Bonding
From elements to bonds
Chemical reactions take place when elements or compounds link together by exchanging electrons. Only electrons on the outermost shell, or valence shell, may be exchanged, and the electrons on the inner shells stay put at all times.
These links, called bonds, explain why table salt dissolves in water, why most snowflakes have six angles, and why most metals are shiny. The three simplest ways of bonding are:
These links, called bonds, explain why table salt dissolves in water, why most snowflakes have six angles, and why most metals are shiny. The three simplest ways of bonding are:
- ionic bonds between a metal and a nonmetal or a molecule, like in table salt
- covalent bonds between a nonmetal and another nonmetal, like in gas stove methane
- metal bonds between a metal and another metal, like in a nugget of cadmium
- dipole-dipole bonds that appear between molecules that have accumulation of charge somewhere within themselves
- hydrogen bonds, a special case of dipole-dipole bonds with hydrogen involved
From bonds to reactions
The key to understanding chemical reactions is the octet rule. It states that every atom wishes to achieve a full valence shell, or in layman's terms, wishes to fill its outermost shell with electrons. There is little to remember, as the first shell takes at most two electrons (goal for H and He) and all subsequent shells take eight.
- Helium He has two valence electrons. It has achieved the octet state without losing or gaining electrons.
- Sodium Na has a single valence electron. It has two alternatives: lose one or gain seven electrons. It chooses the easier and wishes to lose one electron.
- Calcium Ca has two valence electrons. It has two alternatives: lose two or gain six electrons. It chooses the easier and wishes to lose two electrons.
- Oxygen O has six valence electrons. It has two alternatives: lose six or gain two electrons. It chooses the easier and wishes to gain two electrons.
From reactions to compounds
Chemistry is all about predicting how different elements and compounds behave and react together. The rule of thumb is that:
- a metal reacts with a nonmetal to form a salt with ionic bonds Ionic bonding
- a nonmetal reacts with another nonmetal to form a molecular compound with covalent bonds Covalent bonding
- metals behave in a different fashion, with an exception of the amalgams of mercury in dental filling Metallic bonding
- acid-base neutralisation, which is why baking soda alleviates heartburn Acid-base reactions
- galvanic corrosion, which is why boats rust in seawater Galvanic corrosion