The periodic table
Robert Boyle
- Element- substance that cannot be split into simpler substances by chemical means
Mendeleev
Humphry Davy
- Discovered potassium by passing electricity through a compound of potassium
Discovered the elements sodium, calcium, barium, strontium and magnesium
Dobereiners triads
- Bromine seemed half way between chlorine and iodine
- Triad- group of 3 elements with similar chemical properties in which the atomic weight of the middle element is approx equal to the average of the other 2
- Considered properties and atomic weight and noticed patterns
Newlands octaves
- Arranged known elements in terms of their atomic weights
- He noticed that properties of elements seemed to repeat every eight element
- Arrangements of elements in which the first and the eight element counting from a particular element have similar properties
NO Problems
- Should have left gaps for undiscovered elements
- Noble gases not discovered, elements in first 2 periods now repeat after every ninth element
- When elements are arranged in order of increasing atomic weight the properties of the elements recur periodically
- Placed all elements with similar properties in the same vertical column
Mendeleev 2
- Left gaps
- Reversed the order of some elements, make them fall into groups of elements with similar properties
- Predicted the properties of undiscovered elements
- Tellurium placed before iodine
properties were more important than atomic weight
Moseley
- Provided the reason for why mendeleev needed to reverse the order of some elements
- Studied the frequencies of X-rays emitted by atoms of diff elements & realised that the frequencies varied with the quantities of pos charge
- Atomic number- number of protons in the nucleus of that atom
Moseley 2
- Elements are arranged in order of increasing atomic weight not necessary to reverse
- Fall naturally into the correct groups