How can you tell if a molecule is polar? How can you tell the polarity of a molecule?

How to judge the concept of polarity and polar bond of a molecule?

These are two concepts in different ranges, the polarity of the chemical bond should be said to be the polarity of the covalent bond is a matter between the two atoms that form a bond, as long as a covalent bond is formed between two atoms, you can distinguish between polar bonds and non-polar bonds, it is also very simple to distinguish these two small concepts, as long as the electron pairs that form a covalent bond are not offset (in fact, the attraction of two atoms to electrons is the same), it should be that the covalent bond between atoms of the same kind is a non-polar bond, if the bonded atoms are not atoms of the same element, Then there must be a difference in their attraction to electrons, and the chemical bond between them is a polar bond! The electron pair is always biased towards the atomic side of the non-metallic element, then this side behaves as a negative valency!

There is a big difference between distinguishing the polarity of a molecule from a covalent bond, it is actually observing the symmetry of this molecule, and if the symmetry of the molecule is intact, it mainly refers to the central symmetry! Then the molecule is a non-polar molecule! If the symmetry is not good, it is a non-polar molecule!

For example, CH4 is a tetrahedral molecule, the molecule is symmetrical with respect to the center, and although the chemical bond between CH is a polar bond, the molecule is a non-polar molecule.

The CO2 and C2H2 molecule is a linear molecule and the molecule is symmetric with respect to the center and is a non-polar molecule.

CH3Cl and CH2Cl2 are deformed tetrahedral molecules that do not have symmetry in the center of the components, so they are polar molecules!

There is a non-polar bond between two oxygen atoms in the H2O2 molecule, but the whole molecule is in a dihedral angle, and the center of the two H atoms is not at the same point as the center of the O atom, so H2O2 is a polar molecule!

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. To determine whether a substance is a polar molecule, it is measured by the physical quantity dipole moment. The dipole moment is a vector quantity equal in magnitude equal to the amount of charge of the positive and negative charges multiplied by the distance, and its direction is directed from the center of the positive charge to the center of the negative charge.

If the dipole moment is zero, then the molecule is nonpolar. In general, there are the following ways to determine this. Diatoms bound by polar bonds must be polar molecules, and polyatomic molecules bound by polar bonds.

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. Non-polar molecules:

Diatomic molecules made up of the same kind of atoms are all 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.

Simple way to judge.

For the ANBM type.

n=1m>1

If a valency is equal to the number of main families.

is non-polar.

In layman's terms, polarity reflects the electrification of a molecule's yin and yang charges.

If the center of the positive charge in a molecule coincides with the center of its negative charge, then the contribution of the yin and yang charges to the molecule cancels each other out, and we call the molecule a non-polar molecule; And if the center of the positive charge in a molecule cannot coincide with the center of its negative charge, then the contribution of the yin and yang charges to the molecule cannot cancel each other out, and the molecule is a polar molecule.

Here's an example:

Methane CH4 has a negative charge and H atom has a positive charge due to the fact that the common electron pairs are all shifted towards C in the four C H bonds. And because the methane molecule is a solid tetrahedral structure in space, the four h atoms are distributed on the four vertices of the tetrahedron, and the c atom is located in the geometric center of the tetrahedron, so the center of the positive charge (four h atoms) is in the geometric center of the tetrahedron, and the center of the negative charge (c atom) is also in the geometric center of the tetrahedron, and the two coincide, so the methane molecule is a non-polar molecule.

The strictest way to determine whether a molecule is polar or not is to use the definition of polarity mentioned above. And with experience, it can be roughly assumed that, in general, symmetrical molecules are non-polar molecules. For example, acetylene C2H2 is linear, the structural formula H C three C H, the molecule is axisymmetric, and it belongs to non-polar molecules.

1.If the center of the positive charge and the negative charge in the molecule coincide, it is a non-polar molecule; If it does not coincide, it is a polar molecule.

A molecule is divided into two categories according to its polarity, one is a polar molecule and the other is a non-polar molecule, and the non-polar molecule is a charge that is symmetrically distributed in the molecule, such as H2, N2

CO2, CH4, etc.

