Elements are arranged by what in the periodic table?

Answer 1

The elements are arranged in order of increasing atomic number (number of protons), and by groups that have similar properties, and by periods that reflect these properties in increasingly larger atoms.

The Periodic Table of elements is arranged in a number of ways. It was set up to allow the user to immediately understand some things about the different chemical elements, and it does a damn fine job of that. The table isn't "even" in that it seems a bit "jumbled" or "broken" here and there due to the desire to quickly communicate some different things. Let's look at what's up. The table is arranged by atomic number from upper left to lower right, with the numbers increasing as one goes across in a given row. It's like reading a book (in English). We read from left to right, and line by line from the top down. But the table is so much more than that! Why didn't we just post a list? Because there's more we can communicate. A lot more. And it's all about the electron structure of the atom. It's about how the electrons are arranged about a nucleus, about how they "form up" in the "electron cloud" that describes the volume of a given atom. Curious? Let's look. Note that hydrogen, atomic number 1, is in the upper left corner. It has a single electron about its nucleus. The element that is next, that has atomic number 2, helium, is in the upper right. What's up with that? They are in the same (horizontal) row, but are at opposite ends of the chart. And they're the only elements in that horizontal row. To find element 3 we have to go back to the left side of the chart. Why'd we go back? Because we wanted to start a new row, and that's because hydrogen and helium have electrons in the "first" electron shell, and with helium, that first shell is full. Element 3, lithium, has an electron structure that includes a full "inner" shell, and a lone electron in a "new" or "next outer" shell. We put lithium under hydrogen because both have one lone electron in their outer or valence shells. By the way, the valence shell is the outer electron shell of an atom - whatever shell it may be. On to element 4, which is beryllium, which is side by side with lithium. It has two electrons in its outer shell. So does helium, but remember that helium has a full outer shell. Beryllium, with its two electrons in its outer shell, still has more room in that shell; that shell isn't full. What's next? It's boron that has atomic number 5, but we've kicked it over to another area of the chart. It's still in the row with elements 3 and 4, and follows them. But we're arranging by electron shell structure, remember? We're working on the second shell - and there's bad news. There are shells, and there are subshells within the shells. But hang on. This stuff ain't hard to get a handle on. The shells, as they get further from the nucleus, will have more "room" in them, and the electrons will be able to more easily share the same general area or shell. You remember that electrons are negatively charged and don't like each other, right? Sure you do. If electrons are going to be "trapped" by an atomic nucleus and "held hostage" in an orbit, the electrons themselves will have to work something out so they can "get along" in the confined space of the shells. So we're still filling the second shell, and when it gets full to the last electron that will fit, that element, whatever it is, will be posted under helium, which was the first atom to have a full shell. All atoms with a full outer electron shell will line up under helium in the last column. And when all is said and done, the last column is column 18 and we label that column as Group 18. These are all the atoms with a full outer electron shell, and you might recognize them as the noble or inert gases. Back on the left hand side of the chart under hydrogen are all the elements with only 1 electron in their outer, or valence shells. They are the Group 1 elements, the Alkali Metals. Group 2 elements, the next vertical column, have 2 electrons in their outer shell, and they are the Alkaline Earth Metals. See how it's working? Each horizontal row is set up with elements added as a given electron shell fills. At the end of the row is the element with that shell completely full. And each vertical column is set up according to how many electrons are in the outer or valence shell. Over on the right beside Group 18 are the Group 17 elements, which are all the elements that are one electron short of having a full outer electron shell. These are the halogens. Next to them is Group 16, the chalcogens or oxygen group, and they are the elements that are all 2 electrons short of having a full valence shell. It's all about electron structure. And the electron structure is the key to the way atoms react with each other, which is the science of chemistry. A link is provided to Wikipedia, which has a great interactive periodic table of the elements. Each element is a link to the Wikipedia post on that element. Even the groups and rows are links to the characteristics of the elements in each one. The link can be found below.

They are arranged in ascending order by proton number.

There are eight vertical groups. Elements in each group share similar properties and have the same number of valence electrons. Group I elements have one valence electron, and Group V elements have five valence electrons. Group 0 (the eighth group) elements have either two or eight valence electrons.

The elements are also arranged horizontally in Periods. Hydrogen and helium are in Period 1; lithium, neon and the elements between them are in Period 2; and sodium, argon and the elements between them are in Period 3. So on. The Period an element is in indicates the number of electron shells the atom has. Hydrogen has one shell, sodium has three.

Metals are found on the left side of the periodic table. Non-metals are found on the right side. Elements between Group II and Group III are called transition metals. For example, iron, gold, copper, nickel and silver are all transition metals. Some elements found between metals and non-metals are metalloids, which have properties similar to both metals and non-metals.

The periodic table of chemical elements is usually arranged in order of atomic number (as based on the periodic law) in horizontal rows.

Answer 2

in the increasing order of their atomic number

Answer 3

The modern periodic table is arranged in the increasing order of their atomic number and repeating properties.