Atoms, Bonding and the Periodic Table Notes 5-1 Key Ideas: 1. How is the reactivity of elements related to valence electrons in atoms? 2. What does the periodic table tell you about the atoms of elements?

Review of Atomic Structure  Atoms are made of protons, neutrons and electrons.  Most of an atom’s mass comes from the nucleus (protons and neutrons) with VERY LITTLE coming form the electrons.

Valence Electrons 1.Valence electrons are the electrons in the highest energy level and are held most loosely to the atom. 2. The number of valence electrons determines many properties of that element, including the ways the atom can bond with other atoms. 3. Each element has a specific number of valence electrons from 1-8. Electron Dot Diagrams: A model that represents how many valence electrons are in an element Includes a symbol and dot/s representing valence electrons

Bonding Chemical Bonds and Stability Noble gases most nonreactive since they have 8 electrons in their outer shell Small atoms like helium are stable with just two valence electrons When atoms give up their valence electrons are accept valence electrons from other atoms, they become chemically combined forming a chemical bond. This is due to the rearrangement of their electrons. Chemical Bonds and Chemical Reactions Electrons can be transferred forming a bond but they can also be shared forming a bond (more to come on covalent bonding) In either case, the change results in a chemical reaction forming a new substance

How the Periodic Table Works Relating Periods and Groups: As atomic number increases, number of valence electrons increase; Periods (left to right) end when valence electrons reach 8; Elements within a group (top to bottom) always have the same number of valence electrons with similar properties Inert Gases: Group 18=Inert gases, 8 valence electrons except with helium which has 2 They are the most stable group! Reactive Nonmetals and Metals: Group 17=Halogens with 7 valence electrons VERY REACTIVE; Group 1=Alkali metal family with 1 valence electron Other Metals: Groups 2 through 12, most have 1-3 valence electrons, Reactivity increases from top to bottom in Groups 1 and 2 Other Nonmetals: All nonmetals have 4 or more valence electrons (Groups 14-17) Semimetals: fall on zigzag line(Groups 13—16), from 3 to 6 electrons, can lose or share electrons, can behave like metals or nonmetals Hydrogen: In (Group I), 1 valence electron, not a metal

Remember! Most atoms become less reactive after a change to the total number of eight valence electrons.