How do the melting and boiling points of co periodic elements compare?

It is a bit difficult to compare the melting and boiling points, you need to know a little more about crystals, and different crystal types are compared in different ways.

1.Metal crystals.

For example, the melting point of lithium is higher than that of sodium, that is, the metal bond length of lithium is shorter than that of sodium, and the bond energy is larger, so the melting and boiling point is high, from lithium to cesium, the melting and boiling point decreases in turn.

2.Molecular crystals.

Molecular crystals, when they melt, they have to destroy the intermolecular forces (van der Waals forces), so their melting and boiling points are determined by the relative molecular mass, and the greater the relative molecular mass, the higher the melting and boiling point.

Oxygen elements, except for polonium, and halogen elements are all molecular crystals.

Therefore, the melting boiling point of oxygen "sulfur" "selenium" tellurium.

The halogen group is similar. Non-metallic hydrides are also molecular crystals, and the melting and boiling point is also relatively relative to the molecular mass, but because NH3, H2O, and HF also have hydrogen bonds, the melting and boiling point is abnormal, and it is remembered that the hydrogen bonds formed between molecules will rise abnormally.

Carbon group elements become more pronounced in metals and non-metals.

Two crystals of carbon.

Diamond is an atomic crystal, graphite is a mixed crystal, the melting and boiling point is very high, silicon is an atomic crystal, the melting point reaches more than 1400 degrees Celsius, and the melting point of germanium and tin does not seem to be so high.

The regularity of the carbon group is not so good.

For example, the melting and boiling point of NaCl is higher than that of CSCl, because the radius of Na+ is smaller than that of CS+, and the ionic bond between Na+ and Cl- is stronger than that of CScl, so the melting and boiling point of NaCl is high.

That's all I know.

Metal elements are the same as the main group, the larger the atomic number, the lower the melting and boiling point, and the opposite is true for non-metals and noble gases.

It is really difficult to compare the same period, about the closer to group IVA, the higher the melting and boiling point, the metal is higher than the non-metal, and the non-metal is higher than the noble gas.

The melting and boiling point of the elements of the same period is decreasing from left to right.

The elements of the same family are elevated, and there seems to be a special case, I don't remember, sorry.

1. With the increase of atomic number of elements in the same period, the melting point of the metal element of the element increases, and the melting point of the non-metal element decreases;

2. From top to bottom, the melting point of the metal element composed of the elements decreases, and the melting point of the non-metal element increases.

The melting and boiling point of alkali metals in the first main group is determined by the bond energy of the metal, and in the case of the same charge, the smaller the atomic radius, the greater the bond energy of the metal, so the melting and boiling point of alkali metals is determined by the melting and boiling point from top to bottom.

The halogens of the seventh main group, its elemental element is molecular crystals, so the melting and boiling point is determined by the intermolecular force, in the case of similar molecular composition, the greater the relative molecular mass, the greater the intermolecular force, so the melting and boiling point of halogens is gradually changed by the boiling point from top to bottom.

Melting point of elemental matter:

1. With the increase of atomic number of elements in the same period, the melting point of the metal element of the element increases, and the melting point of the non-metal element decreases; 2. From top to bottom, the melting point of the metal element composed of the elements decreases, and the melting point of the non-metal element increases.

What can be discussed here is the elemental melting and boiling point of the main group elements.

In the alkali metals of the first main group, from top to bottom, the melting and boiling point of the metal element gradually decreases.

In the seventh major halogen element, from top to bottom, the melting and boiling point of the metal element gradually increases.

General melting boiling point, ionic crystals, metal crystals, and molecular crystals.

In ionic crystals: the larger the molecular weight, the higher the cation valence, the higher the melting and boiling point of metal crystals, there is no comparison method, check the table.

In molecular crystals, it is more complicated to look at the functional groups and carbon skeleton structure, as well as hydrogen bonds.

This should be aimed at the element, and the law depends on what crystal type the elemental belongs to to be judged.

1. For substances with different crystal types, generally speaking: atomic crystals, ionic crystals, molecular crystals, and metal crystals have a wide range of melting points.

2. Atomic crystal: the shorter the bond length and the greater the bond energy of the atomic crystal, the more stable the covalent bond is, the higher the melting and boiling point of the substance, and vice versa. Such as:

Diamond (C—C) Silicon Carbide (Si—C) Crystalline silicon (Si—Si).

3. Ion crystal: The smaller the anion and cation radius and the higher the charge number in the ion crystal, the stronger the ionic bond, the higher the melting and boiling point, and vice versa.

Such as kf kcl kbr ki, cao kcl.

4. Metal crystal: the more the number of valence electrons of the metal atom in the metal crystal, the smaller the atomic radius, and the more the electrostatic interaction between the metal cation and the free electron.

Strong, the stronger the metallic bond, the higher the melting boiling point, and vice versa. Such as: na mg al.

5. Molecular crystal: the greater the intermolecular force of the molecular crystal, that is, the greater the relative molecular mass, the higher the melting and boiling point of the substance, and vice versa.

Therefore, it depends on what kind of substance it is, for example, IA elemental is a metal crystal, and the melting and boiling point of their elemental element gradually decreases from Li to CS; For example, VIIA elements are molecular crystals, and the melting and boiling points of their elements gradually increase from F2 to I2.

Same as the main family. Metal: from top to bottom, gradually decreasing; Non-metallic: from top to bottom, gradually rising;

Same period. metal, from left to right, gradually rising; Non-metallic, from left to right, gradually decreasing.

The boiling point comparison of elements in the periodic table is as follows:

First of all, the crystal type of the elemental field is judged, and the crystal type is different, and the role of determining its melting and boiling point is also different. The melting and boiling point of a metal is determined by the bond energy of the metal; Molecular crystals are determined by the size of the ridges of intermolecular forces; The ionic crystal is determined by the magnitude of the ionic bond energy; Atomic crystals are determined by the magnitude of the covalent bond energy.

Therefore, the melting and boiling point of alkali metals in the first main group is determined by the metallic bond energy, and the smaller the atomic radius, the greater the metallic bond energy when the charge is the same.

The melting and boiling point of alkali metals decreases sequentially from top to bottom. The halogen of the seventh main group, its element is molecular crystal, so the melting and boiling point is determined by the intermolecular force, in the case of similar molecular composition, the greater the relative molecular mass, the greater the intermolecular force, so the melting and boiling point of the halogen is the law of annihilation

The boiling point rises sequentially from top to bottom.