The periodic table

Presentation by Lisa Allen, Stonington High School

What does periodic mean?

Stanislao Cannizzaro

• 1860 Presentation to Chemists• Demonstrated a reliable way

to determine the atomic mass of an element

• Every chemist who saw the presentation began doing experiments to find the atomic mass of an element. Before long, many atomic masses were known

Another dead chemist...• Dmitri Mendeleev• Born: 8-Feb-1834

Birthplace: Tobolsk, Siberia, RussiaDied: 2-Feb-1907Location of death: St. Petersburg, Russia

Cause of death: Influenza

Dmitri Mendeleev - 1869

• Sorted elements• Began with new

atomic masses• Saw PERIODIC

PATTERNS of elements chemical properties.

• Organized a chart by sorting elements

• See p. 134, Holt Modern Chemistry

The original Periodic table

Sorting can be a powerful tool

A challenge at the start

• Some elements needed to be placed slightly out of sequence to fit the periodic trends.

• What is the thinking that allowed Mendeleev to place iodine AFTER tellurium on his chart?

Support for the structure of the periodic table

• Some spaces existed, where elements should have been. Mendeleev (bravely) predicted the existence of 3 elements based on the spaces in his table. He predicted their properties, too. Those elements (Ge, Ga, Sc) were discovered within 15 years, validating his table.

Activity: Design a Periodic Table

• Cut apart the elements on the sheet provided

• Sort them first by mass, as Mendeleev did

• Organize the “Q values” periodically

• You should have trends in Q that are consistent along both vertical and horizontal axes

• You may need to reorder a few elements by mass, as Mendeleev did

Assignment

• Create a periodic table from the elements provided. Make a map of the table, or glue the cards onto a piece of paper.

• Write a 6-8 sentence paragraph describing the structure of the table you have created, the decisions you made in the organization, and trends it demonstrates.

• Due next class

Advantages you have over D.M.

• You know that there’s some right answer, some validity to organizing these elements.

• He had nothing but intuition to tell him that there is some reason for chemical periodicity.

• DM had no noble gases. They are so similar in their state at room temperature and their lack of reactivity, that they are the easiest family of elements to identify.

Groups of the periodic table

• Elements Mendeleev grouped by property share a valence electron configuration.

• ns1 is the alkali metals. They are reactive, stored under oil in the dark, cut like taffy.

• ns2 is alkaline earth metals. They are harder and denser than ns1, have higher MP

• ns2np5 is the halogen family.• ns2np6 is the noble gas family.

Alkali metal properties

• http://www.youtube.com/watch?v=m55kgyApYrY

• I apologize in advance for the pathetic tone of geeks trying to appeal to teens. This guy has cool toys. You just have to ignore his word choice, his haircut, and his little outfit… sorry. Just don’t say I didn’t warn you!

Homework

• Page 149, #2 and 3• Page 166, #2, 3, 4, 6, 8, 9, 13,

16

• If you have not read chapter 5 in its entirety, please do so this weekend. Also, try the practice problems on pages 143, 146, and 148. These practice problems will not be collected.

Part Two: Periodic Properties

ElectronegativityAtomic radius

Ionization energyElectron affinity

Electronegativity

• Definition The ability of an atom to attract electrons in a bond.

• For example, when forming H2O, the oxygen attracts the shared electrons much more strongly than the hydrogen, because it is more electronegative. This is why water is polar. It has a slightly negative end, where the oxygen is, and a slightly positive end, where the hydrogen is.

Images of water molecules: notice the charges!

Atomic Radius

• Atomic radius: the size of an atom, usually established by dividing the distance between 2 bonded atoms by 2 (distance between nuclei of O2÷2)

What controls atomic size?

• Effective nuclear charge, or z*• Number of energy levels

Other Periodic Properties

• Electron affinity: The energy an atom gives off when it acquires an electron

Ionization energy

Definition: the amount of energy it takes to rip an electron off from an atom

Which elements would be easy to steal from? Which would be hard? What causes the difference?

Ionization, Acrylic on Canvas, Niall Higbee

Periodic trends assignment

ElectronegativityAtomic radius

Ionization energyElectron affinity

What you will do:• Create a 3-D periodic table

illustrating the trend in the property you have been assigned to study.

• Create a 5+ slide power point presentation explaining the reason for the patterns, both down a group and across a period. Include pictures, as well as text. Save it to your own CD or USB flash drive.

• Present your Power point to the class.

• Explain, and handle questions from students and from me.

• Write a paragraph on your trend individually in class.

Rubric for evaluating success3 2 1 0

3-D Table

Table is creative, visually interesting, easy to interpret

Work is easy to interpret. Key is included.

Key is missing, or table does not represent trend in 3-D

I was supposed to make a table? When?

Power point

Visually interesting, good explanations

Meets expectations for length, some visuals.

All text, mostly quotes from the book.

You mean on the computer?

Demonstrated understanding in written paragraph

Links trend to atomic structure, as well as to other periodic properties.

Understands trend, communicates reasons for trend

Understands trend, may not be able to explain why the trend exists.

Oh, yeah, I guess all the big ones are on one side, aren’t they?

Explanation

Audible, clear, no ummmm or uhhh, Easy to follow.

Needs prompting to speak loudly enough to be heard. Good effort to communicate effectively.

Difficult to hear, or hard to follow. Read presentation.

Nothing to hear!

HandlingQuestions

Answers refer to PP as well as to the 3-D table and demonstrate good understanding

Answers demonstrate understanding.

Difficulty explaining trend, or answering questions

Uh, can I call a lifeline on that?

Issues we need to resolve...

• How do we divide up the responsibility for the work so that nobody coasts, and nobody feels (s)he is carrying the group?

• What role does self-assessment play in evaluating this?

• How do you want to handle it if your group says one member didn’t do anything?

• How do you want to handle absentees?