What is a polar molecule and what is a polar molecule and a non polar molecule

The most essential way to judge polar molecules and non-polar molecules is that the positive and negative charge centers within one molecule of a polar molecule do not coincide, and the positive and negative charge centers within a polar molecule do not coincide.

Polar bonds exist between different elements.

A substance with a polar bond is not necessarily a polar molecule.

Methods for distinguishing between polar and non-polar molecules:

Criterion for non-polar molecules: central atom valency method and force analysis.

1. Central atom valency method:

The composition is an ABN-type compound, and if the valency of the central atom A is equal to the ordinal number of the group, the compound is a non-polar molecule. Such as: CH4, CCL4, SO3, PCL5

2. Force analysis method:

If the bond angle (or spatial structure) is known, the force analysis can be performed, and the resultant force of 0 is a non-polar molecule. Such as: CO2, C2H4, BF3

3. Diatomic molecules composed of the same kind of atoms are non-polar molecules.

Either a non-polar molecule is a polar molecule!

It is enough to know the following in high school:

Polar molecules: Hx, Co, NO, H2O, H2S, NO2, SO2, SCL2, NH3, H2O2, CH3Cl, CH2Cl2, CHCL3, CH3CH2OH

Non-polar molecules: Cl2, H2, O2, N2, CO2, CS2, BF3, P4, C2H2, SO3, CH4, CCL4, SIF4, C2H4, C6H6, PCL5, Gasoline.

According to whether the positive and negative charge centers in the molecule coincide, the molecule can be divided into polar molecules and non-polar molecules. Molecules with positive and negative charge centers of gravity that coincide are non-polar molecules; What does not coincide are polar molecules.

For diatomic molecules, the polarity of the molecule coincides with the polarity of the bond. That is, the molecule composed of non-polar covalent bonds must be non-polar molecules, such as H2, Cl2, O2 and other molecules; Molecules made up of polar covalent bonds must be polar molecules, such as HCl, HF, etc.

In the case of polyatomic molecules, the polarity of the molecule does not necessarily coincide with the polarity of the bond. Whether a molecule is polar or not depends not only on the electronegativity of the elements that make up the molecule, but also on the spatial configuration of the molecule. For example, in CO2 and CH4 molecules, although they are both polar bonds, the former is a linear configuration, and the latter is a regular tetrahedral configuration, and the polarity of the bonds cancels each other out, so they are non-polar molecules.

Whereas, in the H2O molecule in the V-shaped configuration and the NH3 molecule in the trigonal conical configuration, the polarity of the bond cannot be canceled out, they are polar molecules.

The magnitude of the polarity of the molecule is measured in the electric dipole moment. The electric dipole moment of the molecule is referred to as the dipole moment ( ) which is equal to the product of the distance between the center of gravity of positive and negative charges ( d ) and the electric charge ( q ) on the center of gravity of positive charge or negative charge

q· d, its unit is 10-30 c·m. The electric dipole moment is a vector quantity that chemically dictates its direction from the center of gravity of a positive charge to the center of gravity of a negative charge. The measured values of electric dipole moments for some molecules are shown in Table 9-5.

A molecule with zero electric dipole moment is a non-polar molecule, and the higher the electric dipole moment, the stronger the polarity of the molecule.

In chemistry, polarity refers to the non-uniformity of the charge distribution in a covalent bond or a covalent molecule. If the charge is not evenly distributed, the bond or molecule is said to be polar; If it is homogeneous, it is said to be non-polar.

Some of the physical properties of a substance like solubility, melting boiling point, etc., are related to the polarity of the molecule.

The polarity of a covalent bond arises because the electronegativity of the two atoms forming the bond is not the same. Atoms with high electronegativity, such as fluorine, oxygen and nitrogen, attract electrons more than atoms with low electronegativity, that is, they "pull" electrons to their side, and electrons spend more time close to atoms with high electronegativity, resulting in uneven distribution of charges.

This forms a set of dipoles, and such bonds are polar covalent bonds. An atom with high electronegativity is a negative dipole and is denoted as δ-; The atom with low electronegativity is a positive dipole and is denoted as δ+. The strength of polarity between two atoms is expressed in the bond dipole moment.

