What is the main difference between the modern and earlier periodic table?

Elements are arranged in increasing atomic number on the modern periodic table while they were arranged in atomic mass/weight in the earlier periodic table.

Earlier periodic table was formed on the basis of increasing order of atomic mass of elements but modern periodic table formed on the basis of increasing order of atomic number of elements.

The main difference between the modern periodic table and Mendeleev's periodic table (the earlier periodic table) is that we order elements by atomic number whereas we used to order them by atomic mass.

1. Mendeleev's periodic table is based on atomic mass. Modern periodic table is based on atomic number.
2. Mendaleev's periodic table contains about 66 elements. Modern periodic table contains presently 118 elements.
3. In Mendeleev's periodic table there were gaps for undiscovered elements. Modern periodic table maintains uniformity.
4. In Mendeleev's periodic table noble gases were not placed (as they are not discovered at that time).In Modern periodic table noble gases in a seperate group named as group-18.
5. In Mendeleev's periodic table transition elements included with other elements. In Modern periodic table transition elements placed in separate block.
6. According to Mendeleev's, the isotopes with different atomic weights, should be placed in different positions, but are not given any position and no justified reason was explained. In Modern periodic table, the isotopes were assigned same position as they have same atomic number.

Hi Annalise - the main difference between the modern Periodic Table (the one you see in every textbook) and earlier Periodic Tables (such as those by Dalton, Dobereiner and Newlands) is that our current periodic table shows not only a list of every known element, but also shows which elements have similar properties by putting them in the same group or period (column or row).

Mendeleev, the designer of what we consider the "modern periodic table" grouped elements by their properties, and noticed that the pattern repeated every few elements. Because of this, he placed them in repeating row, or 'periods' - this meant that reactive metals such as Lithium, Sodium and Potassium end up in the first position (or group 1), the halogens (fluorine, chlorine and bromine) ended up above one another in group 7. However, the pattern didn't always work, and some elements seemed to be in the wrong position - so instead of forcing his ideas on the elements, Mendeleev left gaps so that any elements he may not have known about at the time. Later on, these gaps were able to be filled perfectly by new elements with similar properties, which proved to the scientific community that Mendeleev's table worked!

I hope this helped!

earlier mode; based on atomic mass ( Mendeleev ) .Current model based on Atomic number

The main difference between the Earlier (Mendeleev) and the Modern Periodic Table is that Mendeleev's periodic table orders the elements based on their atomic mass whereas Modern Periodic table orders the elements based on their atomic number. This was because the earlier periodic tables were incomplete and some of the elements were placed in inappropriate groups if the strict order of atomic mass was followed. Mendeleev overcame some of the problems by leaving gaps for elements that had not yet been discovered. Later on the Modern Periodic Table became more convenient and elements were placed in appropriate groups and arranged in order of their atomic (proton) numbers.

The earlier periodic table involved elements being ordered in atomic mass, whereas the modern day periodic table includes elements being ordered in their atomic number. This is due to the presence of neutrons in each element, which was unknown during the earlier periodic table, as well as the presence of isotopes.

Also, the elements not being strict ordered in their atomic number (in the modern day periodic table) if the element fits the properties of one group better.

The first periodic table discovered had many gaps in in. Dmitri Mendeleev discovered many of the first elements but did not discover all of them. The more modern periodic table, has over 100 elements in it and Mendeleev predicted that some elements would slot in to certain gaps (due to similarities in physical and chemical properties).

The older periodic table derived in the 19th century arranged the known elements (more were discovered after the production of this periodic table) based on their atomic mass. The atomic mass identifies the total number of protons and neutrons in the nucleus of the element and is shown on the element information usually below the element symbol. The modern table arranges element according to their atomic number (number of protons) which is the number usually shown above the element symbol.

In the earlier periodic table, often attributed to Dmitri Mendeleev, elements were arranged in rows in order of increasing atomic mass. Elements in the same column shared similar properties. This enabled him to predict new elements, that had not yet been discovered, and to predict the properties that they would have.

The main difference is that the elements in early versions of the periodic table were sorted by mass number, but in the modern table they are sorted by atomic number.

Some more background on this:

The very first chemists first sorted the elements by mass and looked for patterns in the list. Newlands noticed that patterns seemed to repeat every 8 elements (hence the table he deviced became known as Newland's octaves). But this pattern broke down due to the strict ordering by atomic mass. Some elements were placed in the same groups that didn't have the same properties like iron and oxygen.

Mendeleev came closer with his early version of the periodic table, at the time he had no knowledge of subatomic particles like protons, neutrons and electrons.hen he first sorted the elements it was by atomic mass. Because of this he first sorted by the elements by mass, but critically he made exceptions to this rule and swapped some elements around when the chemical properties didn't fit in with the group they were sorted into. He also left gaps where he felt elements should be. That was his genius insight. Those gaps allowed his table to be tested and proven right. Those elements have since been discovered on the modern periodic table and they fit right in where he predicted they would.

The modern periodic table sorts the elements by their atomic number (which tells you the number of protons in the nucleus) and not by mass.

Early versions of the periodic table were incomplete and elements were placed with others that they had nothing in common with. Dimitri Mendeleev in 1869 developed an early version of the periodic table where he arranged chemical elements by their atomic mass. He predicted that there were other elements out there that were yet to be discovered.

The arrangement of the modern periodic table is in increasing atomic number (proton number in the nucleus of the atom of the element) from left to right in the table.

The original periodic table was created before detailed knowledge of atomic structure was known and was arranged in order of the mass of the atom of the element.

Mendeleev's periodic table orders the elements based on their atomic mass whereas Modern periodic table orders the elements based on their atomic number