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Summary
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This activity is aimed to develop another perspective of atoms.
So far you have learned that:
➊ Atoms are the building blocks of matter. It helps to understand the discrete nature of matter.
➋ Atoms are made of a nucleus with tightly bound, positively-charged protons surrounded by loosely bound, negatively-charged electrons. Electrons can be removed by applying relatively small amounts of energy. This helps explain electricity, ions, and the nature of chemical bonds.
➌ The third and most recent perspective of atoms is the concept of atoms as instantaneously flickering dipoles with electron shells capable of spontaneous random shifting. Such shifting changes the distribution of electrons, making atoms sticky.
This helps us understand why atoms with a perfect balance of negative and positive charges still demonstrate very slight attractions. It explains the fundamental notion that every gas can be condensed into liquid. Helium, however, must be just 4 degrees above zero before it becomes liquid.
An extension of this concept addresses atomic polarizability. Or in other words, how well and how far an electron cloud in the atoms can shift. Different atoms can have different shifts; large atoms with greater number of electrons provide more room for such shifting, making stronger dipoles. It helps to grasp why xenon condenses at minus 100 degrees below zero, whereas another noble gas, helium requires minus 260 degrees to get into a liquid state. Indeed, large electron clouds can shift further than small electron clouds. The larger the distance between charges, the stronger the dipole and the harder for heat to bring disorder. It helps to reason why all gases can be condensed and why some are easier to condense than others.
Another dipole-related set of concepts is based on our understanding that atoms connected with a chemical bond are engaged in a tug-of-war for the shared pair of electrons. Atoms with higher "electronegativity" win, "grabbing the pair of electrons toward themselves and allowing for a permanent dipole to appear.
Ions vs. dipoles
The force of ion-to-ion attractions is enormous. This is why rocks are so solid. The interaction between dipoles and ions are gentler, about 100 times milder then ion-to-ion attractions. They are the foundation of aquatic solutions. When salt is dissolved, water dipoles align along the electric field that creates an ion, (a dipole will turn because one part of a dipole will be attracted to the ion, and the other part will be repelled, so there’s pull and push on a dipole, creating rotation). Dipoles will rotate and create a shell around the sodium in salt. A similar shell will appear around chloride. This explains why strong polar solvents dissolve inorganic salts so well.
Dipole moment – modern ID of an atom or a molecule
Water molecules, as well as any molecule made of more than one atom, have permanent dipoles because of the tug of war between the atoms for the electrons. The strength of permanent molecular dipoles is defined by the atomic composition of the molecule. In the same way a molecule is defined by its atomic composition or molecular weight, it can also be characterized by its unique dipole moment.
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