2.1 Nature of Matter

Atoms Atoms are the basic unit of matter Theorized by Democritus, 2500 yrs ago Composed of 3 subatomic particles –Protons –Neutrons –Electrons

Nucleus Center of the atom Made up of the protons and neutrons –Protons (+) charge –Neutrons (= or neutral) charge # of protons and neutrons make up the atomic mass number

Electrons Very important in bonding with other elements (-) charge Attracted to the positively charged nucleus Remains outside the nucleus in a cloud Usually has the same number of electrons as protons Maintains electrically neutral atoms Very small compared to protons and neutrons

Elements A pure substance that consists of entirely of one type of atom A list of all the elements can be found in the periodic table

Isotopes Elements which have different numbers of neutrons All isotopes have the same number of protons giving them the same properties

Isotopes Can be radioactive- unstable nuclei that breakdown over time Can be used for many things- –Dating materials –Detect and treat cancers –Kill bacteria

Chemical Compounds Substance formed by the chemical combination of two or more elements Always form in the same proportions –EX: H 2 O, CO 2 Chemical compounds have very different characteristics compared to their elemental components.

NaCl Sodium- silvery, white metal –Explosive, if exposed to oxygen Chlorine- poisonous green gas –Extremely harmful to humans + =

Chemical Bonds Ionic and covalent bonds are the main types of bonds Ionic- forms between metals and nonmetals –Forms through a transfer of electrons Covalent- forms between two nonmetals –Produced through a sharing of electrons