Chapter 2 Modern Atomic Theory Matter consists of atoms Atoms consist of three fundamental particles found in the nucleus and the space around the nucleus Arrangement of Subatomic Particles not to scale Nucleus contains protons and neutrons If an atom has a diameter of about 100 m a football field the nucleus would be 1 mm in diameter What holds an atom together What holds an atom together Coulomb s Law of electrostatic interactions What holds an atom together Coulomb s Law of electrostatic interactions General Behavior Like charges repel Opposite charges attract What holds an atom together Coulomb s Law of electrostatic interactions If we double a charge from 1 to 2 the force will 1 2 3 4 Double Halve Quadruple Quarter What holds an atom together Coulomb s Law of electrostatic interactions If we double the distance the force will 1 2 3 4 Double Halve Quadruple Quarter What s wrong with this picture Electrons are held near the nucleus by the electrostatic attraction between them but The forces of nature We re not just making it up How could we possibly know that the nucleus is small compared to the size of the atom Why not think the protons electrons and neutrons are all mixed together The Rutherford Experiment We re not just making it up The Rutherford Experiment We re not just making it up The Rutherford Experiment Atom Terminology All atoms of an element have the same atomic number number of protons In a neutral atom no charge the number of positively and negatively charged particles must be equal Number protons number electrons The mass number protons neutrons Isotopes Isotopes are atoms of an element with the same number of protons but different numbers of neutrons and different mass Atom symbols are written using the following format X symbol of element A A mass number Z Z atomic number X 1 1H 2 1H 10 5X 66 30X Isotopes continued Most elements have multiple isotopes 1H 2H deuterium 3H tritium radioactive 79Br 81Br 64Zn 66Zn 67Zn 68Zn 70Zn While atomic mass is the mass of an atom average atomic mass takes into account isotopes and natural abundance We use atomic mass units amu 1 amu 1 661 x 10 24 g about the mass of a proton WHAT TIME IS IT Puppy Dog Isotopes Chiuaua 4 lbs Mastif 120 lbs What is the average weight of a collection of these dogs 96 Chiuauas 4 lbs 4 Mastifs 120 lbs Isotopes and Average Atomic Masses all isotopes Average atomic mass fractional abundance mass of isotope Isotopes and Average Atomic Masses all isotopes Average atomic mass Example Boron fractional abundance mass of isotope B has 2 isotopes B 10 mass 10 0129 amu abundance 19 91 B 11 mass 11 0093 abundance 80 09 What is the average atomic mass of Boron HOW DO YOU KNOW THAT Mass Spectrometry The Periodic Table Groups and Periods The Periodic Table Main and Transition Groups The Periodic Table Metals Nonmetals Metalloids The Periodic Table Groups with names Structures of the Elements