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Frozen water (ice) is less dense than liquid water, so ice floats.

Unlike other substances, water expands as it freezes. This is because the hydrogen bonds of liquid water are continuously breaking and reforming. When water freezes, all of the water molecules are perfectly hydrogen bonded together. In order for them to be hydrogen bonded together, they must all be perfectly aligned with each other. the water molecules must spread out a little in order for them to all line up perfectly as water freezes. This makes them spread out as the water freezes. This spreading during freezing can burst water pipes and automobile radiators.



So far, we’ve studied atoms and compounds and how they react with each other. Now let’s take a look at how these atoms and molecules hold together. Bonds hold atoms and molecules of substances together. There are several different kinds of bonds; the type of bond seen in elements and compounds depends on the chemical properties as well as the attractive forces governing the atoms and molecules. The three types of chemical bonds are Ionic bonds, Covalent bonds, and Polar covalent bonds. Chemists also recognize hydrogen bonds as a fourth form of chemical bond, though their properties align closely with the other types of bonds.

In order to understand bonds, you must first be familiar with electron properties, including valence shell electrons. The valence shell of an atom is the outermost layer (shell) of an electron. Though today scientists generally agree that electrons do not rotate around the nucleus, it was thought throughout history that each electron orbited the nucleus of an atom in a separate layer (shell). Today, scientists have concluded that electrons hover in specific areas of the atom and do not form orbits; however, the valence shell is still used to describe electron availability.

One can determine how many electrons an atom will have by looking at its periodic properties. In order to determine an element’s periodic properties, you will need to locate a periodic table. After you’ve found your periodic table, look at the roman numerals above each column of the table. You should see that above Hydrogen, there’s a IA, above Beryllium there’s a IIA, above Boron there’s a IIIA, and so on all the way to Fluorine, which is VIIA. Also, note that the metals are all in group B—their roman numerals have the letter B afterwards instead of the letter A. For now, we are going to ignore the columns with a B, and focus on the columns with an A (the non-metals, generally speaking). Once you have located the group-A elements, we are going to count across, giving each column a number, like this:



The first A-column is I (1), then counting across, 2-8 (skipping the B group, which consists of metals). In the periodic table we labeled the 8th column as 0, however when counting electrons, we’ll count it as 8. Now, we can determine how many valence electrons each element has in its outermost shell. The elements in the IA column have 1 valence electron. The elements in the IIA column have 2 bonding electrons, and so on. By the time we get to the noble gases (the column labeled 0), we are up to 8 bonding electrons. This means that these gases can stand on their own, or donate electrons to another element, but they cannot accept any more electrons. This is because the electrons they have satisfy the octet rule.


The Octet and Duet Rules


When it comes to bonding, everything is based on how many electrons an element has or shares with its compound partner or partners. The octet rule is followed by most elements, and it says that to be stable, an atom needs to have eight electrons in its outermost shell. Elements that do not follow the octet rule are H, He, B, Li and Be (sometimes). Lithium gives up an electron whereas the other elements listed here gain one. These elements instead follow the duet rule which says that the atoms only need two valence electrons to be stable. When bonding, stability is always considered and preferred. Therefore, atoms bond in order to become more stable than they already are.

Not all atoms bond the same way, so we need to learn the different types of bonds that atoms can form. There are three (sometimes four) recognized chemical bonds; they are ionic, covalent, polar covalent, and (sometimes) hydrogen bonds.



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