Chemical Bonding. Chapter 8 Sections 1 & 2. A chemical bond is : a force of attraction between any two atoms in a compound. Bonding between atoms occurs because it creates a more stable arrangement for the atoms. Lewis Symbols – Dot Diagrams. Convenient way to show the valence electrons.
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Chemical Bonding Chapter 8 Sections 1 & 2
A chemical bond is: a force of attraction between any two atoms in a compound. • Bonding between atoms occurs because it creates a more stable arrangement for the atoms.
Lewis Symbols – Dot Diagrams • Convenient way to show the valence electrons
Three types of bonding • Metallic bonding – results from the attraction between metal atoms and the surrounding sea of electrons • Ionic bonding – results from the electrical attraction between large numbers of cations and anions • Covalent bonding – results from the sharing of electron pairs between two atoms
Ionic Bonding • Many atoms transfer electrons and other atoms accept electrons, creating cations (positive metal ions) and anions (negative nonmetal ions). • The resulting ions are attracted to each other by electrostatic force.
Covalent bonding • In many cases electrons do not completely transfer from one atom to another. • The electrons between atoms are shared.
Covalent bonding between H2 • Hydrogen’s electron configuration is 1s1 • Because both H atoms need 1 more electron to become isoelectronic with He, it is unlikely that either will give up an electron.
Covalent bonding between H2 ↑ 1s ↓ 1s They share the two electrons. H· + H · H : H
Types of Covalent Bonds • When electrons are shared equally the bond is called a NONPOLAR covalent bond. (i.e. H2) • Sometimes the electrons between two atoms are NOT shared equally. The bond created is called a POLAR covalent bond. . . . . H· + ·Cl: H:Cl: . . . .
Polar Covalent Bonding • An example of this would be HCl. HCl molecule Hydrogen atom ↑ 1s [Ne] ↑↓↑↓↑↓ ↓ 3s 3p Chlorine atom
How to classify bond types • Electronegativity – measure of the ability of an atom to attract electrons in a chemical bond • Each element on the periodic table is assigned an electronegativity value (see page 353) that ranges from 0.7 to 4.0. • The difference in the electronegativity determines the bonding type (ionic, polar covalent, or nonpolar covalent).
If the electronegativity difference is: 1.7 and higher ionic 0.3 to 1.7 polar covalent 0.0 to 0.3 nonpolar covalent
What if I get an electronegativity difference that is 0.3 or 1.7? • These cut-off numbers are guidelines. • It is a gradual change not stair-step.
Ionic Character • As the electronegativity difference increases, the ionic character increases as well!
Practice Problems What type of bond will occur between iodine and the following elements: cesium, iron, and sulfur?