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The gold leaf The gold leaf Metals have peculiar properties like ductility and malleability. Due to rearrangement of loosely bound electrons a metal can be hammered into sheets, called malleability and can be drawn into wires, called ductility. Gold is a highly ductile and malleable metal in periodic table. Gold leaf is an ultra–thin layer (sheet) of pure gold used by crafters to create a gilded appearance on projects such as picture frames, sculptures and book bindings. Gold can be hammered into layers of few nanometers thickness. Rutherford used these gold foils in his Alpha–ray scattering experiment to describe the atomic structure.

Learning Objectives

After completing the topic, the student will be able to:

  • Define metals, non-metals and metalloids.
  • Recognize metals, metalloids and non-metals in periodic table.
  • Define metallic bond and recognize how it is different from covalent and ionic bonds.
  • Examine the electron fluid model of metallic bond.
  • Discuss the physical properties of metals such as ductility, malleability etc., of metals.
  • Give the reactivity series of metals based on their chemical behaviour.
  • Discuss the physical and chemical properties of non–metals and compare with metals.
  • List some important non-metals and give their uses.
Classification of elements Across a period, the elements change from metals through metalloids to non-metals. For example, in period 3, sodium (the extreme left element) is a very reactive metal whereas, chlorine (before argon at extreme right) is a very reactive non-metal. Silicon located in between acts as a metalloid. Note that metals occupy a major portion of periodic table.
Grouping of elements

There are about 90 elements, up to Uranium, that are found naturally. Another 26 elements, beyond Uranium, called trans–uranium elements, have been produced artificially in the laboratories by nuclear reactions. The chemical behavior of all elements depends on their electronic configurations. It is the electrons that take part in chemical reactions and therefore their interactions are the main factors that determine the outcome of a chemical reaction.

Depending on the availability of "free" electrons, elements can be classified as metals, metalloids and non–metals. Free electrons are unbound electrons, beyond closed shells. In metals, these unbound electrons are given off or donated during compound formation. Examples of metals are Sodium (Na), Potassium (K), Gold (Au). In non–metals, there are no free–electrons, instead there is a deficiency of electrons. While forming compounds, non–metals borrow electrons. Examples of non–metals are Carbon (C), Oxygen (O), Nitrogen (N), Chlorine (Cl). Metals are shown on the left–hand side and center of the periodic table. Non–metals are placed on the right hand side of the periodic table. Chemically inert gases like Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr) and Xenon (Xe) are included in the category of non–metals.

The electrical and thermal conductivity is relatively high for metals, low for metalloids and negligible for non-metals.

Silicon is a component various gadgets Silicon based devices and gadgets The silicon wafer/disk contains hundreds of individual chips, each consisting of several electronic components. After all the individual components have been added, the disk will be cut to give separate chips and packaged as integrated circuits (ICs) - Top row, which are the heart of any electric gadget such as mobile phones and laptops (bottom row).

Elements placed in between the metals and non–metals in the periodic table are called metalloids. Metalloids (also called semi-metals) form a bridge between strictly metal elements and strictly non–metal elements. These elements have properties in common with metals and non-metals. Metalloids are brittle like non-metals. In general, they are mostly non-metallic in their chemical behavior and form alloys. Metalloids are dull like non–metals but conduct heat and electricity like metals. Metalloids are only seven in number. These are Boron (B), Silicon (Si), Germanium (Ge), Arsenic (As), Antimony (Sb), Tellurium (Te) and Selenium (Se).

Of these Si and Ge are called semiconductors. Silicon, the most abundant metalloid on earth is tetravalent. It is a chemical element with a symbol ‘Si’ and atomic number 14. It is less reactive than its chemical analog carbon.

Silicon devices dominated the micro-electronic industry as silicon is a low-cost material that can be used to build semiconductors. However, there is an increasing interest for silicon-germanium (SiGe) for its low power consumption, and cost saving property and it is a material of choice for both wireless integrated circuits and radio-frequency chips.

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