Chapter 2

• An element contains only one type of atom
• A compound is made of atoms of different elements bonded together
• A mixture contains different elements/compounds which are not bonded together
• Atomic Number - Number of protons in an element
• Nucleon number - Number of protons and neutrons in an element
• Mass number = atomic mass + number of neutrons
• Isotopes have the same atomic number but different nucleon numbers
• Unstable isotopes are called Radiotopes. Their breakdown is a nuclear reaction, not chemical. They give out a lot of energy, including radiation
• Ar is the average mass of an element's isotopes compared to 1/12 the mass of an atom of Carbon-12
• Every atom has an equal number of protons and electrons, so atoms have no overall charge
• Electrons are arranged in shells around the nucleus
• Group 8 elements are unreactive, or inert
• Element


  Contains one type of atom
• Compound


  Made of atoms of different elements bonded together
• Mixture


  Contains different elements or compounds that are not bonded together
• Atomic Number/Proton Number


  Number of protons in the nucleus of an atom, or number of protons in an atom
• Nucleon Number/Mass Number


  Total number of neutrons and protons in an atom
• Atoms have no overall charge, as the number of protons and neutrons are the same
• Electrons


  Arranged in shells around the nucleus
• Isotopes


  Atoms of the same element that have the same number of protons but different number of neutrons
• Relative Atomic Mass


  Average mass of its isotopes compared to 1/12th the mass of the atom of Carbon-12 (unit = amu)