The Simplest MatterThe Simplest Matter

TV sets are common, yet each one is a TV sets are common, yet each one is a complexcomplex system. All of the different system. All of the different materials have one thing in common. They materials have one thing in common. They are made up of even are made up of even simplersimpler materials. materials.

One Kind of AtomOne Kind of Atom

Recall that matter is made up of only Recall that matter is made up of only oneone kind of atom. At least kind of atom. At least 115115 elements are elements are known and about known and about 9090 of them occur of them occur naturallynaturally on Earth. on Earth.

Examples of naturally occurring Examples of naturally occurring elementselements include the include the oxygenoxygen and and nitrogennitrogen in the air in the air you breathe and the metals you breathe and the metals gold, silver, gold, silver, aluminum,aluminum, and and iron.iron.

The other elements are known as The other elements are known as syntheticsynthetic elements. These elements have elements. These elements have been made in nuclear been made in nuclear reactionsreactions by by scientists with machines called particle scientists with machines called particle accelerators.accelerators.

Some synthetic elements are found in Some synthetic elements are found in smoke detectorssmoke detectors and and heart pace makers.heart pace makers.

The Periodic Table – Charting the The Periodic Table – Charting the ElementsElements

Chemists have created a chart called the Chemists have created a chart called the periodic tableperiodic table of the elements to help them of the elements to help them organize and display the elements.organize and display the elements.

Each Each elementelement is represented by a is represented by a chemical symbol that contains chemical symbol that contains 1 1 to to 33 letters.letters.

The symbols are an important part of an The symbols are an important part of an international system that is understood by international system that is understood by chemistschemists everywhere. everywhere.

The elements on the periodic table are The elements on the periodic table are organized by their organized by their properties.properties.

There are There are rowsrows and and columnscolumns that that represent relationships between the represent relationships between the elements. The elements in a row have the elements. The elements in a row have the same number of same number of energy levelsenergy levels. The . The columns are called groups. The elements columns are called groups. The elements in each in each groupgroup have similar properties have similar properties related to their related to their structurestructure..

Identifying CharacteristicsIdentifying Characteristics

Each element is different and has unique Each element is different and has unique properties. These differences can be properties. These differences can be described in part by looking at the described in part by looking at the relationship between the relationship between the atomic particlesatomic particles in each element.in each element.

Number of Protons and NeutronsNumber of Protons and Neutrons

Look at the example. The top number is Look at the example. The top number is the element’s the element’s atomic numberatomic number. It tells you . It tells you the number of the number of protons protons in the nucleus of in the nucleus of each each atomatom of the element. of the element.

IsotopesIsotopes

Every atom of the same element has the Every atom of the same element has the same number of protons. However, the same number of protons. However, the number of number of neutronsneutrons can vary even for one can vary even for one element. These elements are called element. These elements are called isotopesisotopes, which are atoms of the same , which are atoms of the same element that have different numbers of element that have different numbers of neutrons.neutrons.

You can tell someone exactly which You can tell someone exactly which isotope you are referring to by using its isotope you are referring to by using its mass numbermass number. An atom’s mass number is . An atom’s mass number is the number of the number of protonsprotons plus the number of plus the number of neutronsneutrons it contains. it contains.

Atomic MassAtomic Mass

The atomic mass is the The atomic mass is the weightedweighted average average mass of the isotopes of an element. The mass of the isotopes of an element. The atomic mass is the number found atomic mass is the number found belowbelow the element symbol.the element symbol.

The unit that scientists use for the atomic The unit that scientists use for the atomic mass is called the mass is called the atomic mass unitatomic mass unit which which is given the symbol is given the symbol u.u.

The calculation of atomic mass takes into The calculation of atomic mass takes into account the different account the different isotopesisotopes of the of the element.element.

Classification of ElementsClassification of Elements

Elements fall into three categories- Elements fall into three categories- metals, metals, metalloids,metalloids, and and non-metals.non-metals. The elements The elements in each category have similar properties. in each category have similar properties.

MetalsMetals generally have a shiny or metallic generally have a shiny or metallic luster and are good conductors of luster and are good conductors of heat heat and and electricity.electricity.

All metals except All metals except mercury mercury are solids at are solids at room temperature.room temperature.

Metals are Metals are malleablemalleable, which means they , which means they can be bent and pounded into various can be bent and pounded into various shapes. If you look at the periodic table, shapes. If you look at the periodic table, you can see that most of the elements are you can see that most of the elements are metals.metals.

Other ElementsOther Elements

Nonmetals are elements that are usually Nonmetals are elements that are usually dulldull in appearance. in appearance.

Most are poor conductors of heat and Most are poor conductors of heat and electricityelectricity. Many are . Many are gasesgases at room at room temperature.temperature.

The nonmetals are essential to the The nonmetals are essential to the chemical of life.chemical of life.

More than More than 9797 percent of your body is percent of your body is made up of various nonmetals.made up of various nonmetals.

Metalloids are elements that have Metalloids are elements that have characteristics of characteristics of metalsmetals and and nonmetals.nonmetals.

All metalloids are All metalloids are solidssolids at room at room temperature.temperature.

Some metalloids are shiny and many are Some metalloids are shiny and many are conductors, but they are not as good at conductors, but they are not as good at conducting heat and electricity as conducting heat and electricity as metals metals are.are.