History of the Development of the Periodic Table

History of the Development of the Periodic Table

History of the Development of the Periodic Table What is Chemistry? It is the central scienceit links the physical science and the life sciences. Example ionic bonding is an example of attraction of electric chargephysics laws in action

Chemists conduct experiments in the macroscopic world (large things) in order to theorize and understand the microscopic world (atoms and particles) Chemistry at work Empirical knowledge- knowledge that depends on

observations Example, charcoal, graphite, diamond and C60 buckyball Theoretical knowledge- knowledge based on ideas to explain observations Example: buckyball structure is in the form of a soccer ball with pentagon and hexagon shapes on the

surface, Empirical or theoretical? Table salt has a high melting point Table salt is made of a crystal lattice with alternating positive and negative ions that attract each other

Iron is a metal and conducts electricity Iron has valence electrons that are shared with other iron nuclei A theory An explanation of evidence obtained by observation, experimentation and reasoning.

It represents our best understanding about why something happens and allows us to predict future experiments and results. Eg: Daltons atomic theory Eg. String theory is not really a theorycannot be tested

Everyday chemistry Colouring hair, gardening, cooking, exercising. IUPAC 1919 International Union of Pure and Applied Chemistry Helps regulate standards, procedures, promote

the international aspect of chemistry, apply chemistry to the service of humanity Overview Represents 100 years of improvements and increased understanding

Culminated with the publication of a simple table in 1869 Visual representation that certain properties of elements when arranged by atomic mass (earlier table) or atomic number (later table) would repeat periodically Columns and rows display commonalities between

element properties Ancient times People knew about gold, silver, and copper since they can be found in nature in pure element form (copper can be purified from malachite ore as well) Aristotle in 330 b.c. proposed that everything is made of 4 roots in different combinations (fire, earth, water

, air) Democritus invented the word atomos to mean everything is either an atom or empty space. Was ridiculed and is theories were forgotten for 2000 years Age of enlightenment

1643 Henry Brand a bankrupt merchant finds a new element phosphorus while trying to turn cheap metals into gold. He discovered phosphorus when distilling hundreds of litres of human urine 1661 Boyle defines and element as a substance that cannot be broken down into a simpler substance by a chemical reaction

Many people pursuing legend of the philosophers stone try to make gold but instead isolate new elements from compounds the alchemists 1789 Lavoisier published first chemistry textbook with a list of elements that cannot be broken down further including oxygen, hydrogen,

nitrogen, phosphorus, mercury, zinc, sulphur, light, caloric (heat). List is divided between metal and non metal 1817 Dobereiner tried to classify elements and found groups of 3 with related properties like chlorine, bromine and iodine. Weight of middle element was always close to the weight of the

average of the lightest and heaviest. Called triads 1808 Dalton Dalton was a high school teacher He proposed the following theory All matter is made up of tiny indivisible particles called atoms

All atoms of an element are identical Atoms of different elements are different Atoms are rearranged to form new substances but are never destroyed or created Still mostly correct today 1869 De Chancourtois organized elements in a

spiral helix. 63 elements organized by atomic weight . Elements with similar properties are made to line up vertically in the helix 1865 Newlands classified 56 elements in 11 groups . Found many pairs existed with the atomic mass related to each other by a multiple of eight- law of octaves (like music)

but was ridiculed by peers 1897 Thomson Discovered the electron using cathode ray tubes Found an glowing green light that travels through an empty tube from 1 end to the other. The glow was attracted to positive materials

and could deviatebasis of black and white TVs Plum pudding model- dough is the positive part of the atom, raisins are the electrons Mendeleev 1869 published visual representation of periodic tableelements in same family are lined up horizontally in his version Was said to be playing solitaire with index cards of

elements with known properties like atomic mass, density, melting point. Found trends Predicted discovery of missing elements like germanium, gallium, and scandium Pointed out some errors in atomic mass Provided for variance in atomic mass order if necessary (like Argon and potassium reversed)(Co Ni) (Te I)

Predicted properties of some elements using average of lighter and heavier in same family Organized elements by atomic mass but placed elements With similar reactivity one on top of each other Not all elements were known so he left gapspredicted the existence of elements not yet discovered

Some known elements were not well purified and their weights did not correspondpredicted chemists had made mistakes and suggested redoing those experiments Rutherford 1909 Worked at McGill university Created an experiment that

revealed the insides of an atom Famous gold foil experiment Found that most rays went through straightatom is mostly empty space Found some rays bounced straight back the atom has a very tiny positive nucleus Bee hive model

Later additions Meyer published periodic table same time as Mendeleev but not as good- no predictions made (feud endued for credit) Chadwick discovered the neutral neutrons 1932 Noble gasses discovered later (Sir Ramsay)added as group 0

Moseley discovered atomic number and table now organized by atomic number (number of protons) Actinoids and Lanthanoids added in 1943 by Seaborg during Manhattan project Bohr

Discovered that electrons travel in defined rings called orbits. Used light, a prism and cathode ray tubes filled with various element in gas state Every element created its own light spectrum Light emitted is very specificrepresents a specific amount of energy given off. Thus electrons are

stuck in defined energy levels His model is the solar system model A, Z Atomic number- Z Mass number -A Atomic mass- 1 atomic mass unit= 1/12 C-12

1.6605402 x 10 -27 kgall other atoms relative to this mass Protons, Electrons, Neutrons Standard atomic notation Bohr/Rutherford diagrams Charge default is zero

If zero, then it is an atom If non-zero, then it is an ion N =A-Z

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