The Periodic Table Flashcards
The Greeks
- Had idea that universe was made up of a few basic substances/elements
- Thought 4 elements were - earth, air, water, fire
Robert Boyle
- Gave first accurate definition of an element
- Described it as ‘A simple substance that cannot be broken into anything simpler’
Humphrey Davy
- Discovered potassium by passing electricity through a compound of potassium
- Discovered sodium, calcium, barium, strontium, magnesium through same way
Johann Dobereiner
- Noticed that the ‘atomic weight’ (relative atomic mass) of bromine (80) was half way between that of chlorine (35.5) and iodine (127)
- Saw that there was smooth gradation of chemical properties from chlorine to bromine to iodine
- Observed similar pattern with calcium, strontium, barium among others - called triads
- Few other cases of this found but was earliest attempt to trace relationships between properties of elements and their weights
John Newlands
- Arranged elements in order of relative atomic mass
- Noticed properties of elements seemed to repeat with every 8th element
Problems with John Newlands’ thing
- Did not realise some elements had not yet been discovered, left no gaps
- Tried to force all known elements to fit into table + his law of octaves work for only first 16, then some were forced into wrong groups
- Noble gases weren’t discovered - properties in first 2 periods now repeat after every 9th element instead of eighth
Dimitry Mendeleev
-Arranged elements in order of increasing atomic mass too but placed elements with similar properties under each other in groups so every 8th element had similar physical + chemical properties
Mendeleev’s Periodic Law
When elements are arranged in order of increasing atomic weight, properties of elements recur periodically
- Placed all elements w/ similar properties in same column
- Left gaps in table to make all known elements fit into proper group
- Predicted properties of undiscovered elements
- Reversed order of some elements to make properties fit columns
Henry Moseley
- Discovered method of determining number of protons in nucleus - called atomic number (by studying frequencies varied by number of positive charge in nucleus)
- Showed that if elements are arranged in increasing atomic number, not necessary to reverse order of some of elements; elements fall naturally into correct groups
Modern Periodic Law
When elements are arranged in order of increasing atomic number, properties of elements recur periodically i.e. properties displayed by an element are repeated at regular intervals in other elements
Mendeleev Periodic Table (vs Modern Periodic Table)
- Orders elements based on their atomic weight
- Had gaps for missing elements at that time
- Has 8 vertical columns called groups, 12 horizontal rows called periods
- Has elements with dissimilar properties in same group sometimes
- Doesn’t support the fact of the existence of isotopes
Modern Periodic Table (vs Mendeleev Periodic Table)
- Orders elements based on their atomic number
- Has no concept for having gaps for missing elements at time
- Has 18 columns called groups, 7 rows called periods
- Have similar properties repeated at regular intervals
- Supports this fact as the classification is based upon atomic number
Alkali metals
- Easy to cut
- Are reactive w/ air (H2O content in air)
- Dull until cut
- Stored under oil
- Low melting + boiling points
- Low density
Alkaline earth metals
- Shiny
- Reactive due to readily losing their two outer electrons
- Low melting + boiling points
- Low density
Safety procedures for testing reactivity of alkali metals in water
- Goggles + labcoats worn by all present in room
- Protective screen set up in front of demonstration
- Laboratory tongs used to drop metals into bowl of water
Lithium + water
Very minor reaction, some fizzing giving off lithium hydroxide
Made Lithium Hydroxide + Hydrogen
