Chemistry Topic 2 - Atoms and Elements

Element

substance made of only one type of atom that can’t be split into anything simpler by chemical means

Compound

formed when two or more elements chemically combine, harder to separate with a fixed melting/boiling point

Mixture

various substances mixed but not chemically bonded together that can be separated by physical means and melts/boils over a range of temperatures

Groups in the Periodic Table

vertical columns; tells you number of electrons in outer shell

Periods in the Periodic Table

horizontal rows; tells you number of electron shells

Atom

smallest piece of an element that can still be recognised as that element

Atomic/Proton number

number of protons in an atom’s nucleus which determines the element; same as number of electrons (unless ion)

Mass/Nucleon number

total number of protons and neutrons in the nucleus of the atom

Isotope

atom with the same proton number but different mass number (i.e. different number of neutrons)

Relative Atomic Mass (A_r)

the mean weighted mass of all isotopes of an element relative to C-12, which has a mass of 12

electronic configuration

arrangement of electrons in an atom