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Chemical Periodicity History • Dmitri Mendeleev (1834 – 1907) – Russian chemist – Noticed regular (periodic) recurrence of chemical and physical properties after arranging by increasing atomic mass. • Eventually led to grouping by similar properties side by side Predicted properties of then unknown elements with amazing accuracy. • Henry Mosely (1887 – 1915) – British physicist – Identified atomic number (nuclear charge) of the atoms of elements • Arranged periodic table by atomic number Current arrangement of periodic table The Periodic Table • Periods – horizontal rows of the periodic table. • Groups – vertical columns of the periodic table. • 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 Configuration/Periodicity 1. Noble gases – 2. Outermost p and s sublevels are filled Representative elements – – Outermost p and s sublevels are only partially filled Called the Group A elements 1. 2. 3. 3. Transition metals – – 4. Alkali metals – group 1A Alkaline earth metals – group 2A Halogens – group 7A Outermost s sublevel and the nearby d sublevel contains electrons Called the group B elements Inner transition metals – Outermost s sublevel and the nearby f sublevel generally contain electrons Atomic Radius • = half the distance between the nuclei of two like atoms. • Atomic size generally increases as you move down a group. • Atomic size generally decreases as you move from left to right across a period. Largest atoms are towards the bottom and to the left of the periodic table. Ionization Energy • = The energy that is required to overcome the attraction of the nuclear charge and remove an electron from a gaseous atom. • Ionization energy decreases as you move down a group of the periodic table. • For the representative elements, ionization energy generally increases as you move from left to right across a period. Electronegativity • = the tendency for the atoms of the element to attract electrons when they are chemically combined with another element. • Electronegativity increases for the representative elements as you move from left to right and generally decreases as you move down a group.