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    -  Ordering Elements

- In 1864, 60 elements had been discovered. Protons, neutrons and electrons had not been discovered.

- John Newlands used atomic weights (relative atomic masses) to sort these known elements into a table. 

- He realised elements with similar properties appeared every 8 places. he arranged his table in columns of seven elements, with eight columns called the table of Octaves.

- Problems with the table: atomic weights were not accurate, some elements were mixtures, he did not make room for elements not discovered, he put two elements in some boxes.

- 1869, Dmitri Mendeleev published his periodic table. He left gaps for undiscovered elements so that the groups of known elements did have similar properties.  He arranged in a pattern that linked their properties to their masses. He also recalculated some atomic weights.

- He predicted the properties of missing elements and when the missing elements where discovered, his predictions were confirmed and scientists more readily accepted his ideas. He realised the repeating pattern was not always after eight elements.

- His table became the basis for the modern periodic table.

- Noble gasses are so unreactive they were hard to discover as they have a stable configuration.

    -  The Modern Periodic Table

- Electrons, protons and neutrons were discovered in the early 20th century.

- The modern periodic table arranges elements in order of increasing atomic number rather than relative atomic mass.

- The groups are numbered from 1-7-0, this shows how many electrons are in their outer shell. Group 1 is Alkali metals, group 7 are halogens and group 0 are noble gasses.

- Periods are the rows and they show how many electron shells there are in an element.  Elements across a period show a gradual change from metal to non metals.

- Electrons in the highest energy level are rearranged when chemical reactions happen. The number of electrons in the outer shell is linked to an elements chemical properties. Reactivity of metals increase down a group where as reactivity of non-metals decreases down the groups.

    -  Group 1

- Group 1 elements are silvery shiny metals when freshly cut. They are Alkali Metals.

- The elements are Lithium, Sodium, Potassium, Rubidium, Caesium and Francium.

- The density of lithium, sodium and potassium is less than the density of water (1.00g/cm^3) so they float on water. All have low densities.

- Atoms of the elements all have one electron in their outer shell so thus when they react they transfer this electron to another atom (ionic bonding) leaving a positively charged metal ion (+1 charge) and a negatively charged non metal ion (-1 charge). e.g Na --> Na+ + e- (Na+ is sodium ion and e- is the transferred electron). Draw the diagrams like this too, with a line in between the passed atoms.

- The compound formed are white solids that dissolve in water to form colourless solutions. They are soluble.

- They all react with water

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HKS25 :)


thank you!

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