Ions and Isotopes

• Molecules are neutral particles composed of two or more atoms held together by chemical bonds
• A molecule can be made up of similar or different types of atoms
• Example: A water molecule is made up of two hydrogen (H) atoms and one oxygen (O) atom, giving it the chemical formula H2O
• Mass number (atomic mass number) is the number of protons plus the number of neutrons in an atom's nucleus
• Each chemical element has a different atomic number, which is the number of protons in an atom's nucleus
• Chemical symbols represent elements on the periodic table, with each element having its own unique symbol
• Chemical symbols are made up of one or two letters, with the first letter always capitalized and the second letter, if present, in lowercase
• Niels Bohr expanded on Rutherford's atomic theory, proposing that electrons have specific energy levels and travel in certain orbits
• Bohr's model is used to illustrate electron energy levels and how outer orbits determine an atom's chemical properties
• Niels Bohr was awarded a Nobel Prize for physics in 1922 for his work on atomic structure
• An ion is an atom or molecule that has lost or gained one or more of its outer valence electrons, resulting in a positive or negative electric charge
• Anions are negatively charged ions, formed when an atom gains electrons
• Cations are positively charged ions, formed when an atom loses electrons
• Isotopes are atoms of the same element with different numbers of neutrons in the nucleus
• Isotopes have the same number of protons but different numbers of neutrons, leading to different mass numbers
• Example: Isotopes of hydrogen include protium (no neutrons), deuterium (one neutron), and tritium (two neutrons)
• Hydrogen is the lightest and most abundant element in the universe, making up more than 90% of all atoms
• Hydrogen has three common isotopes: protium, deuterium, and tritium
• Protium is the most common isotope of hydrogen with one proton and no neutrons
• Deuterium has one proton and one neutron, while tritium has one proton and two neutrons and is radioactive
• Hydrogen is a fuel for stars like the sun through the nuclear fusion process, releasing large amounts of energy
• Henry Cavendish, an English chemist and physicist, realized that hydrogen gas is a distinct substance and showed that burning hydrogen produced water