Page 186 - Chemistry ICSE Class X

7 Metallurgy

Till now, scientists have discovered 118 elements. Each of the 118 elements
CONTENTS is unique. Each has its own fascinating story. The discovery of the elements
started about 8000 years ago, when people obtained shiny materials from
ͻ ůĂƐƐŝĮĐĂƟŽŶ ŽĨ ĞůĞŵĞŶƚƐ the rocks simply by heating.
ͻ WŽƐŝƟŽŶ ŽĨ ŵĞƚĂůƐ ĂŶĚ ŶŽŶŵĞƚĂůƐ ŝŶ
ƚŚĞ ƉĞƌŝŽĚŝĐ ƚĂďůĞ In this way, soft materials, such as copper, silver and gold were
ͻ ůŬĂůŝ ŵĞƚĂůƐ discovered. These were followed by lead, tin, iron, mercury, carbon and
ͻ ůŬĂůŝŶĞ ĞĂƌƚŚ ŵĞƚĂůƐ sulphur. By the middle of the eighteenth century, phosphorus, zinc,
ͻ KĐĐƵƌƌĞŶĐĞ ŽĨ ŵĞƚĂůƐ arsenic, antimony and bismuth were discovered. The number of known
ͻ DĞƚĂůůƵƌŐLJ elements increased from 21 to 50 between 1775 and 1830.
ͻ ƌƵƐŚŝŶŐ ĂŶĚ ƉƵůǀĞƌŝƐĂƟŽŶ By 1940, all the 90 naturally-occurring elements had been discovered.
ͻ ŽŶĐĞŶƚƌĂƟŽŶ ŽĨ ƚŚĞ ŽƌĞ So far, at least 26 man-made elements have been prepared.
ͻ ĂůĐŝŶĂƟŽŶ ĂŶĚ ƌŽĂƐƟŶŐ
ͻ džƚƌĂĐƟŽŶ ŽĨ ŵĞƚĂůƐ ďĂƐĞĚ ŽŶ ƚŚĞŝƌ Classification of Elements
ƉŽƐŝƟŽŶ ŝŶ ƚŚĞ ĂĐƟǀŝƚLJ ƐĞƌŝĞƐ
ͻ ZĞĮŶŝŶŐ ŽĨ ŵĞƚĂůƐ How are elements classified
ͻ džƚƌĂĐƟŽŶ ŽĨ ĂůƵŵŝŶŝƵŵ
ͻ hƐĞƐ ŽĨ ŝƌŽŶ͕ njŝŶĐ ĂŶĚ ĂůƵŵŝŶŝƵŵ #NN GNGOGPVU CTG ENCUUKſGF KPVQ VJTGG ECVGIQTKGU
ͻ ŽƌƌŽƐŝŽŶ ;Žƌ ƌƵƐƟŶŐͿ ŽĨ ŝƌŽŶ ƒ Metals ƒ Nonmetals ƒ Metalloids
ͻ ůůŽLJƐ
Metalloids are those elements which behave like both metals and
nonmetals.
Table 7.1 Examples of metals, nonmetals and metalloids
Metals Nonmetals Metalloids
Gold (Au) Hydrogen (H) Boron (B)
Silver (Ag) Oxygen (O) Silicon (Si)
Copper (Cu) Nitrogen (N) Germanium (Ge)
Iron (Fe) Sulphur (S) Arsenic (As)
Mercury (Hg) Carbon (C) Antimony (Sb)
Zinc (Zn) Phosphorus (P)

What are metals
Bronze Age artefacts Metals are the elements (except hydrogen) which form cations (positive
ions) by losing electrons. Thus, metals are electropositive elements. Gold,
dŚĞ ĞůĞŵĞŶƚ ϭϬϵ ǁĂƐ ŵĂĚĞ ŝŶ ϭϵϴϮ silver, copper, tin, lead, iron, mercury are typical metals. These metals
ďLJ Ă tĞƐƚ 'ĞƌŵĂŶ ƌĞƐĞĂƌĐŚ ƚĞĂŵ͘ were known to the ancient people.
dŚĞ ŵŽƐƚ ƌĞŵĂƌŬĂďůĞ ƚŚŝŶŐ ĂďŽƵƚ n+ –
ƚŚŝƐ ƌĞƐĞĂƌĐŚ ǁĂƐ ƚŚĂƚ ŽŶůLJ ŽŶĞ ĂƚŽŵ M o M + ne
metal atom cation electrons
ŽĨ ĞůĞŵĞŶƚ ϭϬϵ ǁĂƐ ĚĞƚĞĐƚĞĚ͘ /ƚ
ƐƵƌǀŝǀĞĚ ŽŶůLJ ĨŽƌ ƚŚĞ ƉĂƌƚ ŽĨ Ă ƐĞĐŽŶĚ͘
ŽŵƉƵƚĞƌ ĐĂůĐƵůĂƟŽŶƐ ƉƌĞĚŝĐƚ ƚŚĂƚ What are nonmetals
ƚŚĞ ĞůĞŵĞŶƚƐ ŚĂǀŝŶŐ ĂƚŽŵŝĐ ŶƵŵďĞƌƐ The elements which tend to form anions (negative ions) by gaining
ϭϭϬ͕ ϭϭϲ͕ ϭϮϲ͕ ͘͘͘ ϭϴϰ ƚŽ ďĞ ƌĞĂƐŽŶĂďůLJ electrons are termed nonmetals. There are 22 nonmetals.
ƐƚĂďůĞ͘
tŝƚŚ ƚŚĞ ƉƌĞƉĂƌĂƟŽŶ ŽĨ ďƌŽŶnjĞ͕ ĂďŽƵƚ X + ne – o X n–
ϱϬϬϬ LJĞĂƌƐ ĂŐŽ͕ ďĞŐĂŶ ƚŚĞ ƌŽŶnjĞ ŐĞ͘ atom of nonmetal anion