Chemistry Atomic Structure

Electron

Negligible mass (about 1/2000u), negative charge, located in orbitals.

Neutron

Mass of 1u, no charge, located in the nucleus.

Proton

Mass of 1u, positive charge, located in the nucleus.

Atomic number

Identifies the element and acts like a social security number. Proton

Dalton

Scientist who proposed the atom as a solid indivisible sphere.

JJ Thomson

Scientist credited with discovering the electron using a cathode ray tube.

Rutherford’s Gold-Foil Experiment

Concluded that the atom is mostly empty space and has a small, dense, positive nucleus.

Bohr Model

Model of the atom with electrons orbiting the nucleus in fixed locations.

Modern Model

Model of the atom with electrons in probable locations (Quantum Mechanical Model).

Nucleus density

Dense due to the presence of protons and neutrons, which have significant mass.

Nucleus charge

Positive charge.

Isotope

Atoms of the same element with different mass numbers due to varying numbers of neutrons.

Ion

An atom or molecule with an unequal number of protons and electrons, resulting in a net charge.

Atom

The smallest part of an element that is electrically neutral, with equal numbers of protons and electrons.

Atomic number

Represents the number of protons in an element.

Mass number

Determined by adding the number of protons and neutrons.

Charge of elements/compounds

Usually neutral unless they form ions.

Charge determination

By comparing the number of protons and electrons.

Neutral charge

A neutral atom has equal numbers of protons and electrons, balancing their charges.

Atomic mass vs

Mass number is the total number of protons and neutrons (whole number); atomic mass is the weighted average of all isotopes (often a decimal).

Models of the atom

Dalton (hard sphere), Thomson (discovered electron), Rutherford (mostly empty space with nucleus), Bohr (fixed electron orbits), Modern (probable electron locations).