Wednesday, 7 January 2015

4.3 Group 1 Elements

Physical properties
■ Elements of Group 1

 Lithium, Li Natrium, Na Kalium, K Rubidium, Rb Caesium, Cs Francium, Fr

The following mnemonic method can be used to memorize the sequence of elements in Group 1.
 ○ Little Nasty Kids Rub Cat's Fur
■ Physical properties of alkali metals

All alkali metals are grey in colour with shining surfaces just like other metals.

All alkali metals are soft and can cut easily.
 Elements Density (gcm-3) Melting point (℃) Boiling point (℃) Atomic radius (nm) Lithium, Li 0.534 186 1609 0.133 Natrium, Na 0.970 98 880 0.157 Kalium, K 0.860 64 760 0.203 Rubidium, Rb 1.530 39 700 0.216 Saesium, Cs 1.900 29 670 0.235

All alkali metal conduct heat and electricity.

All alkali metals have high melting and boiling point.
 ○ The melting and boiling point are not as high as other metals. ○ The melting and boiling point decrease down the group. This is because as the atomic radius increases, the bonds between the atoms become weaker.

The atomic radius and density of elements increase down the group.
 ○ An increase in the number of filled electron shells will result in increased atomic size, mass and density.

The animation below shows the changes in physical properties of Group 1 elements down the group.

Chemical properties
■ Arrangement of electron in alkali metals.

 Element Electron configuration Arrangement of electron Lithium 2.1 Natrium 2.8.1 Kalium 2.8.8.1 Rubidium 2.8.18.8.1 Caesium 2.8.18.18.8.1
■ Chemical reaction.

Alkali metals are very reactive elements and therefore must be kept in paraffin.

All alkali metals shows similar properties when reacting with certain compounds.
All alkali metals react vigorously with water to produce alkaline metal hydroxide solution and hydrogen gas.
All alkali metals burn in oxygen gas rapidly to produce solid metal oxides.
All alkali metals burn in halogen gas rapidly to produce white solid metal halides.

Brief explanation on the reaction of alkali metals.
 ○ All alkali metals have one valence electron. ○ They donate this electron to attain the noble gas stability. $Y\to {Y}^{\text{+}}+{e}^{\text{-}}$

The reactivity of alkali metals increases as down the group.

The animation below shows the explanation on the changes on the reactivity of alkali metals.

■ This video contains information about the physical properties and the reactions of the Group 1 elements.

 ⇲ For exercise(objective and subjective), download for free on Android OS.