Greatest Cheat-sheet Ever!!! Periodic Table

History By 1860, 60 elements & their atomic masses had been discovered and were grouped by similar properties: Cu, Ag, & Au = coinage metals Li, Na, & K = alkali metals Cl, Br, & I = halogens

Mendeleev’s Periodic Table Russian chemist Arranged elements by atomic mass. Discovered that the chemical & physical properties of the elements repeated (groups)

Mendeleev cont. In 1869, Mendeleev published a table of elements arranged by increasing atomic mass. Elements with similar properties were placed under each other in horizontal rows. Problems: He left spaces for elements he felt had not yet been discovered (Ga & Ge later discovered!) Atomic mass was not always followed: Te & I Mendeleev felt that the mass for Te was wrong. (atomic number & protons not yet known)

Mendeleev’s Periodic Table

Modern Periodic Table Arranged by Atomic number (# of protons) Because the periodic table is arranged by the number of protons in the nucleus, it is also arranged by the number of electrons. Each element increases by one proton & one electron as you go across the period. When you come to the end of the row (noble gas), the energy level is full

Modern Periodic Table cont. 118 elements have been discovered or synthesized. VALENCE ELECTRONS are the outer most electrons (s +p only) & the ones that react. Noble gases have 8 valence e-

Periodic Law The elements within a column/group, have similar properties. The properties of the elements within a row/period, change as you move from metallic to nonmetallic across the periodic table. Period/Row: 7 horizontal rows; energy levels Group/Family: 18 vertical columns

Modern Periodic Table cont. First period/row: complete with 2 elements hydrogen (H) with 1 electron & helium (He) with 2 electrons. Group/Family 1 all have 1 valence electron Group/Family 18 all have 8 valence electrons (except He). They all have complete or “full” energy levels. Each row, except the first (H), begins with a metal & ends with a noble gas. Each new row begins the next energy level.

Modern Periodic Table cont. Main Group Elements: Group/Family 1,2, 13, 14, 15, 16, 17, 18 (s + p block) Transition elements: Groups 3 – 12. Not predictable & more complicated.

Modern Periodic Table cont. Four groups have common names: Group/Family 1 = Alkali metals Group/Family 2 = Alkaline earth metals Group/Family 17 = Halogens “salt former”; they combine with metals to form “salts”. Group/Family 18 = Noble Gases, “inert”, not reactive

Physical States & Classes of Elements At room temperature, Most of the elements are solids. 2 elements are liquid: Bromine & Mercury Except for Hydrogen, the gases are located in the upper-right corner of the table. Most elements are metals & occupy the entire left side of the table. Nonmetals are located in the upper-right corner of the table. (except H)

Physical States Metals: left side of the periodic table; conducts heat & electricity; malleable (bends without breaking) & ductile (drawn into a wire); has luster (shiny); usually solid at room temperature (except mercury). Nonmetal: upper right side of the periodic table (& H); does not conduct electricity, poor conductors of heat, brittle when solid, usually gas at room temperature.

Physical States & Classes of Elements cont. Metalloids/semimetals are located along the boundary “stairway” between the metals & nonmetals. Metalloids have some properties of metals & some properties of nonmetals.

Metalloids/Semimetals Semiconductor: conducts electricity better than a nonmetal, but not as well as a metal. Example: Si – conducts electricity, but not malleable or ductile.

Rare earth metals Lanthanide: elements 58-71;; natural abundance less than 0.01%; all have similar properties Actinides: elements 90-103; all radioactive; after uranium (92), they do not exist in nature

Periodic Table Long Form & Short

Metals, Nonmetals, & Metalloids Metal: valence electrons held loosely; easily lost; free to move from atom to atom; This flow of electrons is why metals conduct electricity. Nonmetals: valence electrons held tightly & not easily lost; tend to share or gain electrons with other atoms. Metalloids: between metals & nonmetals

Shielding Effect Remember: Protons are positive & electrons negative. Opposite charges attract, but like charges repel. The increase in the number of filled energy levels, shields the electrons from the protons in the nucleus.

Shielding

Periodic Trends Size: In general, atomic size increases from top to bottom in any group/family; more electrons = more energy levels This is different going across a period/row. The size generally decreases; more protons pull the electrons in.

Atomic Size

Electronegativity Electronegativity is the ability of an atom (element) to attract electrons. This forms bonds & compounds. Electronegativity values decrease from top to bottom in a group/family & increase from left to right in a row/period. Noble gases are omitted because they do not form compounds.

Electronegativity

Ionization Energy Energy required to remove an electron from an atom. Trend - increases across a period, due to more nuclear charge. -decreases down a group, due to more occupied energy levels.

Periodic Trends

Label Periodic Table