Question

Identify, define and describe the phenomenon responsible for polarity.

Please show all work and explain your responses.

Answer 1

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Polarity refers to the way in which atoms bond with each other. When atoms come together in chemical bonding, they share electrons. A polar molecule arises when one of the atoms exerts a stronger attractive force on the electrons in the bond. The electrons get drawn more towards that atom, so that the molecule exhibits a slight charge imbalance.

The polarity of a bond is determined by a periodic concept called electronegativity. Electronegativity is an expression of an atom's tendency to attract electrons in a chemical bond. In order to determine the polarity of a bond, you must find the difference in the electronegativies of the atoms involved. If the difference is between 0.4 and 1.7, the bond will be polar. If the difference is greater, the bond will have an ionic character. This means that the electrons will be taken from the less electronegative element, and spend all of their time orbiting the more electronegative element. If the difference in electronegativities is smaller than 0.4, the bond will be nonpolar covalent. This means that the electrons will be shared equally between the atoms and the bond will not have a polar character.

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Identify each molecule as polar or non-polar based on the size of its molecular dipole. The greater the dipole of the molecule, the closer the molecule is to the polar side of the classification scale.

The old adage of like dissolves like comes from understanding the polar or non-polar character of molecules. A molecules polarity rises from the electronegativity of the atoms in the molecule and the spatial positioning of the atoms. Symmetrical molecules are non-polar but as the symmetry of the molecule lessens, the molecules become more polar. Covalent bonds share electrons between the atoms with the larger portion of the electrons residing closer to the atom with the higher electronegativity.

• Determine if the molecule is ionic or covalent. Ionic molecules are polar when dissolved in solution. Ionic molecules release or accept electrons from other atoms in the molecule.
• Identify the atoms of the molecule and the types of bonds between them. Covalent bonding between atoms in the molecule will determine the spatial orientation of the atoms and is important when determining regions of charge.
• Generate an arrow along each bond that indicates the positive and negative end of the bond and the length of the arrow is proportional to the difference between the electronegativities. These are the dipoles of the molecule.

Bond Type	Electronegativity Difference
pure covalent	<0.4
polar covalent	between 0.4 and 1.8
ionic	>1.8