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PERIODIC TABLE OBJECTIVE 1—DEVELOPMENT OF THE PERIODIC TABLE I. ORIGINAL PT A. Dmitri Mendeleev—mid 1800s— Russian B. arranged 63 known elements in order of increasing atomic mass C. found that elements had similar physical and chemical properties – arranged columns D. Certain groups had the same reactivity (# of valence e-, but these hadn’t been discovered yet!) Valence Electrons – The outer electrons, in the highest energy orbital(s) E. concluded that elements had periodic properties (3 elements discovered in his lifetime had properties that he predicted) II. MODERN PT A. Several elements appeared to be out of place B. Rutherford 1908 discovered the nucleus containing proton & neutron A. Shortly after that, (50 yrs after DM) Henry Moseley determined the atomic # of elements by using X rays III. ARRANGEMENT OF PT A. Groups (families)—vertical columns 1. all elements in a family have same # of valence e “A” group elements only 2. similar but not identical properties in some families alkali metals, halogens, noble gases B. Periods—horizontal rows 1. all elements in a period have the same # of quantum energy levels 2. properties change drastically but there is a pattern (periodic or repeating pattern) a. 1st element is a very active solid metal b. last element is a very inactive gas There are 92 naturally occurring elements and several synthetic elements. OBJECTIVE 2—PERIODIC PROPERTIES/TRENDS Can obtain information about an element from its location in the PT Certain properties vary in a periodic way from left to right 1. Reactivity a. Metals—lose electrons easily; will react with water to corrode easily b. Non-metals—gain electrons easily 2.Metallic properties- how easily the atom loses electrons Going from left to right across the period elements change from metals to metalloids and finally nonmetallic elements. Down a group, elements become more metallic. 3. Nuclear Charge- As proton number increases across a period and down a group, the positive charge of the nucleus increases as well. 4. Shielding effect- the reduction of the attractive force from the nuclear charge. The effect results from the addition of quantum energy levels. The inner electrons shield the outermost electrons from the positive attraction of the nucleus. MAKES THE VALENCE ELECTRONS EASIER TO TAKE. 5. Atomic Size/Atomic Radius a. ½ the distance between the nuclei of 2 atoms of the same element when they are combined. b. Atomic size decreases from left to right and increases top to bottom c. As atomic # increases across a period, # of protons increase and electrons are added to the outer level d. the increase in neg. electrons and the increase in pos. protons cause an increased attraction between particles e. Electrons are pulled closer to the nucleus causing atomic size to decrease within a period 6. Electron affinity— the energy change that occurs when an electron is acquired by a neutral atom starting at left of each period and going to the right affinity increases 7. Ionization energy- the energy required to overcome the nuclear charge and remove an electron from an atom that is by itself 8. Electronegativity- the tendency for the atoms of the element to attract electrons when they are chemically bonded to atoms of another element Octet rule – Atoms react and gain or lose electrons to obtain the electron configuration (valence electrons) of noble gases. Usually 8.