✟ 神秘の科学城 ✟: SPM Form 4 Chemistry Notes — Chapter 4『4.3』Group 1 Elements

SPM Form 4 Chemistry Notes — Chapter 4『4.3』Group 1 Elements

4.3 Group 1 Elements

● The Group 1 metals is known as Alkali Metals (except Hydrogen).『在G1的金属都是碱性的- 如果用石蕊试纸去测试,红色石蕊试纸会变蓝色      * Hydrogen在Room Temperature的时候是气体

● Elements in this group are Lithium,Sodium,Potassium,Rubidium,Caesium and Fransium.

● All alkali metals are very reactive.They must be stored in oil (paraffin oil)prevent reaction with oxygen or water vapour in air. 『G1的金属都很Reactive,所以要放进Paraffin Oil里面,防止G1金属和空气中的水分和氧气产生化学反应』

● They are all with one valence electron.


** Physical Properties

● exist as grey solid with silvery and shiny surface at room temperature.

lower melting points and boiling points compared to other metals.

very soft (can be easily cut by knife)

good conductors of heat and electricity

low density (first three floats on water)


** Size of Atom increases

● This is due to the increase of number of electron occupied shells in the atom.



** Density increases

● Density of a substance is given by the equation.



● Down the group,both the mass and the volume increase,but increase of mass is faster than the volume,hence the density increases down the group.『重量和体积一样增加,只不过重量比体积增加得快』


** Melting and Boiling Points Decreases

● All the atoms of Group 1 metals are bonded together by a force called metallic bond.

● The nearer the atoms,the stronger the bond.

● Down the group,the size of the atoms increases,causing the distance of the atoms increases.

● As the distance between the atoms increases,the metallic bond between the atoms decreases.

● Therfore,less energy is needed to overcome the metallic bond during melting process.

● Consequently,the melting point of Group 1 metal decreases down the group.

Atomic size increases causing the metal bond between atoms become weaker.





** Chemical Properties

● Group 1 metals are very reactive metals.

● Lithium,Sodium,and Potassium have similar chemical properties(all of the atoms have one valence electron)but differ in reactivityreactivity increases down the group, the electropositivity also increases down the group

● They tend to react mainly with non-metals to form ionic compounds.

The electopositivity of an element is the tendency of the atom of the element to release its electrons(to form positive ion)

● Alkali metals have one valence electrons in their outermost occupied shell.

● When the atoms reacts,it loses the valence electron to form a positively charged ion to achieve the stable duplet / octet electron arrangement.



Lithium,Sodium and Potassium show similar chemical properties.


Explaining the Reactivity Trend / Electropositivity of the Grouo 1 Alkali Metals.

Electropositivity is the ability of an atom to donate electron to form a positive ion.

● As we go down the group,the atomic radius / size increases.

● The valence electron is further from the nucleus.Thus the attraction force between the nucleus and the valence electron become weaker.

● This causes the valence electron is easier to be released to form an ion when the atom takes part in a reaction.

● So,reactivity / electropositivity increases.


Reactions of Group 1 metals

 Reaction with waterH2O

● to produce metal hydroxide and hydrogen gas.

● Lithium + Water → Lithium Hydroxide + Hydrogen Gas
     2Li + 2H2O 2LiOH + H2

● Sodium + Water → Sodium Hydroxide + Hydrogen Gas
     2Na + 2H2O 2NaOH + H2




Reactions with oxygenO

● to produce metal oxide.

● Lithium + oxygen → Lithium oxide
    4Li + O2 2Li2O

● Sodium + oxygen → Sodium oxide
    4Na + O2 2Na2O



Reaction with Chlorine gasCl2

● to produce metal chloride.

● Lithium + Chlorine → Lithium chloride
    2Li + Cl2 2LiCl

● Sodium + Chlorine → Sodium chloride
    2Na + Cl2 2NaCl








Safety Precaution

● Alkali metals are very reactive.

● Therefore it must be kept in paraffin oil to prevent them from reacting with oxygen and water vapour in the air.『放进Paraffin Oil里面,防止G1金属和空气中的水分和氧气产生化学反应』

● We must avoid to hold group 1 metals with bare hand because they may react with water on our hand.『避免裸手拿取G1的金属,因为它可能和我们手的水分产生化学反应』

● We must wear safety goggles and gloves during handing experiment involving group 1 metal.『在做实验的时候,应该佩戴安全护目镜和手套』

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