Covalent Bonding Lesson Two

Chemical Bonding Two ways: 1. Sharing electrons between two atoms Both atoms are close to having full levels Electrons are shared back and forth between two atoms to make both feel satisfied 2. Transferring electrons between two atoms One atom is close to having a full level, while the other is close to emptying a level Electrons are transferred from the almost empty atom to the almost full atom to make both satisfied

Review Electronegativity: a measure of an atom’s tendency to pull a bonding electron toward itself The closer two atoms’ electronegativity values are to each other, the more they share The cut-off value is considered to be 1.7: Electronegativity difference < 1.7 implies sharing Electronegativity difference > 1.7 implies transfer

Molecules A molecule is a group of atoms joined by covalent bonds Here is a visual to show the sharing of electrons in a covalent bonded water molecule: Water

Polar Covalent Electronegativity - 0.5 and 1.7 Covalent bonds in which the sharing of the electron pair is unequal The more electronegative atom has the greater electron density Polar covalent bond or polar bond is a covalent bond with greater electron density around one of the two atoms

Polar Covalent In such a bond there is a charge separation with one atom being slightly more positive and the other more negative, the bond will produce a dipole moment. The ability of an atom to attract electrons in the presence of another atom is a measurable property called electronegativity.

Non Polar Covalent Electronegativity – 0.5 or less In this covalent bond, the atoms share the electrons equally There is no dipole moment An example of this is a Fluorine molecule Carbon – Hydrogen bond is also non polar covalent Think of three other combinations

Octet Rule Only noble gases are allowed to exist independently in nature They can do this because of the stability of their electron configuration Let’s understand why What is the electron configuration for Ar and Xe?

Octet Rule As you can see, the stability results from the fact that all of the orbitals are completely filled Other atoms can have this stability by filling their outermost s and p orbitals with electrons by sharing electrons through covalent bonding Octet rule: chemical compounds tend to form so that each atom, by gaining or losing or sharing electrons, has an octet of electrons in its highest occupied energy level

Octet Rule Electrons are either shared by single, double, or triple bonds A single bond is a covalent bond produced by the sharing on one pair of electrons between two atoms A double bond is a covalent bond produced by the sharing of two pairs of electrons between two atoms These bonds are created so that each atom in the molecule can have eight electrons

Exceptions to the Octet Rule Atoms in the third period and below are able to accept more than eight electrons in their outer shell Why do you think this is? Remember the rules for creating electron configuration

Electron Dot Notation Recall that covalent bonding occurs between the valence electrons of atoms The most important step of understanding covalent bonding is to be able to visualize the possibilities of electron transfer The electron dot notation is an electron-configuration notation in which only the valence electrons are shown, indicated by placing dots around the electron symbol

Lewis Dot Structures of Atoms A Lewis dot structure is a representation of the atom and the number of valence electrons around it The chemical symbol for each element is surrounded by the amount of valence electrons, depicted as “dots”

Lewis Dot Structures of Atoms Examples: Group Element Valence Electrons Lewis Dot Structure 1A Lithium 1 ·Li 2A 3A 4A

Lewis Dot Structures of Atoms Group Element Valence Electrons Lewis Dot Structure 5A 6A 7A 8A

Lewis Dot Structures of Atoms Practice Lewis Structures: Magnesium Aluminum Potassium Chlorine

Covalent Bonding Tutorial to demonstrate the basics of covalent bonding: Chemical Bonding Tutorial

Common Molecules H· H· :O: H· ·H :O: H2O (water) Composed of two hydrogen atom and a single oxygen atom We will go over the rules of electron bonding later, but this is an example of how Lewis structures of atoms are used to understand chemical bonding: H· H· :O: H· ·H :O: A covalent bond is composed of two, shared electrons Make chemical bond where two electrons are shared