High school chemistry radius comparison problem, high school chemistry how to compare the size of th

There are two main factors that affect the radius: one is the number of electrons outside the nucleus (generally speaking, the more electrons there are, the farther away from the nucleus, the larger the radius).

The second is the number of nuclear charges (generally speaking, the larger the number of nuclear charges, the stronger the ability to attract electrons, and the closer the electrons are to the nucleus, the smaller the radius). These two factors are contradictory, i.e., under different conditions, it depends on who has the most influence on the radius.

Therefore, in middle school, students can generally compare like this:

1.During the same period, from left to right, the increase in the number of nuclear charges plays a major role, i.e., the atomic radius decreases.

2.In the same main group, from top to bottom, the increase in the number of electrons plays a major role, that is, the radius of the atom increases.

3.The same element has different valence states: then you can only look at the number of electrons outside the nucleus (the number of nuclear charges is the same)4Particles with the same structure of the electron layer (i.e. the same number of electrons): then you can only look at the number of nuclear charges, the larger the number of nuclear charges, the smaller the ionic radius!

It is the same nuclear power and number of the same element, the ability to bind electrons is the same, the cationic electrons are few, and the electrons are more difficult to escape, so the radius is small. Anions are the opposite.

For example, if you have several ropes, all of them trap a sheep, and of course it will not be easy to escape. It's still these ropes, which bind a lot of sheep and make it easy to get trapped.

It's easy to understand

There is also coulomb repulsion between electrons, so the analysis should consider the combined effect of gravity and repulsion. There are many electrons, the gravitational force between protons and electrons is large, and the repulsion force between electrons is large, but the repulsion between electrons is dominant, so there are many electrons and a large radius.

1.The comparison of the size of the atomic radius is generally judged according to the periodic table. If it is of the same period, from left to right, the radius gradually decreases as the number of nuclear charges increases; If it is of the same main group, from top to bottom, the radius increases sequentially as the number of electron layers increases.

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2.If the extranuclear electron configuration of several particles is the same, the greater the number of nuclear charges, the smaller the radius. Ruohai Education Network.

3.The radius of the anion in the ions formed by the co-periodic elements must be greater than the radius of the cations, because the number of electron layers outside the nucleus of the cations of the co-periodic elements must be one layer less than that of the anions.

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4.The more positively charged ions (the more electrons lost) the more positive metal ions formed by the same metal element, the smaller the radius.

Ions of different elements of the same period.

How do radii compare?

1. The electron configuration outside the nucleus is different (that is, the number of electron layers is different), and the larger the number of electron layers, the larger the radius.

For example, the chloride ion is greater than the sodium ion.

2. When the electron configuration outside the nucleus is the same, the larger the number of nuclear charges, the smaller the radius.

For example, sodium ions are greater than magnesium ions, and sulfur ions are greater than chloride ions.

How do different ionic radii of the same element (when both are positively charged or both negatively charged) compare?

The more electrons, the larger the radius (i.e., the lower the valence, the larger the radius), such as the iron atom is larger than the divalent iron is greater than the trivalent iron, and the chloride ion is larger than the chlorine atom.

Ions of different elements of the same period.

1. The electron configuration outside the nucleus is different, and the larger the number of electron layers, the larger the radius.

2. When the electron configuration outside the nucleus is the same, the larger the number of nuclear charges, the smaller the radius.

Different ionic radii of the same element, the more electrons, the larger the radius.

I think that in the same horizontal row, the larger the atomic number, the smaller the radius: (this is because the larger the ordinal number, the stronger the ability to attract electrons, and the electrons are attracted closer together, so the radius is reduced).

And the more electron shells (homogeneous), the larger the radius.

So there are two situations to consider (same period, same family). We can't do anything about different cycles and different families.

First of all, the ion structure is the same, the difference is that the more electron layers, the larger the radius.

The same is that the larger the atomic number, the smaller the radius.

The structure of the electron shell of Na (sodium ion) is the same as that of N3- (-3 valence ion of nitrogen); There are 10 electrons outside the nucleus with a negative charge of 10 units;

There are 11 protons in the na (sodium ion) nucleus, which is 11 positive charges;

N3- (-3 valence ion of nitrogen) has 7 protons in the nucleus, which is 7 positive charges;

An ion stability is that positive and negative charges attract each other, similar to gravitational attraction;

The negative charge of the electrons outside the nucleus is the same as 10; The more positive charges in the nucleus, the greater the attraction, and the smaller the space for electron activity, that is, the smaller the radius, in fact, the radius is the radius of the electron cloud, which is the range of electron activity.

The more charges there are in the nucleus, the greater the constraint on the electrons and the smaller the radius. But only if the extranuclear electrons are the same.

