What is Electronegativity – Electronegativity Definition
The electronegativity determines whether a bond between two atoms is polar or nonpolar which is defined by Polarity. The electronegativity is a measurement of how attractive an atom is to electrons. The more electronegative an element is, the more the shared electrons will spend around that atom. When one atom in a bond gets to keep the electrons more than the other, it assumes a partial negative charge. The other bonded atom has the electrons less often, so assumes a slight positive charge. Like the negative and positive poles of a magnet. One end of the bond is positive and one end is negative, so the bond is said to be polar. Carbon and hydrogen bonds, as in methane, are nonpolar because the electronegativity of both are very close. Carbon and oxygen bonds are polar because the electronegativity of them are substantially different.
Electronegativity example in Methane molecule
Polar substances dissolve in polar substances because the partial positive & negative charges of one molecule are attracted to the partial +ve and -ve charges of other molecules. Nonpolar substances will dissolve in nonpolar substances. This is because of other forces of attraction, such as Van der Waals’ forces, can come into play. Nonpolar compounds generally do not dissolve in polar compounds, and vice versa, because there is no attraction between things that are charged and things that aren’t. Since water is polar, compounds which are polar will generally dissolve well.
Therefore, if we have an organic which is polar, such as methyl alcohol, it will dissolve well in water. In general, the more polar an organic is, the more it will be dissolved. More importantly for this chapter, the more nonpolar a compound is, the less it will be dissolved and the more it will tend to be a suspended particle.
SIZE: One other aspect of suspended solids is their size. Very large molecules, even if they are polar, will tend to be particles. For example, we have discussed silica (SiO2) at length. If we look at the bonding between Si and O, we see that silicon has an electronegativity of 1.90 and O has an electronegativity of 3.44. Is this a polar bond? Given that water is polar and hydrogen has an electronegativity of 2.10, silica is more polar than water. Yet we see that sand is a particle and not dissolved.
To summarize, then, the degree of polarity and the size of an organic compound will determine if it is suspended or dissolved.
- Published in Water Chemistry, Water Treatment
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.
- Published in Water Chemistry, Water Treatment
What is Surface Tension
Surface tension is one of the properties of water that is created by the Hydrogen bond. Surface tension is the reason a water droplet can have different shapes on different surfaces. As we all noticed, when we fill a glass of water to the top, water level may actually be above the glass rim. The explanation for this occurrence is the high surface tension of water on a hydrophilic surface like glass due to hydrogen bond.
surface tension of water on plastic hydrophobic
surface tension of water droplet on hydrophilic glass
Hydrophobic and Hydrophilic Examples
On the other hand, a water droplet tends to form a sphere like shape on a hydrophobic surface like for example plastic. Therefore, a drop of water will tend to spread on a clean glass surface. To simply explain why this happens, we will analyse the phenomenon on a molecular level. In the example of plastic and since it is a nonpolar substance; water will tend form hydrogen bonds with itself. In the example of glass which is polar; water molecules will form hydrogen bonds with the silicon dioxide of the glass. And this is what makes water tend to spread on the glass surface; attraction to glass. Read more about polarity.
Another example explaining surface tension, using a small glass tube called a capillary tube. If we place the end tip of this tube in a glass of water, water will drawn. This is because of the hydrogen bond occurring between the SiO2 of the glass tube and the Oxygen atoms in the water molecules. The definition of hydrophilic which is what describes the glass in this situation means water loving. While definition for Hydrophobic which is plastic in the above example means water hating.
surface tension capillary tube example water glass hydrophilic
A unit of measurement for the surface tension of water is dynes/cm at room temperature. Which is the force you have to overcome in order to break the surface tension of a water droplet (1cm in length). The lower the temperature the less surface tension. Hot water makes a better cleaning solution since it is considered a better wetting agent. This is due to low surface tension of hot water which allows it to better react with detergents which are hydrocarbons with a polar end called a functional group.
- Published in Water Chemistry, Water Treatment
What is Polarity Definition
Polarity is basically the difference in electronegativity between two molecules; which is simply the affinity of an atom to electrons. Atoms of the same molecule have influence on each other in many ways. One of the reasons is electronegativity. An example is a water molecule, because of the electronegativity difference between the Oxygen atom (3.4) and Hydrogen atom (2.2) it has areas of partial negative and positive charges. Meaning that one side of the bond possesses a partial negative charge, while the other side has a partial positive charge. This is referred to as polarity, and the water molecule is said to be polar. This polarity is due to the electronegativity of the atom-of-oxygen.
The example of the Oxygen – atom in the water – molecule explains polarity. Oxygen atoms attracts electrons more than the Hydrogen atoms. This results that the pair of electrons shared spend more time around the oxygen nucleus than around the hydrogen nucleus. When a shared electrons’ pair is orbiting the oxygen nucleus, the proton of the hydrogen nucleus is exposed and the oxygen/atom has more electrons than protons. This creates the partial -ve and partial +ve charges making the molecule of water acquire polarity characteristics.
Electronegativity of oxygen cause polarity in water-molecule
The relative electronegativities of the atoms involved is what determines the polarity of bonds determined. These electronegativity values are also determined from a variation of the periodic table of the elements called the periodic table of elements.
Most hydrocarbons (molecules made up of both Carbon and Hydrogen atoms) are extremely nonpolar because of the similarity in the electronegativity of Carbon – Hydrogen. In other words, the hydrogen and carbon atoms share electrons fairly equally.
Polarity caused by electronegativity difference between two atoms in moleculeÂ
Polarity and properties of molecules
Nonpolar molecules do not have significant partial charges, therefore they will not attract polar molecules. Opposite charges attract, similar charges repel one another, but there is no attraction or repulsion between nonpolar molecules. For example, we know that gasoline (a hydrocarbon) will not mix with water. However, if we add oxygen to the hydrocarbon molecules we see that the molecules become polar. Ethanol (drinking alcohol), for instance, completely mixes with water.
Soaps and detergents are unique molecular combinations of polar and nonpolar compounds. Nonpolar part of molecule will react with oils found on soiled hands or clothing while polar part reacts with water. The result is oils removal (nonpolar) from water (high polarity). The polar end of soap is a functional group.
soap made of hydrocarbons and polar end functional group
The incompatibility between nonpolar compounds and water is due to the attraction that water molecules exhibit for one another. Positive charge on the hydrogen of a water-molecule will attract negative charge of atom of oxygen in adjacent water molecule. This attraction, called a hydrogen bond, will cause a type of bond between the molecules themselves.
Because of lack of charges, nonpolar compound won’t have the strength to break the hydrogen bonds between the water molecules. Therefore the nonpolar compound won’t combine with water.
- Published in Water Chemistry, Water Treatment
