Name: ______
Date: ______7th Grade Science- Ms. Lyons
Circle your group: F ~ G ~ H
Atom Theory Reading Homework, 20pts (2pts each)
Directions – Answer the following questions in complete sentences.
It took hundreds of scientists thousands of years to come up with the idea of the atom and to be able to identify the different parts of its structure. The discovery of the atom and its make-up is a good illustration of how science happens because it shows us how scientists made hypotheses, tested their hypotheses, found out that they were incorrect, and created new hypotheses.
- Why is the discovery of the atom a good example of how science happens?
The first scientist to think of an atom was Democritus. Through the work of other philosophers, but mostly his own intellect, Democritus came up with his own atomic theory. Democritus was a Greek philosopher in 400 B.C. He thought the universe was made up of tiny bits of stuff that were so small that they could not be divided into smaller pieces. He called these tiny pieces atoms. The term atom comes from the Greek word that means “cannot be divided.” He came up with the idea that no two atoms are identical, but are different in shape and size. He pictured the atoms characteristics directly connected with the material that it formed its qualities. For example, things that tasted sour had sharp atoms while things that tasted sweet had big round atoms. Hard things were the result of closely packed stiff atoms while soft things were loose atoms. While Democritus was mostly correct, he had no evidence to support his ideas, so no one believed him.
- Where does the word atom come from?
- Who was Democritus and why didn’t people in 400 B.C. believe his ideas?
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- Stop, draw, and label. Draw what Democritus believed the model of an atom looked like.
From 400 B.C. until approximately 1800 A.D., no one really thought about the atom. In the early 1800s, more than 2000 years after Democritus first thought of the idea of an atom, English scientist John Dalton picked up Democritus’ studies. Dalton studied the evidence from other scientist and thought he could design an atomic model that explained the results of those experiments. Dalton believed that the atom was a sphere (3-D circle) that was made of exactly the same material throughout. His theory stated that elements were made up of tiny particles called atoms. Also, the reason elements were pure was because all of the atoms in the elements were identical and had the same mass. The reason elements were different was because the mass differed from element to element.For example, gold atoms made up a gold nugget and gave a gold ring its shiny appearance. Likewise, iron atoms made up an iron bar and gave it unique properties, and so on.
- What was Dalton’s theory?
- Stop, draw, and label. Draw what Dalton believed the model of an atom looked like and why elements were different.
In 1900, J.J. Thompson, another English scientist, showed that the atom was not made of a single material when he discovered the electron, a tiny, negatively charged particle. Thompson proposed that the atom was a sphere of positive charge and that negative charges (electrons) could be found throughout. Thompson’s theory can be compared to chocolate chip cookie dough – the dough would be sphere of positive charge and the chocolate chips would be the negative electrons.
- What was Thompson’s theory?
8. Stop, draw, and label. Draw what Thompson believed the model of an atom looked like.
In 1910, Ernest Rutherford further modified the idea of the atom. He suggested that almost all of the mass of an atom could be found in its center (nucleus) and that this nucleus was positively charged because it contained positively charged particles called protons. Between 1910 and the modern day, many more scientists studied the atom. Today, the atom is known to have center (nucleus) that contains positively charged protons and neutrons that have no charge. An atom also has electrons thatare located outside of the nucleus and are negatively charged.
- What was Rutherford’s theory?
10. Stop, draw, and label. Draw what Rutherford believed the model of an atom looked like.