ZON PENA

Introduction

• The Group I metals is called the Alkali Metals.
• This is because they form oxides and hydroxides that dissolve in water to give alkaline solutions.
• As shown in the diagram on the right, elements in this group are lithium, sodium, potassium, rubidium, caesium and fransium.
• They are the first element of a period, with one valence electron.
• This similarity (1 valence electron) makes them chemically behave in a similar manner.
• All alkali metals are very reactive. They must be stored in oil prevent reaction with oxygen or water vapour in air.

Physical Properties

Name	Proton number	Electron arrangement	melting point	boiling point	Density g/cm3
Lithium	3	2.1	180oC	1342oC	0.53
Sodium	11	2.8.1	98oC	883oC	0.97
Potassium	19	2.8.8.1	63oC	759oC	0.86
Rubidium	37	2.8.18.8.1	39oC	688oC	1.48
Caesium	55	2.8.18.18.8.1	29oC	671oC	1.87
Francium	87	2.8.18.32.18.8.1	27oC	677oC	> 1.87

• The table shows the physical properties and electron arrangement of Group 1 metals.
• All Group 1 metal exist as solid at room temperature.
• Since they are all metal, thus they have all the typical metallic properties, such as:

1. good conductors of heat
2. good conductors of electricity,
3. high boiling points,
4. shinny surface (but rapidly tarnished by air oxidation).

• Nevertheless, Group 1 metals also show some non-typical metallic properties, such as:

1. low melting points,
2. low density (first three float on water),
3. very soft (easily squashed, extremely malleable, can be cut by a knife).

Changes Down the Group

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Size of Atom

• Down the group, the size of atom increases.
• This is due to the increase of number of electron shells.
• Atom with more shells is bigger than atom with less shells.

Boiling Point and Melting Point

• The melting point and boiling point generally decrease down the group.
• All the atoms of Group 1 metals are bonded together by a force called metallic bond.
• The strength of metallic bond depends on the distance between the atoms.
• 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.
• Therefore, less energy is needed to overcome the metallic bond during melting process.
• Consequently, the melting point of Group 1 metal decreases down the group.

Density

• The densities of Group 1 metals are low compare with the other metals.
• The densities of the first 3 elements (Lithium, Sodium and Potassium) are lower than water. Thus, they can float on the surface of water.
• Nevertheless, the density increases steadily down the group.
• 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.

Important trends down the group with increase in atomic number .. size of atoms increases the melting point and boiling point decrease the density increases. the hardness decreases.

Chemical Properties

• Group 1 metals are very reactive metals.
• They all show the same chemical properties.
• They can react with water and non-metal such as oxygen and chlorine to form a new compound.

Electron configuration

Lithium	2.1
Sodium	2.8.1
Potassium	2.8.8.1
Rubidium	2.8.18.1
Cesium	2.8.18.18.1
Francium	2.8.18.32.18.1

• Table above shows the electron arrangement of all the Group 1 metals.
• As we did mention before, all the atoms of Group 1 metal consist of 1 valence electron.
• When an alkali metal atoms reacts, it loses the valence electron to form a positively charged ion. Example

• They tend to react mainly with non-metals to form ionic compounds.
• We will discuss in detail the formation of ion and ionic compound in next chapter.
• In this chapter, we are going to discuss 3 example of reaction of Group 1 metal:

1. Reaction with water.
2. Reaction with chlorine gas.
3. Reaction with oxygen gas.

The Reaction of Alkali Metals with cold water

• Group 1 metal react vigorously with water.
• The video below shows the reaction of Lithium, Sodium, Potassium, Rubidium and Caesium with water.
• Click the play button to play the video or click anywhere on the player to link to the video page in youtube.

More Video Prentice Hall (Quicktime video)

Observation

Metal	Observation
Lithium	Lithium floats on the surface of the water with with 'fizzing' sound. Colourless gas is released around the metal. Lithium metal moves slowly on the surface of water. The gas released can be ignited. If the gas is collected in a test tube, and then a lighted wooden splinter is brought close to the mouth of the test tube, a "pop" sound is heard. The solution turn blue when it is tested with universal indicator.
Sodium	Sodium also floats on the surface of the water with with 'fizzing' sound. Colourless gas is released around the metal, as what happen to lithium. The lump of sodium moves swiftly on the surface of water. The gas released can be ignited. If the gas is collected in a test tube, and then a lighted wooden splinter is brought close to the mouth of the test tube, a "pop" sound is heard. The solution turn blue when it is tested with universal indicator.
Potassium	Sodium also floats on the surface of the water. It reacts violently with water. Colourless gas is released around the metal. The gas produceed is ignited by the heat release by the reaction itself. If the gas is collected in a test tube, and then a lighted wooden splinter is brought close to the mouth of the test tube, a "pop" sound is heard. The solution turn blue when it is tested with universal indicator.

