Subatomic ParticlesAtomic Structure Is it really the smallest thing out there?
Atoms • The smallest particle of an element that retains the properties of that element • These are mostly chemical properties, not physical properties
Subatomic Particles • Particles of matter that make up atoms • Smaller than atoms themselves • Behave differently than whole atoms
Electrons • Negatively charged particles found outside the nucleus in an area known as the “electron cloud” • Discovered by JJ Thomson during the “Cathode Ray Tube” experiment
Protons • Positively charged particles found in the nucleus of the atom • Discovered by Ernest Rutherford (& associates) during the “Gold Foil” Experiment
Neutrons • Particles with no charge found in the nucleus of the atom • Discovered by James Chadwick
Atomic Nucleus • The central core of the atom • Composed of protons & neutrons • it has a positive charge • Held together by the strong nuclear force • One of the four fundamental forces in the universe • It contains almost all of the mass of the atom (very dense)
Atomic Nucleus • It is a very small percentage of the volume of the atom • Marble in a football stadium • As the nucleus gets larger, it becomes harder to create and more unstable • Why?
Atomic Number • The number of protons an atom contains • Found on the periodic table • The number of protons identifies the atom • Atoms of different elements will have different number of protons and different atomic numbers
Number of Electrons • Whole atoms are electronically neutral • They must have the same number of protons (positive charge) and electrons (negative charge) • The atomic number is also the number of electrons an atom contains
Mass Number • An (overwhelmingly) large majority of the mass of an atom is located in the nucleus • Protons & Neutrons are in the nucleus • Mass Number is the sum of the number of protons and the number of neutrons
Isotopes • Atoms that have the same number of protons, but different number of neutrons • They are the same element with a different mass • Same atomic number • Different mass numbers
Identifying Isotopes • Element Name – Mass Number • Oxygen-16 • 8 protons/8 neutrons • Chlorine-35 • 17 protons/18 neutrons • Uranium-238 • 92 protons/146 neutrons
Identifying Isotopes • X: elemental symbol • Z: Atomic Number • A: Mass Number