What is a Covalent Bond
Atoms can bond by sharing electrons in their outermost orbitals and thus giving them the privilege of having a full outermost orbital. For example, the element Hydrogen exists as H2 molecule consisting of two atoms of Hydrogen atom. A covalent bond is simply the force between two atoms resulting from the sharing of electrons in the outermost orbital. Therefore a covalent bond attracts two atoms very close to each others because both atoms share the same electrons in their outermost orbitals.
hydrogen gas formed by covalent bond sharing electron between two hydrogen atoms
The case of Hydrogen cannot be an ionic bond. That is because Hydrogen ions each have the same charge and therefore are not attracted to one another. This is why a covalent bond happens only when two atoms have a difference in electronegativity of > or = 0.9. Instead, electrons are shared between the atoms to fill the outermost orbital. This type of bond is called a covalent bond. Two atoms of chlorine (Cl0) share a pair of electrons to form chlorine gas (Cl2).
electron shared covalent bond chlorine atom forming chlorine gas
Some molecules formed by covalent bonds may still give up or acquire one or more electrons resulting in a net positive or negative charge. These molecules are called molecular ions.
A covalent bond is very strong. The energy needed to break it is bigger than the thermal energy existing at 25°C which is room temperature. The thermal energy at 25°C is <1 kCal/mole kilo calorie per mole, while to break a typical Carbon covalent bond in an Ethane molecule we need about 83 Kilocalorie per mole.
Properties of molecules defined by covalent bond
While a central atom in a molecule attracts other atoms by covalent bonds, the bonds between these atoms are forming particular angles between them. The force of repulsion among these atoms and particularly the outermost electrons is what shape and determine the angles degrees. The angles and the shape formed is what gives the molecule its properties and shape. An example is the angle formed between Oxygen and Hydrogen atoms in a water molecule, an angle of 105°. You can read about the molecular geometry.
When atoms formed in a covalent bond have the same or very close electronegativity – typically less than 0.9 – the bond (the force of attraction) is equal between electrons since they’re almost identical. This kind of bond is called a non-polar bond. Carbon-Carbon and Carbon-Hydrogen bonds (also called Hydrocarbon) is an example on non-polar bonds.
A polar bond occurs when the difference in electronegativity between two atoms are more than or equal to 0.9. In a polar bond, there’s a partial negative charge (δ−) and a partial positive charge (δ+). This is the case in a water molecule H2O. The bond between Oxygen and Hydrogen is polar since difference in electronegativity is 1.2. (Electronegativity of Oxygen is 3.4 and Electronegativity of Hydrogen is 2.2).
- Published in Water Chemistry, Water Treatment
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.
- Published in Water Chemistry, Water Treatment
