- from Chemistry
900L - 1040L
Among scientists, it goes without saying that each “stands upon the shoulders” of those who came before.
With the help of what is already known, each scientist builds, develops, and imagines the future. Here are some of chemists’ greatest (and coolest) contributions.
◀ Boyle discovered that if you keep the temperature of a gas the same but push on it to increase the pressure, the gas will occupy less space, because its volume decreases. And, if you decrease the pressure, the gas takes up more space, because its volume increases. This is known as Boyle’s law. As scuba divers come back up to the surface, they must be careful, because as the water pressure decreases, the gases in their blood expand. This 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 go away—it just transforms 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. ▶
◀ Dalton was curious about what matter was composed of at the very smallest level, so he measured many different elements and compounds, eventually conceiving of the idea that matter consists of atoms. Dalton’s modern atomic theory includes four primary concepts:
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 found that at the same temperature and pressure, equal volumes of different gases have the same number of molecules. Thus, a beach ball full of nitrogen has the same number of molecules as a similar-size beach ball full of oxygen. Avogadro’s work helped other chemists discover the actual number of atoms or molecules in any given sample. ▶
Check It Out!
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 expressed in grams.
◀ Bunsen developed a gas burner to heat elements for experiments. The Bunsen burner lets scientists make the flame hotter or cooler by changing how much gas and air the burner uses. It is an essential piece of laboratory equipment. Bunsen also developed the spectroscope, an instrument that can identify a substance by the colors of light it emits when heated and glowing.
Mendeleev developed the first Periodic Table of Elements, based on experiments others had done on elements. Mendeleev saw similarities and differences among elements and designed a chart grouping those with similarities into columns. Since Mendeleev, other scientists have discovered more elements. The modern Periodic Table is posted in almost every chemistry classroom in the world. ▶
John Joseph (J. J.) Thomson
◀ Thomson experimented with electricity in a glass tube that had the air removed and pieces of metal (electrodes) 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, which he called 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. She discovered the element gave off particles and rays of high energy. She called these effects radioactivity. Curie won the Nobel Prize in Physics in 1903. The first woman to win a Nobel Prize, she was also the first person to win two Nobels, the second in 1911 in chemistry for discovering the radioactive elements radium and polonium. ▶
◀ Pauling studied what happens when atoms bond to make molecules. His experiments showed how the bonds in molecules affect their structure and behavior. He won the Nobel Prize in Chemistry in 1954. While experimenting with molecules in living things, Pauling discovered that a disease called sickle cell anemia was caused by a change in a molecule’s structure.