What is an ion
An Ion is simply an atom with a charge. In order to explain what is an ion, we will briefly review the atom structure. Electron configuration teaches us that an atom is more stable when its outermost orbital has a whole set of electrons. Actually, the tendency of an atom to achieve a complete outer most orbital is very powerful that it will overcome the electrostatic force that hold the atom together.
Like the case of the Fluorine atom, it will accept an extra electron to achieve a full outmost orbital even
though it will end up having  one more electrons than protons. Basically, a neutral atom has the same number of protons and electrons.
Furthermore, an element like Sodium will give up an electron to attain a full outer orbital. This results in a difference and unbalance between electrons and protons in the same atom.
When in an atom protons (+ve) are more than electrons (-ve) = result is positive ion (cation).
Sodium atom loses one electron become Sodium positive ion cation
Some atoms give up more than one electron to have a total outermost orbital. While other atoms will acquire more than one electron in order to fill the outer orbital. Since electrons have a negative charge (negative ion) and protons have a positive charge (positive ion), a difference in the number of electrons and protons results a net charge. This is when an atom is therefore called an ion.
Depending upon whether it gains or loses an electron, an ion will have either a positive or a negative
charge. Cations are ions with a net positive charged and anions are ions with a net negative charge. We know that opposite charges are attracted while same charges are repelled. That means that cations and anions are attracted to one another. The strength of the attraction may make ions form a solid called a crystal lattice.
What is a molecule?
A molecule is a compound that was a substance formed by the chemical bonding of elements. Like an atom is the smallest particle of an element, the smallest discrete particle of a compound is a molecule.
A molecule is made up of atoms from one or more elements. For example, the water molecule consists of two atoms of hydrogen chemically bonded to one oxygen atom. The nitrogen molecule consists of two nitrogen atoms bonded together.
Water Compound formed from Hydrogen Atoms and Oxygen Atoms
One mole equals 6.022×10^23 atoms (602,200,000,000,000,000,000,000 atoms). It is also called Avogadro Number or Avogadro Constant for the man credited for the number. Remember, one mole, or one atomic weight, or one molecular weight, or one Avogadro’s Number of any substance always contains 6.022×10^23 atoms, or molecules of that substance.
In the case of atoms, we describe the weight of one mole; the gram atomic weight. In the case of molecules, we describe it as the gram molecular weight.
Molecules are described by chemical formulas which use the chemical symbols found on the periodic table. Along with numbers to describe the number of atoms of that particular element found in the molecule.
Molecule Name Composition:
– CaSO4 – Gypsum, Calcium Sulfate – One atom of calcium, one sulfur, and four of oxygen.
– NaHCO3 – Baking Soda, Sodium Bicarbonate – One atom of sodium, one atom of hydrogen, one atom of carbon, and three atoms of oxygen.
– Al2(SO4)3 – Alum, Aluminum Sulfate – Two atoms of aluminum, three atoms of sulfur, and twelve oxygen.
– H2S – “Rotten Egg Gas”, Hydrogen Sulfide – Two hydrogens, and one atom of sulfur.
What is Atomic Weight
The atomic weight is simply the weight of one mole (6.022×10^23 atoms) of an element. The periodic table of elements shows the atomic weight on the upper right. The picture below shows an example of Hydrogen and Sodium atoms. Atomic weight of Hydrogen is 1.0079 when rounded to the nearest tenth = 1.0 gram. Same with Sodium atom, atomic weight is equal to 23.0 grams. For a molecule, to calculate the molecular weight we add the sum of atomic weights of the atoms in molecule.
atomic number and atomic weight in periodic table of elements
On the other hand, a gram atomic weight is the weight of one mole of an element, equal to its weight expressed in grams.
What is a Functional Group
Molecular compounds owe their individual properties to functional group. These are combinations of atoms which may appear in various parts of the molecule. A list of major functional group listed below.
| Illustrative Example | Name of Functional Class | Functional Group |
| CH3CH2CH3 | Alkanes | C-C |
| CH3CH=CH2 | Alkenes | C=C |
| CH3CH/CH | Alkynes | C/C |
| CH3CH2CH2OH | Alcohols | C–OH |
 |
Aldehydes |  |
 |
Ketones |  |
 |
Acids |  |
| CH3CH2CH2NH2 | Amines | C-NH2 |
| CH3OCH2CH3 | Ethers | -C-O-C- |
| CH3CH2CH2Br | Halides | C-Br |
The difference in electronegativity of two bonding atoms determines if the bond will be polar or nonpolar (read about polarity). The bond between two identical atoms is always nonpolar, (for example: C-C, C=C, C=C; H-H, O=O, etc…). Bonds between atoms with electronegativities which are nearly the same are nonpolar (for example C-H). Bonds between atoms with electronegativities which are significantly different (commonly 0.9) are polar (for example, C-O, H-O, C=O, and N-H).
One molecule, especially a large complex molecule, may have more than one type of functional group. One specific functional group may be repeated several times.
A functional group may alter the properties of a compound such as melting point, boiling point, solid structure, and solubility. A functional group on an organic molecule also contribute to its hydrophobic and hydrophilic properties. Surfaces composed of nonpolar molecules will be hydrophobic. Surfaces composed of compounds containing polar bonds will be hydrophilic. You can also read about surface tension.
