Physci

• Nucleosynthesis is a thermonuclear reaction that produces new chemical element from another element
• Cosmic background radiation is the thermal leftover of the transition phase that occurred when the hot early universe cooled enough for atoms to combine
• Big Bang nucleosynthesis pertains to the formation of light elements in the early universe
• Galaxy is defined as a gravitationally bound system of stars, stellar remnants, interstellar gas and dusk, and dark matter.
• Dark matter is considered a hypothetical kind of matter that cannot be observed even with the use of telescope.
• The fusion of four hydrogen nuclei into a helium nucleus, commonly referred to as the hydrogen burning phase, supplies energy to the stars.
• This phase is classified into two types- proton- proton cycle and the carbon-nitrogen-oxygen (CNO) cycle.
• Neutron capture processes are responsible for the production of post-iron elements in the stars.
• The s-process occurs at relatively low neutron densities and at intermediate temperature conditions in stars.
• the r-process occurs at high neutron densities
• Supernova nucleosynthesis involves the production of new elements during supernova
• A supernova is an explosion of a massive star (5 to 50 times the mass of the sun) when it runs out of nuclear fuel.
• Thales of Miletus thought that water was the fundamental substance.
• Empedocles proposed the four elemental substances- earth, air, fire, and water
• The first atomic theory of matter was introduced by Leucippus and his pupil Democritus.
• Atoms, derived from the Greek word atomos, meaning “uncutable.”
• The idea of the atomicity of matter was criticized by Aristotle. He argued based on his assumptions that no void or vacuum can exist; therefore, the idea of atoms in continuous motion was not acceptable
• •Lucretius wrote about the concept of atomism in his poem, De rerum natura (On The Nature of Things), which helped the atomic theory survive.
• •Alchemy is the earliest form of chemistry. The term is derived from the French word arquemie, which refers to the mixing of juices and saps obtained from plants.
• Paracelsus introduced the use of metals and minerals to cure illnesses.
• Main goals of alchemy:

  •turning base metals into gold

  •creating an elixir of life
• two major technical problems of alchemy: controlling heat and disregard for mass
• Alchemists invented apparatuses like reaction vessels, alembic, bain-marie, and kerotakis
• •Sir Francis Bacon tagged as the father of empiricism, popularized inductive methodologies in the conduct of a scientific inquiry.•
• Robert Boyle came up with a definition of an element, which we still use today, as “any substance that cannot be broken down into any simpler substance.”
• Antoine-Laurent Lavoisier performed a quantitative experiment that led to an operational definition of an element that was written in his book
• •John Dalton used the idea of the indivisible atom to explain the laws of chemical combination. Dalton pictured the atom as a tiny, indestructible sphere with mass.
• •Jons Jakob Berzelius suggested that the presently known  atomic mass of oxygen should serve as the standard for comparison.
• Dmitri Mendeleev develop and create a periodic table of elements.
• •Dalton’s Atomic Theory

  •law of conservation of mass

  •law of definite proportion

  •law of multiple proportions
• George Johnstone Stoney and William Crookes confirmed the idea that

  matter has an electrical property.
• J. J. Thomson further experiment and establish that cathode rays are negatively charged.
• Robert Millikan determined the charge of an electron through his oil-drop experiment.
• •The accidental discovery of radioactivity by Henri Becquerel in 1896 helped further unravel the structure of the atom
• •Ernest Rutherford, together with his coworkers, studied the nature of Becquerel's rays.
• Hans Geiger and Ernest Marsden carried out an experiment on the scattering of alpha particles using a thin gold foil.
• •Rutherford was the first to suggest the term proton as the particle responsible for the positive charge of the nucleus.
• •James Chadwick discovered a particle with a mass nearly equal to that of a proton and with zero electrical charge. He called this particle neutron.
• The atomic numbers of elements were established through the experiments of Henry Moseley
• •Niel Bohr proposed a model that was considered revolutionary at that time to describe an atom.