Polar molecules are asymmetrically distributed charges in molecules, such as H2O, NH3, HCl, etc.

The law of their judgment is:

Diatomic elemental molecules are all non-polar molecules.

Diatomic compound molecules are all polar molecules, such as HCL, Hi, etc.

The polarity of polyatomic molecules depends on whether their spatial configuration is symmetrical, symmetrical is non-polar molecules, and vice versa, polar molecules such as NH3, H2O2 are polar molecules, CO2, CH4, BF3 and so on are non-polar molecules.

Let me introduce you to an ingenious way to determine the polarity of ABN-type molecules

Valence electronic method. First determine the valency of the central atom a and the outermost electron number of the atom a, if they are equal, then the molecule is non-polar, no.

Equal is a polar molecule.

It is also worth mentioning that the polarity of the molecule is not necessarily related to the polarity of the bond.

1.If the center of the positive charge and the negative charge in the molecule coincide, it is a polar molecule; If it does not coincide, it is a non-polar molecule.

2.The nature of the key.

The configuration of the molecule.

Polarity of molecules: If there is a symmetrical center, it is a non-polar molecule, otherwise it is a polar molecule.

3.Empirical law: in ABN-type molecules, the absolute value of the valency of atom A is a non-polar molecule, and the unequal is the polarity of a polar molecule: if there is a symmetrical center, it is a non-polar molecule, otherwise it is a polar molecule.

Look at whether the structure is symmetrical, and asymmetry is polarity, just like water molecules.

Perfectly symmetrical is non-polar, just like CO2

1. Polarity of the molecule.

Polar molecules: the positive and negative centers do not coincide, and the vector sum of the bonds is not 0.

Non-polar molecules: The positive and negative centers coincide, and the vector sum of the bonds is 0.

2. Judgment method.

1. Diatomic molecules: depending on whether the covalent bonds between bonding atoms are polar or not.

A-B type molecules (HCl): Heteronuclear diatomic molecules are polar molecules;

Type A-A molecules (Cl2): Homonuclear diatomic molecules are non-polar molecules.

There are also non-polar molecules in homonuclear polyatomic molecules, such as: P4, C60, S8, B12, special note: O3 (V type) is a polar molecule.

2. Polyatomic molecule (ABM type): depends on the spatial configuration of the molecule and the polarity of the covalent bond.

Valency method: When the absolute value of the valency of the central atom is equal to the number of valence electrons of the element, the molecule is a non-polar molecule; Otherwise, it is a polar molecule.

Physical model method: covalent bonds are regarded as forces, different covalent bonds are regarded as unequal forces, according to the synthesis and decomposition of forces, to see whether the central atom is balanced by force, if equilibrium is a non-polar molecule; Otherwise, it is a polar molecule.

Bonds & Molecules:

The polarity of a bond and the polarity of a molecule are two different concepts, and there is both a connection and a difference between a polar bond and a polar molecule.

Polar molecules must contain polar bonds, i.e., polar bonds are necessary for the formation of polar molecules, and may also contain non-polar bonds. A molecule containing a polar bond is not necessarily a polar molecule, i.e., a polar molecule not only contains polar bonds but also has an asymmetrical molecular structure. If all the bonds in the molecule are non-polar, such a molecule is generally non-polar.

The common types are as follows:

1. Non-polar molecules containing polar bonds, such as CO2, CS2, CH4, etc.

2. Non-polar molecules containing non-polar bonds, such as H2, Cl2, N2, O2, etc.

3. Polar molecules containing both polar bonds and non-polar bonds, such as h-o-o-h, etc.

4. Non-polar molecules containing both polar bonds and non-polar bonds, such as h-c-c-h, etc.

Generally, it can be judged from the structure and solubility: there are exposed hydroxyl groups, exposed carboxyl groups, and exposed amino groups, and the polarity of substances may be large; Then the solubility test shows that the polarity of the solvent is generally consistent with the polarity of the substance. If the point is very condensed, then the polarity of the substance may be higher than that of the solvent, and with the diffusion of the solvent then the polarity may be lower.

1. Polar molecules:

Molecules with positive and negative charge centers that do not coincide, and polyatomic molecules with polar bonds depend on the structure.

