Section 2 Atoms Bonding and the Periodic Table

Section 2: Atoms, Bonding, and the Periodic Table Mr. Gardner 7 th Grade Science

Key Concepts How is the reactivity of elements related to valence electrons in atoms? What does the periodic table tell you about atoms and the properties of elements

Key terms Valence Electrons Electron dot diagram Chemical bond Symbol Atomic number Period Group Family Noble gas Halogen Alkali metal

How the Periodic Table Works Oxygen has: 8 electrons 8 protons An atomic mass of 15. 99 rounded to 16 Neutrons: 16 -8=8

Valence Electrons Valence Electrons: Have the highest energy level and are held most loosely. Outermost electrons The number of valence electrons determines the properties of that element. This is how they bond together The easiest way to represent electrons is the Electron Dot Diagram: Element symbol surrounded by the number of valence electrons

Chemical Bonds and Stability Atoms want 8 electrons in their valence shell Some atoms live with 8 electrons. These are not reactive. Noble Gases: all elements in group 18 on the periodic table. Some really want balance in life Halogens: atoms with seven valence electrons React very easily by excepting an electron. Alkali Metals: Atoms with one valence electron Reacts very easily by giving an electron.