Organizing the Elements

Dmitri Mendeleev -discovered set of patterns that applied to all elements -1869 published 1st periodic table -total of 63 elements discovered -wrote properties of each on note cards (density, color) -noticed pattern when he arranged them in order of increasing atomic mass

Atomic Mass Periodic Table -average mass of all isotopes of an element -properties of elements repeat in each row of table

Henry Moseley -1913, discovered how to measure protons = atomic number -table rearranged by atomic number

-series of different elements (like days in a week) -horizontal rows -series of different elements (like days in a week) -18 vertical columns -elements with similar characteristics -includes: atomic number chemical symbol name atomic mass Periods Groups/Families Element Squares

Chemical Symbol Average Atomic Mass -one or two letters representing an element -abbreviations of English and Latin names -most elements consist of mix of isotopes -determined from combined percentages of all isotopes

Metals

Metal -shininess, malleability, ductility, conductivity -characterized by physical properties -shininess, malleability, ductility, conductivity -some are magnetic: iron (Fe), nickel (Ni) -most are solid at room temperature, except mercury (Hg) - liquid

Malleable Ductile Conductivity hammered/ pounded into shapes -pulled out into wires -ability to transfer heat or electricity to another object

Reactivity -chemical property -ease at which an element reacts with other elements/compounds -usually react by losing electrons -↓ from highly reactive to less reactive as you move left to right across table

-wearing away of metal -due to chemical reaction -group 1 -loses one electron -extremely reactive -never found uncombined in nature, only in compounds Corrosion Alkali Metals

-when pure: shiny and very soft (cuts with plastic knife) Alkali Metals -when pure: shiny and very soft (cuts with plastic knife) -sodium (Na) and potassium (K) important for life *salt, foods -lithium (Li) *batteries, medicines

Alkaline Earth Metals -group 2 -loses two electrons -fairly hard, gray-white -good conductors -very reactive -never found uncombined -magnesium (Mg) plus aluminum = light weight material used for ladders, wheels, planes -calcium (Ca) essential for bones, teeth in milk, dairy, green veggies

Transition Metals -groups 3-12 -iron (Fe), copper (Cu), silver (Ag) -most hard and shiny -all good conductors of electricity -less reactive than groups 1 and 2

Metals in mixed groups Lanthanides -groups 13-15 -not very reactive -aluminum (Al), tin (Sn), lead (Pb) -top row at bottom of table -soft, malleable, shiny, high conductivity -mixed to make alloys -many found together; difficult to separate

Alloy Actinides -mixture of two or more metals -below lanthanides -only actinium (Ac), thorium (Th), protactinium (Pa), and uranium (U) occur naturally *U used for energy in nuclear power plants -all elements heavier than U created in labs *nuclei very unstable *many only last a fraction of a second after made

Synthetic Elements Particle Accelerators -higher than #92 -synthesized when nuclear particles are forced to crash into each other -move atomic nuclei faster and faster -when crash, enough energy to make a single nucleus -heavier than 95

Nonmetals and Metalloids

Nonmetal -lacks most properties of metals -poor conductors -good insulators -dull and brittle -10 of 16 are gases at room temp -bromine (Br) only liquid at room temp -reactive with other elements; form compounds easily -gain or share electrons -fluorine (F) most reactive element

Carbon Family -group 14 -gain, lose, share 4 electrons -only carbon (C) is nonmetal -C found in all living thing -many fuels contain C: coal, gasoline

Boron Family group 13 have 3 valence electrons Boron (B) is the only metalloid, all other are metals most common metal is aluminum (Al)

Nitrogen Family Diatomic molecule -group 15 -two nonmetals: nitrogen (N) and phosphorous (P) -gain, share 3 electrons -80% atmosphere is N gas (N2) -consists of two atoms (N2, O2)

-P used to make matches (reacts with oxygen) Nitrogen Family -N is useful in fertilizer -P more reactive than N -P used to make matches (reacts with oxygen)

-group 16 -3 nonmetals: oxygen (O), sulfur (S), selenium (Se) -gain, share 2 electrons -O necessary for life (O2) - is ozone (filters radiation from sun) -O highly reactive (reacts with almost all other elements -O most abundant element in crust -S used to make rubber bands, tires Oxygen Family

Halogen Family -group 17 -fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At -salt forming -gains, shares 1 electron -very reactive -dangerous to humans uncombined -useful when combined (F prevents tooth decay, Cl used in table and rock salt)

Noble Gases -group 18 -un-reactive -don’t gain or share electrons -Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), Radon (Rn) -exist in small amounts in atmosphere -used in electric lights, (He) in balloons

Hydrogen -above group 1 -simplest, smallest element -1 proton, 1 electron -makes up 90% of atoms, but only 1% of mass of crust, oceans, atmosphere -most in form of water (H2O)

Metalloids -characteristics of metals and nonmetals -zig za -all solid at room temp -brittle, hard, somewhat reactive -most common silicon (Si) -Si makes up sand, which makes glass -most useful prop is varying ability to conduct electricity *depends on temp, light, impurities

Semiconductors -conduct electricity under some conditions, but not others -used for computer chips, transistors, lasers