chemistry: atoms, the building blocks of matter

atomic number

(Z) is the number of protons of each atom of an element

mass number

(A) is the total number of protons and neutrons that make up an atom

neutrons

neutral particles in the nucleus. heavy like protons (weight a little more)

isotope

number of protons of a given atom never changes. number of neutrons can change. two atoms with different number of neutrons are...

atomic mass

(atomic weight) weighted average mass of an atom in a naturally occurring sample of elements. decimal on periodic table

protons

in the nucleus of the atom, positive charge (+) larger and heavier than electrons

electrons

negative charged (-), move around outside nucleus. tiny light particles

dalton's atomic theory: one

ALL elements are composed of tiny indivisible particles called atoms

dalton's atomic theory: two

atoms of the same element are identical. the atoms of one element are different from those of another element

dalton's atomic theory: three

atoms of different elements can physically mixed together or can chemically combine in simple whole number ratios to form compounds

dalton's atomic theory: four

chemical reactions occur when atoms are separated from each other, joined, or rearranged in different combinations. atoms of one element are NEVER changed into atoms of another element as a result of a chemical reaction

demoritus

atomos

dalton

1808 billyards ball gave us the atom

j.j thomson

1890s Plum Pudding model. his experiment was called the Calthode Ray. he discovered electrons and said the entire atom was positive

ernest rutherford

1911-nuclear model. his experiment was called the "Gold Foil Experiment". he discovered the positive nucleus and said that the atom is mostly empty space

niels bohr

1913-bohr's atomic model of the atom (plantery model) discovered atomic energy levels

heinsberg and schmodinge

1927-quantim model. his theory was "heinsberg uncertainty principle". he discovered that electrons move on a cloud and it's impossible to see where they are because they move so fast in waves

james chadwick

1932- modern model. discovered the neutron