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In the periodic table of the elements, elements are arranged in a series of rows (or periods) so that those with similar properties appear in vertical columns. Elements of the same period have the same number of electron shells; with each group across a period, the elements have one more proton and electron and become less metallic. This arrangement reflects the periodic recurrence of similar properties as the atomic number increases. For example, the alkaline metals lie in one group (group 1) and share similar properties, such as high reactivity and the tendency to lose one electron to arrive at a noble-gas electronic configuration. The periodic table of elements has a total of 109 elements.
Modern quantum mechanics explains these periodic trends in properties in terms of electron shells. As atomic number increases, shells fill with electrons in approximately the order shown below. The filling of each shell corresponds to a row in the table.
- 2s 2p
- 3s 3p 3d
- 4s 4p 4d 4f
- 5s 5p 5d 5f
- 6s 6p 6d
- 7s 7p
In the s-block and p-block of the periodic table, elements within the same period generally do not exhibit trends and similarities in properties (vertical trends down groups are more significant). However in the d-block, trends across periods become significant, and in the f-block elements show a high degree of similarity across periods (particularly the lanthanides).
Seven periods of elements occur naturally on Earth. For period 8, which includes elements which may be synthesized after 2010, see the extended periodic table.
A group in chemistry means a family of objects with similarities like different families.
Chemical elements in the first period
The first period contains fewer elements than any other, with only two, hydrogen and helium. They therefore do not follow the octet rule. Chemically, helium behaves as a noble gas, and thus is taken to be part of the group 18 elements. However, in terms of its nuclear structure it belongs to the s block, and is therefore sometimes classified as a group 2 element, or simultaneously both 2 and 18. Hydrogen readily loses and gains an electron, and so behaves chemically as both a group 1 and a group 17 element.
- Hydrogen (H) is the most abundant of the chemical elements, constituting roughly 75% of the universe's elemental mass. Ionized hydrogen is just a proton. Stars in the main sequence are mainly composed of hydrogen in its plasma state. Elemental hydrogen is relatively rare on Earth, and is industrially produced from hydrocarbons such as methane. Hydrogen can form compounds with most elements and is present in water and most organic compounds.
- Helium (He) exists only as a gas except in extreme conditions. It is the second lightest element and is the second most abundant in the universe. Most helium was formed during the Big Bang, but new helium is created through nuclear fusion of hydrogen in stars. On Earth, helium is relatively rare, only occurring as a byproduct of the natural decay of some radioactive elements. Such 'radiogenic' helium is trapped within natural gas in concentrations of up to seven percent by volume.
Chemical elements in the second period
- Lithium is the lightest metal and the least dense solid element. In its non-ionized state it is one of the most reactive elements, and so is only ever found naturally in compounds. It is the heaviest primordial element forged in large quantities during the Big Bang.
