Atoms and the Periodic Table

Chemists used the properties of elements to sort the elements into groups. Mendeleev used increasing atomic mass to construct his table. He knew some elements had similar chemical and physical properties! He put each element on a card with its melting point (MP) density, color, atomic mass and the # of bonds it would form. He was able to predict undiscovered elements and their properties after he arranged the cards by atomic mass!! Modern periodic table has elements arranged in increasing atomic number (we needed to identify subatomic particles before we could use atomic #)

When Mendeleev arranged his cards of elements he noticed that the pattern was not quite right, but when he moved a few cards over and left spaces the pattern worked. He concluded that the spaces were “yet undiscovered” elements. He was able to predict the properties of these elements! Today the periodic table looks a little different, more elements have been found and we have discovered “sub atomic particles” which allowed scientists to re arrange the elements by atomic number. The pattern became even more regular!

C 6 Atomic number. Atomic symbol Carbon 12.011 Element name Average atomic mass - Review: *To find the number of protons, see the atomic number. *To find the number of electrons (see the atomic number) *To find the number of neutrons, subtract the atomic number from the atomic mass. Use whole number. Atomic mass -- 12 Atomic # - 6 6 neutrons

V. How Do The Structures of the Atoms Differ? A. Atomic Number - # of protons in the nucleus 1. Also tells the number of electrons in a neutral atom 2. Each atom has a unique atomic number; never changes 3. It identifies the atom 4. Usually the smallest number, always a whole # B. Mass Number – sum of the protons + neutrons 1. Usually the biggest number, often a decimal C. Ion – an atom or group of atoms that has lost or gained 1 or more electrons; therefore has a net (overall) charge D. Isotope – atoms of the element with different numbers of neutrons Ex: C-12 and C-14 E. Average Atomic Mass – weighed average mass of a elements isotopes; why the mass is usually not a whole number

B. Period (series) – horizontal rows I: Organization of the Periodic Table A. Elements are arranged based upon atomic number (# of protons). Usually the smallest of the 2 numbers Periodic Law – when elements are arranged the way there are because of similarities in properties and it occurs in a regular pattern. B. Period (series) – horizontal rows Number of protons and electrons increase by 1 as you move across a period. C. Group (family) – vertical columns Elements in these groups have the same number of valence electrons and have similar properties

Groups Or families Periods Because the first shell is full at 2 it is at the end of the period, instead of in the second group with the other elements with 2 valence electrons Groups Or families Periods (when we write a sentence, we go ACROSS the paper and put a PERIOD at the end.)

If you gain an electron e- you increase your (-) charge Group 6 Gains 2 -e Group 7 -1 Gains 1 -e Group 2 +2 Looses 2 -e Group 4 Group 5 -3 Gains 3 -e Group 3 +3 Looses 3 -e Group 8 No charge Group 1 +1 Looses 1 -e If you gain an electron e- you increase your (-) charge Less (electrons) is more (+) of a charge Transition metals Variable charges

How Are Elements Classified Nonmetals (except H) are found on the right side of the chart. They may be solid, liquid or gas…solid ones are usually dull,brittle (shatter if hit with a hamer) Form (-) ions. They are poor conductors of electricity except for C Metalloids (semimetals) have properties of both metals and nonmetals. Ex: Boron, Silicon, Germanium, Arsenic, Antimony and Tellurium Metals are usually shiny solids that can be stretched and shaped They are ductile (put into thin wire) and malleable( hammered into sheets). They are also good conductors of heat and electricity. Most of the elements are metals. They are on the left side of the periodic table Form (+) ions

Alkali Metals - Group 1 Soft, shiny metals that react violently with water and other stuff. 1 valence electron in this group=very reactive. Will give up an electron. Form 1+ ion Ex.: Sodium reacts quickly with Cl to give up an electron to it and become NaCl, salt. Must store in oil

Alkaline Earth Metals- Group 2 Have two valence electrons, are not as reactive as alkali metals, but still reactive enough to form 2+ ions and react to form compounds. Calcium forms many hard compounds used to strengthen organic structures: shells [become limestone and marble], coral and bones and teeth. Magnesium- light structural material, milk of magnesia, Epsom salts, and flares.

Transition metals Much less reactive, but still can forms ions. Transition metals can be +2, +3 and even +4 Many times you will know the charge because of Roman Numerals in () ‘s Ex: Cu (III) is Copper with a +3 charge Mercury- on metal that is liquid at room temp… useful in thermometers and thermostats, but has been replaced due to toxicity. Gold, Silver, Platinum- very shiny=jewelry use.

Other Nonmetals Group 3 – Boron group. These have +3 charge and have 3 valence electrons Ex: Aluminum (Al) Group 4 – Carbon group. These have -4 charge and have 4 valence electrons Ex: Carbon (C) – pure state is found as graphite and diamonds. Group 5 – Nitrogen group. These have -3 charge and have 5 valence electrons Ex: Nitrogen 75% of air is made of nitrogen Group 6 – Oxygen group. These have -2 charge and have 6 valence electrons. Ex: Oxygen 20% of air is made of oxygen. Sulfur – yellow, odorless solid, in compounds give off a terrible smell

Halogens - Group 7 7 valence electrons and have a (-1) charge Very reactive; especially with group 1 Ex: Bromine (Br) – only liquid nonmetal at room temp Ex: Fluorine (Fl) – used in toothpaste Ex: Chlorine (Cl) – used in swimming pools

Nobel gases - Group 8 All gases. Different from most elements, because they are very unreactive. 8 valence electrons, so they won’t react with any other elements. Also known as inert. Ex: Neon (Ne) - used in neon signs (mixed with other elements gives other colors). Ex: Helium (He) - is very light (used in balloons). Ex: Argon (Ar) - used in light bulbs to prevent it from burning up

2 He This group, the Noble gases (group18) is usually very unreactive. This is because they all have full valence electron shells. Helium (He) has 2e in the 1st shell (holds 2), Neon (Ne) has 2e in the lst shell, and 8e in the 2nd shell (full). 10 Ne 18 Ar 36 Kr 54 Xe 86 Rn