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Periodic Properties of Elements 1869 First Modern Periodic Table • • • • • Mendeleev Arranged by atomic weight Modern atomic numbers Atomic number = number of protons in the atom Mass number = the number of protons and neutrons in the atom • Mass number - the atomic number = the amount of neutrons in the atom • Number of electrons = (usually) same number as protons so it is neutral How to distinguish between mass numbers and atomic numbers Periodic Table of Properties • Vertical = families, groups, labeled IA – 2B • Horizontal –periods, series 1,2,3,4 --1A –Alkali Metals 2A -Alkali Earth 7A –Halogen 8A –Noble gasses A group = representative elements B group = transition elements Electrons • number of valance electrons • A group = main group = group number (columns) • 1A means the atom has 1 valance electron • 2A means the atom has 2 valance electrons Metals and nonmetals • metallic nature –metal- silvery or gray, high density, solids, high melting and boiling point, good conductors of heat and electricity, malleable, ductile-thin wires drawn out, Al, Ge, Sb, Po • Nonmetal –solid liquid or gas lower melting pts than boiling pts, lower densities, poor conductors of heat and electricity, brittle as solids, B, Si, As, Te, At Al, Ge,Sb,Po, B, Si,As, Te,At are considered metaloids Metalloids • Between metals and non-metals, some properties of metals, some of non-metals, some have neither Metallic Nature • A, Main group of elements only -down a group = increased metallic nature -across a period = decreases in metallic nature 11Na vrs 19K = K is more metallic in nature 20Ca vrs 31Ga = Ca is more metallic in nature 19K vrs 12Mg = K is more metallic in nature 11Na vrs. 20Ca = they are equal in metallic nature Atomic size in the quantum model • • • • • The outer edge of an atom is fuzzy like a cloud The cloud fades away The electron is in the cloud which is an orbital Electron cloud In a bond where atoms share an electron between them, the distance between the two nuclei determines the covalent radius of atoms Atomic size • Down a group = atomic size increases • Across a period = atomic size decreases Ionization property • Energy required to remove an electron from a neutral gaseous atom • 11Na e- = 11Na+ = no longer has a balanced charge and is not neutral = ion Na still has 11 positive protons but now has only 10 negative electrons = now has a positive charge. • The more an atom loses electrons, the more it will try to hold to what it has left • It takes more Ionization energy to pull off the next electron from the atom • 11Na e- e- = 11Na+2 • Na could have up to 11 ionization energies with each one being stronger than the previous • Down a group = 1st ionization energy decreases • Across a period 1st ionization energy increases regularly