Atoms, Bonding, and the Periodic Table Chapter 5, Section 1 Atoms, Bonding, and the Periodic Table

Valence Electrons Highest energy level Held most loosely – “outermost” electrons The number of valence electrons in an element determines that elements properties In the Bohr model, the first circle, or shell, holds 2 electrons; the second holds 8, and the third holds 8. http://www.youtube.com/watch?v=K-jNgq16jEY Click on this link to see how the various electron orbitals form an electron cloud around an element

Electron Dot Diagram Each element has a specific number of valence electrons, ranging from 1-8 Each dot stands for one electron Atoms of an element are more stable (less reactive) when they have 8 valence electrons What would the electron dot diagrams look like for Lithium (Li)? Carbon (C)? Table Talk: Why do you think the noble gases might be mostly inert or non-reactive?

A quick way to remember the number of valence electrons for several elements:

YOUR TURN! Draw electron dot diagrams for sodium (Na), nitrogen (N), and sulfur (S)

Chemical Bond The force of attraction that holds two atoms together as a result of the rearrangement of electrons between them. Atoms usually react in a way that makes each atom more stable --- they will either gain or lose an electron

Valence Electron A valence electron is the electron or electrons in the outer most orbital of the atom. The number abovethe column in the periodic table tell how many valence electrons are in one atom of the element in the column.The only exception to this is Helium (He), although it is in column 8A meaning it should have 8 valence electrons instead it only has 2.                                                                              How the Periodic Table Works It reveals the underlying atomic structure of atoms, including the electron arrangement As atomic number increases, # of electrons increases A period ends when the # of valence electrons = 8 The next period begins with atoms having valence electrons with higher energy Elements within a group always have the same number of valence electrons (& therefore similar properties) Each element in a period has one more valence electron than the element to its left

Electron Dot Diagrams Showing Patterns of Valence Electrons on the Periodic table

What the Periodic Table tells us about the properties of elements: Inert Gases Reactive Metals & Non-Metals Alkali Metals Group 18; 8 valence electrons; stable Group 17; Halogens; 7 valence electrons easily react Group 1; one valence electron; very reactive

Other Metals Other Non-Metals Groups 3 through 12; 1, 2 or 3 valence electrons; these elements tend to lose these electrons 5 are solids, 4 are gases, one is a liquid Halogens (group 17) are easily reactive (F, Cl, BR, I , AT) Flourine is the most reactive element known Table talk: Why is this so? Hint: think about its position on the table and what you’ve learned about valence electrons.

(metalloids); 3-6 valence electrons; behave like both Semimetals (metalloids); 3-6 valence electrons; behave like both See Discovery Education video, “The Periodic Table” (18:19) end