SCIENCE Q2 G9

• Democritus: He proposed that matter could not be divided into smaller pieces forever.
• Democritus: He claimed that matter was made of small, hard particles that he called "atomos".
• John Dalton: He suggested that all elements are composed of different types of atoms with unique properties.
• Dalton: He created the very first Atomic Theory.
• Dalton: Dalton viewed atoms as tiny, solid, balls.
• Thomson: He showed that the atom was made of even smaller things.
• Thomson: His atomic model was known as the "raisin bun model"
• Rutherford: He discovered protons and the nucleus
• Rutherford: He showed that atoms have (+) particles in the center, and are mostly empty space.
• Niels Bohr: He improved on Rutherford's model.
• Niels Bohr: He proposed that electrons move around the nucleus in specific layers or shells.
• Chadwick: He discovered neutrons.
• Chadwick: Working with Rutherford, he discovered particles with no charge; these particles were called as neutrons.
• Modern: Work done since 1920 has changed the model.
• Modern: The new atomic model has electrons move around the nucleus in a cloud.
• The first quantum number is the principle quantum number (n) that describes the size and energy of the orbital and relative distance from the nucleus.
• Shell: a term called for an electron occupying.
• The wave mechanical model, on the other hand, introduced a mathematical description of the electron's motion called a WAVE FUNCTION or ATOMIC ORBITAL.
• If 1=0, then the orbital is called an s-orbital and has a spherical shape with the nucleus at the center of the sphere.
• If 1=1, then the orbital is called a p-orbital with two lobes of high electron density on either side of the nucleus, for an hourglass or dumbbell shape.
• If 1=2, then the orbital is d-orbital with a variety of shapes.
• If 1=3, then the orbital is an f-orbital with more complex of shapes.
• The third Quantum number is the magnetic quantum number (m1). It describes the orientation of the orbital sound around the nucleus. The possible values of m1 depend upon the value of the 1 quantum number. The allowed values for m1 are -1 though 0 to +1.
• The fourth quantum number is the spin quantum number (ms) and indicates the direction the electron is spinning. There are only two possible values for ms: +1/2 and -1/2. When two electrons occupy the same orbital, then one must have an ms= +1/2 and the other electrons must have an ms = -1/2. These are spin-paired electrons.
• Quantum Mechanics may be used to determine the arrangement of the electrons within an atom if two specific principles are applied: the Pauli exclusion principle and the Aufbau principle.
• Pauli exclusion principle states that no two electrons in an atom ca have the same set of the four quantum numbers.
• The second principle, the Aufabu principle =, describes the order in which the electrons enter the different orbitals and sublevels. The arrangement of electrons builds up from the lowest energy level. The most stable arrangement of electrons has all the electrons with the lowest possible energy. The lowest energy arrangement is the ground state. Less stable (higher energy) arrangements are the excited states.
• S-subshell/orbital can hold a maximum of 2 electrons.
• P-subshell/orbital can hold up to 6 electrons.
• D-subshell/orbital can hold a maximum of 10 electrons.
• F-subshell/orbital can hold up to 14 electrons.