8th Grade Science Chapter 12 Answers
1. The periodic table was created by a Russian chemist, Dmitri Mendeleev in the 1860’s. P 302
2. The term periodic means, “to have a regular or repeating pattern.”
3. The elements are arranged in a Periodic Table because the properties of these elements change in a
periodic (regular or repeating pattern) way. Think about the calendar, every week has 7 days, it is a
“period” of time.
4. Mendeleev arranged his elements in order of their increasing atomic mass. P 303
5. Mosley helped to correct Mendeleev’s order by atomic mass. Instead of using atomic mass, Mosley
determined that it was best to use the elements atomic number or the number of protons in the atom.
Once Mosley was done, all of the elements fell into their proper place on the table.
6. The Periodic Law is a principle that states that the chemical and physical properties of the elements are
periodic functions of their atomic numbers.
7.
the
6 = atomic #
C = symbol
Carbon = Element Name
12.0 = atomic mass
8. The background colors of the Periodic Table actually indicate what type of element it is. The Blue
background is for a metals, the Green’s are metalloids, and the yellow indicates a nonmetal.
9. The color of the chemical symbol indicates the physical state of the element at room temperature. If the
symbol is:
Red = Solid
Blue = Liquid
Green = Gas
10. A row of elements is called a Period.
11. A column of elements is called a Group or Family
12. The number in the parenthesis is the mass number of the most stable isotope of the element.
13. Yes, the elements of the symbols are universally recognized by an International Committee of scientists
that approves the name and symbol for each element.
14. Elements are classified as a metal, nonmetal, or a metalloid, according to their properties.
15. The number of electrons in the outer energy level is used to determine which category an element is
placed.
16. Four properties of metals are: Good Conductors of Thermal Energy, Malleable: they can be flattened
with a hammer without shattering, Ductile: they can be drawn into thin wires and are then good
conductors of electric current, Shiny: you can see a reflection.
17. Nonmetals are: Poor Conductors of Thermal Energy: can’t conduct thermal energy, Not Malleable: can’t
be flattened with a hammer without shattering, Not Ductile: can not be drawn into wires, & Not Shiny.
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8th Grade Science Chapter 12 Answers.doc
18. Metalloids actually contain properties of both metals and nonmetals.
19. Reactive elements are those that are able to undergo the processes of giving, taking, or sharing electrons.
This is because these elements have only 1 or 2 electrons in their outer level.
20. The alkali metals are the elements in Group 1 of the periodic table. They are the most reactive elements
and have 1 electron in their outer level. These elements are soft, soft enough to cut with a knife and have
very low densities. These elements are also silver-colored and shiny.
21. When alkali metals react with water they form hydrogen gas. P 311
22. The Group 2 alkaline-earth metals are very reactive, but not as reactive as the alkali metals. These
elements are also silver-colored, but denser than the Alkali metals.
23. The alkaline-earth metals are not as reactive as the alkali metals because it is more difficult for atoms to
give away two electrons than to give only one away when joining with other atoms.
24. The Transition Metals do not have individual names, but include some of the most well know metals
such as gold, mercury, and iron. They are found in Groups 3-12 of the Periodic Table. These metals are
less reactive than the alkaline-earth metals and do not give away their electrons as easily.
25. While the properties of the Transition Metals do vary in both the chemical and physical means, in
general, properties of the Transition Metals are: they are less reactive than the alkaline-earth metals,
shiny, good conductors, have high densities, and higher melting points than the Group 1 & 2 elements.
26. The short answer, to keep the table from being to wide. However, these metals from periods 6 and 7 do
tend to be very similar within their period.
27. The Lanthanides of period 6 are a group of metals that actually follow the properties of the transition
metal Lanthanum.
28. The Actinides of period 6 are a group of metals that actually follow the properties of the transition metal
Actinium.
29. The properties of the Lanthanide transition metals are shiny and reactive. Some of these metals are used
to make steel.
30. The properties of the Actinides transition metals are unstable, this is because they all include atoms
which are radioactive. Remember, unstable elements have atoms that can change into the atoms of other
elements.
