CHEM Review Chap 8: Covalent Bonding
Compare and contrast ionic and covalent bonding.
Differences: Ionic bonding occurs between atoms that have opposite needs for electrons (metals and nonmetals) and results in a transfer of electrons. Covalent bonding occurs between atoms that have similar needs for electrons (two nonmetals) and results in a sharing of electrons.
Define covalent bonding.
A covalent bond, also called a molecular bond, is a chemical bond that involves the sharing of electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs, and the stable balance of attractive and repulsive forces between atoms is known as covalent bonding.
Determine polarity of bonds.
A polar molecule is one in which one side, or end, of the molecule has a slight positive charge and the other side, or end, has a slight negative charge. This will occur whenever the molecule is not completely symmetric. (Unless, of course, the molecule is a hydrocarbon.) 1 - Is it a hydrocarbon (then nonpolar) 2 - What is its shape (lone pairs or not?) 3 - Symmetric? Not symmetric is polar 4 - If symmetric, Examine outer atoms - all same? not polar, different, polar
Apply the duet and octet rules to covalent bonds.
Duet refers to the first five elements of periodic table. They are most stable when the 1s orbital is filled with two (duet) electrons. Hydrogen looks to gain one electron, Lithium, Beryllium and Boron look to lose 1,2, or 3 electrons respectively in order to have a filled outer shell like Helium. When covalent bonding occurs, each atom should gain a full octet. With covalent bonding, each H atom will share an electron with each other. This gives H atom 2 electrons (a full duet for the 1st shell). Most of the time, the octet rule is used to see what bonds are formed.
Draw the electron (Lewis) dot structures for molecules.
For all but the simplest molecules, Step 1: Determine the total number of valence electrons. Step 2: Write the skeleton structure of the molecule. Step 3: Use two valence electrons to form each bond in the skeleton structure. Step 4: Try to satisfy the octets of the atoms by distributing the remaining valence electrons as nonbonding electrons.
Identify bonds that are single, double, triple, sigma and pi.
Single covalent bonds are sigma bonds, which occur when one pair of electrons is shared between atoms Double and triple covalent bonds are stronger than single covalent bonds and they are characterized by the sharing of four or six electrons between atoms, respectively. A sigma bond is your basic head-on covalent bond, with the bond in line with the bonding orbitals. You can only ever have one sigma bond between any two atoms. A pi bond is a covalent bond between orbitals perpendicular to the bond direction, usually p-orbitals (never s)