- Beryllium has one of the highest melting points of all the light metals. Small amounts of beryllium were synthesised during the Big Bang, although most of it decayed or reacted further within stars to create larger nucleii, like carbon, nitrogen or oxygen. Beryllium is classified by the From Encyclopedia
Periodic Table of Elements PERIODIC TABLE OF ELEMENTS
In virtually every chemistry classroom on the planet, there is a chart known as the periodic table of elements. At first glance, it looks like a mere series of boxes, with letters and numbers in them, arranged according to some kind of code not immediately clear to the observer. The boxes would form a rectangle, 18 across and 7 deep, but there are gaps in the rectangle, particularly along the top. To further complicate matters, two rows of boxes are shown along the bottom, separated from one another and from the rest of the table. Even when one begins to appreciate all the information contained in these boxes, the periodic table might appear to be a mere chart, rather than what it really is: one of the most sophisticated and usable means ever designed for representing complex interactions between the building blocks of matter. As a testament to its durability, the periodic tableâ€”created in 1869â€”is still in use today. Along the way, it has incorporated modifications involving subatomic properties unknown to the man who designed it, Russian chemist Dmitri Ivanovitch Mendeleev (1834-1907). Yet Mendeleev's original model, which we will discuss shortly, was essentially sound, inasmuch as it was based on the knowledge available to chemists at the time. In 1869, the electromagnetic force fundamental to chemical interactions had only recently been identified; the modern idea of the atom was less than 70 years old; and another three decades were to elapse before scientists began uncovering the substructure of atoms that causes them to behave as they do. Despite these limitations in the knowledge available to Mendeleev, his original table was sound enough that it has never had to be discarded, but merely clarified and modified, in the years since he developed it. The rows of the periodic table of elements are called periods, and the columns are known as groups. Each box in the table represents an element by its chemical symbol, along with its atomic number and its average atomic mass in atomic mass units. Already a great deal has been said, and a number of terms need to be explained. These explanations will require the length of this essay, beginning with a little historical background, because chemists' understanding of the periodic tableâ€”and of the elements and atoms it representsâ€”has evolved considerably since 1869. An element is a substance that cannot be broken down chemically into another substance. An atom is the smallest particle of an element that retains all the chemical and physical properties of the element, and elements contain only one kind of atom. The scientific concepts of both elements and atoms came to us from the ancient Greeks, who had a rather erroneous notion of the element andâ€”for their time, at leastâ€”a highly advanced idea of the atom. Unfortunately, atomic theory died away in later centuries, while the mistaken notion of four "elements" (earth, air, fire, and water) survived virtually until the seventeenth century, an era that witnessed the birth of modern science. Yet the ancients did know of substances later classified as elements, even if they did not understand them as such. Among these were gold, tin, copper, silver, lead, and mercury. These, in fact, are such an old part of human history that their discoverers are unknown. The first individual credited with discovering an element was German chemist Hennig Brand (c. 1630-c. 1692), who discovered phosphorus in 1674. The work of English physicist and chemist Robert Boyle (1627-1691) greatly advanced scientific understanding of the elements. Boyle maintained that no substance was an element if it could be broken down into other substances: thus air, for instance, was not an element. Boyle's studies led to the identification of numerous elements in the years that followed, and his work influenced French chemists Antoine Lavoisier (1743-1794) and Joseph-Louis Proust (1754-1826), both of whom helped define an element in the modern sense. These men in turn influenced English chemist John Dalton (1766-1844), who reintroduced atomic theory to the language of science. In A New System of Chemical Philosophy (1808), Dalton put forward the idea that nature is composed of tiny particles, and in so doing he adopted the Greek word atomos to describe these basic units. Drawing on Proust's law of constant composition, Dalton recognized that the structure of atoms in a particular element or compound is uniform, but maintained that compounds are made up of compound "atoms." In fact, these compound atoms are really molecules, or groups of two or more atoms bonded to one another, a distinction clarified by Italian physicist Amedeo Avogadro (1776-1856). Dalton's and Avogadro's contemporary, Swedish chemist Jons Berzelius (1779-1848), developed a system of comparing the mass of various atoms in relation to the lightest one, hydrogen. Berzelius also introduced the system of chemical symbolsâ€”H for hydrogen, O for oxygen, and so onâ€”in use today. Thus, by the middle of the nineteenth century, scientists understood vastly more about elements and atoms than they had just a few decades before, and the need for a system of organizing elements became increasingly