Elements Elements – pure substance that cannot be broken down by physical or chemical means Pure substance – a substance that contains only one type of particle. Elements have characteristic properties that do not depend on amount of material present Most elements are combined in nature –Examples H 2 O (water) CaF 2 - fluorite

Atoms Have  Protons – positive charged particles  Neutrons – neutral charged particles  Protons and neutrons are found in center of atom, called a nucleus

Atoms Surrounding nucleus are  Electrons – negative charge particles  This region is called the electron cloud or energy levels

Atoms Atomic number- number of protons in the nucleus Mass number (atomic mass)- number of protons plus neutrons

Isotopes The number of protons in an element never changes. The number of neutrons in an element may change. Isotope- a variation of an element that differs only in the number of neutrons. Examples (hydrogen): –protons neutrons 1 0(hydrogen) 1 1(deuterium- heavy water) 1 2(tritium- radioactive)

Metals Shiny Good conductors of heat and electricity Malleable – flattened into thin shapes Ductile – drawn into thin wires Can be solid or liquid Copper, lead and tin are examples

Nonmetals Dull (not shiny) Poor conductors of heat and electricity Brittle Can be solid, liquid or gas Bromine, sulfur and neon are examples

Metalloids Have properties of metals and nonmetals Many are called semiconductors Dull or shiny Some can be malleable or ductile Examples include antimony, silicon, boron

Dmitri Mendeléev In 1869, Dmitri Mendeléev created the first version of the periodic table. Grouped elements based on atomic mass Found elements in same group had similar chemical properties. Blank spaces were left open to add the new elements Just over 50 elements were known then.

The Periodic Table Rows = Periods -no similar properties -1 st element = reactive metal -last element = non reactive gas Columns = Groups/Families -have similar properties -have same number of valence electrons - examples lithium, sodium and potassium

Hydrogen -single element with its own classification -sits atop Group IA -1 electron in its only energy level IA

Alkali Metals -Group IA elements, excluding hydrogen (all metals) -always combined with other elements in nature -1 electron in its outer energy shell IA

Alkaline Earth Metals -Group IIA elements (all metals) -always found combined with other elements in nature -2 electrons in its outer energy shell IIA

Transition Elements -Group B elements (all metals) -many found combined with other elements in nature, some found in their elemental state (gold and silver) -varying numbers of electrons in outer energy shell B

Boron Family -Group IIIA elements (boron = metalloid, rest are metals) -always found combined with other elements in nature -3 electrons in its outer energy shell IIIA

Carbon Family -Group IVA elements (nonmetal, metalloids and metals) -mostly found combined with other elements in nature but may be found in its elemental state (e.g. diamond and graphite) -4 electrons in its outer energy shell IVA

Nitrogen Family -Group VA elements (nonmetals, metalloids and a metal) -mostly found combined with other elements in nature –5 electrons in its outer energy shell VA

Oxygen Family -Group VIA elements (nonmetals, metalloids and a metal) -mostly found combined in nature but may be found in its elemental state (e.g. sulfur) -6 electrons in its outer energy shell VIA

Halogens -Group VIIA elements (nonmetals and a metal) -mostly found combined with other elements in nature -7 electrons in its outer energy shell VIIA

Noble Gases -Group VIIIA elements (nonmetals) -never found combined with other elements in nature -contain a full set of electrons in its outer energy shell VIIIA

Rare-Earth and Radioactive Elements -the last two rows of the Periodic Table -Lanthanide series (rare-earth elements) -Actinide series (radioactive elements- most are human-made) B