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“Success in life comes not from holding a good hand, but in playing a poor hand well.” ~Warren G. Lester Chemistry Chemistry is a branch of science that investigates the properties of matter and the ways in which matter interacts, combines, and changes. Chemistry: The Study of Matter and Its Changes Chemistry is the study of matter and its changes. Matter is anything that has mass and has volume. The universe can be divided into two broad categories: Matter and Energy Classification of Matter Definitions for Components of Matter Element - the simplest type of substance with unique physical and chemical properties. An element consists of only one type of atom. It cannot be broken down into any simpler substances by physical or chemical means. Atoms are the smallest particle of an element that retains the properties of that element. Elements are represented by chemical symbols. Examples are H, CO, Co, and Mg. Note that the first letter is capital, second is lower case. Laminated Periodic Tables Elements and Compounds: Pure substance = element or compound – Elements cannot be decomposed to simpler forms by any amount of chemical transformation or physical means. – Compounds are composed of two or more elements in definite proportions, can be broken down by chemical means. General features of the atom. The atom is an electrically neutral, spherical entity composed of a positively charged central nucleus surrounded by one or more negatively charged electrons in an electron cloud. The atomic nucleus consists of protons and neutrons. Ask me about: Wms Brice stadium and a golf ball. Subatomic Particles o A proton is about 2000 times more massive than an electron 1 u = 1 atomic mass unit = 1 amu = 1.66 x 10 -24 grams © 2013 Pearson Education, Inc. Chapter 3 8 Protons Determine the Element • The atomic number, Z, represents the number of protons, p+, in the nucleus of an atom. • The atomic number is usually the biggest number listed in the box for each element (look at periodic table). • The atomic number (or number of protons) identifies an element. • The modern periodic table orders elements according to increasing atomic number. • The charge of a proton is assigned numerical value of +1. • Mass of a proton is 1.0 amu • 1 amu = 1.66 x 10 -24 grams Electrons, e’ • A neutral atom has as many electrons outside its nucleus as protons within its nucleus , # p+ = # e’ • e’ has about 2000 times less mass than a proton. • e’ has a relative charge of - 1. • Atoms can lose and gain one or more electrons to form ions. • Two types of ions: • Cation forms when atom loses e’s. Na ---------> Na +1 + e’ • Anion forms when atom gains e’s. Cl + e’ ----------> Cl -1 Neutrons,n0 • Neutrons are almost as massive as protons but carry no electrical charge. Mass of a n0 is 1.0 amu. • Neutrons are located in the nucleus. • Cannot determine the # n0 ‘s by looking at the periodic table! • The sum of neutrons and protons in an atom is called the mass number, A. It has units of amu. Cannot find mass # on periodic table ! mass # = # p+ + # n0 Check Your Understanding What is the atomic number for phosphorus ? How many protons does a calcium atom have ? How many electrons does an oxygen atom have ? If Z = 24, identify the element. For element Z = 13, determine the number of e’s. Check Your Understanding What is the atomic number for phosphorus ? 15 How many protons does a calcium atom have ? 20 How many electrons does an oxygen atom have ? 8 If Z = 24, identify the element. chromium For element Z = 13, determine the number of e’s. 13 Isotopes The number of neutrons in the atoms of an element can vary resulting in ISOTOPES. – Can be naturally occurring or man-made An example is carbon. Two isotopes of carbon are shown. Top: # p+ = 6 # e’ = 6 # n0 = 6 Bottom: # p+ = 6 # e’ = 6 # n0 = 7 Isotopes Isotopes are named using the MASS NUMBER: Carbon-12 Oxygen-16 Atomic Number, Mass Number, and Atomic Symbol Figure 2.7 X = Atomic symbol of the element A = mass number; A = Z + N Z = atomic number (the number of protons in the nucleus) N = number of neutrons in the nucleus =A-Z Isotopic Symbols 52 Cr Determine #p+,# e’, and # n0 24 32 P Determine #p+,# e’, and # n0 Isotopic Symbols 52 Cr #p+ = 24 # e’ = 24 # n0 = 28 24 32 P #p+ = 15 # e’ = 15 # n0 = 17 Isotopic Symbols What is the name for the isotope that has 92 protons and 143 neutrons ? Uranium-235 (“Little Boy” atomic bomb) Highly enriched Uranium-235 Learning Check Which of the following represent isotopes of the same element? #1 #2 #3 #4 234 234 235 238 91 X 93 X 92 X 92 ID the elements represented above X Average Atomic Mass • Atomic masses listed on the periodic table are weighted averages of the masses of all the naturally occurring isotopes for that element. • Silver has two naturally occurring isotopes. One has a mass of about 107 amu and the other has a mass of about 109 amu. • Silver-107 has an abundance in nature of 51.86%. • Silver-109 has an abundance in nature of 48.14%. • Silver’s average atomic mass is the weighted average of these isotopes. • Look on periodic table, what is silver’s average atomic mass (also called atomic mass)? What is the difference? Average Atomic Mass Mass Number • Found on the periodic table. • Atomic mass is the weighted average mass of an atom based on the relative natural abundance of that element's isotopes. • NOT on periodic table • A count; exact number • The total number of neutrons and protons in a given isotope. Most Common Mass Number --Look at average atomic mass given on periodic table --Round the value to whole number Example: Write the isotopic symbol for the most common isotope of: Phosphorus-see board You try: Write the isotopic symbol for the most common isotope of: Calcium Iodine Zinc Average Atomic Mass See Handout Honors Only Rutherford’s Gold Foil Experiment • Rutherford’s experiment involved firing a stream of tiny positively charged particles (alpha particles) at a thin sheet of gold foil (2000 atoms thick). • Nobel Prize in 1908 • https://www.youtube.com/ watch?v=kBgIMRV895w • Start at 3 min Honors Only Give Handout Handout-Atomic Structure WS