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Democritus was an ancient Greek philosopher around 400 BC. His major was philosophy. He is known for the idea that everything is made of tiny, invisible particles called atoms. This was one of the first ideas about the basic building blocks of matter. -
Plato was a Greek philosopher whose major was philosophy. Around 400 BC, he believed that everything in the world is made from four basic elements: earth, water, air, and fire. Plato thought these elements were important to explain how things are made and how the world works. -
Empedocles, a pre-Socratic philosopher, was the first to propose that everything is made of four elements: earth, water, air, and fire. Later, Aristotle, a Greek philosopher whose major was philosophy, expanded this idea around 350 BC. He believed these four elements combined in different ways to make all materials, but he didn’t know about atoms or smaller particles. -
Alchemists were early scientists who tried to turn metals into gold and find a cure for all diseases. They also searched for the Philosopher’s Stone, which they believed had special powers. One famous alchemist was Hennig Brand, a German alchemist who discovered phosphorus. Their work helped lead to modern chemistry. -
Antoine Lavoisier was a French chemist who made important discoveries around 1789. He showed that matter can’t be created or destroyed in a chemical reaction, called the law of conservation of mass. He also helped name oxygen and hydrogen and explained their role in burning and water. -
In 1803, John Dalton, a British chemist, physicist, and meteorologist, introduced the billiard ball model of the atom. He said atoms are tiny, solid spheres that can’t be broken. Each element has its own type of atom, and atoms combine to make compounds. -
Henri Becquerel was a French physicist who found out in 1896 that some materials, like uranium, give off energy all by themselves. He saw this when a special plate got dark without sunlight. This discovery helped people learn more about tiny particles inside atoms. -
John Alexander Reina Newlands (1837-1898) was an English chemist who first published his findings in 1865. His major findings were the rule of eight, musical analogy, pionerring periodicity, applicable to lighter elements. -
Dmitri Mendeleev was a Russian chemist whose major was chemistry. In 1868, he created the first version of the periodic table. Mendeleev arranged elements by their properties and left spaces for elements that hadn’t been discovered yet. His work helped scientists understand how elements are related and predict new ones. -
Heinrich Hertz discovered the photoelectric effect in 1887 when he saw that light could make sparks jump between metals. In 1905, Albert Einstein explained that light is made of tiny particles called photons, which can knock electrons out of metals. This helped us learn more about how light works. -
Max Planck was a German scientist who, in 1900, discovered that energy comes in small pieces called “quanta” instead of flowing smoothly. This idea helped start a new way of understanding how light and energy work. -
In 1897, J.J. Thomson, a British physicist, discovered the electron while studying electricity in gases. His major was physics. From his experiments, in 1904 he suggested the plum pudding model of the atom. This model showed that atoms are made of a positive “pudding” with tiny negative electrons scattered inside. His findings helped scientists understand that atoms are not solid but have smaller parts inside. -
American physicist Robert Millikan performed the oil drop experiment in 1909. He measured the exact electric charge of an electron, a tiny particle inside atoms. This discovery helped scientists better understand atoms and how electricity works. It was an important step in learning about the basic parts of matter. -
The Gold Foil Experiment was done by a New Zealand physicist and chemist, Ernest Rutherford in 1909. He shot tiny particles at a thin piece of gold foil. Most went through, but some bounced back. This showed that atoms have a small, hard center called the nucleus. This helped people understand what atoms look like inside. -
Neils Bohr was a physics major who created the planetary model of the atom by proposing that electrons orbit the nucleus in fixed paths. He discovered that electrons jump between energy levels by absorbing or releasing energy, explaining atomic spectra. -
Henry Moseley was an English scientist who made a discovery in 1913. He found out that each element has a different number of protons, called the atomic number. This helped fix the order of the periodic table and made it more correct. -
In 1886, Eugene Goldstein was a German physicist who majored in physics, discovered canal rays, which are streams of positive particles in a gas tube. He showed that atoms have positive parts as well as negative ones. His discovery helped lead to the later finding of the proton. Which later on, the discovery of the proton was credited to Ernest Rutherford. -
Erwin Schrödinger and Werner Heisenberg were scientists in the 1920s who helped create the Electron Cloud Model. Schrödinger showed electrons act like waves, and Heisenberg discovered we can’t know exactly where an electron is or how fast it moves at the same time. Their work showed that electrons move in fuzzy clouds, not fixed paths, around the atom’s center. -
Werner Heisenberg was a German theoretical physicist who discovered the Uncertainty Principle in 1927. It says that we can’t know both the exact position and speed of tiny particles, like electrons, at the same time. This discovery showed that there are limits to what we can measure in the tiny world of atoms and changed how scientists think about them. -
In 1932, James Chadwick, a physicist, discovered the neutron. He found that atoms have a particle inside called the neutron, which has no electric charge. This helped scientists understand that atoms are made of protons, neutrons, and electrons. His discovery was very important for learning how atoms work.