# Relationship between electron arrangement and periodic table

### BBC - GCSE Bitesize: Electron arrangement and group number

Learn about the periodic table with Bitesize GCSE Combined Science (OCR The electron arrangement of an atom can be predicted from its atomic number. As you have seen on the previous page, there is a link between an element's electronic structure and its place in the periodic table. You can work out an. How the periodic table was formed has an intimate correlation with electron configuration. After studying the relationship between electron.

You can work out an element's electronic structure from its place in the periodic table.

5.2 Electron Configuration and the Periodic Table

The diagram below shows a section of the periodic table, with the elements arranged as usual in order of their atomic number from 2 to The red numbers above each chemical symbol show the electrons in each shell.

Periodic table showing electron configurations Moving across each period, you can see that the number of shells is the same as the period number. For example sodium Na has the electron arrangement 2.

As you go across each period from left to right, the outer shell gradually becomes filled with electrons. The outer shell contains just one electron on the left hand side of the table, but is filled by the time you get to the right hand side.

## The periodic table, electron shells, and orbitals

Moving, down each group, you can see that the number of electrons in the outermost shell is the same as the group number. Each element in a group therefore has the same number of electrons in its outer shell.

Group 0 is a partial exception to this rule, since although it comes after group 7 it is not called 'group 8', and it contains helium, which has only two electrons in its outer shell. Working out electronic structure from the periodic table Here's how to use the periodic table to work out an electronic structure: Find the element in the periodic table. Work out which period it's in, and draw that number of circles around the nucleus.

## Electron arrangement and group number

The position of each element in the table gives important information about its structure, properties, and behavior in chemical reactions. The periodic table By convention, elements are organized in the periodic table, a structure that captures important patterns in their behavior.

Devised by Russian chemist Dmitri Mendeleev — inthe table places elements into columns—groups—and rows—periods—that share certain properties. The periodic table of the elements Image credit: If two atoms have complementary electron patterns, they can react and form a chemical bond, creating a molecule or compound.

As we will see below, the periodic table organizes elements in a way that reflects their number and pattern of electrons, which makes it useful for predicting the reactivity of an element: Electron shells and the Bohr model An early model of the atom was developed in by the Danish scientist Niels Bohr — The Bohr model shows the atom as a central nucleus containing protons and neutrons, with the electrons in circular electron shells at specific distances from the nucleus, similar to planets orbiting around the sun.

• Connecting Electronic Configurations to the Periodic Table
• The periodic table

Each electron shell has a different energy level, with those shells closest to the nucleus being lower in energy than those farther from the nucleus. By convention, each shell is assigned a number and the symbol n—for example, the electron shell closest to the nucleus is called 1n.

In order to move between shells, an electron must absorb or release an amount of energy corresponding exactly to the difference in energy between the shells. For instance, if an electron absorbs energy from a photon, it may become excited and move to a higher-energy shell; conversely, when an excited electron drops back down to a lower-energy shell, it will release energy, often in the form of heat.

### BBC Bitesize - GCSE Combined Science - The periodic table - OCR Gateway - Revision 3

Bohr model of an atom, showing energy levels as concentric circles surrounding the nucleus. Energy must be added to move an electron outward to a higher energy level, and energy is released when an electron falls down from a higher energy level to a closer-in one. Thus, the electron shells of an atom are populated from the inside out, with electrons filling up the low-energy shells closer to the nucleus before they move into the higher-energy shells further out.

The shell closest to the nucleus, 1n, can hold two electrons, while the next shell, 2n, can hold eight, and the third shell, 3n, can hold up to eighteen. The number of electrons in the outermost shell of a particular atom determines its reactivity, or tendency to form chemical bonds with other atoms.

This outermost shell is known as the valence shell, and the electrons found in it are called valence electrons. In general, atoms are most stable, least reactive, when their outermost electron shell is full.