To use PHET simulation (developed by the University of Colorado, Boulder) to construct these molecules/ions in order to explore their structure and shapes. To practice predicting molecular shapes (using VSEPR theory) and molecular polarity Non-metal atoms bond covalently, resulting in the formation of either neutral molecules or polyatomic ions. A covalent bond is formed when non-metal atoms share their valence electrons, which they do in order to achieve filled valence orbitals like their nearest noble gas neighbor. This means that most bonded non-metal atoms will acquire a total of eight valence electrons via the sharing process – often referred to as the octet rule . A notable exception is hydrogen, which only needs to acquire two electrons to be like its nearest noble gas neighbor, helium. Lewis Structures A Lewis Structure is a representation of covalent molecules (or polyatomic ions) where all the valence electrons are shown distributed about the bonded atoms as either shared electron pairs (bond pairs) or unshared electron pairs (lone pairs). A shared pair of electrons is represented as a short line (a single bond). Sometimes atoms can share two pairs of electrons, represented by two short lines (a double bond ). Atoms can even share three pairs of electrons, represented by three short lines (a triple bond ). Pairs of dots are used to represent lone pair electrons . Examples: The rules for drawing Lewis structures can be found in the Procedure Section of this handout. Molecular Shapes The shape of a molecule depends on the distribution of atoms in space about the central atom, and their bond angles. Bond pair electrons and lone pair electrons repel one another, thus they will be arranged around a central atom as far apart as possible in order to minimize repulsions. This is known as: V alence S hell E lectron P air R epulsion theory, or VSEPR theory. The following VSEPR table supplies the names, sketches and descriptions of the most common types of molecular shapes that you will encounter. Note that several other molecular geometries do exist, however, they are beyond the scope of this course. Shape Name Sketch Description Linear NaN Only two outer atoms surround the central atom. There are no lone pairs on the central atom. Outer atoms are arranged opposite to each other. The bond angles are exactly 180°. Trigonal Planar NaN Three outer atoms surround the central atom. There are no lone pairs on the central atom. The central and outer atoms all lie in the same plane (molecule is flat). Bond angles are exactly 120°. Bent NaN Two outer atoms and one lone pair surround the central atom. Bond angles are slightly less than 120°. Tetrahedral NaN Four outer atoms surround the central atom. There are no lone pairs on the central atom. The four outer atoms are evenly arranged in 3D around the central atom as if at the corners of a regular tetrahedron. The bond angles are exactly 109.5°. Trigonal Pyramidial NaN Three outer atoms and one lone pair surround the central atom. Here the central atom is located slightly above the three outer atoms, like a tripod. The bond angles are slightly less than 109.5°. Bent NaN Two outer atoms and two lone pairs surround the central atom. Bond angles are slightly less than 109.5°. Electronegativity and Bond Polarity Some atoms in molecules have the ability to pull shared electrons closer to themselves than other atoms, an ability referred to as electronegativity . Electronegativity (\(\Chi\)) increases going across a period and decreases going down a group. If two bonded atoms have different electronegativities, then the bond pair electrons will be unequally shared . The atom with the greater electronegativity will pull the bond electrons closer towards itself, causing it to obtain a very slight negative charge (\(\delta ^-\)). The atom with the lower electronegativity will have bond electrons pulled further away from it, causing it to obtain a very slight positive charge (\(\delta ^+\)). The result is a polar covalent bond. However, if two bonded atoms have the same electronegativity, then the bond pair electrons will be equally shared. The result is a non-polar covalent bond. Example: The bond electrons are pulled closer to Cl due to its greater electronegativity. Thus, HCl contains a polar covalent bond. Molecular Polarity Molecular polarity results when the entire molecule (not