Written by: Suzanne Monir, EIS Education Team Member, December 2015
Title of Lesson: Chemical Bonds
Topic: Intermolecular and Intramolecular bonds, Surface tension, Capillary action
Grade (Age) Level: High School (Ages 14-18), University
This course module is a summary of various intramolecular and intermolecular bonds that exist in chemistry with applications to surface tension and capillary action. The impact of bonding should be considered in its own right or as an integral aspect of the majority of microgravity experiments.
Recall that intermolecular forces control the physical properties of a substance, while intramolecular forces control its chemical properties. Such properties include bond energy (heat required to break molecule into individual atoms) and flammability.
Ionic bonds are electrostatic forces ( that arise from the transfer of electrons from one atom to another. This type of bond forms between a metal and a non-metal, where the metal donates electrons to the non-metal, and results in oppositely-charged ions.
Ionic compounds, such as NaCl, form structures called crystal lattices. These structures consist of a network of ionic bonds, where the ions keep the same orientation to one another and repeat at regular intervals. The chemical formula of an ionic compound is the simplest whole number ratio of cations to anions within the crystal lattice and represents one formula unit.
Covalent bonds arise from the sharing of valence electrons between two atoms. This type of bond normally forms between two non-metals. It results in the formation of either molecular compounds or network solids (complex structures composed of a continuous network of covalent bonds).
Coordinate covalent bonds are a special type of covalent bond where one atom donates both electrons in a bond as opposed to both atoms donating one electron. There is no difference in nature between a coordinate covalent bond and an ordinary covalent bond.
Electronegativity is a measure of an atom’s electron attracting ability for a bonding pair of electrons. On a periodic table, it increases from left to right (closer to filling an orbital) and decreases down a group (more electron shielding). The noble gases, which all have an electronegativity of 0, are exceptions to this trend because they already have full orbitals. Elements with a high electronegativity have a strong attraction for electrons, while those with low electronegativity have a weak attraction for electrons. Fluorine is the most electronegative element.
If a molecular has polar bonds, it does not necessarily mean the molecule overall is polar as the forces may cancel each other out, depending on the molecule’s geometry. (eg. CCl4)
Induced-dipole induced-dipole (London Dispersion Forces)
Now go through this animation to see how London Dispersion, Dipole and Hydrogen Bonding looks in an animation
Note, that London Dispersion forces = LD
Watch the following video by Oldsite Vanden Bout:
Or this more thorough explanation by Bozeman Science:
Recall that that there are three basic states of matter: solid, liquid, and gas.
In general, compounds with similar bonds have different physical properties depending on their mass. The heavier a compound is, the more London dispersion forces it has and thus it will be more like a solid. We compare how a solid will be a solid, liquid or gas by comparing their melting points (mp) or boiling points (bp). Melting point is the temperature that a substance is converted from a solid to a liquid, and the boiling point is the temperature that substance is converted from a liquid to a gas.
Have a look at this short animation to help you understand the difference.
The lighter a substance is, the lower the boiling point. For example, the boiling point of CH4 is much lower than SiH4 as the elements in the family get progressively heavier, they keep increasing.
BUT, look at the graph below.
Some substances clearly are not following this trend. In particular, look at H2O compared to H2S. H2O clearly has a smaller mass than H2S but H2O has the higher boiling point! Water is clearly an exception to the trends we just discussed for London Dispersion. And the reason is… there is much more going on than just London Dispersion! What is the more predominate intermolecular bond in H2O? Well, we have hydrogen directly attached to oxygen so that can only be… hydrogen bonds! Water is known as the universal substance and is an important part of all biological beings. Water has a higher boiling point because of its intermolecular forces!
Similarly, NH3 and HF, which also hydrogen bond, are anomalies in the trends of analogous compounds in their groups.Quiz: 1Progress: 0 / 0
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All biological compounds are impacted directly or indirectly by hydrogen bonds.
Proteins, which make up so much of our structures and enzymes, are full of hydrogen bonds.
Similarly, carbohydrates and nucleic acids also are dependent on hydrogen bonds in their 3-Dimensional structure.
And Deoxyribonucleic acid (DNA):
Hydrogen bonds give us many of the coolest things in nature.
- Why water bugs can walk on water
- The reason geckos can walk on walls
- The reason water in plant vesicles seem to go AGAINST gravity in capillary action
- Why paper towels "soak" water
Surface Tension: (from Chemwiki)
So what happens with Surface Tension in Microgravity?
Watch this clip from Plasma Ben:
How this impacts your microgravity experiment design:
And now, as you design your experiments for microgravity, you must consider the differences in bonds. What will happen?
Here are some historical uses of chemical bonding in space exploration:
You may add more historical uses to the Feedback forum at the end of this course.
Here are some other links to articles relating to hydrogen bonding or surface tension in microgravity:
- Effect of microgravity on crystallization
- Condensation of supersaturated hydrogen bonding molecules
- NASA activity on surface tension
- The Dynamic behaviour of surface tension in microgravity