- from Chemistry
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Among scientists, each “stands upon the shoulders” of those who came before.
Building on what is already known, each scientist builds, develops, and imagines the future. Here are some of chemistry’s greatest contributions.
◀ Boyle discovered that if you keep the temperature of a gas the same but push on it to increase the pressure, the gas takes up less space. The volume decreases. And, if you decrease the pressure, the gas takes up more space. The volume increases. This is known as Boyle’s law. Scuba divers returning to the surface must be careful as they come up, because as pressure decreases, the gases in their blood expand and can make them sick.
Lavoisier discovered that during a chemical reaction, the amount of matter stays the same, even though its form may change. This is called conservation of matter. Even when something seems to disappear, it doesn’t. It turns into something else. When a candle burns, the wax and oxygen from the air react and make carbon dioxide and water vapor. The original atoms are still there but have changed into something new. ▶
◀ Curious about what matter was composed of at the smallest level, Dalton measured many different elements and compounds. He came up with the idea that matter is made up of atoms. Dalton’s modern atomic theory includes four key ideas:
Elements are made up of atoms.
Atoms of the same element have the same weight.
Atoms of different elements have different weights.
Atoms combine to form compounds.
Avogadro worked with gases. He found that at the same temperature and pressure, equal volumes of different gases have the same number of molecules. So, let’s say you fill a beach ball with nitrogen. Then you fill another beach ball with oxygen. There will be as many nitrogen molecules in ball one as there are oxygen molecules in ball two. Avogadro’s work helped other chemists discover the actual number of atoms or molecules in any given sample. ▶
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What is Avogadro’s number?
Avogadro’s number is 6.02 x 1023. This is the number of atoms or molecules in one mole of any substance. A mole is the mass, or molecular weight, of a substance, as expressed in grams.
◀ Bunsen developed a gas burner that is used to heat elements for experiments. Scientists can make a Bunsen burner’s flame hotter or cooler by changing how much gas and air it gets. It is an essential piece of lab equipment. Bunsen also developed the spectroscope. That instrument can identify a substance by the colors of light it emits when heated and glowing.
Mendeleev created the first Periodic Table of Elements. He based it on experiments others had done on elements. Mendeleev saw similarities and differences among elements. He designed the chart by grouping elements with similarities into columns. Since his time, other scientists have discovered more elements. The modern Periodic Table is posed in almost every chemistry classroom in the world. ▶
John Joseph (J. J.) Thomson
◀ Thomson experimented with electricity in a glass tube. The air was removed and pieces of metal (electrodes) were at each end. When he put electricity in the tube, a ray of light went from one metal piece to the other. Thomson found that the ray was made of negatively charged particles smaller than atoms. He called these particles electrons. Three main particles make up atoms: electrons (negative charge), protons (positive charge), and neutrons (no charge). Thomson won the Nobel Prize in Physics in 1906.
As a college student in Paris, France, Curie experimented with uranium, which she found gave off particles and rays of high energy. She called these effects radioactivity. Curie won the Nobel Prize in Physics in 1903. She was the first woman to win a Nobel Prize. She was also the first person to win two Nobels. In 1911 she won her second, for discovering the radioactive elements radium and polonium. ▶
◀ Pauling studied how atoms bond to make molecules. He showed that the bonds in molecules affect their structure and how they act. He won the Nobel Prize in Chemistry in 1954. Pauling also found that sickle cell anemia, a disease, is caused by a change in a molecule’s structure.