Bonds can fall into two extremes – polar and non-polar. A completely non-polar bond is produced when the electronegativity of the different ions that make up the covalent bond is exactly the same. Conversely, when the electronegativity difference between the two is large enough that one ion completely removes an electron from the other, a polar bond – or more appropriately, an ionic bond – is created.

The words "polar" and "non-polar" are often used to describe covalent bonds. The degree of polarity of a bond can be measured by the difference between the electronegativity of two atoms. When the difference between to is a typical polar covalent bond, and the difference between to is a non-polar covalent bond, when the two atoms are exactly the same (of course, the electronegativity is also exactly the same), the difference is 0, and the atoms form a non-polar bond.

Triangular boron trifluoride molecule. Although the 3 bonds are all polar bonds, the molecule is a non-polar molecule. Because of molecular symmetry, the centers of positive and negative charges coincide.

A covalent molecule is polar, which means that the charge distribution within the molecule is not uniform, or that the positive and negative charge centers do not coincide. The polarity of a molecule depends on the polarity of the individual bonds within the molecule and how they are arranged. In most cases, polar molecules have polar bonds in them, and non-polar molecules have non-polar bonds in them.

However, non-polar molecules can also be made up entirely of polar bonds. As long as the molecule is highly symmetrical, the positive and negative charge centers of each polar bond are concentrated in the geometric center of the molecule, so that the polarity of the molecule is eliminated. Such molecules are generally linear, triangular (also known as planar because the three atoms are in the same plane) or tetrahedral.

Molecular shape. The shape of a molecule is formed by the mutual repulsion of the atoms that make up the molecule and the unbonded electrons of one of the atoms. Compared with the repulsion between chemical bonds, the repulsion of unbonded electrons to chemical bonds is greater.

For example, carbon dioxide (CO2), in which the carbon atom and oxygen atom have reached the eight-electron stable structure and all the electrons are bonded, so there are no extra electrons, and because of the double bond, the carbon atom and the oxygen atom are in a straight line, so carbon dioxide is a linear molecule.

Ammonia (NH3), on the other hand, has a greater repulsion to three pairs of nitrogen-hydrogen chemical bonds because the nitrogen atom has one pair of electrons that are not bonded, so the ammonia molecule is trigonal pyramidal rather than planar or tetrahedral type.

The positive and negative charge centers in the molecule do not coincide, and the distribution of the charge is uneven and asymmetrical from the perspective of the whole molecule, and such a molecule is a polar molecule. The diatomic molecule bound by polar bonds must be polar molecules, and the polyatomic molecules bound by polar bonds depend on the structural conditions, such as ch4 is not a polar molecule.

A non-polar molecule is a molecule with a dipole moment = 0, that is, a molecule in which the atoms are covalently bonded together, the charges in the molecule are evenly distributed, and the centers of positive and negative charges coincide. When all the bonds in the molecule are non-polar, the molecule is non-polar (except O3). When the bonds in a molecule are exactly the same, they are all polar bonds, but the configuration of the molecule is symmetrical, then the molecule is nonpolar.

Polar molecules: The centers of positive and negative charges do not coincide in the chronological balance, and the distribution of charges is uneven and asymmetrical from the perspective of the whole molecule.

Non-polar molecule: The positive and negative charge centers in the molecule coincide, and the charge distribution is uniform and symmetrical from the whole molecule.

(1) The diatomic molecule formed by the combination of non-polar bonds must be non-polar molecules, such as H2, O2, N2, Cl2, etc.

2) The diatomic molecules formed by the combination of polar bonds must be polar molecules, such as HCL, NO, CO, etc.

3) Polyatomic molecules formed by the combination of covalent bonds (polar or non-polar bonds) may be polar or non-polar, depending mainly on the spatial configuration of the molecule. Non-polar molecules with perfectly symmetrical molecular spatial structure are non-polar molecules, and polar molecules with asymmetrical molecular spatial structure.

4) For ABN-type covalent molecules, if the central atom A reaches the highest positive valence and there are no lone pairs, they are non-polar molecules, such as PCL5, SO3, BF3, etc.; If the central atom does not reach the highest positive valence, when there are arc pairs of electrons, it is a polar molecule, such as SO2, NH3, PCL3, etc.

5) Covalent molecules composed of atoms of three or more elements are generally polar molecules, such as HNO3, CH3Cl, CH3CH2OH, etc.