During the stone age, humans discovered one of the first chemical reactions, fire. Fire is an important discovery for the progress of the human race because it provides warmth, protection, and a method for food preparation. Control of fire also allowed the first chemists to harden mud, this led them to making more effective tools and change substances to match their needs. Eventually this led to production of ceramic and glass things. There wasn’t much need for a theory of matter. Metal was not discovered at this time. That is why it is called the stone age.
There have been traces of humans working with metal as early 40,000 BCE. This was small amounts of natural gold found in Spanish caves. In 3000 BCE, there were Egyptian weapons made from meteoric iron. During the bronze age, (~3500 BCE) people were smelting rocks containing various ores. Smelting at the time was putting rocks into a fire to heat them. The first metals used were used as found. Examples include copper or tin. It was discovered that the combination of copper and tin could produce a superior metal alloy, bronze. It is difficult to extract iron from its ore relative to the extraction of copper or tin. However in 1200 BCE, the secret to this process was discovered. This started the Iron Age.
He thought that :
All matter consists of invisible particles called atoms.
Atoms are indestructible.
Atoms are solid but invisible.
Atoms are homogenous. Ex. An iron atom is identical to another iron atom.
Atoms differ in size, shape, mass, =3d , and arrangement.
Solids were made of small pointy atoms.
Liquids are made of large round atoms.
Oils are made of very fine small atoms that can easily slip past each other.
Democritus was closer to modern day atomic theory than Aristotle was his theory that everything was made of four elements. However, the general public believed Aristotle to be correct. This caused other theories to be overlooked for the next ~2000 years.
He thought that the Earth and everything found on the Earth was made of a combination of four elements. Fire, Earth, Water, Air. Aristotle also added a new element. Aether. He came up with this element because he reasoned that stars could not be made up of these earthly elements.
Although we now know that the foundation Alchemists relied on was false. (That everything on Earth was made of four elements) They made some significant contributions to the atomic theory, and the study of chemistry. Alchemists classified the Aristotelian elements with four basic qualities. “Hotness, Coldness, Dryness, Moistness.” It was thought that every metal displayed two of these qualities on the interior and the exterior. For example, lead was cold and dry, while gold was hot and moist. They theorized that changing the qualities would change the metal. It was also interesting to Muslim alchemists that the noblest metal could be dissolved using a mixture of nitric and hydrochloric acids.
Robert Boyle discovered the atom. Through some experiments, Boyle discovered that atoms must exist because of a relationship he discovered between the pressure and volume of a gas. His theorem, Boyle’s law stated that “the volume of a fixed mass of gas at a constant temperature is inversely proportional to the gas’s pressure.” He reasoned that because a fixed mass of gas can be compressed, gas must be made of particles or atoms. This is due to space between them. Boyle’s discovery helped accelerate science into the modern age.
Lavoisier is famous for his work in understanding the role of oxygen in combustion. He is responsible for naming oxygen and hydrogen. He wrote one of the earliest extensive list of elements. He proposed the idea that there was another element inside quartz. He said that the new element was very abundant. Antoine was correct. Silicon makes up about 27% of the weight of the Earth’s crust. He was the first to discover that sulphur was not a compound, but instead a pure substance. Antoine also discovered that although matter may change form or state, it’s mass will always stay the same. Lavoisier is known as the "Father of Modern Chemistry."
He believed that all matter is made up of elements and that each element is composed of an atom. Dalton developed one of the first modern atomic theories. This was the billiard ball model. It stated that all atoms are made of atoms. All the atoms of one element are identical, but atoms of a different element are different. Atoms of different elements can combine to make compounds. In his model, atoms had no features and were displayed as solid spheres.
Thompson continued Dalton's work on the structure of the atom. Thomson is the first person to discover a particle smaller than an atom. He discovered the electron. By experimenting with cathode rays, he thought concluded that the rays were composed of negatively charged particles. Thomson proved that these particles were smaller than atoms in mass. Even the smallest atom, hydrogen was larger in mass. Many people at this time believed that atoms were the smallest particle and could not be broken down. Thomson also constructed an atomic model called the raisin bun model. His model proposed that an atom was a positively charged sphere with negatively charged electrons embedded. The negative charges equal the positive charge, so the sphere has no electrical charge.
With Thomson’s model in mind, Rutherford held experiments where he shot positively charged particles through a layer of very thin gold. Rutherford predicted that all the particles would pass through undisturbed however, he noted that most particles passed through as predicted but some were reflected. With these results, Rutherford concluded that atoms were mainly empty space except for the center where there was a tiny positively charged particle. He called the tiny particle a nucleus.
Nagaoka improved on Thomson's atomic model. In his new improved model, electrons orbited the large positive charge. Many people disagreed with this model because existing theories did not agree with it.
Niels thought that electrons would not randomly orbit the nucleus. This he believed would be impossible because the electron would give off energy and travel towards the center.Instead he said that they move in particular orbits. Or electron shells.
People accepted Bohr’s model as it complied with most existing theories. Chadwick discovered the positive proton and the neutral neutron. It was found that neutrons have approximately the same mass as a proton, but electrons has a significantly smaller mass.
Describes electrons as existing in a cloud around the nucleus.
Made by Albert 9C for his Grade 9 Theories of Matter Timeline project.