31. Did you fall for this trick question? Actually these groups contain a mixture of two or all three types of
element.
32. Group 13 is called the Boron Group and contains 1 metalloid and 4 metals.
33. The Group 13 elements are reactive, have 3 electrons in their outer level and are all solid at room
temperature. Aluminum is the most common element from Group 13.
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8th Grade Science Chapter 12 Answers.doc
34. Group 14 is called the Carbon Group and contains 1 nonmetal, 2 metalloids and 2 metals.
35. The Group 14 elements vary in their reactivity among the elements, have 4 electrons in their outer level
and are all solid at room temperature. Common elements are silicon, germanium, tin and carbon.
Carbon of course is essential to life on Earth and is found in both diamonds and soot.
36. Group 15 is called the Nitrogen Group and contains 2 nonmetal, 2 metalloids and 1 metal.
37. The Group 15 elements vary in their reactivity among the elements, have 5 electrons in their outer level
and all but Nitrogen are solid at room temperature. Nitrogen is a gas at room temp. and makes up about
80% of the air we breath. Nitrogen is unreactive, but phosphorus is extremely reactive and that is why it
is used on match boxes.
38. Group 16 is called the Oxygen Group and contains 3 nonmetals, 1 metalloid and 1 metal.
39. The Group 16 elements are reactive, have 6 electrons in their outer level & all but Oxygen is solid at
room temp. Oxygen of course is 20% of the air we breath and necessary to make substances burn. Sulfur
is also part of the Group 16 elements & is the most widely used compound in the chemical industry.
40. For Groups 13-16 the one common thing that they have is that the elements within their group all have
the same number of electrons in their outer level. Elements in Group 13 all have 3 electrons in their
outer level, Group 14 have 4, Group 15 have 5, and Group 16 have 6.
41. The elements in Group 17 are the most reactive nonmetals while Group 18 consists of the least reactive
nonmetals. In fact, the elements in Group 18 will not react at all with other elements.
42. Group 17 are the Halogens and all of the elements are nonmetals.
43. The Group 17 elements are very reactive, have 7 electrons in their outer level. These nonmetals are poor
conductors of electric current, react violently with alkali metals to form salts and are never found
uncombined in nature.
44. The Halogens are very reactive and readily combine with metals because their atoms need to gain only 1
electron to have a complete outer level.
45. The chemical properties of the Halogens are similar, however the physical properties are quite different.
If you compare the physical properties in Figure 12 show for chlorine, bromine, and iodine at room temp
you will see that chlorine is a gas, bromine a liquid and iodine a solid.
46. Group 18 consists of the nonmetal Noble Gases.
47. The Group 18 elements are unreactive and all but Helium have 8 electrons in their outer level. The other
shared properties for the Noble Gases: they are colorless and odorless gases at room temperature. They
are also all present in small amounts in our atmosphere.
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8th Grade Science Chapter 12 Answers.doc
48. Again think about why elements are reactive, it is to gain or lose electrons. In the case of the Noble
Gases, they already have a complete set of electrons in their outer level, therefore they are unreactive.
The Nobel Gases do NOT need to gain or lose an electron, therefore they do NOT react with other
elements under NORMAL conditions. Remember the “Brain Food” on pg 316, the Nobel Gases do not
generally react with other elements just like the “Nobels” or Kings and Queens did not often mix with
the commoners.
49. Easily put, Hydrogen does not have properties that match those of any other single group of atoms, so it
is set apart.
50. Hydrogen has only 1 atom and is reactive.
51. Hydrogen is placed above the Group 1 elements because the atoms of the alkali metals also have 1 atom
in their outer level. Like Hydrogen, the alkali metals can give 1 atom away when joining with other
elements.
52. Hydrogen has similar physical properties more like nonmetals than nonmetals. Hydrogen is a colorless,
odorless gas at room temperature, has a low density and reacts explosively with oxygen. Hydrogen is the
most abundant element in the universe.
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