1. Bell Work Those of you who did not take your Test Friday need to sit in the back 2 rows. All others need to sit in the front 3 rows. How are elements arranged on the periodic table?

2. Physical Science – Lecture 57 The Periodic Table

3. Matter Matter is used to create atoms. Atoms are used to create the elements. Elements are used to create molecules.

4. Elements All elements are made of atoms. The differ in weights and organization. All atoms are built the same way. Every element has electrons, protons, and neutrons.

5. Elements on the Periodic Table The elements listed on the periodic table cannot be changed using any chemical method. Each element has a unique number of protons, giving each element its own atomic number.

6. Arrangement of Elements If you examine samples of iron and silver, you can't tell how many protons the atoms have. However, you can tell the elements apart because they have different properties.

7. You might notice there are more similarities between iron and silver than between iron and oxygen. Could there be a way to organize the elements so you could tell at a glance which ones had similar properties?

8. The First Periodic Table Dmitri Mendeleev was the first scientist to create a periodic table of the elements similar to the one we use today. Mendeleev's original table was developed in 1869.

9. Mendeleev's Table When the elements were ordered by increasing atomic weight, a pattern appeared where properties of the elements repeated. This periodic table is a chart that groups the elements according to their similar properties.

10. Why is the Periodic Table Useful? Many elements remained to be discovered in Mendeleev's time. The periodic table helped predict the properties of new elements.

11. Mendeleev's Table The modern periodic table has over 100 elements. Mendeleev's table didn't have very many elements. He had question marks and spaces between elements, where he predicted undiscovered elements would fit.

12. Mendeleev’s Table Mendeleev found he could arrange the 65 elements that were then known in a grid or table so that each element had: 1. A higher atomic weight than the one on its left. 2. Similar chemical properties to other elements in the same column.

13. What about the other elements? In his table he noted gaps - spaces where elements should be but none had yet been discovered. Mendeleev could be said to have discovered germanium (which he called eka-silicon because he observed a gap between silicon and tin), gallium (eka-aluminum) and scandium (eka- boron) on paper, for he predicted their existence and their properties before their actual discoveries.

14. Discovering Elements The gaps in Mendeleev’s table helped him predict the existence of elements that had not been discovered yet.

15. Discovering Elements Elements with different numbers of protons are different elements. The gaps in atomic number on his table showed where new elements existed.

16. Adding to Today’s Table When you look at the modern periodic table, do you see any skipped atomic numbers that would be undiscovered elements?

17. Adding to Today’s Table New elements today aren't discovered. They are made in labs. You can still use the periodic table to predict the properties of these new elements.

18. Properties and Trends The periodic table helps predict some properties of the elements compared to each other.

19. Properties and Trends Atom size, energy required to remove an electron, the ability to form a chemical bond, and other properties form patterns across and down the periodic table.

20. Today's Table The most important difference between Mendeleev's table and today's table is the modern table is organized by increasing atomic number, not increasing atomic weight.

21. Why was the table changed? Henry Moseley worked with Rutherford on the model of the atom. In 1914, Henry Moseley learned you could experimentally determine the atomic numbers of elements.

22. Before that, atomic numbers were just the order of elements based on increasing atomic weight. Once atomic numbers had significance, the periodic table was reorganized.

23. Mendeleev’s Mistake They found that the atomic number (electric charge) is most fundamental to the chemical properties of any element. Mendeleev had believed chemical properties were determined by atomic weight. Moseley correctly predicted the existence of new elements based on atomic numbers.

24. Today’s Arrangement Today the chemical elements are still arranged in order of increasing atomic number (Z) as you go from left to right across the table. We also know now that an element's chemistry is determined by the way its electrons are arranged – by its electron configuration.