Science

• Formation of heavy elements during star formation and evolution
• Protons and neutrons combined after the Big Bang to form light elements like Hydrogen and Helium in Big Bang Nucleosynthesis
• After 200 million years, hydrogen and helium underwent stellar nucleosynthesis, which is the fusion of lighter nuclei in stars to form heavy elements
• Stellar nucleosynthesis is the process of forming heavy elements by the fusion of lighter nuclei in the interior of stars
• Nebula: Giant cloud and dust
• Main Sequence Star: Formed from a nebula due to gravity pulling Hydrogen gas together until it ignites
• Protostar: Forms when nuclear fusion occurs at the core, converting Hydrogen into Helium
• Red Giant: Formed when a star exhausts nuclear fuel, leaving inert Carbon
• White Dwarf: Remains of a cooled down star that no longer emits light and heat
• Supernova: Leads to the formation of a Neutron Star or a Black Hole
• Neutron Star: Formed from a supernova explosion, the smallest star
• Red Super Giant Star: Evolves from a massive main sequence star, fusing Carbon into Oxygen
• Black Hole: Region in space with strong gravity where nothing can escape
• Nuclear processes in the formation of heavy elements
• Proton-Proton Chain Reaction: Converts Hydrogen into Helium in average stars
• CNO (Carbon, Nitrogen, Oxygen) Cycle: Converts Hydrogen into Helium in massive stars
• Tri-alpha Process: Converts three Helium-4 into Carbon in red giant stars
• Alpha Ladder Process: Fusion of alpha particles in red super giants to create heavy elements up to Iron
• Henry Gwen-Jeffrey Moseley demonstrated that atomic number, the number of proton in atom
• Henry Gwen-Jeffreys Moseley was an English physicist who demonstrated that the atomic number, the number of protons in an atom.
• In 1919, Ernest Rutherford successfully carried out a nuclear transmutation reaction process of transforming one element or isotope into another element.
• In 1925, there were four vacancies in the periodic table corresponding to the atomic numbers 43, 61, 85 and 87. Elements with atomic numbers 43 and 85 were synthesized using particle accelerator.
• Elements with atomic number greater than 92 (atomic number of Uranium) are called transuranium elements.
• Dmitri Mendeleev created classification of elements based on their atomic weight. Who devised the PERIODIC TABLE.
• Neutron, a neutral particle was discovered by James Chadwick.
• Ernest Lawrence synthesized element with the atomic number 43 using a linear particle accelerator.
• Edwin McMillan proved that an element having an atomic number 93 could be created. He used particle accelerator to bombard uranium with neutrons and created an element with an atomic number 93 which named neptumium.
• Remember that every atom has a certain number of electrons, which orbit the nucleus in the electron cloud. These electrons orbit in different energy levels, which are known as electron shells.
• Electron configurations describe where electrons are located around the nucleus of an atom.
• The electrons in the outermost shell of an atom are known as valence electrons.
• Partially-filled electron shells are unstable, so all atoms ‘want’ to fill their electron shells completely. Since most shells can hold eight electrons, this phenomenon is known as the Octet Rule.
• When atoms form bonds with other atoms, it is known as chemical bonding.
• Ionic bonds take place when one atom ‘steals’ the electron(s) of another atom, resulting in stability for both atoms.
• Covalent bonds take place when, rather than taking or giving electrons, atoms share their electrons in order to fill their energy shells.
• Non polar molecule There is an equal or symmetrical distribution of electrons among the atoms of a molecule.
• Polar molecule is an unequal or asymmetrical distribution of electrons among the atoms of a molecule.
• The electrons in the outermost shell of an atom are known as valence electrons.
• The tendency of an atom in a molecule to attract the shared pair of electrons towards itself is known as electronegativity
• The main properties of an atom dictate it's electronegativity are it's atomic number as well as its atomic radius.
• The trend for electronegativity is to increase as you move from left to right and bottom to top across the periodic table. This means that the most electronegative atom is Fluorine and the least electronegative is Francium.