Download Comparing Mendeleev's & Modern Periodic Table: Cosmic Chemistry and more Study notes Chemistry in PDF only on Docsity!
Cosmic Chemistry:
Understanding Elements
The Modern Periodic Table
TEACHER GUIDE SUPPLEMENT
READING THE MODERN PERIODIC TABLE
Put a transparency of Mendeleev’s periodic table and the modern periodic table on the overhead projector (or give students a copy of each). Ask students to list ways in which they are similar and different. Post these on the chalkboard. Discuss the differences between groups and periods in both tables. Students should then answer questions one and two.
- Describe how the groups and periods are different in the modern periodic table versus Mendeleev’s version.
In the modern periodic table groups of elements with similar properties appear in vertical columns and periods of increasing atomic number appear in horizontal rows. Mendeleev’s table had groups in rows and periods in columns.
- The modern periodic table is arranged by __________________. atomic number
- Why was the oxide ratio column not shown in earlier Mendeleev periodic tables?
Possible answer: Mendeleev did not know the oxide ratios for elements.
GROUPS
Describe to students that elements in the same group have similar physical and chemical properties. Choose one group and point out the properties for each element in that group. Students may discuss what known characteristics belong to certain groups of elements. The following laserdisc shows this in video format: (Resource: VideoDiscovery^ ^ Chemistry at Work Laserdisc: (http://www.videodiscovery.com) this has a short video clip called “the periodicity of alkali metals.” Students can present this type of information to the class if they complete the “Element Research” activity.
- Why do elements in the same group have similar physical and chemical properties?
Elements in the same group have the same number of electrons in their outermost orbit.
- How are the groups titled?
Either from one to eighteen or with Roman numerals and letters.
- How many groups are there?
Eighteen or 16 with Roman numeral method.
- List all of the elements in group 14 or IV A.
carbon, silicon, germanium, tin and lead.
PERIODS AND CLASSIFICATIONS
Try using the analogy of locating elements on the modern periodic table to finding a location on a map. Just as people can find a town on a map by using latitude and longitude, elements can be found if their group and period is known. Ask the students for other examples locating items by a coordinate system. How are these analogies different than that of the
periodic table? (With other analogies the position is the important part, with the periodic table the properties are the most important factor.)
- Periods are arranged in _____________ rows. horizontal
- How many periods are there? seven
- List all of the elements in period 2.
lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, and neon
- What are the three classifications of elements? metals, metalloids, nonmetals
- Metals are found on the _____ side of the table. Left
- Name the element in period 4 group IA (1). Potassium
- Write the atomic symbol for the element in period 6 group IB (11). Au
METALS
In small groups, have students generate a list of metals. Post these on the chalkboard for discussion. Ask: “What makes a metal?” Ask the groups to eliminate any on the list that do not meet this criterion. Next ask the groups to make list some of the uses of the metals left on the chalkboard. Have students share their use list and discuss.
- List some of the properties of metal.
Metals are dense, have luster, are good conductors of heat and electricity, and are malleable and ductile.
- Why do metals have a luster?
Solid metals are crystals formed from positive ions with mobile electrons that reflect light in many wavelengths.
- Where are the most metallic metals found on the periodic table? On the left side.
For each of the following groups provide either a laminated copy of the periodic table with transparency pens or a paper copy of the periodic table with highlighters. Students can locate and highlight the different groups as the questions are discussed. Students should also develop a color code key for their table.
THE ALKALI METAL GROUP
Sodium can be used to show how reactive Alkali metals can be. For a sodium / chlorine reaction demonstration: http://scifun.chem.wisc.edu/vol1desc.html_. Also if you would like to show a short video of this reaction it can be found on the Windows of Science laserdisc under the physical science section. (_ http://www.opticaldata.com/catalog/wos/wosmain.html )
- List the atomic symbols for the elements in this group.
Li, Na, K, Rb, Cs, Fr
- Describe the relationship between the atomic number and the chemical reactivity of alkali metals.
As the atomic number increases the chemical reactivity of the element also increases.
RARE EARTH METALS
ChemCom’s Nuclear Chemistry in Our World is an excellent resource. Subsections include Radiation, Radioactivity, Nuclear Energy, and Living with Benefits and Risks.
- Name the two periods in this group.
lanthanides and actinides
- Why do you think these elements are sometimes found under the rest of the table?
Possible answer: because they are difficult to find, many are synthetically made
- When radioisotopes decay they emit _____________.
radiation.
- Describe the rate at which different radioisotopes decay.
Some take days or months to decay; others last only a fraction of a second.
- The most well-known naturally occurring actinide is ____________, which can be used in _________________.
uranium, nuclear fission reactions
OTHER METALS AND METALLOIDS
Point out the bold stair step line on most periodic tables. Explain that this separates the metals from the nonmetals. Most of the elements on the border of this stair step are called metalloids. They have the properties of both metals and nonmetals.
- The staircase inside the periodic table separates the ________ from the _________.
metals, nonmetals
- List the atomic symbols for the metalloids.
B, Si, Ge, As, Sb, Te and Po
- What are semi-conductors and what are their use?
Semi-conductors are metalloids that conduct electrons in one direction. They are used for transistors and electronic components.
NONMETALS
Another good ChemCom activity for this section is the laboratory activity “Metal, Nonmetal?”
- Which elements are known as organic chemicals?
carbon, hydrogen, oxygen, sulfur and nitrogen
2. Most of our atmosphere is made up of ___________ gas.
nitrogen
THE HALOGEN GROUP
Teachers interested in teaching building block chemistry using chlorine should try the Chlorine Chemical Council set of activities at their Web site: http://c3.org/classroom/bbc.html
- Name the atomic symbols for the elements in the halogen group.
F, Cl, Br, I, At
- The word “halogen” means ____________.
salt formers
- Define “salt” in your own words.
When a halogen bonds with an alkali metal or an alkaline earth metal.
- Which element is the most reactive element on Earth?
fluorine
THE NOBLE GAS GROUP (INERT GASES)
Chemistry at Work has two good short videos to accompany this section. One shows the Hindenburg explosion and the other shows one balloon filled with hydrogen and one balloon filled with helium. Both balloons are lit showing the reason hydrogen is no longer used in blimps. Another activity to help students understand question 3 below would be to have students draw Bohr models of each of these atoms and determine what they all have in common. This may indicate the extent that students know about electron configuration and how many electrons can exist at various energy levels. Alternatively students may look up this information on the Web page http://www.chemicalelements.com/. Students can look at the atomic structure of each of the noble gases.
- List the atomic numbers of the elements in group 0. 2, 10, 18, 36, 54, 86.
- How was helium discovered?
Helium was discovered from its bright yellow solar spectral line in 1868.
- Why do atoms of these elements not react with other atoms?
Atoms bond when their outer orbits are not full, noble gas elements all have full outer orbits.
- Which elements’ isotope ratios were measured by Apollo astronauts on the moon?
neon
HYDROGEN
- After reading the first paragraph in this section, where would you put hydrogen on the periodic table. Explain your answer.
Answers will vary, some students might put it with the alkali metal group, others might put it by itself away from the other elements because it is such a unique and common element. Students should explain their answer.
