Edexcel Combined science GCSE chem CC4


The key players

Democritus- 450 BC, first mention of Atom.

John Dalton- 1803, solid spheres, can't be split, make up everything, each element contained identical atoms

JJ Thompson- 1897, discovered particles with negative charge (electrons), came up with the plum pudding model

Ernest Rutherford- 1907, investigated if radiation was ever reflected back by metals, discovered most of an atom is empty space

 Ernest Rutherford- 1911, came up with modern nuclear model

Neils Bohr- electrons were fixed distance from nucleus, orbiting in shells, nucleus contains protons.

James Chadwick- 1932, discovered neutrons

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Elements & Periodic Table

Dmitri Mendeleev- ordered the 63 known elements in 1869 in order of increasing relative atomic masses however he left gaps on the table and swapped the positions of elements if he thought it better suited the chemical properties.

Used the gaps in his table to make predictions about the properties of undiscovered elements based on the properties of nearby elements.

Atomic Number

Henry Moseley- discovered atomic number was equal to the number of positive charges in the nucleus of an atom.

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Electronic configurations and the periodic table

Electronic configuration - The way in which an atom is electrons are arranged in shells orbiting the nucleus

The number of protons and electrons in an atom are the same so the number of electrons in an atom can be worked out from the number of protons.

The electronic configuration can then be worked out as an atom's first shell holds two electrons and from there each shell can hold eight.

It can also be worked out using the elements position on the periodic table.

Example: magnesium. Magnesium is on the third row of the periodic table, therefore it has three shells of electrons. In the first row of the periodic table there are two elements so in magnesium's first shell it has two electrons. The second row of the periodic table has eight elements so in magnesium's second shell there are eight electrons. Magnesium is second on the third row so magnesium's last shell has two electrons.

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