Ch4 The Periodic Table Flashcards
What did the Greeks think the universe was made of
4 elements, fire, water, air , earth
Element
A substance that cannot be split up into simpler substances by chemical means
Humphrey Davy
Used electrolysis to break down water into hydrogen and oxygen.
Discovered many elements by passing electricity through their compounds
Eg. Potassium, sodium
Mains scientists who contributed to the modern periodic table
Johann dobreiner
John newlands
Dimitri mendeleev
Henry Moseley
What is a triad
A group of three elements with similar chemical properties in which the atomic weight (relative atomic mass) of the middle element is approximately equal to the average of the other two.
Give an example of a triad and who discovered them
Chlorine, bromine, iodine
Johann Dobreiner
Newlands octaves
Arrangements of electrons in which the first and eight element, counting from a particular element, have similar properties
Problems with newlands octaves
- oxygen and sulfur placed in the same group as iron -> they do not resemble iron in chemical properties
-nitrogen and phosphorus do not resemble manganese in chemical properties.
- Noble gases were missing from newlands octaves as they had not been ‘discovered yet
- Newlands had not left gaps for elements yet to be discovered
- Only worked for the first 16 or so Elements
Mendeleevs periodic law
When elements are arranged in order of increasing atomic weight (relative atomic mass), the properties of the element recur periodically.
I.e the properties displayed by an element are repeated at regular intervals.
What did Mendeleev do
Placed all elements with similar properties in same vertical columns as part of a table
Difference between mendeleevs periodic table and modern
Mendeleevs - elements arranged in order of increasing atomic weight (relative atomic mass)
Modern- elements arranged in order of increasing atomic number
Mendeleevs - only 60 elements approx as not all elements had been discovered
Modern - over 100 elements
Mendeleevs - contains gaps for undiscovered elements
Modern - no gaps
Mendeleevs- trainsiton elements (metals) not out in a separate block
Modern - transition elements in a serparate block
How was Mendeleevs table different to newlands octaves
- he left gaps
To make element fit into proper column
Elements that had yet to be discovered
Able to predict properties of some - he had to reverse the order of the elements to make them fall into groups/columns of elements with similar properties
Realised properties were ore important than atomic weight
Eg iodine and tellurium
Modern periodic table
An arrangement of elements in order of increasing atomic number
Henry Mosley
Found a way to determine/ measure the number of protons in the nucleus of an atom (atomic number) using x-rays.
Atomic number
Number of protons in an atom
