Elements An element is a pure substance that cannot be separated into simpler substances by physical or chemical means An element is a pure substance that cannot be separated into simpler substances by physical or chemical means A pure substance is a substance in which there is only one type of particle A pure substance is a substance in which there is only one type of particle

Because elements are pure substances, each element contains only one type of particle Because elements are pure substances, each element contains only one type of particle For example, every particle in a 5 gram nugget of the element gold is like every other particle of gold For example, every particle in a 5 gram nugget of the element gold is like every other particle of gold The particles of a pure substance are alike no matter where that substance is found. The particles of a pure substance are alike no matter where that substance is found. Although a meteorite might travel more than 248 million miles to reach Earth, the particles of iron in a meteorite are identical to the particles of iron in objects around your home. Although a meteorite might travel more than 248 million miles to reach Earth, the particles of iron in a meteorite are identical to the particles of iron in objects around your home.

Every element has a unique set of properties Each element has a unique set of properties that allows you to identify it Each element has a unique set of properties that allows you to identify it This unique properties are called characteristic properties This unique properties are called characteristic properties Some characteristic properties are physical properties Some characteristic properties are physical properties –Boiling point –Melting point –Density

Some of these characteristic properties are chemical properties Some of these characteristic properties are chemical properties –Flammability –Reactivity with acid –Reactivity with water For example, helium and krypton are unreactive gases For example, helium and krypton are unreactive gases Comparing the density of helium and krypton demonstrates their unique characteristic properties Comparing the density of helium and krypton demonstrates their unique characteristic properties –Helium is less dense than air so a balloon filled with helium will float up –Krypton is more dense than air so a krypton filled balloon will sink to the ground

Identifying elements by their properties Comparing cobalt, iron and nickel you might consider: Comparing cobalt, iron and nickel you might consider: –Melting point –Density –Conduct electricity –React with oxygen Other properties might be Other properties might be –Color –Hardness –Texture –Flammability (ex: hydrogen and carbon) –React with water (ex: sodium and lithium) –React with acid (ex: zinc)

Elements are classified by their properties Elements are classified into groups according to their shared properties. Elements are classified into groups according to their shared properties. For example, cobalt, nickel, and cobalt For example, cobalt, nickel, and cobalt –All three are shiny, and all three conduct thermal energy and electric current Scientists have grouped these three elements, along with other similar elements, into one large group called metals Scientists have grouped these three elements, along with other similar elements, into one large group called metals Metals are not all exactly alike, but they do have some properties in common Metals are not all exactly alike, but they do have some properties in common

If you know the category--- you know the properties It is shiny, hard, malleable and conducts electricity-----it must be a METAL!!

3 Categories of Elements Metals Metals –Shiny, good conductors of thermal energy,and electrical current, malleable and ductile Nonmetals Nonmetals –Dull, poor conductors of thermal energy and electric current, brittle and unmalleable Metalloids (semiconductors) Metalloids (semiconductors) –Have properties of both metal and nonmetals –Some or shiny, they are somewhat malleable and ductile. Some conduct thermal energy and electric current

Examples of Metals: Examples of Metals: –Iron, cobalt, nickel, aluminum, magnesium, calcium, zinc, chromium, copper, silver, gold, mercury Examples of Nonmetals: Examples of Nonmetals: –Carbon, nitrogen, oxygen, sulfur, chlorine, argon, neon, helium, hydrogen, radon, krypton All of the Metalloids All of the Metalloids –Boron, silicon, germanium, arsenic, antimony, tellurium

Elements are displayed in a Periodic Chart of Elements Elements are displayed in a Periodic Chart of Elements Elements in the periodic chart are assigned a symbol Elements in the periodic chart are assigned a symbol A symbol is a short hand way of identifying the element A symbol is a short hand way of identifying the element Examples of element symbols are: Examples of element symbols are: –H for hydrogen, C for carbon Some symbols have two letters: Some symbols have two letters: –He for helium, Co for cobalt Some symbols derive from other languages: Some symbols derive from other languages: –Fe for iron, Au for gold, Ag for silver

Periodic Table of Elements Black is solid blue is liquidpurple is gas Symbols are in different colors to indicate state of matter