About the law of gradual change of the properties of alkali metal elements!

1.Similarity: The outermost number of electrons is 1

2.Degrading: 1The number of electron layers gradually increases; 2.The melting point gradually decreases; 3.The boiling point gradually decreases; 4.The density showed an increasing trend (but Na>k); 5.The metallicity gradually increases.

3.Main chemical properties of alkali metal elements:1

Reacts with oxygen. Both can react with oxygen, but the combustion product of Li is the ordinary oxide Li2O, while the combustion product of Na is the peroxide Na2O2, and the combustion products of K, Rb, and CS are more complex. 2.

can react with H2O, and the reaction becomes more and more violent. General Formula:

2r+2h2o=2roh+h2 (r is an alkali metal)3In the flame color reaction, sodium is yellow and potassium is purple (through blue cobalt glass).

li na k rb cs

As the radius increases, the ability to lose electrons increases, and the metallicity gradually increases.

Phenomena and conclusions.

na mg al

React with cold water React violently with cold water The reaction is slow, and a small number of bubbles are produced There is no obvious phenomenon.

Phenolphthalein is red when dropped, and phenolphthalein does not turn red when dropped.

Reaction with hot water There are many bubbles on the surface, and the solution is light red without obvious phenomenon Conclusion Na reacts violently with cold water, Mg can react with boiling water, and Al reacts with boiling water hard.

Metallic na>mg>al

2.Law of gradual change: from lithium to cesium.

1) The density is decreasing (but potassium is abnormal).

2) The melting point and boiling point gradually decrease.

Generally speaking, as the atomic number increases, the density of the elemental increases. However, there is an "anomaly" phenomenon from Na to K, according to the density formula = m v, the increase in the relative atomic mass from Na to K plays a smaller role than the increase in atomic volume, so the density of K is smaller than that of sodium.

Chemical properties of alkali metals.

Alkali metals can react with oxygen, from lithium to cesium, the reaction is more and more intense, and the products are oxides (lithium), peroxides (sodium), and oxides more complex than peroxides (potassium, rubidium, cesium).

Alkali metals can react with water to form hydroxides and hydrogen. From lithium to cesium, the reaction with water is becoming more and more violent.

From lithium to cesium, the atomic radius increases with the increase of the number of nuclear charges, the electron loss ability and metallicity of alkali metals gradually increase.

By the periodic table.

, the metallicity of the same main group element is enhanced from top to bottom, and the alkalinity of hydroxide is also enhanced.

1) Alkali metals.

The alkalinity of the constituent bases is arranged from weak to strong:

Lithium hydroxide. Sodium hydroxide Potassium hydroxide.

Rubidium hydroxide, cesium hydroxide, francium hydroxide (francium is a radioactive element, generally not said it) They are all strong bases, and the alkalinity is enhanced in turn, in fact, lithium hydroxide should be a medium-strong base.

2) The alkalinity of the metal hydroxide of alkaline earth elements is also enhanced from top to bottom

Beryllium hydroxide, magnesium hydroxide, calcium hydroxide, strontium hydroxide, barium hydroxide, radium hydroxide (radium is a radioactive element, it is generally not said to be).

Beryllium hydroxide is a weak base and has amphoterides, magnesium hydroxide is a medium strong base, calcium hydroxide is a strong base, strontium hydroxide and barium hydroxide are strong bases, and the alkalinity is also enhanced in turn.

3) The alkalinity of alkali metal and alkaline earth metal hydroxide is generally not compared, but must be compared, remember, the alkalinity of calcium hydroxide is stronger than sodium hydroxide, weaker than potassium hydroxide, and the alkalinity of barium hydroxide is almost equal to potassium hydroxide, which is a little weaker.

With hydrogen as the standard, the activity of the metal from left to right is weakened by the strong, and the metals in front can be displaced from their salt solution, and theoretically speaking, the metals in front of hydrogen (H) can react with acid and replace hydrogen.

The lower the metals, the easier it is to be displaced, and the more they are displaced. The easier it is for the metal to be ranked first, and the more likely it is to replace the metal in the other compounds.

Alkali metals and alkaline earth metals are located in the two main groups of the periodic table, respectively, and both have very strong activity, and with the increase of the number of periods (nuclear charge number), the activity increases.

Alkali metals Li, Na, K, Rb, CS, Fr

Alkaline earth metals BE, MG, CA, SR, BA, RA

The atomic number increases sequentially, and the metal activity increases.

Answer]: Alkali metal elements (group ia) include: lithium, sodium, potassium, rubidium, cesium, francium, and the valence electron configuration of their atoms ns1

All of them are typical metal elements, which are easy to lose ns electrons and are therefore reducible, and the oxidation number of the stable oxidation state is +1. There is a regular change in the balance of the top-down properties of alkali metal elements. From top to bottom, the sub-radius and ionic radius of alkali metal elements gradually increase, the ionization energy and electronegativity gradually decrease, and the metallicity and reduction property gradually increase.

The alkali metal element laughing wheel is very metallic and can only exist in nature in a chemical state.

The similarities and rarcades of alkali metal elements are as follows:

Atomic Structure: Similarity: The outermost shell is 1 electron Incrementality:

The number of nuclear charges increases, the number of electrons increases, and the radius of atoms increases Elemental properties: Similarity: all active metal elements, and the highest positive valence is +1 Valence Degradualness:

The ability to lose electrons is enhanced sequentially, and the metallicity is enhanced in turn.

Deterioration: the reducibility increases sequentially, the density tends to increase, the melting and boiling point decreases sequentially, and the hardness tends to decrease.

The melting point of cesium gradually decreases from lithium to caesium, which is the opposite of halogen elements. This is because metallic bonds are present in alkali metals, and metallic bonds weaken as the atomic radius increases. There are intermolecular forces in halogen elements, and the intermolecular forces increase with the increase of relative molecular weight.

Compound Properties: Similarity: Hydroxides are all strong bases Denaturement:

The alkalinity of hydroxides increases sequentially. General and special features of alkali metals: Na and K need to be stored in kerosene.

However, the density of LI is less than that of kerosene, so LI must be kept in less dense paraffin oil or sealed in paraffin. In alkali metals, the density increases from Li to CS, but (K)=0 862g cm3< (Na)=.