EL 1

• JJ Thompson discovered the electron and introduced the plum pudding model, suggesting that atoms were not solid but made up of positive and negative particles
• In the periodic table, the mass number (top number) indicates the number of protons and neutrons in the nucleus, while the atomic number (proton number) indicates the number of protons in the nucleus. All atoms are neutral, so the number of protons equals the number of electrons
• Relative charges and masses of particles in an atom: Proton - charge +1, mass 1; Neutron - charge 0, mass 1; Electron - charge -1, mass ~1/1836 of a proton
• John Dalton in 1803 proposed that all atoms are spheres
• Ernest Rutherford, discovered the nucleus of the atom, which is incredibly small and positively charged. He also concluded that atoms are mainly empty space with a negative cloud of electrons surrounding the nucleus
• Atoms are incredibly small, with the nucleus being a tiny fraction of the overall size. The nucleus contains protons and neutrons, while electrons orbit in shells around the nucleus
• During the gold alpha particle test, Alpha particles deflected straight back

  Indicating they hit a nucleus in the gold atoms.
• Quantum model includes subshells in atoms
• Alpha particles are positively charged
• Niels Bohr proposed fixed energy shells in atoms
• Proton number uniquely identifies elements
• Fusion reactions are common in the Sun
• Electrons absorb electromagnetic radiation

  Move from lower energy shell to a higher one, then emit radiation when moving back down
• Alpha particles deflected back

  Due to hitting something with the same positive charge
• Gold leaf experiment

  Particles were fired at a thin gold leaf, most passed through indicating empty space, some were deflected back due to hitting positively charged nucleus
• Electrons move between defined energy levels
• Nuclear fusion forces together two nuclei to form a heavier nucleus
• Larger stars can fuse nuclei to form heavier elements than helium, like oxygen and silicon
• Helium is formed from two isotopes of hydrogen in nuclear fusion
• Supernovae send elements and fragments across the universe, some of which have formed the elements on Earth
• Large stars have higher temperatures and pressures to allow fusion to happen
• Electron shells are split into four sub shells: S, P, D, and F
• The P sub shell has three orbitals and can hold six electrons
• Orbital shapes: S orbital is spherical and holds two electrons, P orbital has three orbitals (px, py, pz) each holding two electrons, forming a figure of 8, vertical, and coming out towards you respectively
• Larger stars can fuse nuclei to form heavier elements than helium
• Shell number one (1s) can hold two electrons, shell number two (2s and 2p) can hold eight electrons, and shell number three (3s, 3p, and 3d) can hold 18 electrons
• Stars bigger than the Sun can fuse oxygen and silicon together
• Large stars eventually explode at the end of their life, known as a supernova
• We are a product of a star that exploded a long time ago
• The S sub shell has one orbital and can hold two electrons
• The higher the shell number, the further away from the nucleus it is and the more energy it has
• Each orbital can hold two electrons
• The D sub shell has five orbitals and can hold ten electrons
• Electron configuration for calcium 2 plus: loss of two electrons from the 4s orbital
• Electron configuration for iron: 1s2 2s2 2p6 3s2 3p6 4s2 3d8, totaling 26 electrons
• Diagrams with arrows going up and down show the spin direction of electrons
• Formation of p subshell

  PZ orbital coming out towards you, forming a 3D shape, all orbitals are 90 degrees to each other and cluster together to form the p subshell
• Spin pairing involves two electrons occupying one orbital, spinning in opposite directions for the lowest energy conformation
• Electron configuration: Big number in the front indicates the shell number, letter indicates the subshell, and the little number on top indicates the number of electrons in that subshell
• Electron configuration follows filling orbitals singly first, then pairing them up due to electron repulsion