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Name: __________________________ Class: ____________________ Date: _____________ Atoms and the Periodic Table The Atom All matter in the universe is made of atoms. Atoms are the smallest component of an element that still have all the properties of that element. Atoms are so small that they are assigned their own unit of mass, called the Atomic Mass Unit, or AMU. One AMU is equal to 0.000000000000000000000001.7 grams! Atoms are mostly empty space, and if one was drawn to scale, it would look something like the picture to the right. The center cluster of the atom is called the nucleus. Two particles reside within the nucleus: - Protons, which have a positive charge and a mass of 1 AMU. - Neutrons, which have no charge and a mass of 1 AMU. Orbiting around the nucleus in the electron cloud (or orbitals) at extremely high speeds are negativelycharged particles called electrons. Electrons are much lighter than protons and neutrons, with a mass of 1/1847AMU. Electrons are so light that when we calculate the mass of an atom, we ignore them (Mass of electrons = 0 AMU). How many electrons, protons, and neutrons are present in this atom of carbon? Protons: ___________ Neutrons: ____________ Electrons: _____________ Normally, atoms have the same number of protons and electrons. Since they have no net charge, they are sometimes referred to as neutral atoms. Fill out the following chart: Charge Protons Neutrons Electrons Mass (in AMU) Location Periodic Table Each particle of the atom determines something different about its characteristics. - Protons determine the identity of the element. Neutrons determine the atom’s mass and stability. Electrons determine how reactive the atom is and how it bonds. The Periodic Table is a chart that lists each of the known elements in the universe, starting with hydrogen, which only has one proton, and ending with Ununoctium, which has 118 protons in its nucleus. Each element has its own box in the periodic table, containing four pieces of information. Label each of these on the box for helium on the right. The element name. The element’s chemical symbol. The atomic number (abbreviation = Z). The mass number (abbreviation = A) The atomic number gives the number of protons. In a neutral atom, there will also be an equal number of electrons. Helium has an atomic number of 2. Therefore, it has ______ protons and __________ electrons. Helium has a rounded mass number of 4. Therefore, it has ___________________ neutrons. You can only have whole numbers of neutrons. Fractions of neutrons do not exist, so round the element’s mass before you calculate the number of neutrons. Practice Identify the number of protons, neutrons, and electrons in a neutral atom of each of these elements. Isotopes Isotopes and Atomic Mass All atoms of the same element will always have the same number of protons. Protons determine the identity of the element. Different atoms of an element may have different numbers of electrons; this forms ions. Atoms may also differ in their number of neutrons, creating isotopes. Isotopes of the same element only differ from each other by their atomic mass and the number of neutrons. Atoms with more neutrons will be heavier, while atoms with less neutrons will be lighter. Look at the three isotopes of hydrogen: How many protons are present in each isotope? How many electrons are present in each isotope? How many neutrons are present in each isotope? Isotope Notation When writing the chemical symbol or name of an element, it is important to indicate if it is not the most common isotope. The most common isotope is the one that you get by rounding the atomic mass shown by the periodic table. Which isotope of hydrogen is the most common? (Circle below) Hydrogen-1 Hydrogen-2 When writing the chemical symbol for an unusual isotope, it is important to indicate the atomic mass. This will tell the reader which isotope you are referring to, and they will be able to calculate the number of neutrons in that isotope. How many neutrons are in 14C? How many neutrons are in 41K? There are two ways to write out isotopes: Element Name – mass number 𝑀𝑎𝑠𝑠 𝑛𝑢𝑚𝑏𝑒𝑟 Ex.) Carbon – 12 Ex.) 12𝐶 𝐸𝑙𝑒𝑚𝑒𝑛𝑡 𝑆𝑦𝑚𝑏𝑜𝑙 Practice Circle the most common isotope for each of the elements below. You can find this by comparing the atomic masses given to the rounded mass number from the periodic table of each element. 1. Helium-3 Helium-4 2. Barium-135 Barium-136 Barium-137 3. Argon-36 Argon-38 Argon-40 4. Chlorine-35 Chlorine-37 5. Nitrogen-14 Nitrogen-15 6. Silicon-28 Silicon-29 Silicon-30 7. Uranium-234 Uranium-235 Uraniuim-238 Barium-138 For each of the isotopes given below, add the correct symbol (using isotope notation), the name (showing atomic mass), and the number of protons, neutrons, and electrons. Symbol Name # of Protons 11B Boron-11 5 10B Boron-10 # of Neutrons # of Electrons 5 18O 131Xe Xenon-131 Sulfur-35 Titanium-48 60Co 51 72 43 56 42 HINT Protons = atomic number Neutrons = Mass number – atomic number Electrons = atomic number (only when it is a neutral atom) Mass number = protons + neutrons 33 Isotope and Ion Notation Extra Practice Background Isotopes are atoms of the same element with different numbers of neutrons. Ions are atoms of the same element with a charge due to the gain or loss of electrons. Ions are isotopes are both expressed with specific forms of notation. Ions will have a + or – sign next to the chemical symbol of the element. Magnesium has a 2+ charge, indicating that it has lost two electrons. Bromine has a – charge, indicating that it has lost one electron. Isotopes must be accompanied by the mass number, since the number of neutrons has changed. The atomic number may also be included. Each of these isotopes of carbon has 6 protons. Carbon-12 has 6 neutrons, while carbon-14 has 8 neutrons. Practice For each of the element symbols below, indicate whether it represents an ion, isotope, or neutral atom. Use a periodic table to identify element name and the number of protons, neutrons, and electrons present. Symbol Name Classification # of Protons # of Neutrons # of Electrons Al3+ Aluminum Cation 13 14 10 Hydrogen-3 Neutral Atom Chlorine 18 Ag+ 18 O Neutral Atom Scandium 21 34 19 46 S-2 41 K 19 Gold-198 P-3 15 Modified from James Dauray