A molecule is the smallest unit of a compound that still has the compound’s properties attached to it. Molecules are made up of two or more atoms held together by covalent bonds.
In the space where electrons from different atoms interact with each other, chemical bonds form. The electrons in the outermost shell are the ones that form the bonds with other atoms.
When the atoms share the electron(s), a covalent bond is formed. Electrons aren’t perfect, though, and usually an electron is more attracted to one atom than another, which forms a polar covalent bond between atoms (like in water, H2O).
While it may seem a bit random right now, with a little bit of study, you’ll find you can soon understand how molecules are formed and the shapes they choose once you figure out the types of bonds that can form.
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Let’s take an example:
Why does ice float? In the water molecule (H2O) is held together by polar covalent bonds. Water molecules are also attracted to each other by weak (hydrogen) bonds between the atoms. As water cools below 4°C, the hydrogen bonds forms a hexagonal crystal lattice (known as ‘ice’). The solid form of water is a larger structure than the liquid form, as the crystal structure has a hole in the center. In other words, ice takes up about 9% more space than liquid water, so a liter of ice weighs less than a liter water. By peeking into the molecules closely, you can explain why ice is one of the very few solids that is lighter than its liquid form.
Water is also a polar molecule, which happens because one end of the molecule has slightly more charge than the other end.
When two different kinds of atoms, like oxygen and hydrogen form a bond, one attracts the shared pair of electrons more strongly than the other. (When a bond forms between two of the same kind of atom do we assume the attraction is equal, so atoms like O2 and N2 are not polar).
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