"Periodic changes in the properties of elements" PPT courseware on the periodic law of elements

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"Periodic changes in the properties of elements" PPT courseware on the periodic law of elements

Part 1: Essential knowledge and foundation of literacy

1. Periodic changes in atomic structure

【Smart Judgment】

(1) In the second period, the elements go from left to right, and the highest positive price increases from +1 to +7. ()

Tip:×. The oxygen element does not have the highest positive valence (+6), and the fluorine element does not have a positive valence.

(2) The element with the smallest atomic radius in the third period is Ar. ()

Tip:×. The element with the smallest atomic radius in the third period is Cl.

2. Gradual changes in the properties of elements in the third period

1. Reaction of sodium, magnesium and water

2. Amphoteric hydroxide

(1) Concept: It can react with both strong acids and strong bases, and both generate salts and water hydroxides.

(2) The amphoteric properties of aluminum hydroxide

①Add excess ammonia to the AlCl3 solution, phenomenon: _____________,

Reaction equation:__________________________________________.

②Add NaOH solution dropwise to the AlCl3 solution to excess, phenomenon: _______________________________, reaction equation:

____________________________, ____________________________

③ Add hydrochloric acid to the Al(OH)3 precipitate, and the ionic equation of the reaction is:_________________________.

3. The highest valence oxides of sodium, magnesium and aluminum correspond to the alkalinity of hydrates

【Situation·Thinking】

Aluminum products are commonly used in daily life, such as aluminum pots, but aluminum pots are prone to corrosion if they contain acidic or alkaline food for a long time.

(1) The metallicity of aluminum is relatively active and easily reacts with O2, etc. However, aluminum pots can be used for a long time. Please explain the reason.

Tip: Aluminum reacts with oxygen to form a dense oxide protective film on the surface of the aluminum pot, which prevents aluminum from continuing to react with oxygen, so the aluminum pot can be used for a long time.

(2) Aluminum pots tend to corrode if they hold acidic or alkaline foods for a long time. Why?

Tip: Alumina is amphoteric and can react slowly with acidic or alkaline foods, causing the alumina to lose its protective effect.

[Do it] Among the elements of the third period, except for rare gas elements:

(1) The most metallic element is ___ (fill in the element symbol);

(2) The hydrate with the highest valence corresponding to the most acidic oxide is _____ (answer with a chemical formula, the same below);

(3) The amphoteric oxide is _____.

3. Periodic law of elements

1. Content: The properties of elements change periodically as the atomic number increases.

2. Essence: The periodic changes in the properties of elements are the inevitable result of the periodic changes in the atoms' ______________.

Key capabilities and literacy formation

Knowledge point 1: Periodic changes of main group elements in the periodic table of elements

[Key points to clarify doubts]

【Think·Discussion】

(1) H2SO3 is more acidic than HClO. Can it be proved that S is more non-metallic than Cl?

Tip: No. Neither H2SO3 nor HClO is a hydrate of the highest valence oxide of the corresponding element.

(2) Try to explain the reason why the properties of elements with the same period change periodically from the perspective of atomic structure.

Tip: The number of electron layers outside the nucleus is the same. As the atomic number (nuclear charge) increases, the attraction of the atomic nucleus to the electrons outside the nucleus gradually increases, the atomic radius gradually decreases, the ability of the element atoms to gain electrons gradually increases, and the ability to lose electrons gradually increases. Weakening, eventually leading to the gradual enhancement of the non-metallic properties of the elements and the gradual weakening of the metallic properties.

