University:
California State University, Northridge
Course:
CHEM 100 | Principles of Chemistry
Academic year:

2023
Views:

98

Pages:

2
Author:

SMauren

ALKALI METALS The alkali metal (IA) elements consist of lithium, sodium, potassium, rubidium, cesium, and francium. This element has the smallest ionization energy because it has the electron configuration ns1 . Therefore, alkali metal elements easily release electrons and are the strongest reducing agents. Alkali elements are soft metals, shiny white, good conductors, and have low melting points, and are found in the form of salts. 1. Physical Properties From table above it can be seen that as a metal, it is in the alkaline earth group has unusual properties, namely its relatively low melting point, its relatively low density, and its softness. All alkali metal elements these can be easily reshaped by squeezing them in between thumb and index finger (protecting the skin well). Elements This group has the lowest average ionization energy and electronegativity. This is due to the size of the atoms and the distance between them relatively large between the outer electrons and the nucleus. 2. Chemical Properties Alkali metal reactions are as follows. a. Reaction of Alkali Metals with Halogens The reaction between alkali metals and halogens takes place very quickly, forming metal halides. Reaction: 2 M(s) + X2 2 MX(s) with: M = alkali metal (Li, Na, K, Rb, Cs) X = halogen (F, Cl, Br, I) The reactivity of alkali metals increases as the ionization energy decreases, so that Cs > Rb > K > Na > Li . b. Alkali Metal Reactions with Hydrogen and Nitrogen Alkali metals react with hydrogen gas to form white, crystalline compounds called hydrides, MH. The reaction occurs slowly at room temperature and requires heating to melt the alkali metal . Reaction: 2 M(s) + H2 (g) 2 MH(s) Not all alkali metals react with nitrogen, only lithium forms lithium nitrite (Li3 N). Reaction: 6 Li(s) + N2 (g) 2 Li3 N(s) c. Reaction of Alkali Metals with Oxygen The reaction between alkali metals and oxygen takes place very quickly.The resulting products differ depending on the reaction conditions and how much oxygen is present, such as oxide (oxidation number O = –2), peroxide (oxidation number O = – 1), and superoxide (oxidation number O = –½). Reaction: 4 Li(s) + O2 (g) 2 Li2 O(s) ——— Oxide, O = –2 2 Na(s) + O2 (g) Na2 O2 (s) ——— Peroxide, O = –1 K(s) + O2 (g)KO2 (s) ——— Superoxide, O = –½ d. d. Reaction of Alkali Metals with Water Alkali metals react with water to form hydrogen gas and alkali metal hydroxides, MOH. Reaction: 2 M(s) + 2 H2 O(l) 2 M+ (aq) + 2 OH– (aq) + H2 (g) with M = Li, Na, K, Rb, Cs The reaction The reaction of alkali metals with oxygen is a redox reaction, where the metal (M) loses electrons and hydrogen from water gains electrons. e. Reaction of Alkali Metals Metals with Ammonia Alkali metals react with ammonia to form H2 gas and metal amide (MNH2 ). This reaction is the same as the reaction of alkali metals with water. Reaction: 2 M(s) + 2 NH3 (l) 2 M+ (s) + 2 NH2 – (s) + H2 (g) with M = Li, Na, K, Rb, Cs

Alkali Metals (Lecture Notes)

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