The Periodic Law

 Cannizzaro  presented a new method for determining mass of elements  gave scientists a way to organize elements

 Mendeleev-Russian 1869  organized elements according to mass and properties  noticed that properties repeated periodically  predicted elements, later identified as Sc,Ga,Ge

 Moseley-1911  Used X-rays for determining the # of protons  This is how our current periodic table is arranged.

 Physical and chemical properties repeat periodically if arranged according to atomic number. Recurring or reappearing from time to time; intermittent.  Look for overall patterns- may see some variation.

 Changes since Moseley  Noble gases-Ramsay  Lanthanides/Actinides- Seaborg

The Periodic Table

 tells us the size of the atom  measured using ½ the distance between the nuclei of identical atoms bonded together

 TREND:  going across the atoms get smaller  going down the atoms get larger

 tells us the size of the ion  positive or negative atom because of loss or gain of electrons  Cation-positive ion  Anion-negative ion

 Cations are smaller than the parent  Lose electrons

 Anions are larger than the parent.  Gain electrons.

 Why do ions form?  Atoms try to become stable.  Achieve a noble gas configuration.  Become isoelectronic with noble gases  Having the same electron configuration

 Examples:  Calcium  Nitrogen

 You try these:  Potassium  Iodine  Aluminum

 Amount of energy required to remove an electron from an atom

 energy change when an electron is added to an atom  energy release means it is easier to add e-  opposite of ionization energy

 measure of the ability of an atom to attract electrons when it is bonded to another atom  Think: sharing with a partner, equal sharing or unequal sharing