Look at the ordinal number in the same layer, the order is small and the radius is large.

For example, sodium ions and magnesium ions, the extra electrons are two layers of 28 structures with 10 electrons, sodium has 11 protons in the nucleus, and magnesium has 12Protons are positively charged, electrons are negatively charged, and they attract each other! The attraction of MG positive electrons is greater than that of Na, the suction power is large, the electrons are wound closely, and the radius is small! Sodium ions are judged in the same way as nitrogen ions.

Number of electron layers. There are many electron layers and a large radius. It can be understood in this way that the electrons are arranged in layers outside the nucleus, similar to an onion, and the radius of the onion (atom) is naturally larger.

If the number of electron layers is the same, then the number of nuclear charges is compared, and if there are more nuclear charges, the radius is smaller.

Explanation: When the electron shell is the same, the more nuclear charges, the greater the attraction of the nucleus to the electrons outside the nucleus, and the nucleus naturally pulls the electrons closer! )

If the number of electron layers is still the same, then compare the number of electrons, the number of electrons is more, and the radius is large (image memory: more"Eat"One electron, then you gain weight! Explanation:

There is a repulsive force between electrons and electrons, and the more electrons, the stronger the repulsion between each other, and naturally they have to occupy a larger space).

Example: 1. Comparison of the radius of mg and o.

Mg > O, Reason: Mg has three electron shells, which is more than O (2 electron shells), so the radius is large.

2. Comparison of the radius sizes of Mg2+ and O2-.

Their electron shells are all 2, but the nuclear charge of O is less than Mg, so the radius of O2- is greater than that of Mg2+.

3. Comparison of the radius size of cl and cl-.

They have the same number of electrons and nuclear charges, but Cl- has one more electron than Cl, so the radius: Cl->Cl

Look at the number of electron shells of the ion....The number of electron layers is the same, the smaller the number of cores in nuclear power, the larger the radius....

If the number of electrons is equal after becoming an ion, the number of electrons is the smaller.

1. Atoms of the main group elements with the same number of electron layers (same period): the smaller the number of nuclear charges, the larger the atomic radius.

The main group elements of the second period: r(li) >r(be) >r(b) >r(c) >r(n) >r(o) >r(f).

The main group elements of the third period: r(na) >r(mg) >r(al) >r(si) >r(p) >r(s) >r(cl).

2. Mononuclear ions with the same electron shell structure (the same number of electrons outside the nucleus): the smaller the number of nuclear charges, the larger the atomic radius.

A single nuclear ion with 10 electrons outside the nucleus (the electron shell structure is the same, and the schematic diagram of the ion structure is the same).

r(7n3-) r(8o2-) r(9f-) r(11na+) r(12mg2+) r(13al3+)

A single nuclear ion with 18 electrons outside the nucleus (the electron shell structure is the same, and the schematic diagram of the ion structure is the same).

r(8s2-) r(9cl-) r(11k+) r(12ca2+)

3. Atoms of the main group of elements with the same number of electrons in the outermost shell (same group): the larger the number of nuclear charges, the larger the radius.

Alkali metal elements: r(cs) >r(rb) >r(k) >r(na) >r(li).

Halogens: r(i) >r(br) >r(cl) >r(f).

Group 0 elements: r(rn) >r(xe) >r(kr) >r(ar) >r(ne) >r(he).

4. Single nuclear ions of the main group elements with the same number of electrons in the outermost shell (same group): the larger the number of nuclear charges, the larger the radius.

Alkali metal elements: r(cs) >r(rb) >r(k) >r(na) >r(li).

Halogens: r(i) >r(br) >r(cl) >r(f).

5. Single-nucleated particles with the same number of protons: the more electrons, the larger the particle radius.

Metallic elements: R(Na) >R(Na+).

Transition elements: r(fe)> r(fe2+)> r(fe3+).

Non-metallic elements: r(cl-)>r(cl), r(h-)>r(h)> r(h+).

6. The main group elements with different numbers of electrons, electrons and protons in the outermost shell: the atomic radius of the element in the lower left corner (position) of the periodic table is greater than the atomic radius of the element in the upper right corner (position).

In the periodic table, the sodium element is located in the lower left corner of the fluorine element: r(na) > r(f).

Note: Atomic radius: r(na)> r(f), ionic radius: r(f-)>r(na+) It can be seen that the gain and loss of electrons has a considerable impact on the particle radius, and the particle radius has changed completely between the gain and loss of electrons.

Refers to the ratio of the atomic radii of two atoms in a molecule. It should be the ratio of the atomic radius of lithium iodide that is the largest.