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 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 reactivity（reactivity 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
● 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 oxygen，O2
● to produce metal oxide.
● Lithium + oxygen → Lithium oxide
4Li + O2 → 2Li2O
● Sodium + oxygen → Sodium oxide
4Na + O2
→ 2Na2O
Reaction with Chlorine gas，Cl2
● to produce metal chloride.
● Lithium + Chlorine → Lithium chloride
2Li + Cl2
→ 2LiCl
● Sodium + Chlorine → Sodium chloride
2Na + Cl2
→ 2NaCl
● 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』
