Periodic Table: Atoms, Classification & Representation 4-Ch 1

Review: The Atom What is an atom? What are the parts of 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