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Learning Goal #3: Discriminate between the relative size, charge, position, and number of protons, neutrons, and electrons of different elements. MATTER UNIT WHAT IS AN ATOM? Atom: the smallest unit of matter that retains the identity of the substance SIZE OF THE ATOM http://learn.genetics.utah.edu/content/begin/cells/scale/ The nucleus has a diameter 10,000 times smaller than the atom. The great amount of empty space in an atom can be illustrated by the following analogy. Imagine the nucleus to be the size of a golf ball. Then on this scale the first electron shell would be about one kilometer from the golf ball, the second shell about four kilometers, the third nine kilometers and so on. If you find that hard to visualize then try this. The period at the end of this sentence, (depending on your monitor and the font you are using), is probably about 1/2 a millimeter in diameter. If that period represents the nucleus then the electrons in the first shell would be orbiting with a diameter about 50 meters around you. in fact, the actual diameter of an atom is very small and it would require some two hundred million of them side by side to form a line a centimeter long. ATOMIC STRUCTURE Atoms are composed of 2 regions: Nucleus: the center of the atom that contains the mass of the atom Electron cloud: region that surrounds the nucleus that contains most of the space in the atom Electron Cloud Nucleus ATOMIC STRUCTURE The nucleus contains 2 of the 3 subatomic particles: Protons: positively charged subatomic particles Neutrons: neutrally charged subatomic particles The 3rd subatomic particle resides outside of the nucleus in the electron cloud Electron: the subatomic particle with a negative charge and relatively no mass Atomic Particles Particle Charge Mass # Location symbol Electron -1 0 Electron cloud e- Proton +1 1 Nucleus p+ 0 1 Nucleus n0 Neutron HOW DO THESE PARTICLES INTERACT? Protons and neutrons are in the tiny positively charged nucleus accounting for most of the mass of the atom The negatively charged electrons are small and have a relatively small mass but occupy a large volume of space outside the nucleus HOW DO THE SUBATOMIC PARTICLES BALANCE EACH OTHER? In an atom: The # of protons = The # of electrons If 20 protons are present in an atom then 20 electrons are there to balance the overall charge of the atom—atoms are neutral The neutrons have no charge; therefore they do not have to equal the number of protons or electrons THE NUMBER OF PROTONS IDENTIFIES THE ATOM. An atom with 6 protons = Carbon An atom with 8 protons = Oxygen An atom with 20 protons = Calcium ATOMIC STRUCTURE He 2 4 Atomic number the number of protons in an atom Atomic mass the number of protons and neutrons in an atom Number of electrons = Number of protons Number of neutrons = Atomic mass – Number of protons DETERMINING THE NUMBER OF PROTONS AND NEUTRONS Li has a mass number of 7 and an atomic number of 3 Protons = 3 (same as atomic #) Neutrons= 7-3 = 4 (mass # - atomic #) Ne has a mass number of 20 and an atomic number of 10 Protons = 10 Neutrons = 20 - 10= 10 WHAT ABOUT THE ELECTRONS? The electrons are equal to the number of protons So e- = p = atomic # Ex: He has a mass # of 4 and an atomic # of 2 p+ no =2 =2 e- = 2 DETERMINE THE NUMBER OF SUBATOMIC PARTICLES IN THE FOLLOWING: Cl has a mass # of 35 and an atomic # of 17 p+ = 17, no = 18, e- = 17 K has a mass # of 39 and an atomic # of 19 P+ = 19, no = 20 e- = 19 HOW EXACTLY ARE THE PARTICLES ARRANGED? Bohr Model of the atom: All of the protons and the neutrons The 3rd ring can hold up to 8 eThe 4th ring and any after can hold up to 18 e- The 1st ring can hold up to 2 eThe 2nd ring can hold up to 8 e- ATOMIC STRUCTURE Electrons are arranged in Energy Levels or Shells around the nucleus of an atom. • first shell a maximum of 2 electrons • second shell a maximum of 8 electrons • third shell a maximum of 8 electrons WHAT DOES CARBON LOOK LIKE? Mass # = 12 atomic # = 6 6 p and 6 n live in the nucleus p+ = 6 no = 6 e- = 6 PRACTICE BOHR DIAGRAMS A unit created to describe atoms because the gram and kilogram are too large to use to define an atom. 1amu = 1.66 x 10-24g .00000000000000000000000166g Listed on the periodic table as the atomic mass. The average mass of all of the isotopes of an atom. Element amu Hydrogen 1.008 Carbon 12.01 Nitrogen 14.01 Oxygen 16.00 Sodium 22.99 Aluminum 26.98 1 atom = 1 amu Example › 1 atom of carbon = 12.001 amu of carbon › 3 atoms of carbon = 36.003 amu of carbon › 3.00 X 1020 amu =2.50 x 1019 atoms of carbon The unit all chemists use in describing numbers of atoms. Defined as the number equal to the number of carbon atoms in 12.01 grams of carbon. A sample of on element with a mass equal to that element’s average atomic mass expressed in grams contains 1 mol of atoms. 6.022 X 1023 One mole of something consists of 6.022 X 1023 units of that substance. › One mole of eggs is 6.022 X 1023 of eggs. Elements # of atoms Mass of sample (g) Aluminum 6.022 X 1023 26.98 Gold 6.022 X 1023 196.97 Iron 6.022 X 1023 55.85 Sulfur 6.022 X 1023 32.07 Boron 6.022 X 1023 10.81 Xenon 6.022 X 1023 131.3 The mass of one mole of a substance. › The sum of all the masses of the atoms in a compound. CH4 C - 1x12.01=12.01 H – 4x1.008=4.032 Total = 16.04g