Download Helpful Science Notes Chapter 4.1 Atomic Structure Vocabulary: 1

Accelerated / Advanced Science 8
Helpful Science Notes
Chapter 4.1
Atomic Structure
Vocabulary:
1. Nucleus
Studying Atoms
Studying the structure of atoms is like studying wind. We must use indirect evidence to
determine atomic structure.
Ancient Greek Models of Atoms
A. Democritus
Believed that all matter consisted of extremely small particles that could not be divided.
Called these particles atoms from the Greek word atomos, which means “uncut” or
“indivisible.”
B. Aristotle
Believed there was a limit to the number of times matter could be divided.
Believed there were only four elements – Fire, Earth, Water, Air
His belief was widely accepted until the 1800s, when scientists had enough data to
support an atomic model of matter.
Dalton’s Atomic Theory
Dalton noticed that no matter how large or small the sample, the ratio of the masses of the
elements in the compound is always the same.
example: magnesium oxide (page 101)
Dalton proposed that all matter is made up of individual particles called atoms, which
cannot be divided.
o
Pictured atoms as solid spheres that were indestructible.
Thomson’s model of the Atom
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Accelerated / Advanced Science 8
Used a vacuum tube to demonstrate that the particles in a glowing beam generated in the
tube consisted of smaller, negatively charged particles.
Thomson’s experiments provided the first evidence that atoms are made of even smaller
particles.
o
He shot a beam of particles through a tube with a positive charge at one end and a
negative charge at the other.
o
When electricity was passed through the tube, a glowing beam appeared in the
space in between.
o
When Rutherford put positive and negative plates on either side of the tube, the
beam bent toward the positive plate, indicating that the beam was negative.
In Thomson’s model of the atom, the negative charges were evenly scattered throughout
an atom filled with a positively charged mass of matter. This model is called the “plum
pudding” model.
o
These two opposite charges resulted in the atom having an overall neutral charge.
Rutherford’s Atomic Theory
In 1899, Ernest Rutherford discerned that uranium emits fast-moving particles that have a
positive charge. He named them alpha particles.
Rutherford is most well-known for his gold-foil experiment.
o
He shot a beam of alpha particles at a very thin sheet of gold, surrounded by a
screen that produced a flash of light when struck with an alpha particle.
o
Rutherford expected the alpha particles to go straight through the gold, but instead
observed that many of the particles were actually deflected, bouncing off at
varying angles.
o
Rutherford concluded that the positive charge of an atom is not evenly spread
throughout atom. It is concentrated in a very small, central area that Rutherford
called the nucleus.

The nucleus is a dense, positively charged mass located in the center of the
atom.
According to Rutherford’s model, all of an atom’s positive charge is concentrated in its
nucleus.
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Accelerated / Advanced Science 8
Now we can compare an atom to a stadium, where a marble would represent the actual
mass of the nucleus of an atom.
Complete the Section 4.1 Assessment question from page 105 numbers 1-8 on the back of this
page.
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