Fig 8.17 Periodic Table of the Elements Alkali Earth Metal Noble Gas Halogen Alkali Metal Period Group

Show only valence electrons! Electron dot notation for the representative elements Fig 8.18 Show only valence electrons!

CHEMICAL BONDS CHAP 9

Homework for Chap 9 Read p 229 - 246 Applying the Concepts: 1 – 13, 16 – 35, 38 – 44, 47 - 5

Compounds and Chemical Change Elements are composed of extremely small particles called atoms. Compounds are composed of atoms of more than one element held together by chemical bonds. 3. Molecule – smallest particle of a compound that can exist and still retain characteristic chemical properties Compounds occur as solids, liquids, and gases

Fig. 9.2 Common gases exist as atoms or molecules

Fig. 9.3 Energy is released Example of a chemical reaction Burning magnesium (Mg) in air to produce magnesium oxide (“milk of magnesia”) Energy is released

Fig. 9.4 (A) Photosynthesis stores solar energy Reactants Products Fig. 9.4 (B) Combustion releases solar energy

Fig 8.20 Electron dot notation for representative elements 1 8 3 4 5 6 7 Valence electrons – outermost electrons in an atom Octet rule – atoms attempt to acquire 8 valence electrons

Fig. 9.5

Fig 8.21 energy + Na → Na+ + e− energy + Ca → energy + Al → Ca2+ + e− Al3+ + e− 1 8 2 3 4 5 6 7

Three Types of Chemical Bonds Ionic bonds Electrons are transferred from one atom to another Occur between a metal atom and a nonmetal atom (2) Covalent bonds Electrons are shared between two atoms Occur between two nonmetal atoms Metallic bonds Metal atoms share many electrons in a “sea” that is free to move throughout the metal

This energy is called the heat of formation Formation of an ionic bond Na 11 protons 11 electrons Na+ 11 protons 10 electrons + e− Cl- 17 protons 18 electrons Cl 17 protons 17 electrons Net reaction: Na + Cl → Na+Cl− + energy This energy is called the heat of formation

Fig. 9.6 Model of the sodium chloride crystal No molecules in an ionic compound! Formula unit + − Na+ ions Cl− ions

Fig. 9.7 The cubic crystal structure of sodium chloride

Ionic compounds consist of a combination of Ionic compounds consist of a combination of positive ions and negative ions Ions are formed as nonmetal atoms gain and metal atoms lose electrons to achieve stable noble gas structure The sum of the charges on the positive ions and negative ions in each formula unit must equal zero How do we determine the formula for an ionic compound?

Formula of Ionic Compounds 2 x +3 = +6 3 x -2 = -6 Al2O3 Al and O Al3+ O2- 1 x +2 = +2 2 x -1 = -2 Ca and Br CaBr2 Ca2+ Br-