Elements on Planet Earth In the Air , In the Crust, In the Water. Background • Our understanding of the elements has progressed from the Fire, Air, Earth, Water stage to the current theory that everything is composed of atoms. Elements In the Atmosphere • In the atmosphere there are a number of elements. • These are – Nitrogen 78.03 % – Oxygen 20.99 % – Argon 0.94 % – CO2 0.04 % Surprised? Elements In the Atmosphere • Oxygen is so reactive it cannot exist for more than a moment as an uncombined atom. It combines to form O2 • This is called a diatomic molecule • Nitrogen is essential to all life. It is also a diatomic molecule. • Let’s look at Nitrogen… Nitrogen In the Atmosphere • Nitrogen is an element • It’s symbol is N • The smallest particle of nitrogen is the nitrogen atom - N • Nitrogen exists in the atmosphere as a diatomic molecule - N2 • There are other elements in the atmosphere – H2O , H2S CO2 In the Atmosphere • In the 17th century people began to burn coal to heat houses and provide energy for commercial use. • In the 19th century we began to burn petroleum fro cars and industry. • The result has been an increase in the amount of CO2 in the atmosphere. • Increased CO2 is predicted to cause global warming. – How will warming affect the earth? The Hydrosphere • Many elements are locked in compounds. • One of the most important compounds is H20. • Water is essential for life and is a solvent for many other substances. • Most compounds are soluble in water. • All of the water in the hydrosphere contains dissolved compounds. The Hydrosphere • Animals living in water depend on dissolved O2 to breathe • Plants that live in water depend on dissolved CO2 to breathe • Sea water contains NaCl , KCl and CaCl2 • These compounds come from rocks and soil that have been washed into solution by rain. The Crust • There are many elements in the Earth’s crust • Some - Au, Ag, C - are found as elements. Others are found combined as compounds. • Elements that are stable can be found as atoms of pure substance. • Atoms that are very reactive are found as parts of compounds. Cycling The Elements • Elements and compounds cycle through the atmosphere, hydrosphere and crust. • This prevents a buildup of elements in a particular part of the Earth. • Life on Earth needs this cycling – CO2 to O2 + C – Nitrogen • Photosynthesis and respiration make use of the elements hydrogen, oxygen and carbon, cycling them through the atmosphere. Photosynthesis and Respiration • Respiration: what animals do Glucose + oxygen --> carbon dioxide + water + energy Or C6H1206 + 6 O2 -----------> 6 CO + 6 H2O + ENERGY • Photosynthesis: what plants do Sunlight + carbon dioxide + water --> glucose + oxygen Or 6 CO + 6 H2O + ENERGY -----> C6H1206 + 6 O2 Metals Metals • All elements can be classified as metals , non-metals or metalloids. • Metals comprise the majority of the elements. • Metals have a characteristic set of properties. Metals • Metals … – can be moulded into shapes (malleable) – can be formed into thin wires (ductile) – conductors or heat and electricity (conductivity) – have characteristic lustre or sheen – High melting and boiling point (except mercury) Non-metals • Non-metals … – Are usually brittle. – Are poor conductors of heat and electricity. – Have a dull surface (solids) – Have lower melting and boiling points - often gaseous at room temperature. Metalloids • Metalloids have some metal and some non-metal properties. They are usually – Solid at room temperature with high boiling temps – Good thermal insulators – Brittle and non-ductile – May or may not be good conductors of electricity. In the Periodic Table • Metals are found on the left side of the table with the most active metal in the lower left corner. • Nonmetals are found on the right side with the most active nonmetal in the upper right hand corner of the chart. • Since the most active metals react with water to form bases, the Group I metals are called alkali metals. • Elements found along the dark line in the periodic table are called metalloids. They are the elements which have certain characteristics of metals and other characteristics of nonmetals. • Some examples of metalloids are boron, silicon, arsenic, and tellurium.