The periodic table is a map of the elements. Section 1.3D

The periodic table has distinct regions. An atom’s position on the periodic table indicates the properties of its element. 3 main regions Metals on the left Nonmetals (except hydrogen) on the right Metalloids in between

An element’s position in the table also indicates how reactive it is. Reactive – how likely an elements is to undergo a chemical change Most elements are somewhat reactive and combine with other materials. The atoms of the elements in Groups 1 and 17 are the most reactive. The elements of Group 18 are the least reactive.

Most elements are metals. Metals – elements that conduct electricity and heat well and have a shiny appearance Malleable - can be shaped easily by pounding, bending, or being drawn into a long wire Metals are solid at room temp. (except mercury – liquid at room temp.)

Reactive Metals Group 1 (alkali metals) Very reactive Sodium and potassium stored in oil to keep away from air (react rapidly with oxygen and water vapor when exposed to air) Sodium and potassium ions, Na+ and K+, are important for life and play an essential role in the functioning of living cells

Reactive Metals Group 2 (alkaline earth metals) Less reactive than the alkali metals, but still more reactive than most other metals Calcium ions – essential part of your diet (bones and teeth) Magnesium – a light, inexpensive metal that is often combined with other metals when a lightweight material is needed (airplane frames)

Transition Metals Groups 3-12 Copper, gold, silver, iron Generally less reactive than most other metals Jewelry and coins from gold and silver because they are easily shaped and do not react easily Dimes and quarters – copper and nickel Pennies – zinc with a coating of copper

Transition Metals Important for industry Important for technology Steel is made partly of iron and is used for bridges and buildings. Most electric wires are made of copper Copper is used to make water pipes Important for technology Tungsten – tiny coil of wire inside incandescent light bulbs Platinum – in the catalytic converters that reduce pollution from cars

Transition Metals Alloys – two or more metals are combined to make materials that are stronger, less likely to corrode, or easier to shape than pure metals Steel – stronger than the pure iron that it contains and includes nickel, chromium, or manganese Brass – copper and zinc and is stronger than either metal alone Jewelry – alloy of copper and silver, stronger than pure silver

Rare Earth Elements Rare earth elements – the elements in the top row of the two rows of metals that are usually shown outside the main body of the periodic table (makes the table more compact) Often referred to as lanthanides – they follow the element lanthanum on the table

Rare Earth Elements Called rare earth elements because scientists once thought that they were only available in small amounts in Earth’s crust As mining methods improved, scientists learned that they were not so rare – just hard to isolate in pure form Uses Europium (Eu) – coating for some television tubes Praseodymium (Pr) – protective coating against harmful radiation in welder’s helmets

Nonmetals and metalliods have a wide range of properties. Nonmetals – to the right side of the periodic table and have properties the opposite of metals Many are gases at room temp, and one – bromine – is a liquid Solid nonmetals – often have dull surfaces and cannot be shaped by hammering or drawn into wires Generally poor conductors of heat and electric current

Halogens Group 17 – from the Greek words meaning “forming salts” Very reactive nonmetals that easily form compounds called salts with many metals Often used to kill harmful organisms (ex. Chlorine is used to clean drinking water and prevent growth of algae in swimming pools/iodine – used in hospitals to kill germs on skin)

Noble Gases Group 18 – noble, or inert gases – almost never react with other elements Argon gas – makes up about 1% of the atmosphere Colorful lights in signs – tubes filled with neon, krypton, xenon, or argon gas

Metalloids Metalloids – elements that have properties of both metals and nonmetals Lie on either side of a zigzag line separating metals from nonmetals Most common metalloid – silicon (2nd most common atoms in Earth’s crust)

Metalliods Make up semiconductors found in electronic devices (conduct electricity under some conditions and not under others) Silicon, gallium, and germanium are 3 semiconductors used in computer chips

Some atoms can change their identity. The identity of an element is determined by the number of protons in its nucleus. Chemical changes do not affect the nucleus, so they don’t change one type of atom into another. Isotopes have different numbers of neutrons and stability depends on the right balance of protons and neutrons. Too few or too many neutrons = unstable nucleus – particles are produced from the nucleus to restore balance

Some atoms can change their identity. When the particles are released, the change is accompanied by a release of energy. If the production of particles changes the number of protons, the atom is transformed into an atom of a different element. Radioactivity – the process by which atoms produce energy and particles (named by physicist Marie Curie in the early 1900’s)

Some atoms can change their identity. Most elements have radioactive isotopes, but are rare for small atoms Beyond bismuth (Bi) all of the isotopes are radioactive Study radioactivity with a Geiger counter, which detects the particles from the breakup of the nucleus with audible clicks; more clicks = more particles are being produced

Uses of Radioactivity in Medicine Radiation produced by unstable nuclei is used in hospitals to diagnose and treat patients To destroy harmful tumors without operation To monitor the activity of certain organs in the body In large doses it is harmful to living things and should be avoided Can damage or kill cells Energy from its particles can burn the skin Prolonged exposer has been linked to cancer and other health problems

Radioactive Decay Radioactive atoms produce energy and particles = identity changes because # of protons changes = radioactive decay Over time, all of the atoms of a radioactive isotope will change into atoms of another element. Radioactive decay occurs at a steady rate characteristic of the particular isotope. Half-life – the amount of time that it takes for one-half of the atoms in a particular sample to decay

Half-Life 1000 atoms of a radioactive isotope with a half-life of 1 year ­= 500 would change into another element over the course of a year In the next year, 250 more atoms would decay, (and so on) Half-life is not affected by conditions such as temp. or pressure. Half-lives can range from a small fraction of a second to many billions of years.