Chapter 4-the periodic table-leaving cert chemistry

A triad

Is a group of three elements with similiar chemical properties in which the the atomic weight of the middle element is approximately equal to the average of the other two

Newlands octaves

Are arrangements of elements in which the first and eight element, counting from a particular element, have similar properties

Mendeleevs periodic law

When elements are arranged in order of increasing atomic weight, the properties of the element recur periodically, I.e; the properties displayed by an element are repeated at regular intervals in other elements

The atomic number

Is the number of protons in the nucleus of an atom

Modern periodic law

When elements are arranged in order of increasing atomic number, the properties of the elements recur periodically, I.e; the properties displayed by an element are repeated at regular intervals in other elements

An element

Is a substance that cannot be split into simpler substances by chemical means

The modern periodic table

Is an arrangement of elements in order of increasing atomic number

The mass number

Of an element is the sum of the number of the protons and neutrons in an atom of that element

Isoptopes

Are atoms of the same element (have the same atomic number) which have different mass numbers due to the different number of neutrons in the nucleus

Relative atomic mass

Is defined as:
•the average of the mass numbers of the isotopes of the element,
•as they occur naturally
•taking their abundance's into account and
•expressed on a scale in which the atoms of the carbon 12 isotope have a mass of exactly 12 units

The principle of mass spectrometry

Is that charged particles moving in a magnetic field are deflected to different extents according to their masses and are thus separated according to these masses

The electron configuration

Shows the arrangement of electrons in atom of an element

Aufbau Principle

When building up the electron configuration of an atom in its ground state, the electrons occupy the lowest available energy levels

Hands rule of maximum multiplicity

States that when two or more orbitals of equal energy are available, the electrons occupy them singly before filling them in pairs

The Pauli Exclusion Principle

States that no more than two electrons may occupy an orbital and they must have opposite spin