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(Part 2 of this Unit) MATTER , ELEMENTS AND THE PERIODIC TABLE PA STANDARDS: 3.2.7.A1 – IDENTIFY GROUPS OF ELEMENTS WITH SIMILAR PROPERTIES 3.2.7.A2 – IDENTIFY ATOMS AS THE BASIC BUILDING BLOCKS OF MATTER 34. CHAPTER 3, SECTION 1 – ORGANIZING THE ELEMENTS Scientists need to organize the elements in a useful way The first Periodic Table of Elements was proposed by a Russian – Dmitri Mendeleev in 1869 35. OBSERVATIONS MADE BY MENDELEEV Mendeleev grouped elements that had similar chemical and physical properties. Within these groups, he listed the elements top to bottom by their atomic masses; The elements also line up in rows across the table by bonding power; this is the number of chemical bonds an element can form by attaching other atoms to itself. 36. PERIODIC TABLE ARRANGEMENT Today’s modern table reflects some changes from Mendeleev’s original (it’s now read leftright) The table is called “periodic” because it has a regular repeated pattern in each row Each row is called a period. Each column is called a group or family. Now the table is listed in order of increasing atomic numbers (# of positive protons inside the nucleus) TODAY’S MODERN PERIODIC TABLE 37. TABLE FACTS: The atomic number tells how many protons are inside the atom (#7 N has 7+) Elements in the same group (column) have the same chemical properties The period (row) that an element is in tells us how many energy levels (orbital rings) surround the nucleus (ex: N is in period 2 and has 2 rings) 38. ATOMIC STRUCTURE SUMMARY At the core of an atom is the nucleus. The nucleus consists of protons and neutrons. Electrons are found outside the nucleus in energy levels (also called orbital rings). EXAMPLE: ATOMIC STRUCTURE OF HELIUM Electron (black dot) Nucleus (dark center) Helium’s atomic # on the Periodic Table is 2 because it has 2 protons in its nucleus. 39. SUBATOMIC PARTICLES - PROTONS Protons have a positive charge (+) They are found in the nucleus Number of protons is the same as the atomic number The # of protons always equals number of electrons so that + and – charges balance The mass of a proton is equal to 1 a.m.u. (“atomic mass unit”) 40. SUBATOMIC PARTICLES - NEUTRONS Neutrons do not have a charge; they are neutral They are found in the nucleus The mass of a neutron is also 1 a.m.u. The number of neutrons can vary for one element; a different # will change the mass of the atom 41. SUBATOMIC PARTICLES - ELECTRONS Electrons have a negative charge ( - ) Are found moving outside the nucleus Electrons have practically no mass Electrons on the outermost ring control the chemical behavior of the atom; we call these outside electrons: valence electrons ATOMIC STRUCTURE OF SODIUM QUIZ YOURSELF: Refer to this block from the periodic table to answer the following questions for this element: What is the symbol for this element? What is the atomic number of this element? What is the atomic mass of this element? How many protons does it have? How many neutrons does it have? (Hint: the mass comes from counting protons + neutrons) How many electrons does it have? (Hint: the # of + and – charges in an atom want to be equal (to cancel out any overall charge) 7 N Nitrogen 14 QUIZ YOURSELF: QUIZ YOURSELF: (Part 3 of this Unit) CHEMICAL REACTIONS AND EQUATIONS PA STANDARDS: 3.2.7.A4 – DESCRIBE HOW REACTANTS CHANGE INTO PRODUCTS IN A CHEMICAL REACTION 42. SYMBOLS Symbols represent elements. They can consist of 1 capital letter or, if has 2 letters, a capital letter and a lower case letter. Examples: Si Silicon S Sulfur 43. CHEMICAL FORMULAS Formulas represent compounds Contain symbols of 2 or more elements Subscript # after a symbol show the number of atoms of that element (no subscript assume 1 atom) Examples: C02 = 1 carbon, 2 oxygen HCl = 1 hydrogen, 1 chlorine WHAT AM I, SYMBOL OR FORMULA? Si NH3 Co NaCl C3H8 Al NaHCO3 CH4 S