The History of the Atom - Student Worksheet
Directions: Answer the following questions using your project. An “A” project should answer
all of these questions.
1. What did Democritus say about the atom?matter is made of small particles called atoms- it is
indivisible.
Democritus believed that atoms were uniform, solid, hard,
incompressible, and indestructible and that they moved in infinite
numbers through empty space until stopped.
2. Explain the parts of Dalton’s Atomic Theory.
Dalton's Atomic Theory states that all matter is composed of tiny,
indivisible particles called atoms, where atoms of the same
element are identical, atoms of different elements are different,
and chemical reactions involve the rearrangement of these atoms
without creating or destroying them
3. What was significant about Dalton’s Atomic Theory as opposed to what Democritus said.
Based on experimental data.
Dalton said that all atoms included in an element are the same
4. Which portions of Dalton’s Atomic Theory are considered incorrect?
Same element, same atoms (x- isotopes)
Atoms are small particles that can’t be divided into smaller
particles (x)
5. What are cathode rays? Electrons.
Cathode rays are essentially a stream of electrons emitted from
the negative electrode (cathode) in a vacuum tube
6. Describe JJ Thomson’s Cathode Ray Experiment. Include a drawing of the cathode ray
experiment
Discovered that electrons were smaller particles of an atom and
were negatively charged. Furthermore, Discovered isotopes.
7. What particle did Thomson discover?electrons
Thomson announced his discovery that atoms were made up of
smaller components.
8. Describe Thomson’s “Plum Pudding” model of the atom. Include a drawing.
In Thomson's plum pudding model of the atom, the electrons
were embedded in a uniform sphere of positive charge, like
blueberries stuck into a muffin.
9. Describe Ernest Rutherford’s Gold Foil Experiment.
The Rutherford gold foil experiment worked by firing positively
charged alpha particles through gold foil and observing where
they ended up.
Include a drawing.
10. Describe Rutherford’s model of the atom
The atom, as described by Ernest Rutherford, has a tiny, massive
core called the nucleus. The nucleus has a positive charge.
Electrons are particles with a negative charge. Electrons orbit the
nucleus.
Include a drawing.
11. Describe Bohr’s model of the atom.
Bohr’s model of atom is a small positively charged nucleus
surrounded by revolving negatively charged electrons in fixed
orbits.
12. Explain why Bohr’s model of the atoms is sometimes called the planetary model.
Because these orbits look similar to that of planets orbiting the
sun.
13. Explain why electrons orbit around the nucleus.
Nucleus is positively charged, electrons are negatively charged. +
and - attract.
14. Who discovered the neutrons and when? Chadwick
15. Who figured out the charge of an electron? What is the name of the experiment?
Oil drop experiment. Millikan
