Atomic structure and the periodic table

• The plum pudding model is: an atom is a ball of positive charge with negative electrons embedded in it. 1897 by JJ Thomson.
• In 1909, Ernest Rutherford conducted the alpha particle scattering experiment. He discovered that most of the atom is empty space.
• Neil Bohr suggested that electrons orbit the nucleus in shells. His theory was supported by many experiments.
• Rutherford discovered protons after Bohr’s discovered fixed shells. Then 20yrs later, James Chadwick discovered neutral particles called neutrons.
• The mass number of an element is the total amount of protons and neutrons in the nucleus of an atom.
• Relative atomic mass = sum of isotopic mass / sum of atomic mass
• In chemical reactions, metal atoms loose electrons to form positive ions.
• relative atomic mass is the average mass of the atoms of an element compared to one-twelfth of the mass of a carbon-12 atom.
• Ions are formed when atoms gain or lose electrons.
• Metals tend to lose electrons to become cations (positive ions). Nonmetals tend to gain electrons to become anions (negative ions).
• Period number tells us the number of occupied electron shells in an atom.
• The subatomic structure in an atom responsible for isotopes, is the neutron.
• Mendeleev left gaps in the periodic table because he didn't know what elements were going to be discovered.
• Group 7 elements are halogens.
• Group 0 or 8 elements are noble gases. They are inert and non-reactive.
• Group 1 elements are called alkali metals because they react with water to form alkaline solutions.