CHEM001C_Atomic Theory & Structure

Democritus 

Expressed the belief that all matter consists of very small, indivisible particles.

Atomos

Meaning uncuttable or indivisible.

John Dalton

Formulated a precise definition of the indivisible building blocks of matter that we call atoms.

Atom

The basic unit of an element that can enter into chemical combination.

atoms, cannot, identical, different, Compounds

The Postulates

1. All matter consists of _____.

2. Atoms of one element ______ be converted into atoms of another element.

3. Atoms of an element are ______ in mass and other properties and are _______ from atoms of any other element.

4. _________ result from the chemical combination of a specific ratio of atoms of different elements.

Joseph John Thomson

- Studied electrical discharges in partially evacuated tubes called cathode-ray tubes.

- Found that when high voltage was applied to the tube, a “ray” he called a cathode ray (because it emanated from the negative electrode, or cathode) was produced.

Electrons

Stream of negatively charged particles.

Robert Millikan

- Oil-drop experiment

- These experiments allowed him to determine the magnitude of the electron charge.

Ernest Rutherford

- The experiment involved directing alpha particles at a thin sheet of metal foil.
- He expected the alpha particles to travel through the foil with, at the most, very minor deflections in their paths.
- Most of the alpha particles passed straight through, yet many of the particles were deflected at large angles.
- The large deflections of the alpha particles could be caused only by a center of concentrated positive charge that contains most of the atom’s mass.

- He calculated that an atom is mostly space occupied by electrons, but in the center of that space is a tiny region called nucleus.

Nucleus

Contains protons and neutrons.
Contains all the positive charge and essentially all the mass of the atom.

Protons

Positive charged particles.

Neutron, James Chadwick

An uncharged dense particle that also resides in the nucleus.
It was discovered by ____________.

Electrons

Negatively charged particle.

Isotope

Atoms of an element with the same number of protons, but a different number of neutrons.

Ion

Contains charge. Either positive or negative charge.

Cation

- A type of ion that contains positive charge.
- It tends to lose electron.
- The magnitude of the charge is the number of electron that can be lost by an ion.

Anion

- A type of ion that contains negative charge.
- It tends to gain electron.
- The magnitude of the negative charge is the number of electron that can be gained by an ion.

TRUE

[TRUE/FALSE] The mass #, # protons, and # neutrons do not change for all ions. The only thing that will change for an ion is the # of electrons.

Electrons, Protons, Neutrons

The components of an atom are: _____________________

Neutral

Atoms are electrically ________. (e^- = p⁺)

Mass of an atom/ion

___________ is equal to the number of protons plus the number of neutrons.

Ions

____ are not neutral. The number of protons are not the same with the number of electrons.