The modern periodic table is organizes it elements by atomic mass or number?
957398
Atomic number\nThis was an idea by Mossely
789494
Basic Atomic Structure\n\nThe definitions of atoms and elements seems, at first glance, almost circular: an element is a substance made up of only one kind of atom, and an atom is the smallest particle of an element that retains all the chemical and physical properties of the element. In fact, these two definitions do not form a closed loop, as they would if it were stated that an element is something made up of atoms. Every item of matter that exists, except for the subatomic particles discussed in this essay, is made up of atoms. An element, on the other hand, is—as stated in its definition—made up of only one kind of atom. "Kind of atom" in this context refers to the number of protons in its nucleus.\n\nProtons are one of three basic subatomic particles, the other two being electrons and neutrons. As we shall see, there appear to be particles even smaller than these, but before approaching these "sub-subatomic" particles, it is necessary to address the three most significant components of an atom. These are distinguished from one another in terms of electric charge: protons are positively charged, electrons are negative in charge, and neutrons have no electrical charge. As with the north and south poles of magnets, positive and negative charges attract one another, whereas like charges repel. Atoms have no net charge, meaning that the protons and electrons cancel out one another.
878474
Um, there's over a hundred elements.  I'm not going to name them all for you.  Look at a periodic table.  I'm sure there's one in your chemistry book.
504733
The atomic number of an element is equal to the number of electrons it has. Do you mean something more than that?
449354
An atomic number is the number of protons in the nucelus of one atom of an element. This is used to identify each element as unique.
171047
He weighed the atomic mass of elements and arranged them from the lowest to the highest. Also, he put them into the same column if they have the same chemical properties. But he didn't known that the last group (noble gases) exists because they have no reactions with other substances. So his periodic table just had 7 columns (groups).
47846
Look up the atomic mass (sometimes called atomic weight) on the periodic table, and subtract the atomic number from it.  The atomic mass is (practically) equal to the total number of protons and neutrons, and the atomic number is equal to the number of protons.  When you subtract atomic number from atomic mass your subtracting the number of protons from the total number of protons and neutrons, which leaves you with just neutrons.
232753
An atom is the smallest divisible partical that can exist on its own. Its divisibble because it contains three subatomical particals known as protons, neurons, and electrons while an element is a substance that cannot be split into two or more substance like the periodic table has a list of different elements, so examples of elements are those on the periodic table and atoms make up matter.
923272
There are various trends/properties observable in the periodic table of elements:\n1. The elements in a column have same number of electrons in the outermost orbit of the atom. And this number is same as the column number. e.g. column no. 7 has elements (Fluorine, chlorine, bromine, iodine, astatine) that have exactly 7 electrons in their outermost orbit.\n2. The last column (8) are all inert gases.\n3. First three columns are metalic (conductors), last four are insulators, the middle (4th) is semiconductor (with Carbon and Silicon).\n4. The number assigned to an element is same as no.of protons in the nucleus of the atom.\n5. As the atomic number increases, weight of element increases. Thus Hydrogen is the lightest of all. Also first few are gases, then liquids, then light metals, then heavy metals.\n6. First two columns are rare earths and earths.\n7. After and including Uranium (92), all elements are radioactive.\n\nYou can find more info online.
573382
Magnesium is the 12th element (atomic number 12).\n\nCarbon is the 6th element, but has an atomic mass of 12.
399707
Atoms consist of protons and neutrons in a nucleus, with electrons in shells round it. \nIn an uncharged/neutral atom, the number of protons and electrons are equal and this is the same as the atomic number. In the periodic table, the elements are arranged in order of increasing atomic number. \nA molecule is two or more atoms chemically bonded together.\ne.g. Ne is an atom and H20 is a molecule.
471015
google it and type 'periodic table, first twenty elements'\nn u'll get sumthing, far quicker than lettin sum1 write them up 4 u.
