Dr. Saidane
Chem. 152
Early Model of the Atom
Skills you should have mastered
Conceptual
1.
Describe the experiments associated with the discovery of the subatomic
particles.
2. Compare and contrast the properties of electrons, neutrons and protons.
3. Distinguish between atomic number and mass number.
4. Use atomic number and mass number to distinguish between isotopes.
5. Using the concept of isotopes, explain why atomic masses of elements are not
whole numbers.
6. Distinguish between an atom and an ion.
7. Distinguish between an anion and a cation.
Problem-solving
1. Use atomic number and/or mass number to determine the number of different
subatomic particles.
2. Calculate the average atomic mass of an element from isotope data.
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The Greek Model: Atom basically just has each atom as a little tiny, solid ball like marbles just smaller. Atoms from different elements may be balls of different
sizes or materials, but they're all just little solid balls. And when they form
molecules or solids, they fit together just like a stack of marbles would

The J.J.Thomson Model:
Sometimes called the "plum pudding" model,
Thomson thought of an atom as being composed of a positively charged material
with the negatively charged electrons scattered through it.

The John Dalton Model: Solid sphere model or billiard ball model. Atoms are
tiny, indivisible, indestructible particles. Each one has a certain mass, size, and
chemical behavior that was determined by what kind of element they were. A
Summary of Dalton’s Atomic Theory:
1) An element is composed of tiny, indivisible, indestructible
particles called atoms.
2) All atoms of an element are identical and have the same
properties.
3) Atoms of different elements combine to form compounds.
4) Compounds contain atoms in small whole number ratios.
5) Atoms can combine in more than one ratio to form different
compounds.

The Rutherford Model: Rutherford's model proposed that an atom is mostly
empty space. There is a small, positive nucleus with the negative electrons
scattered around the outside edge.

The Nuclear Atom. The current model of the atom is called the nuclear atom and
can be summarized as follows:
1.
Atoms are made up of subatomic particles called electrons, protons, and
neutrons.
2.
The protons and neutrons are jointly known as nucleons. They form a
compact, central body called the nucleus of the atom.
3.

The electrons are distributed in space like a cloud around the nucleus.
Properties of Subatomic Particles:
* 1 amu (atomic mass unit) = 1.660540 x 10–24 g

The mass of an electron is negligible compared to the mass of a neutron and a
proton. Therefore the mass of an atom is considered to be the mass of its
nucleus.

The atomic number (Z) of an element is the number of protons in the nucleus of
each atom of that element. The atomic number identifies an element.

The mass number (A) is the total number of protons and neutrons in the nucleus
of an atom.

Isotopes: All atoms of the same element have the same number of protons. Most
elements occur naturally with varying numbers of neutrons. Atoms of the same
element that have a different number of neutrons in the nucleus are called
isotopes. Isotopes have the same atomic number but different mass numbers.
Since not all isotopes of an atom are present in equal proportions, we must use the
weighted average.

Ions: Atoms have an equal number of electrons and protons. When atoms gain or
lose electrons, they are called ions. When an atom gains electron it becomes
negative and is called an anion. When an atom gains loses electrons it becomes
positive and is called a cation.