Discussion

• The reaction with water is highly exothermic (release a lot heat), very fast and violent.
• If a lump of lithium, sodium or potassium is placed in cold water, the metal floats, move around the surface of the water and then dissolve in the water.
• This shows that lithium, sodium and potassium are less dense than water.
• The substance produced is soluble in water.

• The colourless flammable gas is hydrogen. It produces "pops" sound with lit splint.
• Lithium and sodium do not normally cause a flame but the potassium reaction is exothermic enough to ignite the hydrogen.
• Rubidium and caesium are explosive with water. Normally, your teacher does not do this experiment in the school lab.

• If universal indicator is added, it changes from green (pH 7) to purple (pH 13-14), showing that the products are alkali (solution of hydroxide).

• The more reactive the metal, the more vigorous the reaction.
• The reactivity of the metal increases down the group.

Equation of the reaction
Lithium + Water → Lithium Hydroxide + Hydrogen Gas

Sodium+ Water → SodiumHydroxide + Hydrogen Gas

Potassium + Water → Potassium Hydroxide + Hydrogen Gas

The Reaction of Alkali Metals with Non-metals

• Group 1 Alkali Metals react with non-metals to form colourless or white ionic compounds.
• These compounds dissolve in water to give colourless solutions.

Reaction with oxygen

• The diagram above shows that when hot alkali metal is put into a gas jar filled with oxygen gas, the alkali metal will burn with bright flame.
• They form white oxide powders after reaction.
• These oxides dissolve in water to form strongly alkaline metal hydroxide solutions with pH value 13-14.
• Lithium, sodium and potassium have similar chemical properties. All react with oxygen to produce white metal oxide.
• The reactivity increases down the group from lithium, sodium to potassium.
• Table below shows the observation of lithium, sodium and potassium when burn in oxygen gas.

Observation

Lithium	Lithium burns with red flame and produces white powder immediately after reaction. When the white powder is dissolved in water, it produces a solution which turned red litmus paper blue.
Sodium	Sodium burned with bright yellow flame, forming white powder immediately after reaction. When the white powder is dissolved in water, it produces a solution which turned red litmus paper blue.
Potassium	Potassium burned with very bright purplish flame, forming white powder immediately after reaction. When the white powder is dissolved in water, it produces a solution which turned red litmus paper blue.

Equation

Lithium+ Oxygen Lithium Oxide

Sodium + Oxygen Sodium Oxide

Potassium + Oxygen Potassium Oxide

Reaction with chlorine

• The diagram above shows that when hot alkali metal is put into a gas jar filled with chlorine gas, the alkali metal will burn with bright flame.
• All alkali metals react with chlorine gas to form white metal chlorides salt.
• Lithium, sodium and potassium have similar chemical properties.
• The metal chlorides salt formed is soluble in water to give a neutral solution of pH 7.
• The reactivity increases down the group from lithium, sodium to potassium.
• Table below shows the observation of lithium, sodium and potassium burn in chlorine gas.

Observation

Lithium	Lithium burned slowly with a reddish flame . A white solid is produced.
Sodium	Sodium burned brightly with a yellowish flame. A white solid is produced. (The reaction is shown in the youtube video below.)
Potassium	Potassium burned very brightly with a purplish flame . A white solid is produced.

Equation

Lithium + Chlorine Lithium Chloride

Sodium + Chlorine Sodium Chloride

Potassium + Chlorine Potassium Chloride

Others related video: www.youtube.com/watch?v=VBReOjo3ri8&eurl Prentice Hall (Quicktime video): Showing reaction of sodium with chlorine gas to form white sodium chloride salt.

Explaining the Reactivity Trend of the Group 1 Alkali Metals

• When an alkali metal atom reacts, it loses its valence electron to form a positively charged ion.
  

Example

• As we go down the group from one element down to the next, the atomic radius gets bigger due to an extra filled electron shell.
• The valence electron is further and further from the nucleus. Thus the attraction force between the nucleus and the valence electron become weaker and weaker.
• This causes the valence electron is easier to be released to form an ion when the atom takes part in a reaction.

Solubility of the Oxide, Hydroxide and Salt of Alkali Metal

• All the oxide and hydroxide of group 1 metal are soluble in water to form an alkali solution.
• All the salt (salt of chloride, nitrate, sulphate, carbonate....) of group 1 metal are soluble in water. The solution formed are neutral.

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 tbe air.
• We must avoid to hold group 1 metals with bare hand because they may react with water on our hand.
• We must wear safety goggles and gloves during handling experiment involving group 1 metal.