503241
British chemist, John Newlands had the idea of arranging chemical elements in order of their relative atomic masses and he arranged his elements in columns. However, Russian chemist, Dmitri Mendeleev greatly improved on Newlands' idea and convinced other chemists to use it, so Mendeleev has been credited with the invention of the periodic table. Dmitri Mendeleev came up with his first version of the periodic table in 1864, since then more than 700 versions of the table have been proposed.\n\nNo chemistry textbook, classroom, lecture theatre or research laboratory is complete without a copy of the periodic table of the elements. Since the earliest days of chemistry, attempts have been made to arrange the known elements in ways that revealed similarities between them. However, it required the genius of Mendeleev to see that arranging elements into patterns was not enough; he realised that there was a natural plan in which each element has its allotted place, and this applies not only to the known elements but to some that were still undiscovered. Today we have the so-called long form of the table. This has emerged supreme from well over 100 designs that have been proposed since the time of Mendeleev. With the advantage of hindsight we can now see why this form of the table was bound to succeed.\n\nToday there are 111 elements recognised by IUPAC, and these are usually displayed in the form of a matrix called a periodic table. The term periodic came from the regular occurrence of certain chemical properties in the list of known elements when these are arranged in order of increasing relative mass. The common form, complete with the new group numbers (1-18) were finally agreed by the International Union of Pure Applied Chemistry, IUPAC, in 1985, after years of wrangling. In truly Parkinsonian fashion, this least important of changes has probably consumed the most effort!\n\nSince Antoine Lavoisier first defined a chemical element and drew up a table of 33 of them for his book 'Traité Elémentaire de Chimie' (Treatise on the Chemical Elements) published in 1789, there have been attempts to classify them. Lavoisier himself grouped them into four categories on the basis of their chemical properties: gases, nonmetals, metals and earths. In the first category he listed substances that we now know as oxides but which at the time had defeated all attempts at separation.\n\nThis desire to identify and classify elements continued in chemistry for another 80 years until Mendeleev stumbled upon the correct classification - the periodic table. Today the periodic table is securely based on the properties of atomic number of the nucleus and the electron energy levels which surround it. Both of these concepts postdate Mendeleev by several decades. He, however perceived them indirectly through the related properties of atomic weight and chemical valency and arrived at the periodic table in 1869.\n\nBecause atomic weight, relative atomic mass, is roughly proportional to atomic number, and because valency, which manifests itself in the chemical composition, is based on the outermost electrons of an atom, Mendeleev had chosen the two properties that in his day most nearly reflected the fundamental principles on which the table today is based. Consciously or subconsciously, he arrived at the idea that a table existed with positions that were to be occupied by the elements, rather than the other way round - that the known elements determined the arrangement of the table, as others imagined.\n\nThis being so, Mendeleev then put the 65 elements he knew into his table and at the same time pointed out the many unoccupied positions in the overall scheme. He took the further and much bolder step of predicting the properties of these missing elements. Moreover, the gap in atomic weights between cerium (140) and tantalum (182) suggested to him that a whole period of the table remained to be discovered. Later in the century many of these elements,
482427
The "atomic" number refers to the place in the periodic table which corresponds directly (is equal to) the number of protons. The mass number is a weighted average involving commonly found isotopes.
778176
Use the periodic table of the elements.  The "weights" are in grams per mol.  Just use algebra and solve for the number of mols.  Then you know how many atoms there are by the number of mols which is a definite number.
670884
I believe you already asked that a few days ago. But here is a refresher of the best answer yoy chose.:\nChemistry is Chemistry (derived from alchemy) is the science of matter and study of inner molecules and atoms. You study metal properties, its characteristics and behaviour. You study about Organic and InOrganic Materials. You will also learn about mixing chemicals - Reactants and Products. Don't worry now, it will soon become interesting.\n\nThe atomic mass of a chemical element is the mass of an atom at rest and Atomic number (Z) is the number of protons found in the nucleus of an atom.
214181
It is a table of all the atomic elements and the different building blocks of our world.\nThe periodic table is a table in which the chemical elements are arranged in order of their atomic numbers. With this arrangement, elements with similar chemical properties and electronic structures are displayed as vertical columns of the table.