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CHAPTER 6 Chemical Periodicity Development of the Periodic Table Scientists needed a way to organize and refer to the growing number of known elements Categorize the elements according to similarities in their physical and chemical properties Relationship between atomic structure and properties of elements Development of the Periodic Table Mendeleev listed the elements in vertical columns in order of increasing atomic mass Regular recurrence of physical and chemical properties Blank spaces left where unknown elements belonged, but able to predict their properties Development of the Periodic Table Moseley determined atomic number of the atoms of the elements Arranged the elements by order of atomic number Modern Periodic Table The horizontal rows of the periodic table are called periods (organized by increasing atomic number) The vertical columns are called groups or families (organized by chemical properties) Periodic Law: when the elements are arranged in order of increasing atomic number, there is a periodic pattern in their physical and chemical properties Electron Configurations and Periodicity Electron plays the greatest part in determining the physical and chemical properties of an element Elements can be classified into four different categories based on their electron configurations Electron Configurations and Periodicity 1. The noble gases are elements in which the outermost s and p sublevels are filled (group 0) – Called inert gases because they do not partake in chemical reactions – Valence: outermost s and p orbitals – Octet: 8 electrons in valence shell Electron Configurations and Periodicity The representative elements are elements whose outermost s or p sublevels are only partially filled (group A) 2. – – – – Alkali metals: group 1A elements Alkaline earth metals: groups 2A elements Halogens: nonmetallic elements of group 7A Group number = number of valence electrons Electron Configurations and Periodicity 3. 4. The transition metals are elements whose outermost s sublevel and the nearby d sublevel contain electrons (group B) The inner transition metals are elements whose outermost s sublevel and the nearby f sublevel contain electrons Electron Configurations and Periodicity S block: groups 1A and 2A and He P block: groups 3A, 4A, 5A, 6A, 7A, and 0 except He D block: transition metals F block: inner transition metals Period number corresponds to the principal energy level Periodic Trends in Atomic Size The radius of atoms: atomic radii Atomic size increases as you move down a group of the periodic table and decreases as you move form left to right across a period The shielding effect of these electrons on the nucleus is constant within a period Periodic Trends in Ionization Energy The energy that is required to overcome the attraction of the nuclear charge and remove an electron to create a positive atom is the ionization energy First ionization energy decreases as you move down a group of the periodic table and increases as you move form left to right across a period Periodic Trends in Ionic Size Ionic radii is the size of an ion compared to same neutral atom – – Cations (positive ions) are smaller because of the reduced energy level with the same number of protons Anions (negative ions) are larger because of a reduced effective nuclear charge on outer electrons Periodic Trends in Electronegativity The electronegativity of an element is the ability of an atom to attract electrons within a bond Electronegativity increases as you go across a period form left to right and decreases as you move down a group