Atoms…A Matter of Fact! STRUCTURE of the ATOM • Atoms are made of smaller particles called protons, neutrons and electrons. Parts of the Atom • Particle Charge Location Proton Positive Neutron Neutral (no charge) Negative In the Nucleus In the Nucleus Orbiting the Nucleus Electron Where does an atoms mass come from? • The mass of an atom comes from the nucleus. • The protons and neutrons are responsible for the mass of the entire atom! IDENTIFYING AN ATOM • ATOMS CAN BE IDENTIFIED BY THE NUMBER OF PROTONS THAT ARE IN THE NUCLEUS. • THE NUMBER OF PROTONS EQUALS THE ATOMIC NUMBER ATOMIC NUMBER • Atomic number = the number of protons. • Sodium Na has an atomic number of 11. Therefore it has 11 protons in the nucleus. Neutral Atoms • Atoms are neutral because they have the same number of protons as electrons. ISOTOPES • Atoms with the same number of protons and a different number of neutrons. Identifying an Isotope • Isotopes can be identified by their mass number. • Mass numbers are found by adding the protons and neutrons. • Atomic mass of an element is the average mass of all the isotopes of that element. Isotope example • Carbon has a mass # of 12 because there are • normally 6 protons and 6 neutrons. 6+6=12 Carbon’s isotope has a mass # of 14 because there are 6 protons and 8 neutrons. 6+8=14 History of the Atom ATOMIC THEORISTS • • • • • • JOHN DALTON J.J. THOMSON ERNEST RUTHERFORD NIELS BOHR JAMES CHADWICK PRESENT MODERN MODEL JOHN DALTON • The first modern scientist to propose the existence of atoms. He described an atom as an invisible, indestructible, solid sphere, like a billard ball. Thomson Model • Proposed that the atom is a solid mass of positively charged material with negative charges scattered throughout. He is credited with discovering the electron. • Described as the “blueberry muffin” or “plum pudding” model. RUTHERFORD MODEL • Says that the atom is mostly empty space. • Electrons orbit around positively charged nucleus. He discovered the nucleus. BOHR’S MODEL • Proposed that electrons move in different orbits, or energy levels, around the nucleus like planets orbit the sun. Each level contains a certain number of electrons. CHADWICK’S MODEL • Discovered the neutron. This explained why atoms were heavier than the total mass of their protons and electrons. Present Modern Model • Electrons form a negatively charged cloud around the nucleus. It is impossible to determine exactly where an electron is at a given time.