OB: intro to understanding the Periodic Table

1. OB: intro to understanding the Periodic Table A salute to Dimitri Mendeleev

2. 1817 — Bavarian chemist Johann Döbereiner developed the law of triads where, for example, lithium, sodium, and potassium displayed similar properties. 1862 — French geologist Alexandre-Emile Béguyer de Chancourtois’ proposed a system ordered by increasing atomic weight and with similar elements lined up diagonally in a cylinder. 1863 — English chemist John Newlands classified the elements into 11 groups, based on similar physical properties. He noted that there existed many pairs of elements, which differed by multiples of eight the law of octaves. 1869 — Russian scientist and educator Dmitri Mendeleev unveiled the hidden order of the natural world by developing the comprehensive periodic table—combining the law of triads, octaves, and diagonals. He surprisingly and boldly included "holes" in his table for as yet undiscovered elements and he even had the audacity to predict their properties!

3. In our class, poor metals are other metals, or transitional, the rare earth are the inner transitional You should memorize the names of the groups of atoms on the table.

4. The up and down columns of the periodic table are the GROUPS. Atoms in the same group share many similarities of chemical properties, because they have similar electron orbitals, which means they will bond in similar ways. Look at group 1, lithium, sodium, and potassium. How will they each bond with chlorine, with oxygen, or with phosphorous?

5. Note how each metal bonds in the same ratio with chlorine, and then a different ratio with oxygen, and a third ratio with phosphorous. Each of the group one metals is similar in that it has 1 valence electron, so they all will make similar ionic bonds.

6. In group 18, all the gases are called “noble” because they do not make bonds with other atoms. They are nearly inert! Group 2 metals all have 2 valence electrons, they too bond in similar ways. Atoms in groups are similar in chemical ways. Groups go up and down. Our periodic table has 18 groups.

7. The periods of the table go left to right. The periods contain many elements that have little similarities. Period numbers are 1 to 7, and they correspond to the number of electron orbitals in the atoms of that period. What are the electron configurations of the first four elements in groups 3 + 4?

8. Quick check: what’s the electron configuration for Fr Francium # 87

9. Fr 2-8-18-32-18-8-1 which is a total of 7 orbitals, which is good since Fr is in period 7 How many protons, neutrons, and electrons are in the element Zr, zirconium?

10. Zirconium - 40 That’s 40 protons And 40 electrons (since the positives = the negatives) And because… Atomic mass = protons plus neutrons, and atomic number = the number of protons Atomic Mass of zirconium = 91.224 which rounds to 91 91 – 40 = 51 neutrons

11. Demetri Mendeleev created the first real, modern style periodic table, one that you might recognize, just after the American Civil War, around 1869. This was not a small task. He literally took almost one hundred known substances thought to be elements, and figured out a way to put them into one table so that their properties all made sense. That is, some properties, but which ones? Which elements were missing? Any, two? More? Where to start? Which properties are more important than others? Wow!

12. We will look at several properties of the elements and how this puts them into particular places on the table. We’ll watch how these properties change as you move down the table, or across the table. Even the name of this table is important: The Periodic Table of the Elements. What does that Periodic part even mean here? Did you ever even give that word a thought?

13. thirteen

14. The elements of the Periodic Table are arranged in order of increasing atomic number, and by doing this, the properties of the elements will periodically repeat themselves. That means: by keeping the atoms in this order of atomic number (number of protons and number of electrons), in this shaped table, the elements that all bond in similar ways will be in the same groups, and the atoms with the same number of electron orbitals will all be in the same period. You just wait for the Periodic Table Puzzle Lab. The complexity of Mendeleev’s thoughts are astonishing, and were literally shocking in their perfection. He predicted that several elements were not yet found, because of the way the properties aligned, he “knew” that other elements belonged on the table he constructed, but he did not have them. He told scientists: go find me the missing ones, here are their properties!

15. Within the table there are many trends of properties. We will look at some of these trends this week. The first and simplest trend is atomic mass. To determine the group trend for atomic mass we’ll look at atomic mass of four elements in two different groups. Let’s do group 2 and group 17:

16. It should be clear that going down these and all the groups of the periodic table, that the atomic mass gets larger (because the atoms get larger. To state this properly: The group trend for atomic mass is increasing.

17. This time let’s do the period trend for atomic mass, we’ll examine period 3 and 4. Remember, whenever possible, use 4 atoms in a row to measure a trend.

18. This time let’s do the period trend for atomic mass, we’ll examine period 3 and 4. Remember, whenever possible, use 4 atoms in a row to measure a trend. How can we state this trend???

19. The period trend for atomic mass is increasing. When ever you state a trend, it’s always a complete sentence. It’s always starting with “period trend” or “group trend”. Then the end part is increasing or decreasing. It’s easy, the rules are clear. Memorize the way to do this, but not the trends. The trends are right on the table to figure out every time you need them. Always use 4 atoms in a row to measure a trend.