Science q3 part 1

Study Notes

Atomic Structure

Democritus (460 BC) proposed that the world is made of two things: empty space and "atomos" (Greek word for uncuttable).
He believed that atoms are the smallest possible particles of matter and that there are different types of atoms for each material.

John Dalton's Atomic Theory (1804)

All matter is made of atoms.
Atoms of one element are all the same.
Atoms cannot be broken down into smaller parts.
Compounds form by combining atoms.

Dalton's Early Atomic Model

The "Billiard Ball" model, where atoms are solid, hard spheres like billiard balls.

J.J. Thomson's Contributions

Discovered the electron, showing that atoms are made of even smaller things.
Used the Cathode Ray Tube to discover electrons.

Eugen Goldstein's Contributions

Discovered canal rays, which are beams of positively charged particles, using a cathode ray tube.
Credited with the discovery of protons in an atom.

Millikan's Oil Drop Experiment

Determined the charge on an electron.
Used Thomson's charge to mass ratio to calculate the mass of an electron.

Ernest Rutherford's Contributions

Discovered the nucleus of a gold atom with the "gold foil" experiment (1913).
Found that the atom is mostly empty space, with a small, dense center having a positive charge.
Discovered the nucleus in atoms.

Structure of the Atom

An atom is the smallest particle of an element that can exist alone.
Two regions of an atom: the nucleus and the electron cloud.
The nucleus is the center of the atom, containing protons and neutrons.
The electron cloud is the area surrounding the nucleus, containing electrons.

Protons, Neutrons, and Electrons

Protons have a positive charge (+), 1 atomic mass unit (amu), and are found in the nucleus.
Neutrons have a neutral charge (0), 1 amu, and are found in the nucleus.
Electrons have a negative charge (-), a very small mass, and are found in the electron cloud.

Counting Atoms

Atomic number: the number of protons in the nucleus, determining the identity of the element.
Mass number (atomic mass): the number of protons + neutrons, measured in units of g/mol.
Isotopes: atoms of the same element with varying numbers of neutrons, having different mass numbers.

Atoms and Ions

In a neutral atom, the number of protons equals the number of electrons, resulting in an overall charge of zero (0).
When an atom gains or loses electrons, it forms ions, with a negative charge when gaining electrons and a positive charge when losing electrons.

Physical and Chemical Changes

Change: the act of altering a substance, an event, not a trait.
Physical change: does not alter the chemical composition or identity of a substance, only the form (e.g., melting ice, freezing Kool-aid).
Chemical change: alters the chemical composition or identity of a substance.

Description

Explore the contributions of Democritus and John Dalton to the atomic theory. Learn about the concepts of atoms being the smallest particle of matter and the idea that all elements are made of identical atoms. Discover the early atomic model proposed by Dalton.