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8 Cards in this Set
- Front
- Back
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Who proposed the law of octaves, and what was it? |
The law of octaves was a method of classifying elements proposed by John Newlands in 1863. It stated that similar properties are repeated every eighth element, and so ordered the 62 known elemt into seven groups according to their atomic weights. However after calcium the properties did not match very well within the groups, so his ideas were not accepted. |
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How did Dimitri Mendeleev classify elements in 1869? |
Mendeleev ordered the elements in atomic mass, and in groups with similar properties. He also took account of elements they had yet to discover, and so left gaps for these and predicted their properties. When some of the missing elements were discovered abd Mendeleev's predictions were confirmed, scientists more readily accepted his ideas. Mendeleev's table became the basis for the modern periodic table. |
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Why did scientists in the 19th century use atomic weights rather than proton numbers to classify the elements? |
Because scientists did not yet know about the structure of atoms. (They found out about protons and electrons at the start of the 20th century). |
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Why was Mendeleev's table better than Newlands' table? |
Because the properties matched well within the groups and he left gaps for undiscovered elements, which were found over time. |
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What were two other reasons Newlands' law of octaves was not accepted? |
In some cases there were two elements in one space, where he was not sure, and there were lots of elements in the same group with dissimilar properties. |
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How is the modern periodic table ordered? |
The modern periodic table arranges elements in order of their atomic numbers, and in groups with the same number of electrons in their outermost shells. This therefore means groups will share similar chemical properties. |
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What happens to the reactivity of alkali metals as you go down the group? |
The reactivity increases, as the futher down the group the larger the atoms are and the more energy levels are occupied. This means the electrons on the outermost energy level have a weaker attraction to the nucleus, and so as metals lose electrons to react, the elements become more reactive. |
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What happens to the reactivity of Halogens as you go down the group? |
The reactivity decreases as to react, non- metals have to gain electrons, but the futher down the group the larger the atoms are and so the weaker the attraction of electrons to the nucleus, making it harder for the atoms to gain electrons and the less reactive they become. |
