The modern periodic table
In the modern periodic table:
- elements are arranged in rows, called A horizontal row in the periodic table., in order of increasing The number of protons in the nucleus of an atom. Also called the proton number.
- elements with similar properties are placed in vertical columns, called A vertical column in the periodic table containing elements with similar chemical properties.
The table is called the periodic table because elements with similar properties occur at regular intervals.
The modern periodic table with some elements left out for simplicity
Resolving pair reversals
Mendeleev did not know about Atoms of an element with the same number of protons and electrons but different numbers of neutrons., but their existence explains pair reversals. The positions of iodine and tellurium were reversed in Mendeleev's table because:
- iodine has one naturally occurring isotope, iodine-127
- the most If there is a lot of something, it is described as being abundant. tellurium isotopes are tellurium-128 and tellurium-130
The high relative abundance of these tellurium isotopes gives tellurium the greater relative atomic mass. The atomic number of tellurium is 52 and the atomic number of iodine is 53, so these elements are in the correct order in the modern periodic table.