behaved similarly and put them in groups. • When the known elements were ordered by weight, “periodicities” were found, where properties would repeat after 8 elements. • Elements were then ordered left to right, top to bottom in order of increasing atomic weight (later atomic number) and lining up elements with similar properties in columns.
is either sharing of electrons or transfer of electrons. • An atom’s electrons are organized into “electron shells” - when an electron shell is filled, it is in a lower energy state (it’s “happy”). • The first electron shell holds two electrons, the second shell holds eight, the third shell holds 18, and the fourth holds 32. • All but the first shell repeat, leading to row counts: 2, 8, 8, 18, 18, 32, 32.
• Atoms with only one or two electrons in their outer shell will often “donate” those electrons, so that the previous shell, which is full, is then the outermost shell – hence, the two columns on the left. • Atoms with their outer shell filled are unreactive, they form the right-most column. • Atoms that are missing only a few electrons from their outer shell will often “borrow” the missing electrons to fill it, hence the other columns on the right.
rows actually belong in the corresponding blank spaces in the two rows above them, but to conserve page space, they are moved to their own rows. • There is actually a “wide form” periodic table, but it is not used nearly as much as the standard form.
they tend to be less stable – the nucleus “decays”, either emitting a particle or splitting into two or more parts. • Atomic weight is not the only factor in stability, but it is the most important. • An element that is unstable and decays is termed “radioactive”, because it emits radiation as it decays. • Some of the elements near the end of the standard table are so unstable that it has not been possible to create them. Others have been created, but only last a very short time. • The shortest so far: Darmstadtium has a half-life of 3 * 10-6 s.
alloy that is a good conductor of both electricity and heat. Metals are usually malleable, ductile and shiny. • A nonmetal is simply any element that is not a metal. • A metalloid is an element with properties that are in-between or a mixture of those of metals and nonmetals, and which is considered to be difficult to classify unambiguously as either a metal or a nonmetal.
were named after their properties: “alkali metals”, “noble gases”, etc. • Another naming convention is to name them after the lightest element in the group: “lithium group”, “beryllium group”, etc. • The “old IUPAC” and American “CAS” system names them with a roman numeral and usually a letter “A” or “B”: “IIA”, “VIB”. Note that old IUPAC and CAS are incompatible! • The new IUPAC convention is a simple numbering, “Group 1” through “Group 18”, corresponding to the column in the standard periodic table.
in their outer shell. • Hydrogen is not considered an Alkali Metal, even though it is Group 1: it is also missing exactly one electron in the outer shell, and so has properties very different from the other group 1 elements. • This group is also known as the Lithium group. • Alkali Metals are all shiny, soft, highly reactive metals at standard temperature and pressure and easily lose their outermost electron to form cations with charge +1.
electrons in their unfilled outermost shell. • This group is also known as the beryllium group. • They are all shiny, silvery-white, somewhat reactive metals at standard temperature and pressure and readily lose their two outermost electrons to form cations with charge +2.
Metals”. Group 12 is sometimes counted to the transition metals as well, sometimes counted to “Post-Transition Metals”. • The word transition was first used to describe the elements now known as the d-block by the English chemist Charles Bury in 1921, who referred to a transition series of elements during the change of an inner layer of electrons. • When the groups are individually named, they are usually named by their first element: Scandium group, Titanium group, etc. • Group 11 is also known as the “Coinage metals”: it contains copper, silver and gold.
called the “Triels”, derived from the Latin prefix “tri”. • Boron is considered a “metalloid” • Aluminium and the rest of group 13 are considered “poor metals” or “earth metals”. • Note: Americans generally spell and pronounce Element 13 differently - “Aluminum” instead of “Aluminium”.
as the “Tetrels” and is still commonly referred to as “Group IV” in the field of semi-conductor physics. • Carbon is nonmetallic • Silicon and germanium are “metalloids” • Tin and lead are metals.
as the nitrogen group. • The term “pnictogen” comes from the greek root “pnikta”, “suffocated things” - nitrogen without oxygen suffocates. • Nitrogen and phosphorus are nonmetals • Arsenic and antimony are metalloids • Bismuth is a post-transition metal
as the oxygen group. • The name chalcogen comes from the Greek words χαλκος (chalkos, literally "copper"), and γενές (genes, born), because they are often found in copper ore. • The chalcogens are all two electrons short of a full outer shell. • Oxygen is a gas. • Sulfur and selenium are nonmetal solids. • Tellurium is a metalloid. • Polonium is a post-transition metal.
as the fluorine group. • The halogens is the only group which contains elements in all three familiar states of matter at standard temperature and pressure (20°C, 1 atm). • Fluorine and chlorine are a gases. • Bromine is a liquid. • Iodine and astatine are solids.
group are gases. • The members of this group are chemically unreactive, because their outer shell is filled. • The term “noble” is used because of their unreactivity.
through 71 (lutetium), 15 elements total. • Promethium (element 61) is the only radioactive Lanthanide. • The Lanthanides, together with similar elements scandium and yttrium, are often collectively known as the rare earth elements.
through 101 (lawrencium), 15 elements total. • All actinides are radioactive. • Most of the actinides are not found in significant quantity in nature. The exceptions are thorium, uranium and small amounts of plutonium. • The Lanthanides and the Actinides together, minus their last elements (lutetium and lawrencium) form the “f-block”.
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