碱金属性质（Alkali metal property）.doc

碱金属性质（Alkali metal property） 1. To master the atomic structure of alkali metals, and to understand the similarities and differences in the properties of alkali metals by the similarities and differences of atomic structures. Master the operation skill of Na + and K + with flame color reaction. [explanation of knowledge] 1. Alkali metals The alkali metals contain lithium, sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). Since francium is an artificial radioactive element, middle school chemistry is not introduced. The atomic structure of alkali metals Similarity: the atoms of the alkali metals have only one electron in their outermost shell, and eight electrons in the outer shell (of which there are only two electrons in the outer shell of Li atom). So in the chemical reaction, the atoms of the alkali metals always lose one of the electrons in the outermost shell and they show a plus one. Pass degeneration: Li, Na, K, Rb, Cs alkali metal elements such as the number of nuclei outer shell, atomic radius increases gradually, check the outermost electron appeal gradually, gradually enhance its capability of electron donors, elements gradually enhanced. 3. Physical properties of alkali metals and their changing laws (1) color: silver and white metal (Cs slightly aureate luster). (2) hardness: small, and with Li, Na, K, Rb, Cs, the hardness of metal gradually decreases. This is due to the gradual increase in the number of electrons in the atom, the increasing atomic radius, and the gradual weakening of the force between atoms. Alkali metals are small in hardness and can be cut with knives. (3) low melting point of alkali metal. Melting point of the highest lithium is 180.5 ℃, the melting point of cesium was 28.4 ℃. As the number of atomic number increases, the melting point of the single substance gradually decreases. (4) the density of alkali metals is small. The density of Li, Na and K is less than the density of water, and the density of lithi