The Periodic Table of the Elements is a way to arrange the elements to show a large amount of information and organization.We number the elements, beginning with hydrogen, number one, in integers up to the largest number (118). The Periodic Table is arranged in order of increasing atomic number.
The Periodic Table lists the following:
- Element symbol (one or two letters). For every element there is one and only one upper case letter. There may or may not be a lower case letter with it.
- Atomic number (the integer number listed just above the element symbol). The atomic number is the number of protons in the nucleus of each atom of the element.
- Atomic mass or atomic weight (the number below the element symbol). The atomic mass is not an integer. This number is the sum of the number of protons plus the average number of neutrons in that element.
- Other information may also be listed.
The periodic chart came about from the idea that we could arrange the elements in a way that would show similarity among groups. As you read across the chart from right to left, a row of elements is a Period. As you read down the chart from top to bottom, a column of elements is a Group or Family.
The original idea for organizing the elements came from noticing how they combined with oxygen. Oxygen combines in some way with all the elements except the inert gases. The Groups or columns are numbered from left to right, beginning with 1
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Group IA elements are called the alkali metals.
They include lithium (Li), sodium (Na), potassium (K), rubidium (rb), cesium (Cs), and francium (Fr).
This group does not include hydrogen since H is not a metal even though H is in Group IA.
These elements usually have +1 charge in compounds.
Each atom of oxygen combines with two atoms of any element in Group 1.
Group IIA elements are called the alkaline earth metals.
This is the column of elements including and below beryllium (Be).
These elements usually have +2 charge in compounds. Each atom of oxygen combines with one atom of any element in Group 2.
Group IIIA is the column including and below below boron (B). All of these elements combine with oxygen at the ratio of one-and-a- half to one oxygen.
Group IVA, beginning with carbon (C), combines two to one with oxygen.
Group VA is the nitrogen (N) column.
Group VIA is the oxygen (O) column.
Group VIIA is the fluorine (F) column. These elements are called the Halogens. These elements tend to have -1 charge in compounds. When found as a pure element, the halogens are found as diatomic (two-atom) molecules: F2, Cl2, etc.
Group VIIIA elements, along the right side of the table, are called the noble gases or inert elements.
They include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn).
They are fairly unreactive, so not commonly charged. They do not react with or combine with oxygen or any other element.
The transition elements or transition metals, are in the central section of periodic table (numbers 21-30 and 39-48 and 71-80 and 103 up). They tend to have positive charges in compounds, but can have multiple charges (i.e., their charges are not generally predictable).
These elements have never been adequately placed into the original scheme relating to oxygen. The transition elements vary in the ways they can attach to oxygen, but in a manner that is not readily apparent by the simple scheme.
Most Periodic Charts have two rows of fourteen elements below the main body of the chart.
These elements are called the inner transition elements or inner transition metals.
These two rows, the Lanthanides and Actinides really should be in the chart from numbers 57 – 70 and from 89 – 102. To show this, there would have to be a gap of fourteen element spaces between numbers 20 – 21 and numbers 38 – 39. This would make the chart almost twice as wide as it is now.
The Lanthanides belong to Period 6, and the Actinides belong to Period 7.
Lanthanides, elements 57 – 70, are also called the rare earth elements. The Lanthanide elements are so rare that you are not likely to run across them in most beginning chemistry classes.
No element greater than #92 is found in nature. They are all man-made in the laboratory.
None of the elements greater than #83 have any isotope that is completely stable. This means that all the elements larger than bismuth are naturally radioactive. Another oddity of the Periodic Chart is that hydrogen does not really belong to Group I — or any other group. Despite being over seventy percent of the atoms in the known universe, hydrogen is a unique element.
The Periodic Table can also be divided up into several categories, including metals, non-metals, semi-metals, noble gases, and hydrogen.
1. Metals: left side of stairstep line in the Periodic Table shown above (including lanthanides and actinides) except H. The majority of the elements are metals. Metals have the following properties:
b) malleable (can be hammered into sheets and shaped — like coins and jewelry)
c) ductile (can be drawn into wire)
d) often shiny
e) tend to lose electrons (become positively charged) in chemical reactions
2. Nonmetals: right side of stairstep line in the Periodic Table shown above plus hydrogen (H). This category does not include last column of inert elements or noble gases.
3. Semi-metals or Metalloids: The staircase-shaped line between metals and non-metals has several elements on or near it that have properties somewhere between the two categories or exhibit some of the qualities of both.
For this reason they are called semi-metals or metalloids (meaning metal-like).
This category includes silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), and tellurium (Te).
Some chemists also include boron (B), aluminum (Al), polonium (Po), and astatine (At) in the semi-metals.
Many of the semi-metals are semiconductors of electricity, meaning that they have the ability to conduct electricity somewhere between almost none and full conduction. This property is useful in the electronics industry.
4. Noble gases or inert elements: –He, Ne, Ar, Kr, Xe and Rn, which are not considered metals or nonmetals.
5. Hydrogen: Elements in the same group tend to have similar chemical properties, but H is a nonmetal, so why is it grouped with the alkali metals?
Although H is considered a nonmetal, it often behaves chemically like the alkali metals because of its unique electron configuration. Because of its unique electron configuration, H can frequently be found with a +1 charge like the alkali metals and therefore it often undergoes chemical reactions that alkali metals undergo.
On the other hand, because of its unusual electron configuration, H can often be found with a -1 charge (like the halogens). In its pure form, hydrogen is also a diatomic molecule (H2) like the other halogens.
The halogens are nonmetals, so when H acts like the other halogens, it is behaving more like a nonmetal. Because of this ambivalent behavior of H, some people place H in two places on the Periodic Table: in Group IA and also in Group VIIA. Other Periodic Tables place H at the top of the Periodic Table — leaving it out of all Groups. Most Periodic Tables, however, show H in Group IA.
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