【Case Demonstration】

[Typical example] (2017·National Volume II) a, b, c, and d are short-period main group elements with increasing atomic numbers. The total number of electrons outside the nucleus of a atom is the same as the number of electrons in the sub-outer shell of b atom; c is in the period The number and family number are the same; d and a are in the same family. Which of the following statements is correct ()

A. Atomic radius: d>c>b>a

B. Among the 4 elements, b has the strongest metallicity

The hydrate of the oxide of C.c is a strong base

D. The oxidizing property of element d is stronger than that of element a.

[Thinking Modeling] The thinking process for answering this type of test questions is as follows:

[Analysis] Choose B. Since a, b, c, and d are short-period main group elements with sequentially increasing atomic numbers, and the total number of electrons outside the nucleus of a atom is the same as the number of electrons in the outer shell of b atom, then the atomic number of a should be 2 or 8; c is where If the period number is the same as the group number, then c can only be Al, and since d and a are in the same group and d has the largest atomic number, d and a can only be elements from group IIIA and later, so the atomic number of a is 8, which is O ,d is S; then b is Na or Mg. Since b, c, and d are in the third period, the atomic radius is b>c>d, and d and a are in the same main group, then the atomic radius d>a, so item A is wrong; from left to right in the same period, the metallicity gradually weakened, then the metallicity b>c, a and d are non-metals, and the metallicity is weak, so item B is correct; c is Al, and the hydrate of its oxide is aluminum hydroxide, which is an amphoteric hydroxide, not a strong base , so item C is wrong; d and a belong to group VIA, which are S and O respectively. The non-metallic properties of elements in the same main group gradually weaken from top to bottom, so the oxidizing property of element a is stronger than that of element d, so Item D is wrong.

Knowledge point 2: Comparison of particle radius sizes

[Key points to clarify doubts]

【Think·Discussion】

(1) For elements of the same period, from left to right, does the atomic radius gradually decrease?

Hint: No. When comparing atomic radii of the same period, only main group elements are often compared, because the measurement method of atomic radii of non-main group elements is different from that of main group elements.

(2) In short-period elements, the more electron shells an atom has, the larger the atomic radius will be?

Tip: Not necessarily. The atomic radius of lithium is abnormal, only smaller than the atomic radius of sodium and magnesium in the third period.

【Case Demonstration】

[Typical example] Among the following comparisons of particle radius sizes, the correct one is ()

A.Na+

B.S2->Cl->Na+>Al3+

C.Na

D.Cs+>Rb+>Na+>K+

[Regular Method] "Three Looks" method compares the radius of simple particles

(1) "One look" at the number of electron layers: When the number of electrons in the outermost shell is the same, the more electron layers there are, the larger the radius.

(2) "Second look" at the nuclear charge: When the number of electron layers is the same, the greater the nuclear charge, the smaller the radius.

(3) "Three Looks": The number of electrons outside the nucleus: When the number of electron layers and the number of nuclear charges are the same, the more electrons outside the nucleus, the larger the radius.

【Migration·Application】

1. Compare the particle radii of the following groups, the correct one is ()

①Cl

④S2-

A. ① and ③ B. Only ② C. Only ③ D. ① and ④

[Analysis] Choose A. ①The anion radius is larger than the atomic radius of the same element, so Cl->Cl, and the number of electron shells Br->Cl-, so ① is correct; ② For particles with the same electron layer structure, the one with a larger nuclear charge has a smaller radius, ② is incorrect; ③ The cation radius is smaller than the atomic radius of the same element, ③ is correct; ④ should be Se2->Br->S2-, ④ is incorrect.

2. Which of the following particle radius ratios is less than 1 ()

A.r(Na+)/r(Na)B.r(Cl-)/r(Cl)

C.r(Na)/r(Mg)D.r(Ca)/r(Mg)

[Analysis] Choose A. Item A, the radius of the sodium ion is smaller than the sodium atom, so the ratio is less than 1, so it is correct; Item B, the radius of the chlorine ion is greater than the chlorine atom, so the ratio is greater than 1, so it is wrong; Item C, the atomic radii of elements in the same period gradually increase from left to right. decreases, so the ratio is greater than 1, so it is wrong; item D, the atomic radius of elements in the same main group gradually increases from top to bottom, so the ratio is greater than 1, so it is wrong.

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Update Time: 2024-07-31

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