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The Atomic Nature of Matter Conceptual Physics Chapter 17 Atoms • Building blocks of most matter Elements • • • • Atoms of the same kind of make up Approximately 115 elements know 90 occur in nature 99% of material on Earth is made from 12 different elements • Living things are composed of O, C, H, N and Ca. Atoms are recyclable • Atoms are older than the material they compose • Atoms in your body have been around since before the solar system • We are only the present caretakers Atoms are small • There are about 10 to the 23 atoms in a gram of water (thimbleful) • Atoms are always moving • It takes 6 years for one of your exhaled breaths to mix evenly with the atmosphere Evidence for Atoms • Brown (1827) was studying pollen grains under a microscope • Brownian motion—atoms are perpetually moving • Today—electron microscopes, scanning tunnel microscopes allow us to see atoms Scanning tunneling microscope Molecules • Atoms are combined to form larger particles (not crystalline salts or metals) compounds • Made of atoms of different elements in a fixed proportion • May or may not be made of molecules Atomic nucleus • Atom is mostly empty space • Nucleus-most mass is located in this central region • Rutherford discovered the nucleus in his gold foil experiment in 1911 • Nucleus contains neutrons and protons Nucleus con’t • Protons are positively charged • Neutrons have no charge • Also known as nucleons (protons and neutrons) • Isotopes: same element with different numbers of neutrons Atomic number • Atoms are classified by atomic number • Number of protons in the nucleus Electrons • Negatively charged • Orbit the nucleus in an electron cloud • Ion: when an atom has a charge Shell Model of the Atom • • • • Shows have electrons orbit the nucleus Each shell has a capacity for electrons First shell 2 Second 8 etc. Periodic table • Chart that lists atoms by atomic number and electron arrangement • Group: in same column Periodic table Phases of Matter • • • • • • Four phases (all have movement) Solid Liquid Gas Plasma All can be changed from one phase to the next plasma • Matter consists of positive ions • High temperatures
