Polarity And Covalent Bonding

Non-polar covalent bonds form when electrons in the molecular orbital are shared equally among the atoms in the bond, this usually occurs when the atoms being bonded are the same. If the atoms have significantly different electronegativity values, the electrons are shared unequally between atoms in the molecular orbital. When this happens, the bond formed is a polar covalent bond. In this bond, the shared electrons in the molecular orbital are more likely to be found close to the atom with the higher electonegativity. However, if the elctronegativity values of the atoms vary greatly, an electron will be removed from the electron with lower electronegativity and the atoms will be bonded ionically. Polar covalent bonds are called polar because the ends of them are opposites. In these polar molecules, the atom that attracts the most electrons has a partial negative charge (symbolized by δ-) while the other atom has a partial positive charge (symbolized by δ+). When a molecule has one end partially positively charges and the other end partially negatively charged, it is called a dipole. Even though positive and negative charges are present, the bond is not ionic, as an electron is not removed from one atom and transferred to the other. The electrons are still shared, but the shared pair is more likely to be found near the atom with the highest electronegativity. This makes the charge unequal and the bond is therefore polar covalent. The greater the polarity of a bond, the greater the electronegativity difference will be. The greater electronegativity differs between atoms, the stronger the bond will be.

Covalent Bonding, In-Depth

Covalent Bonding requires the sharing of electrons to fill outermost orbitals. For this to happen, the repulsive and attractive forces of each atom must be in a proportion that allows electrons to move around between both atoms. The space that the shared electrons move in is called a molecular orbital, as a molecule is what is formed when the two atoms bond. After bonding covalently, the atoms are stable, and have a low potential energy. This decrease in energy causes the extra energy to be released. As atoms are moving closer to each other the potential energy of these atoms is decreasing, until the atoms are at a point where the attractive and repulsive forces between the two atoms balance, and the atoms are bonded. At this point the atoms are no longer moving closer together, and do not give off any more energy. When two atoms are bonded covalently, they are at their minimum potential energy (as stated before). The distance between these atoms at their minimum potential energy is called their bond length. Covalent bonds are flexible, the nuclei of the bonded atoms move back and forth. Because of this, bond length is actually the average distance between the two nuclei. In order to break a bond, energy is required. This is called bond energy.

Some Slideshows About All Aspects Of Chemical Bonding

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Chemical Bonding - 1

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Basics of Chemical Bonding - 2

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Ionic Bonding

Ionic Bonding is another concept that can be challenging. Ionic bonds tend to form between metals and non-metals. Unlike covalent bonding, ionic bonding involves the removal of electrons from one atom and the consequent attachment of those electrons to another atom, resulting in the formation of attracting positive and negative ions. The element that loses the electrons is the atom that started with the least amount of electrons. This is because it is easier to lose a small number of electrons than it is to gain a large number of electrons. The atom that then gains the electrons is the one that has the most starting electrons, because it is easier to gain a small number of electrons than it is to lose a large number of them. The atom that lost electrons now has a positive charge, and is called a cation. The atom that gained electrons now has a negative charge and is called an anion.

Covalent Bonding

Covalent Bonding can be complicated. It involves atoms combining to share electrons and attempting to attain an octet, or set of eight electrons. Nonmetals usually form covalent bonds, and the electron affinities of the different atoms need to be very close in order for the atoms not to make ions.  For example, to make a hydrogen molecule, two hydrogen atoms must come together. (Hydrogen of course being an exception to the octet rule, as it has only one energy level, but its the same idea.) When these atoms come together, they share their respective electrons to form a molecule, H2. For the bond to be the strongest, the two atoms need to be at a distance that allows the forces of attraction and the force of repulsion between the two atoms to be in a proportion that will keep the atoms together.