10/6/14 Objective: How are ionic and covalent bonds formed? Do Now: Sodium’s atomic mass is 23 and atomic number is 11. How many protons are there? Neutrons? Electrons? Chapter 4: The Chemical Basis of Life

Energy Levels The electrons in an atom determine how it will react with other atoms Electrons are found in clouds outside the nucleus Energy Levels –First level = lowest, nearest to nucleus can hold 2 electrons – Second level = can hold 8 electrons –Third level = can hold 8 electrons –Most reactive when they have partially full energy levels Nitrogen

- Are their highest energy levels full? - Are these atoms chemically reactive or inert?

ion: atoms that have become electrically charged as a result of gaining or losing electrons ionic bond: an atom transfers an electron to another atom and the attraction between them is the ionic bond. ex. NaCl

Covalent Bonds covalent bonds: two atoms share electrons –Number of bonds that will form= number of additional electrons that will fill the highest level

How many additional electrons will fill the highest energy level? How many bonds can oxygen form? Hydrogen How many additional electrons will fill the highest energy level? How many bonds can hydrogen form? O + H + H  O H

Chemical Reactions chemical reactions: bonds break or form new bonds which result in the formation of one or more new substances reactants: starting material products: ending materials

Fig. 2-3 Sodium Chlorine Sodium chloride