Notes on the periodic table

1. The Periodic Table of The Elements

2. Elements are like a collection As more and more elements were discovered it became more important to organize and classify them

3. Between the late 1700’s and mid 1800’s scientists, using mostly atomic spectroscopy, doubled the number of known elements.

4. In early 1800’s, German chemist J.W. Dobereiner observed that several of the elements could be classified into groups of three which he called triads

5. Ca, Sr, and Ba Li, Na, K Cl, Br, I Dobereiner based his triads on similar chemical properties

6. In addition: Many of the properties of the middle element in each triad are approximate averages of the properties of the first and third element

7. Element Atomic Density Mass (amu) Cl 35.5 1.56 g/L Br 79.9 3.12 g/L I 126.9 4.95 g/L Ca 40.1 1.55 g/cm 3 Sr 87.6 2.6 g/cm 3 Ba 137 3.5 g/cm 3

8. In 1865, English chemist J.A.R Newlands presented another way to classify and organize the 62 elements known at the time

9. Newlands placed the elements in order of increasing atomic mass He noticed that the properties of the eighth element were like those of the first, the ninth like those of the second, and so on….

10. He called this repeating pattern of every eight elements THE LAW OF OCTAVES After the eight notes of the musical scale

11. Because he linked chemistry to music, he was not taken seriously! It took 20 years for him to receive credit for recognizing periodicity

12. In 1869 Russian Chemist Dimitri Mendeleev and German chemist Lothar Meyer published nearly identical ways of classifying

13. But Mendeleev is generally more credited with the 1 st periodic table for 2 reasons: He published first He was better at explaining it than Meyer

14. Mendeleev also saw the “periods” Credited with publishing the first “periodic table”

16. Mendeleev got lots of credit because he left gaps for missing elements!

17. In 1913, English Chemist James Moseley Presented a way of organizing the elements that we still use today.

18. Moseley was the first to put the elements in order of increasing Atomic #

19. Atomic # represents the number of protons in the nucleus of each element

20. When he did this, he saw the same repeating periodic pattern, without the exceptions that Mendeleev had to switch around

21. Periodic Law When the elements are arranged in increasing order by their atomic numbers, their properties repeat periodically

22. The Modern Periodic Table

23. Each Square Tells about a different element H Element Symbol Hydrogen Element Name Not always there 1 Atomic Number Represents the number of PROTONS in each atom of this element 1.009 Atomic Mass Represents the number of PROTONS AND AVERAGE NUMBER OF NEUTRONS in each atom of this element

24. Atomic Number 1: 1 proton (positive charge particles) in nucleus of EVERY hydrogen atom Atomic Number 1: ALSO means 1 electron (negatively charged particle) OUTSIDE the nucleus Atoms are NEUTRAL: Same number of positives as negatives Atomic Mass of 1.009 means that there is an average of 1.009 PROTONS AND NEUTRONS in the nucleus… Since there is already 1 proton (AND THAT CAN NOT CHANGE AND STILL BE HYDROGEN) That means that the average atom of Hydrogen has 0 Neutrons! H Hydrogen 1 1.009

25. Let’s do another 4 Particles 2 MUST BE Protons 4-2 = 2 Neutrons in nucleus He Helium 2 4.003

26. Each block tells us about the element… The periodic table arranges the elements into rows and columns based on similarities

46. The periodic table can also show larger “Groups”

47. METALS Non-METALS METALLOIDS

51. Periodic Trends