2. Non-polar molecules:

A molecule in which the center of positive and negative charge coincides.

3. Judgment of molecular polarity:

The polarity of a molecule is determined by both the polarity of the covalent bond and the spatial configuration of the molecule.

Judgment on polar molecules and non-polar molecules1、A diatomic molecule composed of polar bonds (covalent bonds formed by different kinds of atoms) must be polar molecules. Such as: CO, NO, HF, HBR, HI, HCL, etc.

2. A diatomic molecule composed of non-polar bonds (covalent bonds formed between atoms of the same kind) must be non-polar molecules. Such as: H2, O2, N2, F2, Cl2, B2, I2, etc.

3. Polyatomic (three or more atoms) molecules composed of polar bonds may be polar or non-polar. (1) If it is an ABN or BNA type molecule, the key is to see whether the electrons on the outermost shell of the central atom (atom A) are provided to form a covalent bond with the B atom. If the electrons on the outermost shell of atom A are provided to form a covalent bond with atom B, the molecule is non-polar; Such as:

CO2, CH4, BF3, SO3, CS2, PCL5, CCL4, etc. If the electrons on the outermost shell of atom A are not all provided to form a covalent bond with atom B, the molecule is a polar molecule; Such as: H2S, H2O, NH3, PCL3, SO2, etc.

2) Some polyatomic molecules composed of polar bonds can be judged based on the configuration of the molecule. For example, CH3CL, CH2CL2, and CHCL3 are asymmetrical tetrahedra, so they belong to polar molecules.

4. If the above three conditions are not met, it can be judged according to the principle of solubility of similar ones (the solute composed of polar molecules is easily soluble in the solvent composed of polar molecules, and the solute composed of non-polar molecules is easily soluble in the solvent composed of non-polar molecules). For example, H2O2, ethanol, acetic acid, etc. are soluble in water, and water is a polar molecule, so they are also polar molecules; C2H4, C2H2, C6H6, gasoline, white phosphorus, noble gases, etc., are insoluble in water, so they are non-polar molecules.

I wish you success in your studies!!

Diatomic molecules, if they are elemental, are non-polar molecules, such as H2, N2, stool Cl2, etc.

It is a compound, that is, a polar molecule, such as HF, HCl, CO

No polyatomic compound molecule, if yes.

ABN type, empirical rules can be applied.

The absolute value of the valency of a =

The outermost electron number of an atom is a nonpolar molecule, such as.

The valency of CO2,C is.

And the outermost shell of the c atom is.

With 4 electrons, CO2 is indeed a non-polar molecule.

If it is not equal, it is a polar molecule, such as.

The valency of H2O, O is 2, and the outermost shell of the O atom has 6 electrons. H2O is the polar molecule.

You can use this rule to determine the polarity of the following molecules: BF3, NH3, CH4, CCL4, SF6, PCL3, etc.

Repentant elements who are not of the ABN type can also draw on the above empirical rules and the shape of the molecule to aid in judgment.

If CCl4 is nonpolar and tetrahedral, then Ch3Cl, Ch2Cl2, and ChCl3 are all polar pre-guessing molecules.

The method of judging the vertical purity of polar molecules is as follows:

Molecules are divided into two categories according to their polarity, one is polar molecules, and the other is non-polar molecules, non-polar molecules are charged in the molecule distributed symmetrically, such as orange H2, N2, CO2, CH4, etc. Polar molecules are asymmetrically distributed charges in molecules, such as H2O, NH3, HCl, etc.

The polarity of polyatomic molecules depends on whether their spatial configuration is symmetrical, symmetrical is non-polar molecules, and vice versa, polar molecules such as NH3, H2O2, etc. are polar molecules, and CO2, CH4, BF3, etc. are non-polar molecules.

Characteristics of polar molecules:

The centers of positive and negative charges in the molecule do not coincide, from the perspective of the whole molecule, the distribution of charges is uneven and asymmetrical, such a molecule is a polar molecule, a diatomic molecule bound by a polar bond must be a polar molecule, and a polyatomic molecule bound by a polar bond. <>