Early Ideas of Atomic Structure

Early Ideas of Atomic Structure

• The term "atom" derives from the Greek word meaning "uncuttable."

John Dalton and Elements

• John Dalton first articulated the differences between elements around 1800.

Dalton's Atomic Theory

• Proposed atoms as tiny, indivisible spheres.
• Atoms are the smallest units of an element retaining its properties.
• All atoms of the same element are identical, while those of different elements vary.

Structure of Atoms

• 1800s experiments revealed atoms are composed of two electrically charged components.
• Positive charges identified as protons, while negative charges are electrons.
• J.J. Thomson provided an explanation for these findings.

Thomson's Plum Pudding Model

• Describes the atom as a positively charged "pudding" with negatively charged particles (electrons) embedded within.

Rutherford's Gold Foil Experiment

• Conducted by Ernest Rutherford in 1909, significantly shifted concepts of atomic structure.

Rutherford's Atomic Model

• Proposes that atoms consist primarily of empty space.
• Most of an atom's mass is concentrated in a small nucleus at its center.
• The nucleus contains positively charged protons and neutral neutrons, with negative electrons orbiting around it.

Atomic Number

• Defined as the number of protons in an atom.
• The atomic number uniquely identifies an element and remains constant.

Atomic Mass

• Calculated as the sum of protons and neutrons in the nucleus.
• Mass Number = Protons + Neutrons.

Isotopes

• Atoms of the same element can vary in the number of neutrons.
• Example: Most hydrogen atoms have no neutrons, but some contain one neutron, resulting in different mass numbers.

Charges in Atoms

• An electrically neutral atom maintains equal numbers of electrons and protons.
• It is possible to change the electron count, thereby altering the atom's charge.