Question

Outline IN DETAIL the procedure you would use to determine the geometry of a molecule, if you start with just its chemical formula.

Answer 1

:Molecular geometry or molecular structure, is the three-dimensional structure or arrangement of atoms in a molecule.

   To determine the shapes of molecules, we must become acquainted with the Lewis electron dot structure.Lewis Structures(Lewis Theory) are visual representations of the bonds between atoms and illustrate the lone pairs of electrons in molecules. Principles of this theory

1. Valence electrons, or the electrons in the outermost electron shell, have an essential role in chemical bonding.

2. Ionic bonds are formed between atoms when electrons are transferred from one atom to another. Ionic bond is a bond between nonmetals and metals .

3. Covalent bonds are formed between atoms when pairs of electrons are shared between atoms. A covalent bond is between two nonmetals.

4. Electrons are transferred/shared so that each atom may reach a more stable electron configuration i.e. the noble gas configuration which contains 8 valence electrons. This is called octet rule.

The valence-shell electron-pair repulsion (VSEPR) theory states that electron pairs repel each other whether or not they are in bond pairs or in lone pairs. Thus, electron pairs will spread themselves as far from each other as possible to minimize repulsion. VSEPR focuses not only on electron pairs, but it also focus on electron groups as a whole. An electron group can be an electron pair, a lone pair, a single unpaired electron, a double bond or a triple bond on the center atom. Using the VSEPR theory, the electron bond pairs and lone pairs on the center atom will help us predict the shape of a molecule.The shape of a molecule is determined by the location of the nuclei and its electrons. The electrons and the nuclei settle into positions that minimize repulsion and maximize attraction. Thus, the molecule's shape reflects its equilibrium state in which it has the lowest possible energy in the system. Although VSEPR theory predicts the distribution of the electrons, we have to take in consideration of the actual determinant of the molecular shape. We separate this into two categories, the electron-group geometry and the molecular geometry.

Number of electron groups   Name of electron group geometry

2               linear

3               trigonal-planar

4               tetrahedral

5               trigonal-bipyramidal

6               octahedral

Molecular geometry, on the other hand, depends on not only on the number of electron groups, but also on the number of lone pairs. The VSEPR notation for these molecules are AXn. "A" represents the central atom and n represents the number of bonds with the central atom. When lone pairs are present, the letter Ex is added. The x represents the number of lone pairs present in the molecule. For example, a molecule with two bond pairs and two lone pairs would have this notation: AX2E2.

So Below are the few example of molecular structure.