TAKS 8 th Grade Science Review Objective 3

1. TAKS 8th Grade Science ReviewObjective 3 Structures and Properties of Matter

2. Remember all the information given to you on this page!

3. Information from the Periodic Table • Groups – columns (18) – elements with similar physical and chemical properties • Periods – rows (7) – energy levels of the outermost electrons (valence electrons) • Valence Electrons – farthest from the nucleus or most loosely held (key to how an atom reacts!)

4. Note the locations of the metals, halogens and noble gases.

6. Elements found in which shaded area of this periodic table undergo the fewest chemical reactions? A Q B R C S D T

7. Element Information Atomic Number 6 Number of Protons - + C - Symbol n Starts w/ a Capital + n n + - + - + + n n 12.011 + Atomic Mass n Protons + Neutrons + n - Name of Element Carbon - How do you determine the number of Neutrons ? n Subtract the Atomic Number from the Atomic Mass 12 – 6 = 6 - = + n + n How do you determine the number of Electrons ? - In a stable atom, the number of protons equals the number of electrons 6 = 6 = + -

8. Parts of an Atom + n - - - - - n + + O n n Valence Electrons – farthest from the nucleus or most loosely held (key to how an atom reacts!) n - - + + + n + n n n + + - - Dot Diagram – consists of the symbol for an element surrounded by the number of valence electrons - H +

9. Atom vs Molecule Molecule – a combination of two or more atoms bonded together Atom – the smallest particle of an element - - - - - n - - + - + n n n n - + - + + + + n n n + n - n n n - + + + n + + + n n n + + - - - - - + - + What is this element? Which molecule does this represent?

10. TAKS Questions

12. A certain atom has a nucleus containing six protons and eight neutrons and has six electrons orbiting the nucleus. This atom is a form of the element — A silicon B carbon C magnesium D calcium

13. Ions • Ions are atoms with either extra electrons or missing electrons. • A normal atom is called a neutral atom,that is an atom with a number of electrons equal to the atomic number. You are a sodium (Na) atom. You have 11 , one too many to have your outer shell filled. You need to find another element who will take that away from you. Bring in chlorine (Cl). Chlorine (Cl) will take that electron away and leave you with 10 inside of two filled shells. You are a happy atom. Now you are also an ion, missing 1 . You are a sodium ion (Na+). You have one less electron than your atomic number. What about the chlorine atom? Is it an ion? - - - - - + + NaCl Sodium Chloride

14. Isotopes Let's say an atom is missing a neutron or has an extra neutron. That type of atom is called an isotope. An atom is still the same element if it is missing an electron. The same goes for isotopes. They are still the same element. They are just a little different from every other atom of the same element. Let’s look at carbon isotopes. There are a lot of carbon atoms in the universe. The normal ones are carbon-12. Those atoms have 6 neutrons. There are a few straggler atoms that don't have 6. Those odd ones may have 7 or even 8 neutrons. Carbon-14 actually has 8 neutrons (2 extra). C-14 is considered an isotope of the element carbon. RETURNING TO NORMAL If we look at the C-14 atom one more time we can see that C-14 does not last forever. There is a point where it loses those extra neutrons and becomes C-12. That loss of the neutrons is called radioactive decay. That decay happens regularly like a clock. For carbon, the decay happens in a couple of thousand years. Some elements take longer and others have a decay that happens over a period of minutes.

15. Practice with Molecules

16. Interpreting Chemical Formulas CO2 3Fe2O3 2C6H12O6 • List your elements • How many atoms of each element? The number behind the symbol. If there is no number behind the symbol, there is 1 atom of that element. • Multiply by the number of molecules (coefficient - the number in front) C O 1 2 Fe O 2 3 x 3 C6x 2 = 12 H12x 2 = 24 O6x 2 = 12 6 9 x 3

17. Practice with Compounds

18. Law of Conservation of Mass • Two lab students in IPC class mix calcium with zinc carbonate. According to the law of conservation of mass, what other product was produced and how much? A 0.088 kg of zinc B 0.088 kg of calcium C 0.104 kg of zinc D 0.104 kg of calcium Zn 104 g

19. Balancing Equations Mg + O2 MgO 2 2 Mg O 1 1 x 2 = 2 Mg O 1 2 x 2 = 2 x 2 = 2 2 2 4 3 4 • List your elements • How many atoms of each element? • Multiply by the number of molecules (coefficient) • Total. If they are even on both sides, the equation is balanced. • Balance the equation by adding molecules only! (Use multiplication)

20. TAKS Questions K + H2O → KOH + H2 What is the coefficient for H2O when the above equation is balanced? A 1 B 2 C 3 D 4

21. Types of Chemical Reactions • Have you heard of Hydrogen Peroxide? • What are some of its uses? H2O2 H2O + O2 • What happens to H2O2? • What happens when something decomposes?

22. Decomposition Reaction • The breakdown of hydrogen peroxide is known as a decomposition reaction. • Let’s balance the chemical equation: ___H2O2 ___H2O + ___O2

23. Single and Double Replacement Reactions Cl2 + NaBr NaCl + Br2 Mg + HCl MgCl2 + H2 A B C B A C A B C D A D C B K2SO4 + CaCl2 KCl + CaSO4 Al(NO3)3 + NaOH Al(OH)3 + NaNO3 A B C D A D C B A B C A C B

25. Recognize this chemical reaction! • Plants use carbon dioxide and water with sunlight to provide animals sugar, oxygen and energy. • Help us translate this sentence into a chemical equation. CO2 + H2O + sunlight C6H12O6 + O2 + ATP

26. Respiration • In the chemical reaction, Respiration, animals produce some CO2and H2O • Can we leave the chemical reaction like this? What are we suppose to do? __C6H12O6 + __O2  __CO2+ __H2O

28. Balancing Equations CO2 + H2O C6H12O6 + O2 Mg + HCl MgCl2 + H2 Mg + O2 MgO Cl2 + NaBr NaCl + Br2 K2SO4 + CaCl2 KCl + CaSO4 Al(NO3)3 + NaOH Al(OH)3 + NaNO3