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Using the Periodic Table 6 Carbon C 12.011 amu • Atomic number- always a whole number, increases in order, represents the number of protons in each atom • Atomic name, often in Latin, sometimes uses a common name, sometimes there are disagreements • Atomic symbol – often, but not always, matches the name; Always capitalize the first (only the first ) letter • Atomic mass- the mass of the atoms based on the average of all the most common isotopes Chapter 6 Atoms • Philosophy question: If you jump half-way across the room, and then continue jumping half-way, how many jumps until you reach the other side? • Aristotle, the famous Greek philosopher and scientist, argued that a substance could be divided again and again, forever getting smaller and smaller pieces • During his time people believed the universe was made of four elements; fire, water, earth and air. • The idea of “uncuttable” particles was first suggested by Democritus around 440 B.C. • “Atomos” means indivisible Antoine Lavoisier • Considered the Father of Chemistry due his extensive research and many experiments, including how things burn (food, wood etc) and the Law of Conservation of Mass • Executed in 1794 during the French revolution Section 1 Atomic Theory • Atomic Theory (by John Dalton) published in 1803 – All substances are made from atoms. Atoms cannot be created, divided or destroyed. – Atoms of the same element are exactly alike. – Atoms can join together to form new substances. Parts of the Atom Particle Charge Location Size Proton Positive In the nucleus 1 a.m.u. Neutron No charge (neutral) In the nucleus Almost 1 a.m.u. Negative Outside the nucleus, orbiting at nearly the speed of light Very tiny, 1/1000th a.m.u. Electron Structure of the Atom • Protons + – Positively charged – Found in the nucleus of the atom (center) – Mass of 1 amu (atomic mass unit) – Gives the element its atomic number on the periodic table • #1 (hydrogen) has 1 proton • #4 (beryllium) has 4 protons Protrons were discovered by Ernest Rutherford in 1911 and he discovered the empty space within an atom in 1909 • Neutrons – Neutral charge ( no charge) – Found in the nucleus (center) – Mass slightly smaller than a proton, still considered 1 amu – Protons + Neutrons @ atomic mass (rounded to the nearest whole number) N Electron • Electrons – Negatively charged particles – Found outside the nucleus, moving at nearly the speed of light, in specific levels – Most commonly atoms are neutral particles having equal numbers of protons and electrons – Very small ( about 1/1000th of a proton) Electrons were discovered by J.J. Thompson in 1897 Proton Neutron * In 1913 Niels Bohr suggested that electrons travel in specific paths called Electron Shells • Each level can only contain a certain number of electrons before it is full • Each level will fill completely before electrons go to the next level • Lower levels fill first • Isotope Hydrogen (H-1), most common 99.9% – Atoms can often be found with different numbers of neutrons • Some atoms have only one stable isotope, others have several • Averaging the masses of the isotopes in their correct percentages gives the exact atomic mass for each element • Unstable isotopes break down (radioactive decay) deuterium (H-2), tritium (H-3), least common, radioactive For example 12 • Different isotopes are identified by their mass numbers C 13 C 14 C 6 protons + 6 neutrons 6 protons + 7 neutrons 6 protons + 8 neutrons Sometimes written C-12, C-13, C-14 Mass number is the protons + neutrons Calculating Atomic Mass Using Isotopes • Determine the mass of each isotope based on its abundance (percent of each isotope found) – Remember, convert percents into decimals – Multiply by the mass number of the isotope Cl-35 76% 35 x 0.76 = 26.6 Sample of chlorine * Your calculated answer should be very close to the mass on the periodic table Cl-37 24% 37 x 0.24 = 8.88 26.6 + 8.88 = 35.48 amu Actual mass = 35.453 amu • Slides 1 – 15 for honors • Slides 17-20 for reg Chapter 6 Atoms Section 1 Atomic Theory • Atomic Theory (by John Dalton) published in 1803 – All substances are made from atoms. Atoms cannot be created, divided or destroyed. – Atoms of the same element are exactly alike. – Atoms can join together to form new substances. Parts of the Atom Particle Charge Location Size Proton Positive In the nucleus 1 a.m.u. Neutron No charge (neutral) In the nucleus Almost 1 a.m.u. Negative Outside the nucleus, orbiting at nearly the speed of light Very tiny, 1/1000th a.m.u. Electron Structure of the Atom • Protons + – Positively charged – Found in the nucleus of the atom (center) – Mass of 1 amu (atomic mass unit) – Gives the element its atomic number on the periodic table • #1 (hydrogen) has 1 proton • #4 (beryllium) has 4 protons Protrons were discovered by Ernest Rutherford in 1911 and he discovered the empty space within an atom in 1909 • Neutrons – Neutral charge ( no charge) – Found in the nucleus (center) – Mass slightly smaller than a proton, still considered 1 amu – Protons + Neutrons @ atomic mass (rounded to the nearest whole number) N Electron • Electrons – Negatively charged particles – Found outside the nucleus, moving at nearly the speed of light, in specific levels – Most commonly atoms are neutral particles having equal numbers of protons and electrons – Very small ( about 1/1000th of a proton) Electrons were discovered by J.J. Thompson in 1897 Proton Neutron * In 1913 Niels Bohr suggested that electrons travel in specific paths called Electron Shells • Each level can only contain a certain number of electrons before it is full • Each level will fill completely before electrons go to the next level • Lower levels fill first