Chapter 3 Atoms & the Periodic Table Chapter 3 Section 2 The Simplest Matter Pages 80-85
The Elements There are many different types of atoms. An element is matter made up of only one kind of atom. An element is the simplest form of matter. At least 115 elements are known and 90 of them occur naturally on Earth.
The Periodic Table To organize and display all of these elements, chemists have created a Periodic Table. The elements in the periodic table are organized by their properties. Periodic means a regular, repeating pattern.
History of the Periodic Table French chemist Antoine-Laurent Lavoisier created one of the first lists of elements in the 1790s. John Dalton (Britain, 1803) used symbols to represent elements and assigned masses to elements. Dmitri Mendeleev (Russian, 1869) arranged the 63 elements known at the time into groups based on chemical properties.
Periodic Table of Elements
Rows = Periods The rows in a periodic table are called periods. Elements that are in the same row have the same number of shells or orbitals. The number of shells that an element has is equal to the The number of shells that an element has is equal to the row number it is in.
Rows = Periods What is the minimum and maximum number of shells an element can have? Minimum = 1 and Maximum = 7
Columns = Groups The columns in a periodic table are called groups. Elements that are in the same column have similar properties related to their structure. How many columns or groups are their in the periodic table? 18
Element Key Each element has it s own key on the periodic table. The name of each element is represented by a chemical symbol that contains one to three letters. The symbols are a form of chemical shorthand to save time and space when writing formulas. What is the chemical symbol for: Chlorine: Cl Zinc: Zn Calcium: Ca Nitrogen: N
Atomic Number The atomic number is on the top of the element key. The periodic table is arranged in order of increasing atomic number. The atomic number tells you the number of protons in the nucleus of each element s atom. What is the atomic number for Chlorine? Atomic Number = 17 How many protons are there in an atom of Chlorine? # Protons = 17
Isotopes The number of protons determines the element. Adding or removing protons creates a new element. The number of protons for each element is always the same, however the number of neutrons in an element can vary. Isotopes are atoms of the same element that have a different number of neutrons. Example: Hydrogen
Atomic Mass vs. Mass Number The bottom of the key contains the atomic mass of the element. The atomic mass of an element is the average mass of the element (in AMUs), taking in account all the isotopes. An atom s mass number is the number of protons + the number of neutrons it contains. Therefore, # neutrons = mass number protons Example The mass number of an atom of chlorine is 35. How many neutrons are in the atom? Answer = 35 (mass number) 17 (protons) = 18 neutrons
Practice Finding the # of Neutrons To estimate the number of neutrons for any element in the periodic table, follow these steps. 1. Round the atomic mass of the element to the nearest whole number. Example: Fluorine (18.998 amu) = 19 2. Subtract: Rounded atomic mass Atomic Number (# of protons). Example (Fluorine): 19 9 3. # Neutrons (Fluorine) = 10 Estimate the number of neutrons for the following elements: Nickel (Ni) Potassium (K) # Neutrons = 59 28 = 31 Neutrons # Neutrons = 39 19 = 20 Neutrons
How do you find ELECTRONS? Since atoms are neutral, electrons are equal to the atomic number or the number of protons. How many electrons are in the following: Nitrogen 7 Mg Na 12 11
Atomic Model - Bohr What is the name of this element? Lithium (Li) How did you figure this out?
Bohr Models HELIUM BORON ALUMINUM
The electron dot diagram is used to model the number of valence electrons in an element. The dots represent the number of electrons in the outermost shell of the atom. Examples: Electron Dot Diagram
Periodic Table and Valence Electrons
Classification of Elements Elements fall into 3 general categories 1. Metals 2. Non-Metals 3. Metalloids
Metals Most of the elements on the periodic table are metals. The metals are found on the left side of the periodic table. Characteristics of metals: Generally are shiny and have a metallic luster. Good conductors of heat and electricity. All metals, except mercury, are solid at room temperature. They are malleable (can be bent into different shapes) They are ductile (can be stretched without breaking)
Nonmetals Except for Hydrogen, the nonmetals are found on the right side of the periodic table. Characteristics of nonmetals: Are usually dull in appearance. Poor conductors of heat and electricity. Many are gases at room temperature. They are brittle (break easily when bent) Essential to life.97% of your body is made of nonmetals. Examples: Oxygen (65%), carbon (18.5%), etc.
Metalloids Metalloids are elements that have characteristics of metals AND nonmetals. They are found between the metals and the nonmetals on the table (see zig-zag staircase line) Characteristics of metalloids: Solids at room temperature. Fairly good conductors of heat and electricity. Some used to make electronic circuits in computers, televisions, and other electronic devices. Example: Silicon