Term | Definition |
an element | is a substance that cannot be split up into simpler substances by chemical means. |
a triad | is a group of three elements with similar chemical properties in which the atomic weight of the middle element is approximately equal to the average of the other two. |
Newlands' Octaves | are groups of elements arranged in order of increasing atomic weight, in which the first and the eight element of each group have similar properties. |
Mendeleev's Periodic Law: | when elemnets are arranged in order of increasing atomic weight (relative atomic mass), the properties of the elements vary periodically. |
The atomic Number of an atom | is the number of protons in the nucleus of that atom. |
The modern Periodic Table | is an arrangement of elements in order of increasing atomic number |
elements arranged in order of increasing atomic number: | the properties of the elements vary periodically. |
the mass number of an element | is the sum of the number of protons and neutrons in the nucleus o an atom of that element. |
Isotopes | are atoms of the same element (have the same atomic number) that have different mass numbers due to the different number of neutrons in the nucleus. |
Relative atomic mass | -the average of the mass of the isotopes of the elemnet
-as they occur natually
-taking their abundences into account
-expressed on a scale in which the atoms of the carbon-12 isotopes have a mass of exactly 12 units. |
the aufbau Principle | states that when building up the electronic configuration of an atom in its ground state, the electrons occupy the lowest available energy level. |
Hund's rule of Maximum Multiplicity | states that when two or more orbits of equal energy are available, the electrons occupy them simply before filling them in pairs. |
The Pauli Exclusion principal | states that no more than two elecrtons may occupy an orbital and they must have opposite spin. |