3. The Periodic Table

i zinc all the good jokes about this argon!

element

a substance that cannot be split into simpler substances by chemical means

greek philosophers thought…

four elements - earth, air, water, fire

robert boyle

defined an element as a substance that cannot be split into simpler substances

humphry davy

used electrolysis to split compounds into their elements

humphry davy discovered…

strontium, potassium, calcium

johann dobereiner

introduced triads

triad

a group of three elements with similar chemical properties in which the atomic weight (relative atomic mass) of the middle element is approxiamtely equal to the average of the other two

dobereiner triad example

Li, Na, K

john newlands <3

introduced the law of octaves

newland's law of octaves

when elements are arranged in order of increasing atomic weight, the properties of the elements repeat every eighth (after seven) elements

dimitri mendeleev

left gaps for undiscovered elements, reversed order of Te and I to fit into groups which better suited their chemical properties

mendeleev's periodic law

when elements are arranged in order of increasing atomic weight, the chemical properties of the elements recur periodically

modern periodic law

when elements are arranged in order of increasing atomic number, the chemical properties of the elements recur periodically

henry moseley <3

arranged elements in order of increasing atomic number

vertical columns of periodic table are called…

groups

horizontal rows of periodic table are called…

periods

groups are made up of elements that…

share chemical properties

group 1 name

alkali metals

group 1 properties

very reactive - stored in oil, soft - cut with knife, lustrous - dulls when exposed to air

group 1 reactions

metal + O2 -> metal oxide, metal + H2O -> hydrogen gas + metal hydroxide

group 2 name

alkaline earth metals

group 2 properties

not as reactive as group 1

group 7 name

halogens

group 7 properties

very reactive non-metals, low boiling points

group 8 name

noble gases

group 8 properties

very stable, unreactive. helium used in balloons, argon used in lightbulbs