How Atoms Stick Together
Atoms sometimes create connections (bonds) with other atoms, allowing them to form relationships we call molecules or compounds. Sometimes these bonds are long-lasting, and other times they are shorter-lived than that thing you had with that drummer back in high school. Bonds between atoms are generally created by the attraction of opposite charges. For that reason, if an atom has an outer shell (orbital) that is already filled with electrons, it is unlikely to form molecules or compounds with other atoms/elements.
However, if the atom has room in its life (outermost orbital), it is more receptive to a bond. A bond can be accomplished by the atom either giving or receiving electrons from other atoms, or by sharing electrons with other atoms.
Ionic Bond
An ionic bond is when 2 atoms form molecules by giving up or taking electrons from others to complete their outermost orbitals. The classic example is the compound salt (sodium chloride, NaCl). Na (sodium) has a single electron in the outermost (third) orbital. That is one lonely electron. To fill the outermost orbital, sodium could recruit 7 more electrons from other atoms, but that would be a lot of work and impractical and is totally against the law in several states. Therefore, Na gives up the single electron and leaves the complete second orbital filled with 8 electrons, a very stable arrangement. However, now this atom has 10 electrons and 11 protons. This imbalance between protons and electrons yields an ion. In this case, the sodium ion with 10 electrons has an overall positive charge.
On the other hand, chlorine (Cl) has the dilemma of needing a single electron to complete its outermost shell. With an atomic number of 17, there are 7 electrons in the third orbital of chlorine and there is room for 8, making it a natural partner for sodium (and it didn’t even have to join an online dating service). Sodium gives up its electron to chlorine, which then uses the electron to complete its shell. Since it now has 1 more electron than proton, it has become a chloride ion with an overall negative charge.
This is where the bond happens. The positive charge of the Na+ ion is attracted to the negative charge of the Cl- ion, and the two will form a moderately strong chemical bond to create NaCl, or salt.
Anatomy of a Word
ion
An ion is a charged atom that has an unequal number of electrons and protons. An ion can be positively or negatively charged depending on whether it has fewer electrons than protons (positively charged) or more electrons than protons (negatively charged).
Hydrogen Bond
Hydrogen bonds are formed when atoms share electrons unequally in compounds. Water is the classical example of this type of bonding. Hydrogen has an atomic number of 1, so its shell is half full. Oxygen, with an atomic number of 8, lacks 2 electrons from filling its outermost shell. Thus, oxygen will share an electron with 2 hydrogen atoms, which will complete the outer shells of all three members of this compound, creating H2O, or water. (The subscript 2 on the chemical abbreviation for hydrogen indicates that there are 2 atoms of hydrogen in the compound.)
However, with more protons in the nucleus of oxygen, the shared electrons will spend more time around that nucleus than around either hydrogen nucleus. This imbalance will create a slight negative charge on the oxygen side and slight positive charge on the hydrogen arms. This polarization of charge will cause water molecules to be attracted to each other. In this way, water will adhere to itself. This type of bond is the weakest of the three chemical bonds. It is also the type of bond that holds two strands of DNA (genetic code) together in chromosomes, which are the instruction books that tell an organism how to be what it is supposed to be.
Covalent Bond
The strongest of the chemical bonds, the covalent bond is when a molecule or compound shares electrons equally. Carbon, the foundation atom of organic molecules, is well adept at this type of bond formation since its atomic number of 6 means it needs 4 electrons to fill its outermost shell. Because of this, carbon can form 4 single covalent bonds with other atoms.
What is an example of a compound with a covalent bond?
A great example of a compound with a covalent bond is the basic structure of an amino acid. Amino acids are organic compounds that combine to form proteins (which are necessary to create tissue, organs, hair, skin—you name it, it needs an amino acid to help build it). The carbon is the central atom in an amino acid, onto which four components attach, each using one of the available bonds: a carbon group, a nitrogen group (called an amino group), a single hydrogen atom, and a fourth group, the structure of which changes from amino acid to amino acid. This variable side group (sometimes referred to as a side chain) is called an R group.
pH: Ions, Acids, and Bases
A pH measurement tells you whether a substance is an acid or base. An acid has a low pH and will release hydrogen ions (under certain circumstances) and a base has a high pH and will release hydroxide ions (under certain circumstances). Vinegar is an example of an acid. Baking soda is an example of a base. Acids and bases react if combined. If you mixed vinegar and baking soda together, you would produce a gas (which creates those bubbles and that hissing noise).
A mixture’s pH is essentially a measure of its hydrogen ions. If a substance has molecules or compounds that will yield a large number of H+, the substance, based on a mathematical logarithm, will result in a lower pH number and be considered an acid or acidic solution (pH < 7.0). Conversely, with lower H+ concentrations, the pH will be above 7 and considered a base (also called a basic solution or alkaline). This standard is set internationally using known materials, such as pure water (pH of 7.0).
Most living organisms can survive only within a small pH range. Change the pH range and you’ll create a reaction, and change (or kill!) the organism. Cells can change pH through the process of metabolism (think of your muscle cells creating lactic acid when you exercise hard).
Your slightly alkaline bodily fluids
The pH of plasma and body fluids is approximately 7.3–7.4. This is on the alkaline side of neutral (7.0). It is called the physiological neutral point. Your body will try to maintain this level of pH through various cellular processes.