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Periodic Table: Atoms, Classification & Representation 4 - CH 1 Review: The Atom • What is an atom? • Definition: An atom is the smallest particle of matter. It cannot be divided chemically • What are the parts of an atom? • In the nucleus: Protons and Neutrons • Outside of the nucleus: Electron • Protons have a positive charge, neutrons have no charge, and electrons have a negative charge How Small is an Atom? The Rutherford-Bohr Atomic Model • Named after two scientists: Ernest Rutherford and Niels Bohr • Rutherford: Discovered that most of the atom is empty space and contains a very small but dense nucleus • Bohr: Electrons surround the nucleus in orbits (pathways) but can move from one orbit to another • Definition: A representation of the atom as a very small nucleus made up of positively charged protons, surrounded by negatively charged electrons moving in defined orbits Representing Atoms (Rutherford-Bohr) • To keep things simple, protons and neutrons are represented as a “ball” in the center (the nucleus) • Electrons are arranged on orbits (also called shells or valences) around the nucleus • Each orbits has a MAXIMUM number of electrons it can support • The number of protons and electrons are EQUAL and we know this number as the ATOMIC NUMBER How Many Electrons? • For the first 20 elements: • 1st orbit = 2 electrons • 2nd orbit = 8 electrons • 3rd orbit = 18 electrons BUT after 8 electrons the 4th begins to fill too… • Examples: • Helium: Atomic Number = 2 • Aluminum: Atomic Number = 13 • Calcium: Atomic Number = 20 Example of an Exam Question • Which of the following best represents the aluminum (Al) atom according to the Rutherford-Bohr model? Representing Atoms (Lewis Notation) • A simplified representation of the atom • Only valence electrons are shown • Valance Electrons: the electrons located FURTHEST from the nucleus The Periodic Classification of the Elements The Periodic Table • Periodic Classification: A way to group the elements according to certain properties • Periodic Table of Elements: a visual presentation of the elements in groups according to their physical and chemical properties Review: Physical vs Chemical Properties • Physical Property: A property that can be observed or measured without changing the make-up of the matter of the object (ex: colour, odor, texture, density, melting point, boiling point) • Chemical Property: Cannot be determined by simply viewing or touching the object; only becomes evident during a chemical reaction (ex: reactivity with other chemicals, flammability, heat of combustion) Periodic Table Organization Activity • Each team will be given a collection of shapes • Each shape (piece) has two numbers on it • You task is to decide how to best organize ALL of the pieces into one table where each row (goes across) and each column (goes up and down) share similar characteristics (you cannot simply put them in a single line) • When your team is done, you will have a work sheet to complete based on the activity. How the Periodic Table is Divided/Organized • Each element has its own box/square • For each element: • Symbol of the Element: This is universal (same for all languages) • Atomic Number: always located at the top • Atomic Mass: always located at the bottom • Name of the Element: Written in the language of the document First Major Division: Metals, Non-Metals & Metalloids • All the elements can be placed into these three categories • The “staircase” helps locate and identify the categories Metals • Location: To the LEFT of the staircase • Properties: • Conduct heat and electricity well • Ductile (can stretch) • Malleable (can bend) • Usually shiny • Solid at room temperature EXCEPT for Mercury (liquid) Non-Metals • Location: To the RIGHT of the staircase EXCEPT for Hydrogen • Properties: • Poor conductors of heat and electricity • Many are gases at room temperature Metalloids • Location: Found along the “staircase” • Properties: • Only 7 in total (Boron, Silicon, Germanium, Arsenic, Antimony, Tellerium, Astatine) • Have some properties of metals AND some of non-metals • Some are very good conductors, others are very poor – used as semiconductors in circuits and lasers Groups of the Periodic Table • All the elements found in one COLUMN (going up and down) belong to a GROUP • All elements in a group have: • Similar chemical properties • The same number of valence electrons • Groups are labeled using Roman numerals (1 = I, 2 = II) and either A or B • “A” = main elements (biggest columns) • “B” = transition elements (short columns) • Roman numeral = number of valence electrons Alkali Metals • Location: The first column on the left of the periodic table (except Hydrogen) • Properties: • Soft • HIGHLY reactive metals Alkaline Earth Metals • Location: The second column on the periodic table • Properties: • Highly malleable (soft) • Reactive • Burn easily in the presence of heat Halogens • Location: The second-last column on the periodic table • Properties: • Non-metals • React easily to form compound • Commonly form salts Noble Gases (Inert Gases) • Location: The final column of the periodic table (on the right) • Properties: • Very stable, do not react well • Commonly found in nature The Periods of the Periodic Table • Elements found in each row (going across) have the same number of shells around the nucleus • The period number corresponds to the number of electron shells