clear. By mid-century, a number of chemists had attempted to create just such an organizational system, and though Mendeleev's was not the first, it proved the most useful. By the time Mendeleev constructed his periodic table in 1869, there were 63 known elements. At that point, he was working as a chemistry professor at the University of St. Petersburg, where he had become acutely aware of the need for a way of classifying the elements to make their relationships more understandable to his students. He therefore assembled a set of 63 cards, one for each element, on which he wrote a number of identifying characteristics for each. Along with the element symbol, discussed below, he included the atomic mass for the atoms of each. In Mendeleev's time, atomic mass was understood simply to be the collective mass of a unit of atomsâ€”a unit developed by Avogadro, known as the moleâ€”divided by Avogadro's number, the number of atoms or molecules in a mole. With the later discovery of subatomic particles, which in turn made possible the discovery of isotopes, figures for atomic mass were clarified, as will also be discussed. In addition, Mendeleev also included figures for specific gravityâ€”the ratio between the density of an element and the density of waterâ€”as well as other known chemical characteristics of an element. Today, these items are typically no longer included on the periodic table, partly for considerations of space, but partly because chemists' much greater understanding of the properties of atoms makes it unnecessary to clutter the table with so much detail. Again, however, in Mendeleev's time there was no way of knowing about these factors. As far as chemists knew in 1869, an atom was an indivisible little pellet of matter that could not be characterized by terms any more detailed than its mass and the ways it interacted with atoms of other elements. Mendeleev therefore arranged his cards in order of atomic mass, then grouped elements that showed similar chemical properties. As Mendeleev observed, every eighth element on the chart exhibits similar characteristics, and thus, he established columns whereby element number x was placed above element number x + 8 â€”for instance, helium (2) above neon (10). The patterns he observed were so regular that for any "hole" in his table, he predicted that an element to fill that space would be discovered. Indeed, Mendeleev was so confident in the basic soundness of his organizational system that in some instances, he changed the figures for the atomic mass of certain elements because he was convinced they belonged elsewhere on the table. Later discoveries of isotopes, which in some cases affected the average atomic mass considerably, confirmed his suppositions. Likewise the undiscovered elements he named "eka-aluminum," "eka-boron," and "eka-silicon" were later identified as gallium, scandium, and germanium, respectively. Over a period of 35 years, between the discovery of the
From Yahoo AnswersQuestion:i'm doin a chemistry assignment and thats wut i have to do on one of the questions. i know that ones rows and ones columns but i cant explain better.
Answers:Period- 7 rows, # elctrons genarrally rises going down ... Lanthanides&Actinides dont fit in periodic table. 18 columns called groups/families- group 1 alkali metals, group 2, alkaline earth metals, group3-12 transition metals, group 17 halogens, group 18 noble gas....Question:I know that a group catergorizes the elements into their famalies, but what does the period in a periodic table do?
Answers:A group is represented by a column in the table and its members have similar properties. A period is a row, and the properties change in a somewhat repeatable way as you go across. At the left are active metals, then less active multivalent ones, then transitional elements and finally active halogens (but it's more complicated than that in detail.)Question:actinide series group alkali metal alkaline earth metal metalloid periodic law atomic mass atomic number noble gas halogen lanthanide series nonmetal period metal transition element periodic table Moseley family Dmitri Mendeleev developed a chartlike arrangement of the elements he called the __(1)__. He stated that if the elements were listed in order of increasing __(2)__, their properties repeated in a regular manner. He called this the __(3)__ of the elements. The arrangement used today, devised by __(4)__, differs from that of Mendeleev in that the elements are arranged in order of increasing __(5)__. Each horizontal row of elements is called a(n) __(6)__. Each vertical column is called a(n) __(7)__, or, because of the resemblance between elements in the same column, a(n) __(8)__. In rows 4-7, there is a wide central section containing elements, each of which is called a(n) __(9)__. Rows 6 and 7 also contain two other sets of elements that are listed below the main chart. These are called the __(10)__ and the __(11)__, respectively. Each of these elements, as well as those in the first two columns at the left end of the chart, is classified as a(n) __(12)__. Each of the elements at the right side of the chart is classified as a(n) __(13)__. Each of the elements between these two main types of elements, having some properties in common with each, is called a(n) __(14)__. Each of the elements in the column labeled 1 is called a(n) __(15)__. Each of the elements in the column labeled 2 is called a(n) __(16)__. Each of the elements in column 17 is called a(n) __(17)__. Each of the elements in column 18 is called a(n) __(18)__.
