4-2: Organizing the Elements. 8 th Grade Physical Sciences

Transcription

1 8 th Grade Physical Sciences

2 Mendeleev s Periodic Table By 1869, a total of 63 elements had been discovered a few gases, 2 liquids, but most solids.

3 Mendeleev s Periodic Table At this time, a Russian scientist named Dmitri Mendeleev discovered a set of patterns when trying to organize these elements.

4 Mendeleev s Periodic Table He used known chemical and physical properties to organize them such as melting points, color, reactivity, and atomic mass.

5 Mendeleev s Periodic Table He created the first periodic table, which are the elements ordered in a way that shows their repeating pattern of properties.

6 Mendeleev s Periodic Table He left blanks in some places, predicting that someday those elements would be discovered which they were!

7 Modern Periodic Table The modern periodic table has over 100 elements. You can predict their properties by looking at where they are in the table.

8 Awesome web site of the periodic table: Slide the temperature scale!

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10 Color Coding The colors indicate which elements are metals, semimetals, and nonmetals.

11 Periods Each row is called a period from 1 to 7. Period 1 has 2 elements. Periods 2 and 3 have 8. Periods 4 and 5 have 18. Period 6 and 7 has 32. To save space, parts of periods 6 and 7 are off the table.

12 Groups Each column is called a group or family. Each group shares properties. e.g: Group 1 reacts violently with water. e.g.: Group 2 reacts slowly or not at all with water. e.g.: Group 18 doesn t react with anything.

13 Reading the Data Each element in the table is a square with 4 pieces of information in it. 1. Element Name 2. Chemical Symbol 3. Atomic Number 4. Atomic Mass

14 Reading the Data The element name is usually assigned by its discoverer.

15 Reading the Data A Chemical Symbol is a 1 or 2 letter representation of an element. The second letter is always lower case.

16 Reading the Data Atomic number is how many protons are in the nucleus. Also the number of Electrons!!!!

17 Reading the Data Atomic mass is an average of all the isotope masses. e.g.: Iron is a mixture of 4 isotopes. About 92% of Iron is Iron-56 (having 30 neutrons).

18 Reading the Data Example Calculation Internet history of elements:

19 Summary It took trial and error to find the patterns in the known elements. The modern periodic table is organized to show repeating patterns of properties. Scientists can quickly find elements with the properties they desire. Metals, semimetals, and nonmetals are color coded in the table.

20 Let s use this information to identify elements. Remember the shoe box? What s inside?

21 I do an experiment on my shoe box and find that there are 16 protons. What element has 16 protons?

22 Sulfur has 16 protons. I know this because the Atomic Number tells me how many protons there are.

23 I do an experiment on my shoe box and find that there are 33 electrons. What element has 33 electrons?

24 Arsenic (As) has 33 electrons. I know this because the Atomic Number tells you how many protons there are AND this must match the number of electrons so the overall charge is neutral or zero.

25 I do an experiment on my shoe box and find the element has 2 more protons than Phosphorus. What element is it?

26 Chlorine (Cl) has 2 more protons than Phosphorus. I know this because the Atomic Number of Phosphorus is 15, which I add with 2 to get 17 Chlorine.

27 Here is the more difficult one Neutrons!! I do an experiment on my shoe box and find that the element has 8 neutrons. Which element has 8 neutrons?

28 Oxygen has 8 neutrons. Protons + Neutrons=Atomic Mass I know this because I add the 8 neutrons to the 8 protons of Oxygen and it is close to its atomic mass.

29 They will never add up perfectly to the atomic mass, so you must make a judgment as to which element it matches with the best. Note: Sometimes it will match two elements so you will need more information to determine which element is in your box.

30 I do an experiment on my shoe box and find that the element has 42 neutrons. Which element has 42 neutrons?

31 42 is a lot of neutrons! Must be a large atom. Add 42 to each atomic number until you are able to match the atomic mass of an element.

32 42+16=58 Nope! 42+17=59 Nope! 42+33=75 YES! 33 is Arsenic. It has an atomic mass of 75 when rounded to a whole number is about 75