Models of the Atom

The Development of Atomic Models Dalton’s Atomic Theory: all elements are composed of tiny indivisible particles called atoms. atoms of the same element are identical. atoms of different elements combine in simple whole-number ratios to form compounds. chemical reactions occur when atoms are separated, joined, or rearranged.

Dalton’s atomic theory (1766-1844) Dalton thought the atom was indivisible and a solid sphere. yet to discover protons and electrons.

Eugen Goldstein (1850-1930) In 1886, observed a cathode-ray tube and found rays traveling in the direction opposite to that of the cathode rays. called these rays canal rays and concluded that they were composed of positive particles.

J.J. Thomson (1856-1940) discovered electrons based on the behavior of cathode rays in 1897. electrons are negatively charged and has a mass 1/1840 of a proton. in a cathode-ray tube, electrons travel as a ray from the cathode (-) to the anode (+). Robert Millikan (1868-1953) calculated the mass of the electron in 1916.

Thomson’s Plum pudding model

James Chadwick (1891-1974) in 1932, James Chadwick confirmed the existence of the neutron. neutrons are subatomic particles with no charge but with a mass nearly equal to a proton.

Rutherford’s atomic model due to the gold-foil experiment results, Rutherford suggested that the atom is mostly empty space. he concluded that all the positive charge and almost all the mass are concentrated in a small region called the nucleus. the nucleus is the central core of an atom and is composed of protons and neutrons.

Rutherford’s atomic model also known as the nuclear atom. in the nuclear atom, the protons and neutrons are located in the nucleus. the electrons are distributed around the nucleus and occupy almost all the volume of the atom.

the bohr model Rutherford’s atomic model also could not explain the chemical properties of elements. a student of Rutherford, Niels Bohr (1885- 1962) changed the model to include how atoms change energy when they absorb or emit light. in 1913, Bohr proposed that an electron is found only in specific circular paths (orbits) around the nucleus.

the bohr model each possible electron orbit in borh’s model as a specific energy. the specific energies an electron can have are called energy levels. to move from one energy level to another, an electron must gain or lose just the right amount of energy.

the bohr model a quantum of energy is the amount of energy required to move an electron from one energy level to another energy level. the amount of energy an electron gains or loses in an atom is not always the same. the energy levels in an atom are not equally spaced, the higher energy levels are closer together. the higher the energy level occupied by an electron, the less energy it takes to move from one energy level to the next.

the bohr model

erwin schrodinger (1887-1961) erwin schrodinger used new results on electron motion to obtain and solve a mathematical equation describing the behavior of the electron in a hydrogen atom. the mathematical solutions to the schrodinger equation lead to the quantum mechanical model.

the quantum mechanical model (Electron cloud) the quantum mechanical model determines the allowed energies an electron can have and how likely it is to find the electron in various locations. the probability of finding an electron within a certain volume of space surrounding the nucleus can be represented as a fuzzy cloud.

the quantum mechanical model (Electron cloud) the cloud is denser where the probability of finding an electron is high. the cloud is less dense where the probability of finding the electron is low. it is unclear where the cloud ends, and there is at least a slight chance of finding the electron a considerable distance from the nucleus.

the quantum mechanical model

the quantum mechanical model quantum mechanical model of h2o (water)