First 9 weeks Study Guide 8 th Grade

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Wilfred Sparks
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1 Elements and Compounds 6.5ABC Key Concepts First 9 weeks Study Guide 8 th Grade Read this MULTIPLE times to prepare for the exam! An element is a pure substance that cannot be broken down into simpler substances. A substance that consists of two or more different elements is a compound. Living matter is made up mostly of oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus which form organic compounds. Elements Molecules Compounds Carbon O2 Oxygen C6H12O6 Glucose Hydrogen H2 Hydrogen H2O water Oxygen CH4 Methane Protons, Neutrons, and Electrons the subatomic particles that make up atoms Atoms Atoms are the smallest part of an element. All atoms of the same element have the same number of protons. Elements Made up of atoms with the same number of protons, arranged on the periodic table. Elements can be metals, metalloids, and non-metals. Compounds two or more different elements H 2 O C 6 H 12 O 6 Molecules made by two of the same elment such as O 2 1

2 Atomic Structure/Properties 8.2C/8.3BD/8.5AB Key Concepts An atom is the smallest unit of an element that upholds all of the properties of that element. Atoms are made up of subatomic particles called protons, neutrons, and. Atomic Number Element Name Symbol Atomic Mass Atomic number = P =E rotons lectrons Mass number - Atomic number =Neutrons The protons give you an elements identity. The protons give you the atomic number which is like the address for that element on the periodic table. The atomic mass is the sum (the total) of the protons and neutrons. Protons + Positive charge Identity of the atom In the nucleus 1 amu Neutrons Neutral charge In the nucleus 1 amu Atom Electrons _ Negative charge orbit the nucleus are in the electron cloud way almost nothing are farthest from the nucleus 2

3 Atoms Protons Valence Electrons Postive Charge Negative Charge Located in the nucleus Outer most shell Determines an elements identity Determines an atoms reactivity Always equal to the atomic number Same group, same # of Valence 3

4 Periods Groups Metals Metalloids Non Metals Elements of the periodic table are Metals, Non-Metals or Metalloids Metals have four characteristics that are very important: o Conductivity ability to transfer heat and electricity o Luster refers to the level of shininess or light reflection o Malleable ability to be shaped without breaking like a shield o Ductile ability to be hammered thin or turn into wire: Copper has high ductility. Periods Groups Increasing Atomic Number from left to right Same Decreasing Atomic Radius or Atomic Size from left to right Similar chemical properties Decreasing Metallic properties from left to right Similar reactivity 4

5 Important HIGHLY REACTIVE Groups to remember Group 1 has 1 electron Group 2 has 2 electron 8 a full shell 8 a full shell Group 17 has 7 Group 16 has 6 Nobel Gases have a full shell so they are stable and will not react with other element s atoms. The have 8. Chemical Formulas, Reactions, Equations 8.2C/8.3BCD/8.5DEF Key Concepts During a chemical reaction, the atoms of substances rearrange themselves into a new configuration, forming new substances. The reactants combine to produce new products. A chemical formula is the combination of all of the elemental symbols found within a substance. The atom numbers of each element are identified by subscripts to the right of the elemental symbol. Chemical equation shows the atom numbers and molecules making up the reactants and products of a chemical reaction. A number, or coefficient, in the front of the molecule s chemical formula represents the molecule number in each reaction. 2H 2 + O 2 2 H 2 O The subscript tells how many atoms of that element there are. O2 means 2 Oxygen The co-efficient tells how many molecules There are two water molecules. 2 H2 means 4 hydrogen How many: 3 C6H12O6 Elements: 3 Carbon, Hydrogen, and Oxygen Molecules: 3 (the coefficient tells us) Atoms: 3x6+3x12+3x6 = 72 atoms Reactants Products In a chemical reaction two elements or compounds come together and yield something new. All of the reactants must be accounted for (balanced) and should show up in the products. 5

6 A chemical equation is balanced when the reactants and products have the same number of each atom on each side in a chemical equation No new atoms can appear on the product side and no atoms can be lost. The Law of Conservation of Mass means we can rearrange the atoms like stacks of coins, but the total must be the same. The ways we know a chemical reaction has taken place when we see: o Change in temperature (heat is produced, or heat is absorbed) o Light is produced (welders torch) o Production of bubbles which means gas (remember the vinegar and baking soda made CO2) o Formation of a precipitant (solids formed in a liquid) o Change in color (remember the cabbage) Balanced Fe + Cl2 FeCl3 Fe = 1 Fe = 1 Cl = 2 Cl=3 2 Fe + 3 Cl2 2 FeCl3 Fe = 2 Fe = 2 Cl = 6 Cl=6 6

20.2 Chemical Equations

20.2 Chemical Equations All of the chemical changes you observed in the last Investigation were the result of chemical reactions. A chemical reaction involves a rearrangement of atoms in one or more reactants to form one or more