كيمياء لغات - الباب الرابع| Elements of group (I A) [alkali metals] | كايرو دار
للصف الثالث الثانوى
كيمياء لغات - الباب الرابع| Elements of group (I A) [alkali metals] | كايرو دار
للصف الثالث الثانوى
كيمياء لغات - الباب الرابع| Elements of group (I A) [alkali metals] | كايرو دار
للصف الثالث الثانوى
The representative elements of some regular groups
First: - Elements of group (I A) [alkali metals] * Elements of this group are known as alkali metals [ forming Alkali ] * Moslem scientists, gave the name (Al-kale) to both Sodium and potassium com. G.R.F
* Abundance of alkali metals in the nature
* Sodium and potassium abundant in the earth's crust, they take the sixth and seventh arrangement of elements in the earth's crust. * Most important ore of sodium is rock salt (NaCl) *The most important ore of potassium is (KCl) which is found in sea water. & carnallite deposits (KCl. MgCl2. 6H2O) *Francium is a radioactive element, it's produced from disintegration of Actinium and its half life time equals 20 minutes , its properties are similar to Caesium.
227 89AC 87Fr 223
+ 2He4
Elements of group 1A are called alkali metals. G.R.F * Because their oxides when dissolve in water give alkali
GENERAL PROPERTIES OF ALKALI METALS
1) Each element of this group has a single electron in the outer most energy level ns1 . and it's easily losed. That's tends to: -
G.R.F
a) They have an oxidation number (+1).
G.R.F
b) They are chemically active. due to easy to lose electron G.R.F c) They are strong reducing agents.[substance which gives electron.]. d) They have a weak metallic bond. So they are the most malleable [soft metals] ,they have low (M.P and B.P) G.R.F e) The first ionization potential is less than the other elements. f) The second ionization potential is a very high . G.R.F *Because it must need a large amount of energy to break down the completely energy level. g) Most of their compounds are ionic and the ion of each element similar to the inert gas before it in the electronic structure. 2) They have a large volume in their periods. That's tends to: a)- Increasing their atomic radius from up to down and decreasing attraction force of nucleus so electron easily losed so , they are called electropositive. and they are chemically active. [the top of chemical activity series] b)-Decreasing ionization energy so. They are used in photoelectric cells. "Because their elements when exposed to light they lose electrons from its surface G.R.F .
c)- They have low densities. G.R.F Because they have large volume [ density is inversely proportional to volume] d)- They have low electronegativity compared to other elements. Def: - Photoelectric phenomena: It's the emission of electrons from the surface of some metals when exposed to light. such as ( Cs, K).
*Caesium and potassium are used in photoelectric cells G.R.F
3) Excitation
*When the electrons of these elements are excited to higher energy levels by heating. They give characteristic colours of these elements.
* This property is used to detect this elements by a dry test (Flame test) G.R.F * Because each element gives characteristic colour on heating it by bunsen flame. The element Lithium Sodium Potassium Caesium Flame test exp. · Platinum wire is cleaned by dipped it in concentrated HCl then dipped in unknown salt then exposed to Bunsen flame Colour of flame Crimson Golden yellow Pale violet Bluish violet
· It gives a specific colour which detect the cation in this salt. *How can you differentiate between Sodium carbonate and lithium carbonate 4) They are stored under surface of liquid hydrocarbons such as kerosene Because: They are very active metals so they react with air So :- They are stored under the surface of Kerosene . 5) Action of atmospheric air ( O2 , N2 , H2O , CO2 ) G.R.F
*Elements of group 1A are chemically reactive . *Elements of group 1A loses their metallic luster [ brightness ] when they are exposed to air due to the formation of layer of oxide. Reaction with Nitrogen *Only lithium can react with Nitrogen of air *Lithium reacts with Nitrogen of air forming Lithium nitride which reacts with water and Ammonia gas evolves. 6Li + N2 Li3N + 3H2O heat 2Li3N (lithium nitride)
3LiOH + NH3
* This reaction used to obtain Ammonia * How can you obtain Ammonia from alkali metals? 6) Reaction with water: * These elements react strongly with water because they are chemically reactive [ at the top of the chemical activity series] so thy replace Hydrogen atom in water and a large amount of heat which is produced is enough to burn hydrogen. 2Na + 2 HOH 2NaOH + H2 + heat
Sodium fires are not extinguished by water.
G.R.F
Because: When Sodium reacts with water a large amount of energy is produced and it's enough to burn Hydrogen *Reaction of these elements with water increases from up to down. G.R.F 7) Reaction with Oxygen *On burning these elements they give three types of oxides as following: (O.N) Of Oxygen 4Li + O2 2Na+ O2 K + O2 2Li2O Na2O2 KO2 (Lithium oxide) (Sodium peroxide) (potassium super oxide) -2 -1 -1/2
* potassium , Rubidium and Caesium give super oxides G.R.F * Potassium super oxide is used in submarines and high altitude . In general [ closed places.] [very important ] Because: They react with CO2 giving Oxygen. [It's used for replacing CO2 by Oxygen in closed places ] 4KO2 + 2CO2
CuCl2
2K2CO3 + 3O2
*These oxides can be prepared by dissolving it in a liquefied ammonia gas then adding the amount of Oxygen * With the exception of Li2O the oxides of group 1A react with water to give a strong alkaline solution * X2O is the best oxide because it reacts with water forming strong alkali.
8) Reaction with acid {active metal + acid 2Na + 2HCl Salt + Hydrogen } 2NaCl + H2
Sodium Replaced Hydrogen in acid and it is a vigorous reaction leading to explosion 9) Reaction with Hydrogen:Alkali metals react with Hydrogen to form "Hydrides" such as :-. 2Li + H2 2Na + H2 heat heat 2LiH 2NaH (Lithium hydride) (Sodium hydride)
Def:- Hydrides are ionic compounds, oxidation number of hydrogen in it equals.(1) 10) Reaction with halogens 2Na + Cl2 2K + Br2 2NaCl 2KBr (Cl2 F2 Br2 I2)
potassium bromide.
*These reactions will be strongly accompanied by explosion forming ionic halides which are more stable. 11) Reaction with non-metals * Hot alkali metals react directly with sulphur or phosphorus 2Na + S 3K + P Na2S K3P (Sodium sulphide) (potassium phosphide)
12) The effect of heat on the salts of alkali metals
* Oxygenated alkali metals are characterized by their thermal stability. *All alkali metal carbonates are not decomposed by heat except lithium carbonate. which decomposed at 1000C0 Li2CO3 1000 Li2O + CO2 (lithium carbonate)
Alkali-metal nitrate are decomposed by heat into alkali metal nitrite and oxygen .
2NaNO3 2KNO3
2NaNO2 + O2 2KNO2 + O2
(Sodium nitrite and Oxygen) (potassium nitrite and Oxygen)
G.R.F. Sodium nitrate can't be used in the manufacture of bombs. Because: It's a deliquescent substance , It absorbs water vapour from air G.R.F Potassium nitrate is used in the manufacture of bombs. Because: a great explosion is produced when potassium nitrate decomposed by heat