CHEMICAL BONDS CHEMICAL BONDS CHAP 9 CHAP 9
Dec 21, 2015
3
Compounds and Chemical ChangeCompounds and Chemical Change
1.1. ElementsElements are composed of extremely small particles are composed of extremely small particles called called atomsatoms. .
2.2. CompoundsCompounds are composed of atoms of more than one are composed of atoms of more than one element held together by element held together by chemical bondschemical bonds..
3. MoleculeMolecule – smallest particle of a compound that can – smallest particle of a compound that can
exist and still retain characteristic chemical properties exist and still retain characteristic chemical properties
4. Compounds occur as solids, liquids, and gases
Fig. 9.3Example of a
chemical reactionchemical reaction
Burning magnesium (Mg)
in air
to produce magnesium oxide
(“milk of magnesia”)
Energy is released
Fig. 9.4 (A) Photosynthesis stores solar energy
Fig. 9.4 (B) Combustion releases solar energy
Reactants Products
Fig 8.20 Electron dot notation for representative
elements1
5 6 7
8
3 42
Valence electronsValence electrons – outermost electrons in an atomOctet ruleOctet rule – atoms attempt to acquire 8 valence electrons
Three Types of Chemical BondsThree Types of Chemical Bonds(1) 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
(3) Metallic bonds
• Metal atoms share many electrons in a “sea” that is free to move throughout the metal
Na 11 protons11 electrons Na+ 11 protons
10 electrons
Cl 17 protons17 electrons
Cl-17 protons18 electrons
Formation of an ionic bond
+ e−
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!No molecules in an ionic compound!
Na+ ionsCl− ions
Formula unit
14
• 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?