Answers:Actinide Series, a series of 14 radioactive elements in the periodic table with atomic numbers 89 through 102. Alkali Metals, series of six chemical elements in group 1 (or Ia) of the periodic table. They are soft compared to other metals, have low melting points, and are so reactive that they are never found in nature uncombined with other elements Alkaline Earth Metals, series of six chemical elements in group 2 (or IIa) of the periodic table Periodic Law, in chemistry, law stating that many of the physical and chemical properties of the elements tend to recur in a systematic manner with increasing atomic number. Noble Gases, also inert gases, group of six gaseous chemical elements constituting the group 18 (or VIIIa) of the periodic table. Halogens (Greek hals, salt ; genes, born ), in chemistry, group of five closely related chemically active elements fluorine, chlorine, bromine, iodine, and astatine. The name halogen, or salt former, refers to the property of each of the halogens to form with sodium a salt similar to common salt Lanthanide Series, series of metallic elements of the periodic table commonly defined as the elements cerium (atomic no. 58) through ytterbium (atomic no. 70). Yttrium (atomic no. 39) and lanthanum (atomic no. 57) are often included in the lanthanide series Metals, group of chemical elements that exhibit all or most of the following physical qualities: they are solid at ordinary temperatures; opaque, except in extremely thin films; good electrical and thermal conductors Transition Elements, series of chemical elements that share similar electron orbital structures and hence similar chemical properties. The transition elements are commonly defined as the 30 elements with atomic numbers 21 to 30, 39 to 48, and 71 to. Periodic Table, table of the chemical elements arranged to illustrate patterns of recurring chemical and physical properties.Question:Thanks!
Answers:A group of elements is a vertical column of elements in the periodic table. Although the elements may have different physical properties, they resemble one another in their physical properties.
From YoutubeChemistry: Creating the Periodic Table :www.mindbites.com This lesson examines the creation of the Periodic Table of the Elements. Professor Harman walks you through the thought process involved in the grouping and the changes that led to the periodic table we are familiar with. Initially, many organization methods were tried, but Mendeleev's method was the most successful. The Mendeleev table used two characteristics for organizations, the atomic mass and the chemical reactivity. This method better organized the elements and made it possible to accurately predict unknown elements and their physical and chemical properties. Later discoveries changed the ordering of the periodic table. Ramsay discovered Argon, which doesn't have any chemical reactivity and whose mass fits in between two existing elements. This suggested a missing family that eventually came to be known as the Noble gases. Then, the discovery of the nucleus led to a change in ordering of atomic number (number of protons), instead of atomic mass. Using the atomic number better aligns the elements in their reactivity groupings. Taught by Professor Harman, this lesson was selected from a broader, comprehensive course, Chemistry. This course and others are available from Thinkwell, Inc. The full course can be found at www.thinkwell.com The full course covers atoms, molecules and ions, stoichiometry, reactions in aqueous solutions, gases, thermochemistry, Modern Atomic Theory, electron configurations, periodicity, chemical bonding, molecular geometry ...Periodic Table Of Elements :He realized that the table in front of him lay at the very heart of chemistry. In his table he noted gaps - spaces where elements should be but none had yet been discovered. In fact, just as Adams and Le Verrier could be said to have discovered the planet Neptune on paper, Mendeleev could be said to have discovered germanium (which he called eka-silicon because he observed a gap between silicon and tin), gallium (eka-aluminum) and scandium (eka-boron) on paper, for he predicted their existence and their properties before their actual discoveries. Although Mendeleev had made a crucial breakthrough, he made little further progress because the Rutherford-Bohr model of the atom had not yet been formulated. In 1913, Henry Moseley, who worked with Rutherford, showed it is atomic number (charge) and not (as Mendeleev had proposed) atomic weight that is most fundamental to the chemical properties of any element. Like Mendeleev, Moseley was able to predict correctly the existence of new elements based on his work. And today the elements are still arranged in order of increasing atomic number (Z) as you go from left to right across the table. We call the horizontal rows periods and the vertical rows groups. We also know an element's chemistry is determined by the way its electrons are arranged - its electron configuration.