Atom: An atom is the smallest particle of an element that retains all the chemical properties of that element. It is electrically neutral. ex. Na, H, K, S, Fe, Ag, Sn
Molecule: A molecule is any electrically neutral group of atoms that is held together tightly enough to be considered a single particle. ex. H2O, CO2, H2SO4, CH4, N2, O2, C2H4
Chemical Bonds: A chemical bond is a strong force of attraction holding atoms together in a molecule, resulting from the sharing or transfer of electrons. Molecules are more stable than the isolated atoms from which they are formed. Only valence electrons are involved in bonding.
Stable Octet: There is a special stability of an atom with 8 valence electrons. All noble gases, except He (which is happy with its 2 electrons), have a stable octet and so are very stable and relatively inert with respect to bonding with each other or with other elements.
Ionic Bonding
When a metal (low ionization energy) reacts with a non-metal (high ionization energy, high electron affinity), electrons are transferred from the metal to the non-metal. The atoms of the non-metal, having gained electrons become negatively charged ions, while the atoms of the metal, having lost electrons, become positively charged ions. These oppositely charged ions attract each other and an ionic bond is formed. The resulting molecule is electrically neutral.
Isoelectronic: When an atom has the same electron arrangement as another atom, the two atoms are referred to as isoelectronic. In the first example below, Na+ is isoelectronic with Ne and Cl- is isoelectronic with Ar.
TryIts!: Provide the Lewis diagram for the bonding of (a) sodium chloride, (b) calcium oxide, (c) aluminum sulfide. Answers are below.
Covalent Bonding
When electrons are shared between two atoms, a covalent bond is formed.
Structural Diagram: The structural diagram resembles the Lewis dot diagram, except that single lines are used to represent each shared pair of electrons.
Octet Rule: When atoms combine, the bonds are formed in such a way that each atom finishes with an octet of valence electrons (except hydrogen).
Single Covalent Bond
A single bond is formed when one pair of electrons are shared between two atoms.
TryIts!: Provide the Lewis diagram and the Structural
diagram for (a) chlorine gas, (b) water. Answers are below.
Double Covalent Bond
A double bond is formed when two pairs of electrons are shared between two atoms.
TryIt!: Provide the Lewis diagram and the Structural
diagram for oxygen gas. Answer is below.
Triple Covalent Bond
A triple bond is formed when three pairs of electrons are shared between two atoms.
TryIt!: Provide the Lewis diagram and the Structural diagram for nitrogen gas. Answer is below.
Coordinate Covalent Bond
A coordinate covalent bond is a bond in which both electrons of the shared pair come from only one of the bonded atoms.
TryIt!: Provide the Lewis diagram and the Structural diagram for POCl3. Answer is below.
Homework:
- Draw the Lewis diagram showing the ionic bond. For each ion formed, state with which noble gas atom the ion is isoelectronic.
- Draw the Lewis diagram and structural diagram for each of the following molecules.
(a) H2 (b) NH3 (c) CH4 (d) F2 (e) HCN (f) CCl4 (g) CO2 (h) NI3
- Lewis Dot Diagrams & Structural Diagrams (LDD & SD) #1bcde, 2befhi - if you are in SCH4C don't do this part of the HW - the rest of you, get at it!
Answer Keys (TryIts! & HW):
