The Periodic Table Flashcards
What is the current accepted model of the atom and who developed it?
The current accepted model of the atom is called the cloud model of the atom developed by Erwin schrodinger in 1927-35. The electrons are visualised as probability waves surrounding a nucleuswith the cloud being denser where there is more of a chance for an electron to be present.
What were the origins of the periodic table?
- knowledge of elements and their properties very limited up until the 17th century
- before that time chemists and alchemists were busy in their laboratories trying to understand the chemical nature of matter
- also sought to develop chemicals or elixirs that could prolong youth and prevent old age
- first stumbling block was not knowing what constituted as a pure substance, in 1660 Robert Doyle defined the terms element and compound, some substances thought to be elements were eventually discovered as compounds
By the late eighteenth century, chemists had identified 33 elements and could now begin to classify them
What was Antoine Lavoisiers contribution to the development of the periodic table?
He established that elements were the fundamental building blocks of chemical substances
He examined their physical and chemical properties and began classifying elements into four groups which were metals, semi metals, elastic fluids and earths
Also established the importance of gravimetric analysis and mass conservation in a reaction
What was Johann Dobereiners contribution to the periodic table ?
Developed triads, groups of three elements with chemical similarity
Arranged each element of triad in order of atomic weight, noticed that the density of the middle term was intermediate between the first and last and the atomic weight was close to an average
Such an example is lithium, sodium and potassium
What was John Newlands contribution to the periodic table?
Published a new classification of the elements based on increasing atomic weight in 1864
Represented this data in tabular form with spaces for undiscovered elements
Noted that every eighth element from a given one possessed similar properties. An example of this was lithium, sodium and potassium and he named these a family of elements ** law started to breakdown
Despite these problems John laid the foundation for the modern periodic table and was awarded the prestigious Davy medal for his contributions by the Royal society
What was Demitri Mendeleevs contribution to the periodic table?
Used similarities in elements physical and chemical properties to produce his own classification of the elements
Based his table on order of atomic weights,
elements with the same chemical properties occupied vertical groupings, left spaces for unknown elements,
if the atomic weight was not well known, he placed it in a position consistent with its properties
What did William Ramsay discover between 1852 and 1916?
Discovered a family of unreactive gases and implied that they should be added to the end of Demitris table as a new group, which was called the inert gases
What did Henry Moseley contribute to the periodic table?
Henry suggested that the elements should be placed according to the change in the charge of their nucleus
Discovered a mathematical relationship between the x Ray frequency and a ‘fundamental quantity’ for each element.
Fundamental quantity renamed to atomic number for schrodinger, due to his work modern table is arranged according to increasing atomic number
What was JJ Thomsons contribution to the periodic table?
Discovereds the electron in 1897. Proposed that each element contained a unique number of electrons arranged in concentric rings within the atom
Suggested those elements that belonged to the same family had similar properties because of similar arrangements of electrons
