Chapter 17 Section 3

1. The Periodic Table Chapter 17Section 3

2. Periodic • The word periodic means “repeated pattern”. • Lunar Cycle • Days of the week • Months of the year • Seasons

3. Dmitri Mendeleev • A Russian chemist in the late 1800’s who looked for a way to organize the elements using a “periodic pattern”. Mendeleev organized his chart from lightest-to-heaviest elements and then used a repeating pattern based on the Physical & Chemical properties of the elements.

4. Period Table: Version 1.0 Looks Confusing!

5. Leave the empties! • Mendeleev had to leave some places in his chart blank because there where no known elements that fit into that spot. • Mendeleev predicted that there might be more elements that had not yet been discovered that could fit into those spots. • Once these predictions were made, other scientists started looking, and guess what?

6. Found it! The prefix Eka mean close to or related to. Germanium was discovered by a ________ scientist. Gallium was discovered by a ________ scientist.

7. There’s Always Room for Improvement • Every time a new element was discovered the periodic table would be updated. This is what is looks like today. Every empty green slot is a spot where Mendeleev predicted an unknown element would go. Mendeleev’s Predicted Elements Every white slot represented a possible unknown elements, but Mendeleev did not have enough information to make predictions about the properties of these elements.

8. Organizing the periodic table • Mendeleev organized elements by mass and chemical properties. • The Vertical columns are called groups, or families. • These are elements that have similar chemical properties. • The chemical properties of an atom are based on the number of electrons orbiting around the nucleus.

9. Organizing the periodic table • The first family or group called the alkali metals contains: • Li, Na, K, Rb, Cs, Fr • These are dull grey, soft, metallic compounds that react violently with water. Disposal of Sodium Brainiac – Alkali Metals

10. Electron cloud structure • Not all electrons orbit at the same distance from the nucleus. • Each separate orbit is called an energy level or shell. • The 1st orbital shell can only hold a maximum of 2 electrons. Hydrogen & Helium

11. More orbital shells Lithium • Once the 1st shell is filled, we move on to a new orbital shell. • The second shell can hold a maximum of 8 electrons. Neon

12. Electron energy levels • Level 1 – 2 electrons • Level 2 – 8 electrons • Level 3 – 18 electrons • Level 4 – 32 electrons • Level 5 – 50 electrons

13. Let’s make this easier! • With the exception of the first energy level, all other elements repeat their chemical properties in a patter of 8’s • We call this an Octave. • Every atom wants to be stable. • This means getting as close to 8 electrons as possible in the outer shell. • These electrons in the outer shell are called Valence electrons. • Valence electrons are responsible for all chemical reactions between atoms.

14. Here’s the easy part • Instead of drawing pictures of the entire atom, we will ONLY draw the valence electrons. • We will use the chemical symbol for the atom and dots to represent the electrons.

15. 4 rooms, 2 to a room. • Each group is labeled by the number of valence electrons in the outer electron shell.

16. This is the Lewis dot structure! • We will use the Lewis dot structure (a.k.a. – electron dot diagram) to help us figure out how elements interact with each other to do chemistry! • Let’s get in some practice!