physical science

• Thales of Miletus was the first to ask and propose an answer to the question “What is matter composed of?”
• H2O as the ultimate substance that constituted matter.
• Empedocles asserted that all things are composed of four primal elements: Earth, air, fire, and water.
• Leucippus (5th century BCE) and his student Democritus (460-370 BCE) introduced the first glimmers of atomic theory by asking whether or not a substance could be divided continuously.
• Leucippus concluded that one would arrive at fragments of a material that can no longer be divided.
• Democritus, the father of atomism, thought atoms were solid and indestructible.
• Democritus proposed that all matter is made up of very small particles called atoms, which cannot be divided into smaller units.
• Democritus also believed that the universe only had atoms and empty space, which he called void.
• Aristotle rejected Atomism and stated that only observable things could be proven true.
• Robert Boyle (1627-1691) believed that atoms indeed exist even though they are not visible to the naked eye.
• Robert Boyle used J-shaped tube experiment.
• Antoine-Laurent Lavoisier proposed the law of conservation of mass.
• In Chemistry, law of conservation of mass states that in chemical reaction, mass is neither created nor destroyed.
• Joseph Proust proposed the law of definite proportion.
• In Chemistry, law of definite proportion states that a given chemical compound always contains its component elements in fixed ratio (mass) and does not depend on its source and method of preparation.
• John Dalton formulated the atomic theory and proposed the law of multiple proportion.
• When two elements combine with each other to form two or more compounds, the ratios of the masses of one element that combines with the fixed mass of the other are simple whole numbers.
• John Dalton published a polished version of his atomic theory in a book New System of Chemical Philosophy.
• The combination of Ca and Cl is represented as CaCl.
• Robert Millikan found that the charge of an electron is equal to 1.6022x10-19C.
• During chemical reactions, the number of protons remains the same in the atomic nucleus, but the electron may be lost by an atom and gained by another.
• The charge(q) of an atom is written as a subscript at the right-hand side of the chemical symbol.
• The discovery of subatomic particles prompted other scientists to study the variations in the characteristics of elements.
• In a neutral atom, the number of protons is equal to the number of electrons.
• Ions are charges atoms, cation is a positive charged ion, and anion is a negative charged ion.
• The atomic number (Z) serves as the identity of an atom and refers to the number of protons in the nucleus of each atom of an element.
• Dmitry Mendeleev arranged the known elements in a periodic table based on their atomic mass.
• All atomic nuclei contain both protons and neutrons, except H which has 1 proton and no neutron.
• Wilhelm Rontgen discovered X-rays.
• James Chadwick discovered neutrons.
• A neutral magnesium atom loses two electrons to form its most stable cation.
• Ernest Rutherford observed that atoms are mostly empty space.
• Ernest Rutherford discovered protons.
• A neutral potassium atom loses one electron to form a stable potassium ion.
• Isotopes are atoms that have the same atomic number but different atomic masses.
• Chemical reactions involve only the electrons that are found outside the nucleus.
• The atomic number (Z) and atomic mass (a) are used in formulas to determine the properties of elements.
• The combination of Beryllium and Oxygen is represented as BeO.
• Antoine Becquerel and Marie Curie observed that radioactivity causes some atoms to break down spontaneously.
• Neil Bohr proposed an atomic model that shows electrons move in concentric orbits around the nucleus.