The Periodic Table

History  Created by Dmitri Mendeleev, a Russian chemist (1869)  Organized the elements (~60) in order of atomic mass  Noticed that certain similarities appeared at regular intervals  These repeating patterns were called periodic

Definition – Periodic Table of Elements  An arrangement of the elements in order of their atomic numbers so that elements with similar properties fall in the same column, or group

Groups (Families) Vertical columns are called groups or families

Periods Horizontal rows are called periods

Noble Gases (Inert Gases)

Noble Gases  very unreactive with other elements because outer shell of electrons is full (8 electrons) Helium (He) Neon (Ne) Argon (Ar) Krypton (Kr) Xenon (Xe) Radon (Rn)

Halogens

 Most reactive nonmetals Fluorine (F) Chlorine (Cl) Bromine (Br) Iodine (I) Astatine (At)  Halogens commonly react with metals to form salts (ex. NaCl)  Seven electrons in outer shell

Alkali Metals

 Very reactive Lithium (Li) Sodium (Na) Potassium (K) Rubidium (Rb) Cesium (Cs) Francium (Fr)  Only one electron in outer shell

Alkali Metals  Highly reactive with water and air!!!  Usually stored in kerosene to prevent reactions with air and moisture  Silver appearance  Soft; can be cut with a regular butter knife 

Step One – Na added to H 2 O

Step Two – Na begins to melt

Step Three – Kaboom! H 2 ignites

Step Four – H 2 burns

Alkaline Earth Metals

 Contain two electrons in their outer shell  Less reactive than alkali metals  Harder, denser, and stronger than alkali metals  Higher melting points than alkali metals

Alkaline Earth Metals  Beryllium (Be)  Magnesium (Mg)  Calcium (Ca)  Strontium (Sr)  Barium (Ba)  Radium (Ra)

Transition Metals

 Less reactive than alkali metals and alkaline earth metals Palladium (Pd), Platinum (Pt), and Gold (Au) are very unreactive  Good conductors of electricity  High luster (shiny)

Main-Group Elements (BCNO)  Consists of non-metals, metalloids, and metals  Properties among these elements vary greatly  Some very common elements are located here

Lanthanides

 Similar reactivity to Group 2 alkaline earth metals  Shiny metals

Actinides

 All are radioactive  Only four occur naturally on Earth Thorium (Th) Protactinium (Pa) Uranium (U) Neptunium (Np)  All others are synthetic (made in a lab)

Exceptions  Hydrogen – has properties that do not resemble those of other elements  Helium – although it only has two electrons in its outer shell, He is very stable and unreactive

Element  Def. - an elementary substance consisting of one type of atom  Elements are the building blocks of all substances  The smallest part of an element that can exist is called an atom

Atoms  Atoms are made up of smaller subatomic particles, but these particles DO NOT have the properties of the elements  The three subatomic particles are: Protons Neutrons Electrons

What an Atom Looks Like  Theoretically, an atom looks like this: Nucleus of the atom – Contains the protons and neutrons Electrons spin around the outside of the nucleus

Protons  Positively charged (+)  Located in nucleus  Abbreviated with a lowercase p  Mass of a proton = x g

Neutrons  No charge  Located in nucleus  Abbreviated with a lowercase n  Mass = x g  This mass is slightly greater than that of a proton

Electrons  Negative charge (-)  NOT found in nucleus  Electrons are contained in an orbital – a cloudlike region around the nucleus that contains various levels  Abbreviated as e -  Mass = x g (much smaller than protons and neutrons)  Number of electrons in an atom = the number of protons in that same atom

Movement of Electrons  Because electrons are not held together in the nucleus, they have the ability to move from atom to atom (more on this later)

Compounds  A distinct substance composed of two or more elements combined in a definite proportion by mass  Examples: H 2 O (water) NaCl (sodium chloride) C 9 H 8 O 4 (acetylsalicylic acid)

Mixtures  Matter containing two or more substances, which can be present in variable amounts  Two types – Homogeneous – matter that has uniform properties throughout (ie. Salt water) Heterogeneous – matter without a uniform composition, having two or more components or phases (ie. Trail mix – yum!)