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Bellwork 10/19/15 • Tell me about one or more of your family traditions. • Minimum 5 sentences. P. Sci. Unit 8 Chapter 4 Atoms Atomic Structure – timeline • Ancient Greece - Democritus proposed the atom – a tiny solid particle that could not be subdivided. • 1904 – J.J. Thomson – discovered that atoms contained small, negatively charged particles called electrons. • 1911 – Ernest Rutherford – proposed that the atom had two parts – the nucleus in the center (most of the mass) surrounded by the electrons. • 1913 – Niels Bohr – hypothesized that electrons traveled in fixed orbits around the atom’s nucleus. • 1913 – James Chadwick – concluded that the nucleus contained positive protons and neutral neutrons. • 1926 – Erwin Schrodinger – developed the quantum mechanical model – which is based on the wavelike properties of the electron. (not a particle – leads to quantum physics) • 1927 – Werner Heisenberg – (the Heisenberg uncertainty Principle) described that it is impossible to know precisely both an electron’s position and path at a given time. Led to the electron cloud theory. electron neutron proton Atoms • The smallest particle that has the properties of an element. Dalton’s Atomic Theory • Every element is made of tiny, unique, particles called atoms that cannot be subdivided. • Atoms of the same element are exactly alike. • Atoms of different elements can join to form molecules or compunds Parts of an Atom • Nucleus – small, dense center of an atom made up of 2 subatomic particles that are identical in size and mass. –Protons – have a positive charge –Neutrons – have no charge Parts of an Atom cont. • Electrons – are tiny subatomic particles that have very little mass that moves around the outside of the nucleus. These particles are negatively charged and form a “cloud” around the nucleus. • The number of protons and electrons an atom has is unique for each element. Atomic Charge • Atoms have no overall charge because the protons (+) cancel out the electrons (-). Helium 2 protons - +2 2 neutrons 0 2 electrons - -2 total charge 0 Protons • positive (+) charge • Found in the nucleus • # of protons = atomic # • The number of protons identify the element (atomic #) Neutrons • no charge • Found in the nucleus • Along with protons makes up atomic mass • Atomic Mass – atomic number = # of neutrons (rounded to whole #) Electrons • negative (–) charge • travel in orbitals (or energy levels) around the nucleus. (electron cloud) • Equals atomic number in neutral atoms • valence electrons - the # of electrons in the outer shell and relates to the oxidation # • Unit of measure for atomic particles is Atomic mass unit (amu) protons and neutrons = about 1 amu (electrons are about 1/2000 of the size of protons and neutrons)) Chemical symbols • The one or two letter abbreviation of the element name. • Some are based on Latin name • ALL 1st letter is upper case • ALL 2nd letter is lower case Mass Number or Atomic Mass • the sum of the number of protons and the number of neutrons in the nucleus of an atom. • # of neutrons = Neutrons mass # - atomic # Protons + Atom Summary • Atomic Number = protons = electrons • Atomic Mass = Protons + Neutrons • Neutrons = atomic mass – atomic number • Atomic symbols – First letter is ALWAYS upper case – Second letter is ALWAYS lower case • Example: Oxygen element 6 with mass 16 P=8 E=8 N = 16-8 = 8 Isotopes • Atoms of the same element that have a different # of neutrons and a different atomic mass. (identified by the element name followed by the mass # ) • ex. C-12, C-14, B-10, B-11) Carbon 14 = 8 neutrons 6 electrons 6 protons 6 protons 6 electrons Carbon 12 = 6 neutrons Average atomic mass • the weighted - average mass of the mixture of all an atoms isotopes. The average atomic mass is close to the mass of its most abundant isotope. • This is the number found on the periodic table