Molecular Geometry Pt.1
- Molecular geometry simply means the arrangement of atoms in a given compound or a molecule; Based on simple electrostatic repulsion. Every compounds has its own unique molecular geometry for example CO2 or carbon dioxide creates a geometrical linear shape or linear. There are different guides in easily determining the geometrical shape formed by the compound like AX2, AX2E2, AX5E1 and etc.
Wherein: A = central atom
X = bonded atoms
E = lone pairs
1) LINEAR OR AX2
-consist of a central atom and two bonded atoms. Creates 180 degree or linear angle.
*Examples: CO2 (carbon dioxide), BeCl2 (beryllium chloride)
*Let’s make a diagram for BeCl2:
Step 1: Write down the compound given (which is BeCl2). Periodic table is necessarily needed for this topic in stoichiometry or if you know the different atomic number of each element is also okay. State the atomic number of the given elements in the compound: Beryllium (Be) with an atomic number of 2 and Chlorine (Cl) with an atomic number of 7 and add them together.
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Step 2: Before adding the atomic numbers of the element in the compound always look if it has a subscript or number of atoms of a specific element in a compound. In this case, there is only one Beryllium atom and 2 Chlorine atom in beryllium chloride. Multiply the number of atoms of chlorine to its atomic number.
Step 3: Subtract the number of electrons in each bond (each bond contains 2 electrons) therefore, you only need to distribute 12 electrons. Draw a diagram for it. Always determine the geometrical shape it formed so you can identify or draw the molecular geometry of it. Using the Lewis dot formula, create dots for every element corresponding to its atomic number.
Step 4: Stabilize all the elements in the compound by making all them have a 0 e- charge. Since beryllium belongs to group 2A (1 bond, there are 2 electrons) and it bonded with 2 electrons with chlorine and chlorine belongs to group 7A and it has 7 electrons surrounding it, giving rise to 0e- .
2) TRIGONAL PLANAR OR AX3:
-consists of a central atom and three bonded atoms. The topmost atom and the left or right side atom creates a 120 degree angle.
*EXAMPLE: AlCl3 (aluminum trichloride)
3) V-SHAPED (BENT OR ANGULAR) OR AX2E1:
-consists a central atom, two bonded atoms and a lone pair. Due to repulsion of lone pairs in the orbital space, a v-shaped or bent angle is formed.
*EXAMPLE: SO2 (sulfur dioxide)
4) TETRAHEDRAL OR AX4:
-consists of a central atom and four bonded atoms. Creates a 109.5 degree angle at the topmost atom and the left or right side atom.
*EXAMPLE: CH4 (METHANE)
5) TRIGONAL BIPYRAMIDAL OR AX5:
-consists of a central atom and five bonded atoms and has no lone pairs. Creates a star-like structure and creates 90o angle and 120 degree angle.
*EXAMPLE: PCl5 (phosphorous pentaflouride)
*SEATWORKS:
1. State the following geometrical shapes formed by each compound and draw them.
a) PO4
b) BCl3
c) CCl5
*SOURCES:
written by: Sydney Santiago