just a bond in the molecule) ends up with an unequal distribution of electrons. In general, a molecule will be polar if it contains polar bonds that are distributed in a non-symmetrical arrangement around the central atom. A polar molecule is said to have a net dipole moment. A non-symmetrical arrangement typically results when there are lone pairs on the central atom, or, when different outer atoms surround the central atom. Not surprisingly, a molecule will be non-polar if it contains all non-polar bonds. It will also be non- polar if it contains polar bonds distributed in a symmetrical arrangement around the central atom. The symmetry causes the individual bond polarities to cancel out, resulting in a net non-polar molecule. A symmetrical arrangement typically results when there are no lone pairs on the central atom, and if all the outer atoms are identical. Examples: Procedure Drawing Lewis Structures Draw Lewis structures for each of the molecules and polyatomic ions given on your Report Form. Clearly show all bond pair electrons as lines and lone pair electrons as pairs of dots. Rules for Drawing Lewis Structures Total the number of valence electrons that each atom contributes to the molecule/polyatomic ion. For polyatomic anions, you must add electrons (equal to the negative charge) to the total number of valence electrons. For polyatomic cations, you must subtract electrons (equal to the positive charge) from the total number of valence electrons. Draw a stick structure for the molecule. The least electronegative atom is the central atom. Hydrogen is the only exception to this, as it forms only 1 bond. The central atom will usually need to form multiple bonds. The other atoms are arranged around the central atom, and are attached to it via single bonds. The octet rule must be obeyed for all elements except hydrogen (follows a “duet” rule). Starting with the outside atoms, place the remaining electrons around each atom until it has a total of 8 electrons (except hydrogen – it only requires 2 electrons). If there are not enough electrons available to obey the octet rule using single bonds, this indicates that double or triple bonds between two atoms are required in your structure. If short by two ele ctrons, try a double bond, and if short by four electrons, try a triple bond or two double bonds. Constructing Models, Determining Molecular Shapes and Molecular Polarity using Simulation Click on the following link to access molecular modelling simulation PhET: Molecule Shapes 1. Press the “play” arrow. 2. Click on model 3. Click on bond angle, molecular geometry, and electron geometry boxes 4. You can bring is as many bonds as you want, single, double, or triple 5. You can also add as lone pairs on the central atom by clicking the lone pairs 6. You can click the red cross on the right side to “remove” the added features 7. Just play around with the features before working with molecules on the lab sheet. 8. You can write down the bond angle, electron geometry, and molecular geometry from the simulation. Also, you can check and improve the molecular structure that you have already drawn on the lab sheet. The Colorado State University provides the link. It may be sensitive to browsers. It works best on explorer window. It is difficult open it on Mac. However, it works well on cell phones. Rules for Constructing Molecules with the Simulation Use the first one bond for single bonds. Use two bonds for a double bond (second from the top right) and for a triple bond. Use the balloon kind of lone pair of each pair of lone pairs on the central atom You can click on the red cross on them to remove the bonds or the lone pairs. Evaluate the polarity of the bonds in each molecule as well as its overall symmetry in order to determine whether it is polar or non-polar. Lab Report: Lewis Structures and Molecular Shapes \(\ce{CH4}\) Total # of Valence Electrons: 3-D Model Sketch (show dipole arrows): Lewis Structure (show all resonance structures if applicable): VSEPR shape name: Is there a polar bond in this molecule? Molecule Polarity: Polar/Non-Polar Resonance: Yes/No \(\ce{CO2}\) Total # of Valence Electrons: 3-D Model Sketch (show dipole arrows): Lewis Structure (show all resonance structures if applicable): VSEPR shape name: Is there a polar bond in this molecule? Molecule Polarity: Polar/Non-Polar Resonance: Yes/No \(\ce{NH4}\) Total # of Valence Electrons: 3-D Model Sketch (show dipole arrows): Lewis Structure (show all resonance structures if applicable): VSEPR shape name: Is there a polar bond in this molecule? Molecule Polarity: Polar/Non-Polar Resonance: Yes/No \(\ce{H2O}\) Total # of Valence Electrons: 3-D Model Sketch (show dipole arrows): Lewis Structure (show all resonance structures if applicable): VSEPR shape name: Is there a polar bond in this molecule? Molecule Polarity: Polar/Non-Polar Resonance: Yes/No \(\ce{N2}\) Total # of Valence Electrons: 3-D Model Sketch (show dipole arrows): Lewis Structure (show all resonance structures if applicable): VSEPR shape name: Is there a polar bond in this molecule? Molecule Polarity: Polar/Non-Polar Resonance: Yes/No \(\ce{SO2}\) Total # of Valence Electrons: 3-D Model Sketch (show dipole arrows): Lewis Structure (show all resonance structures if applicable): VSEPR shape name: Is there a polar bond in this molecule? Molecule Polarity: Polar/Non-Polar Resonance: Yes/No \(\ce{O2}\) Total # of Valence Electrons: 3-D Model Sketch (show dipole arrows): Lewis Structure (show all resonance structures if applicable): VSEPR shape name: Is there a polar bond in this molecule? Molecule Polarity: Polar/Non-Polar Resonance: Yes/No \(\ce{O3}\) - use yellow ball for central atom Total # of Valence Electrons: 3-D Model Sketch (show dipole arrows): Lewis Structure (show all resonance structures if applicable): VSEPR shape name: Is there a polar bond in this molecule? Molecule Polarity: Polar/Non-Polar Resonance: Yes/No \(\ce{CO}\) Total # of Valence Electrons: 3-D Model Sketch (show dipole arrows): Lewis Structure (show all resonance structures if applicable): VSEPR shape name: Is there a polar bond in this molecule? Molecule Polarity: Polar/Non-Polar Resonance: Yes/No \(\ce{CO3^{-2}}\) Total # of Valence Electrons: 3-D Model Sketch (show dipole arrows): Lewis Structure (show all resonance structures if applicable): VSEPR shape name: Is there a polar bond in this molecule? Molecule Polarity: Polar/Non-Polar Resonance: Yes/No \(\ce{NO3^-}\) – use a blue ball for phosphorus when constructing this model Total # of Valence Electrons: 3-D Model Sketch (show dipole arrows): Lewis Structure (show all resonance structures if applicable): VSEPR shape name: Is there a polar bond in this molecule? Molecule Polarity: Polar/Non-Polar Resonance: Yes/No \(\ce{CF2Cl2}\) (\(\ce{CFC}\) = chlorofuorocarbon) Total # of Valence Electrons: 3-D Model Sketch (show dipole arrows): Lewis Structure (show all resonance structures if applicable): VSEPR shape name: Is there a polar bond in this molecule? Molecule Polarity: Polar/Non-Polar Resonance: Yes/No Questions When molecules and energy interact, there are different results. Atoms may dissociate, a molecule may rotate, or bonds may stretch and bend. Carbon dioxide has four possible vibrations. What is the effect of each vibration on the molecule: stretching, bending, or breaking? What is the definition of a greenhouse gas? Various atmospheric gases are listed below: Unnamed: 0 Chemical Formula VSEPR Shape (Sketch) Greenhouse Gas (yes or no) carbon dioxide NaN NaN NaN methane NaN NaN NaN nitrogen NaN NaN NaN oxygen NaN NaN NaN ozone NaN NaN NaN sulfur dioxide NaN NaN NaN water NaN NaN NaN Contributors and Attributions The experiment is from Chem 10 Experiments shared under a CC BY-NC license and was authored, remixed, and/or curated by Santa Monica College . Manjusha Saraswathiamma, Minnesota State Community and Technical College, Moorhead, has modified this to fit to a home school environment with less hazardous and cost-effective lab supplies. This simulation link is for the Molecular Shapes simulation from PHET Colorado State University Boulder. PhET: Molecule Shapes: Basics is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts. PhET: Molecule Shapes: Basics is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts. Simulation by PhET Interactive Simulations, University of Colorado Boulder, licensed under CC-BY-4.0 ( https://phet.colorado.edu ). General Chemistry Lab Manual, Santa Monica College 2.9: Lewis Structures and Molecular Shapes (Experiment)-Home Version-PHET is shared under a CC BY-NC license and was authored, remixed, and/or curated by Santa Monica College . 6: Lewis Structures and Molecular Shapes (Experiment) by Santa Monica College is licensed CC BY-NC 4.0 .