Chemistry - Important figures in Atomic Structure

John Dalton, Joseph John Thomson, Ernest Rutherford, James Chadwick, Niels Bohr

John Dalton

-He stated that Atoms were indivisible groups of matter (incorrect - P+ No E-) and that atoms of elements have different weights.

-All atoms of an element are identical (incorrect - isotopes)

Joseph John Thompson (JJ Thompson)

-Plum Pudding Model

-He discovered that particles (electrons) within an atom are negatively charged and move toward the positive electrode in an electric field

-concluded that particles must be negatively charged and present in all atoms

-He proposed that atoms must also contain positive particles as well.

Plum Pudding model

-Model made by JJ Thompson

-Model of the atom where negatively charged particles were spread throughout the positively charged sphere of the atom like raisins of a plum pudding.

-Was incorrect

Ernest Rutherford

-Conducted the “Gold Foil” experiment

-concluded that most of an atom must be empty space.

-most of the mass of an atom and its positive charge must be located in a tiny, central region (nucleus)

-The nucleus of the atom is surrounded with electrons similar to planets orbiting the sun

Gold Foil Experiment

-Fired alpha particles (positively charged) at thin gold foil

-Most particles passed through (empty space in atom)

-Some deflected at small angles

-A few bounced back (hit dense, positive centre)

Gold Foil Experiment conclusions

-Atoms have a small, dense, positively charged nucleus

-Electrons orbit around the nucleus

-Disproved Thomson’s model, led to the Nuclear Model of the Atom

James Chadwick

Proved the existence of the neutron

Niels Bohr

Bohr model

Bohr Model

-Electrons revolve around the nucleus in fixed, circular motion

-The Electrons’ orbits correspond to specific energy levels or shells in the atom

-Electrons can only occupy one of these fixed energy levels and cannot exist between two energy levels

-Electron orbits of larger radii correspond to energy levels of higher energy

Electron Shell

Region of space the electron occupies

Energy Level

-The shell corresponds with a fixed quantity of energy and any electrons occupying that shell possess that same quantity of energy

-the lowest energy shell is labelled n=1.

-Shells with higher values of n correspond to higher energy levels.

Niels Bohr (energy levels)

He suggested that electrons could move between the energy levels by absorbing or emitting energy in the form of light