group “IA” has ONE valence electron Group “IIA” has TWO valence electrons; etc.

Name that GROUP: The Alkali Metals IA = one outer shell electrons therefore Oxidation state? +1

Name that GROUP: The Alkali Earth Metals IIA = two outer shell electrons Oxidation state? +2

Name that GROUP: The Noble Gases VIIIA = eight outer shell electrons (except Helium which has 2 but is FULL) therefore Oxidation state? NOT!

Name that GROUP: The HALOGENS The Salt Formers VIIA = SEVEN outer shell electrons therefore Oxidation state?

Name that GROUP: The Transition Metals B series = usually 2 or 3 outer shell electrons therefore Oxidation state? +2 or +3

Chemical Bonding

The information within the boxes on the periodic table can provide you with the atomic symbol, atomic number, atomic mass, state of matter at room temperature

Atomic Number: The number of protons in an atom determines what element it is. Add or subtract even one proton from an atom of any element and you no longer have the original element in any form. Now you have a different element! It is also the number of electrons in a neutral atom Atomic mass is the average mass of all the isotopes of an element Neutrons can be determined by subtracting the atomic mass from the atomic number.

Atomic Structure: Isotopes- have the number of protons but different number of neutrons How many neutrons in the following isotopes? Hydrogen – 1 Helium – 4 Lithium – 6 Sodium – 22

The number of electrons in the outermost energy level determines an element’s chemical properties and chemical reactivity

Atoms react to form chemically stable substances that are held together by chemical bonds and are represented by chemical formulas C CO 2

Recognizing chemical equations Combustion Reaction Organic gas and oxygen CH 4 + O 2 CO 2 + H 2 O Combustion Reactions always have carbon dioxide and water as products

To become chemically stable, atoms lose, gain, or share electrons

Metal to nonmetal ionic bond Nonmetal to nonmetal covalent bond

When a metallic element reacts with a non- metallic element, the metallic element’s atoms gain or lose electrons forming ionic bonds

When two nonmetals react, atoms share electrons forming covalent molecular bonds

When matter undergoes physical change, the chemical composition of the substances does not change. When matter undergoes a chemical change, different substances are formed

The Law of Conservation of Mass states that in a chemical reaction, the starting mass of the reactants equals the final mass of the products

A chemical equation represents the change that takes place in a chemical reaction In a chemical equation, the chemical formulas of the reactants are written on the left; an arrow indicates a change to a new substance; and the chemical formulas of the products are written on the right

Chemical Equations The number of atoms on the left side of the equations must equal the number of atoms on the right side of the equation. The equation must be balanced using coefficients - a number placed in front of the molecule or atom He H 2 O CO 2 four atoms nine atoms six atoms A subscript is the number behind the chemical symbol, it never changes.

Balancing H 2 + O 2 H 2 O unbalanced Left side: Right Side H 2 + O 2 H 2 O balanced Left side: Right side:

Balancing Simple Equations Aluminum + Oxygen Aluminum Oxide Al + O 2 Al 2 O 3 Left side: Right side: Al + O 2 Al 2 O 3 2 Al + O 2 Al 2 O 3 Left side: Right Side: Al + O 2 Al 2 O 3 Left side: Right side:

Chemical reactions are classified into two broad types: ones in which energy is released (exothermic) and ones in which energy is absorbed (endothermic)

Nuclear reactions produce a large amount of energy but there are potentially negative effects of using nuclear energy such as disposal of nuclear waste, fission has more waste than fusion Fission (I break) breaks a radioactive nuclei into new products and energy (Nuclear power plant and atomic bomb) Fusion ( You make) takes 2 nuclei and fuses them into one (power of the sun and stars)