The Alkali Metals Group - 1 / A

Agenda Introduction Lithium (Li) Sodium (Na) Potassium (K) Rubidium (Rb) Caesium (Cs) Francium (Fr)

Introduction The elements of 1st A group are all solid but soft at room temperature All are shiny metals that have to be kept under oil or in inert atmospheres because they are very reactive With the exception of the radio active and extremely rare Francium, these shiny metals react rapidly with oxygen in the air, so that their surfaces quickly become dull. Caesium is the most chemically reactive of all the elements in this group, and spontaneously catches fire in air.

Introduction – cont. The atoms of this elements all have just one electron in there outer shell – this is why they are so reactive. All group-1 elements react violently in water displacing hydrogen ions to produce hydrogen gas (H+), leaving an excess of hydroxide ions (OH-) in solution in the remaining water. Any solution with more (OH -) than (H+) ions is alkaline, hence the name of the group : dissolving these elements in water results in a strongly alkaline solution.

Lithium (Li) Lithium is the least dense solid element, and one of the most reactive metals It was discovered in 1817 by Swedish chemist Johan Arfwedson. Its atomic number is 3 The surface of the metal reacts slowly with oxygen from the air to form a dull grey layer of lithium oxide and hydroxide Lithium compounds are used in the glass and ceramics industry. Characteristic red light produced by a lithium compound in a flame – the light is produced by electrons that after being excited by heat drop to a lower energy level.

Sodium (Na) Sodium is the sixed most abundant element in Earth’s crust, and there are more than 10 kg of it, as dissolved sodium ions (Na+), in every cubic metre of sea water. Sodium metal is a soft, silvery metal similar to lithium, which will react violently with water, producing hydrogen gas. Liquid sodium is used as a coolant in some nuclear power stations. Pure sodium is used in the manufacture of sodium lamps (street lighting). Atomic number - 11

Potassium (K) Potassium is the seventh most abundant element in Earth’s crust The pure metal is produced industrially by heating potassium chloride (KCl) from potassium –bearing minerals with pure sodium vapour. Potassium metal reacts violently with water being dripped on to it from above. The three most important potassium compounds are: Potassium chloride (KCl) Potassium nitrate (KNO3) Potassium hydroxide (KOH) Potassium was first discovered by English chemist Humphry Davy Atomic number - 19 b

Rubidium (Rb) It is the sixteenth most abundant element in Earth ‘s crust. It was discovered in 1861 by German chemists Robert Bunsen and Gustav Kirchhoff. Only about 3 tonnes of pure rubidium are produced each year Rubidium melts at 39.3 Celsium; it can become molten on a hot summer day. The radioactive isotope rubidium – 87 is used in medicine: it is absorbed into blood cells. Atomic number - 37

Caesium (Cs) Unlike other elements in Group- 1, pure cesium has a slide golden tinge. It was discovered in 1861 by Robert Bunsen and Gustav Kirchhoff. The name is from the Latin Caesius, meaning “sky blue” Melting point – 28.4 C. / Caesium can become liquid in a warm room. Used in atomic clocks. Atomic number - 55

Francium (Fr) This is the last of the alkali metals, discovered in 1939 by French physicist Marguerite Perey. The element was named after Perey’s native country. It has a melting point of 28 C. The largest sample of francium ever prepared, consisting of only about 300,000 atoms was made by bombarding gold atoms with oxygen atoms. Francium occurs naturally, probably not more than a few grams at any one time in the whole world It is the product of other radioactive elements

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