Chapter 4 Development of Atomic Theory Flashcards
the smallest unit of an element that maintains the properties of the element
atom
a subatomic particle that has a negative charge
electron
in a physical science, an atom’s central region, which is made up of protons and neutrons
nucleus
a region around the nucleus of an atom where electrons are likely to be found
electron cloud
Greek philosopher who thought that you would eventually end up with a particle that could not be cut . He said that atoms were “hard and small”. He thought the atoms were made of a single material formed into different shapes and sizes. 440 BCE
Democritus
Greek philosopher who disagreed with Democritus’s ideas. He believed you would never end up with a particle that could not be cut. He had peoples attentions and most people though he was right.
Aristotle
Late 1700s. British chemist who wanted to know why elements combine in certain proportions based on mass to form compounds. He experimented with different substances. His experiment suggested that elements combine in certain proportions because they are made up of single atoms. He published his atomic theory with included his ideas of
-All substances are made of atoms. Atoms are small particles that can not be created, divided, or destroyed.
-Atoms of the same element are exactly alike, and atoms of different elements are different.
-Atoms join other atoms to make new substances.
Some of his ideas were incorrect.
Dalton
- British scientist who showed that there was a mistake in Dalton’s theory. Thomson discovered that there are small particles inside the atom, and that atoms can be divided into even smaller parts. Thomson experimented with a cathode-ray tube and discovered that positively charged plate attracted the beam. He concluded that the beam was made of negatively charged particles and also concluded that the particles are present in every kind of atom. These are now called electrons. He proposed a new model of atoms, which is incorrect because the atoms should be on the inside.
Thomson
- A student of Thomson’s decided to test his theory. Rutherford designed an experiment to study the parts of an atom. He aimed a beam at positively charged particles at a thin sheet of gold foil. He wanted to see where the particles went after hitting the foil. What surprised him was the beam scattered and didn’t go in a straight like like he thought.
Rutherford
- Danish scientist who worked with Rutherford and studied the way atoms react to light. His results led him to propose that electrons move around the nucleus in certain paths or energy levels. His model showed no paths but electrons can jump from one level to another. The model was valuable in predicting some atomic behavior but had room for improvement.
Bohr
