CHEMICAL BONDING Cocaine Chemistry I – Chapter 8 To play the movies and simulations included, view the presentation in Slide Show Mode.

What is a Chemical Bond? Chemical bonds involve ONLY the valence electrons of atoms. The nucleus is unaffected, so each atom keeps its identity (carbon stays carbon) Chemical bonds seek stability in the octet rule – Most atoms want to have 8 valence electrons. 2 ways to achieve this: Transferring electrons – Ionic bonds Sharing electrons – Covalent bonds

What do you notice about the elements? Ionic Compounds Covalent Compounds MgCl2 NaBr Al2S3 FeO Pb3P4 Li2Se Fe2O3 N2O CO2 SF6 P4Br7 C6H12O6 NH3 C2H6

Types of Chemical Bonds Ionic Bond: Chemical bonding that results from the bonding between metals (left side of PT) and nonmetals (right side of PT). Electrons are transferred from one atom to another, from the metal to the nonmetal In general, what was the trend for electronegativity moving from left to right?

Atoms that lose valence electrons become positively charged and are known as CATIONS. Atoms that gain valence electrons become negatively charged and are known as ANIONS. Cations and Anions come together to form a NEUTRAL 3D crystal

Properties of Ionic Compounds Are hard, rigid, brittle crystalline solids which may or may not dissolve in water. Have high melting and boiling points. Good conductors of electricity when melted or when dissolved (aqueous solution); nonconductors when solid.

Covalent bond: Chemical bonding that results from the sharing of electrons between two nonmetals Covalent bonds equally (NONPOLAR) or unequally (POLAR) share the electrons between the atoms. This depends on electronegativity again! A group of covalently bonded atoms is called a molecule

Properties of Covalent Compounds Because covalent bonds are generally weaker than ionic bonds, the melting points and boiling points of covalent compounds are generally lower than those of ionic compounds. Many covalent compounds exist as gases at room temperature.

Review of Chemical Bonds _________bonds—complete transfer of 1 or more electrons from one atom to another (one loses, the other gains) forming oppositely charged ions that attract one another _________bonds—some valence electrons shared between atoms _________ - the property that is used to predict the type of bonding Most bonds are somewhere in between ionic and covalent.

Electronegativity and Polarity The difference in electronegativities between bonding atoms may be used to predict the type of bond that forms. For right now we will consider bonds between metals and nonmetals to be ionic and bonds between two nonmetals to be covalent.