Periodic Table for Chemistry
Dmitri Mendeleev (1834-1907)
What is the Periodic Table?
The Periodic Table of Elements is a way of organising all 118 known elements, according to their physical properties and chemical behaviour. The table allows us to accurately predict the behaviour of different elements when they react together. But this raises a more basic question:
What is an element?
Put simply, an element is a 'pure' substance made of only one type of atom. Atoms themselves are made of protons, electrons and neutrons; each element has a different and fixed number of protons, neutrons and electrons. For example, Helium (He) has 2 protons, 2 electrons and 2 neutrons.
How is the Periodic Table Arranged?
As you move across the periodic table, the number of protons in the nucleus of the atom increases by one. Lithium has 3 protons, Beryllium has 4 protons, Boron has 5 protons, and so on.
There are several organisational elements to the periodic table. Most importantly are the rows and columns:
- The rows of the table are known as periods. These go across the table (My chemistry teacher taught me to remember this by thinking that girls get cross on their periods, and periods go across the table). Moving left to right atomic radius tends to decrease, and electronegativity increases.
- The columns of the table are known as groups. These go up and down the table (My chemistry treacher taught me to remember this by thinking that groups go up and down in the charts, and groups go up and down in the table) Every element in a group has the same number of electrons in it's outer shell - giving each group similar chemical properties. Moving down a group, atomic radius tends to increase and electronegativity decreases.
The table can also be organised as metals, metalloids and non-metals; as well as according to blocks.
What is the Periodic Table?
Printable Periodic Tables
- Printable Periodic Tables
A great collection of different periodic tables, all printable, all free. A great resource!
Trends of the Periodic Table
Who Invented the Periodic Table?
There were several attempts to organise the known elements before the modern Table was invented. John Newlands thought he found groups of seven elements, which he termed 'octaves'. Unfortunately, when a new element was discovered (in the 19th Century they were being discovered at a rate of about 1 per year) the new elements did not fit neatly into Newlands' pattern.
A Russian chemist, Dmitri Mendeleev, was the first person to create an organisational method for the elements that not only incorporated newly discovered elements, but actively and accurately predicted their existence and their potential properties.
Mendeleev did three things differently to his colleagues:
- He did not try to make a completely regular grid - some rows were longer than others.
- If the elements didn't fit his table, he swapped things round. If they still didn't fit, he told the experimenters they must have got the masses of the elements wrong.
- He left gaps for elements that had not been discovered yet.
The Elements Song!
Interactive Periodic Table
- Dynamic Periodic Table
Interactive Web 2.0 periodic table with dynamic layouts showing names, electrons, oxidation, trend visualization, orbitals, isotopes, search. Full descriptions. An Award winning resource!
What do the Numbers on the Periodic Table Mean?
One of the impressive things Mendeleev managed was to accurately predict the physical and chemical properties of undiscovered elements. The fact that Mendeleev could predict the existence of an element that nobody had discovered is amazing enough, but how could he also predict their properties?
It's all down to what the numbers on the Periodic Table mean.
Each symbol is flanked by two numbers:
- The Atomic number: This shows the number of protons in the nucleus of the atom. This is also the number of electrons in the atom
- The Mass number: this shows the numbers of protons and neutrons in the atom. This constitutes most of the mass of the atom (electrons have negligible mass)
The properties of an atom depend on it's electronegativity, ionisation energy and number of electrons in the outer valence. All of these properties are determined by the number of protons and electrons in the atom. As Mendeleev could accurately predict the number of protons and electrons in an atom, he could predict the chemical properties that would go with them. Mendeleev also knew the properties of the elements surrounding his predicted gaps - which further helped him to predict the properties of the undiscovered elements.
What do Atomic Symbols Mean
Periodic Table Summary
Who Decides if Something is an Element?
The International Union of Pure and Applied Chemistry is the body that decides what goes on the Periodic Table, and what that element is called.