Discovering Elements & The Periodic Table

 The periodic table is made of elements ◦ What are elements?  Pure substances that cannot be broken down into simpler substances

 Protons (+): ◦ Positively charged ◦ Same as the atomic number  Neutrons (neutral)  Electrons (-) ◦ Negatively charged

 1850’s: there were 58 known elements ◦ Today there are 112! ◦ Scientists tried to organize elements  Atomic mass: the average mass of an atom of an element

 Russian chemist  He wrote down information about elements on cards and put elements with similar properties in columns.

 When Mendeleev arranged elements in order of increasing atomic mass, he found that some properties were similar!  He left some gaps in the table for elements that he thought would eventually be there based on properties.

 By about 1915, the periodic table became based on a special number for each element, called its atomic number: ◦ Is the number of protons an element has in its nucleus.

 All atoms are neutral ◦ Their positive and negative charges balance ◦ SO, atoms contain an equal number of electrons and protons

 The total number of protons and neutrons in an atom. # of protons + # of neutrons = mass number  How do we find the number of neutrons?

Mass number – atomic number = # of neutrons Let’s do some!! How many neutrons do the following elements have? a. magnesium b. nitrogen c. argon d. copper e. hydrogen

 Each element has a symbol of 1-2 letters ◦ Ex: Ag – silver, H - hydrogen  Elements are commonly named after the people who have discovered them ◦ Ex: Einstein- Einsteinium

Element NameElement Symbol #of Protons# of Electrons# of Neutrons carbon O 16 aluminum 34 lithium Ne 79 barium

 Page 117 ◦ Symbols for Elements  # 1-5 (procedure)

 II0 II0

 GROUPS/FAMILIES: (1-18) ◦ VERTICAL ◦ UP and DOWN ◦ Usually have common properties  PERIODS: (1-7) ◦ Horizontal ◦ LEFT TO RIGHT

 Separates metals from non-metals.  The elements touching the staircase:  These are called METALLOIDS. ◦ Have properties of both metals and non-metals ◦ Few in number ◦ Solids

 Good conductors of heat and electricity  Bright metallic shine (lustre)  Easily shaped (malleable)  Solids (except mercury)  Poor conductors of heat and electricity  Dull, various colours  Brittle  Solid or gas (except bromine)

 Metals in the periodic table that run from Group 3 to the staircase.  Metal properties

 Metals are to the left of the staircase  Non-metals are to the right of the staircase

 Except for hydrogen  Most reactive ◦ Require special storage  Why? ◦ Each alkali metal has an unpaired electron and tends to get rid of the electron by forming a compound  List them!  pYrY pYrY

 Similar to group 1, but they are not as intense  Ex: magnesium reacts with water but less vigorously than sodium does.  List them!

 Very un-reactive – INERT  Is a useful property when it comes to light bulbs! ◦ Argon is commonly used inside a light bulb to keep the tungsten from burning out  Stable ◦ Do not have any unpaired electrons  List them!

 Naturally found in compounds because they react vigorously with almost every other element  Also have an unpaired electron ◦ They GAIN an electron ◦ Corrosive and harmful  List them