Chemistry Unit 3 Unit 3 Chemistry key notes 3.5 / 5 based on 2 ratings ? ChemistryChemical patterns and reactivity seriesGCSEAQA Created by: Emma JayCreated on: 23-05-12 13:22 The Early Periodic Table The periodic table of the elements developed as an attempt to classify the elements. It arranges them in a pattern according to their properties. Early versions of the periodic table failed to take account of the fact that not all elements had been discovered yet. Dmitri Mendeleev's table took account of unknown elements, and so provided the basis for the modern periodic table 1 of 5 The Modern Periodic Table The group that an element is in is determines by its proton number (atomic number). The number of electrons in the highest energy level/outer shell of an atom determines its chemical properties. We can explain trends in reactivity as we go down a group according to the number of energy levels (shells) in the atoms. 2 of 5 Group 1: Alkali Metals The group 1 elements are called the alkali metals. They are very reactive and their reactivity increases going down the group. They have a low density and are very soft. They are silvery and shiny, but go dull when they react with the air. They melt and boil at low temperatures. They all react with water to produce hydrogen and an alkaline solution containing the metal hydroxide. 3 of 5 Group 7: Halogens They have low melting and boiling points. They are poor thermal and electrical conductors. The halogens exist as diatomic molecules. The halogens all form ions with a single negative charge. The halogens form covalent compounds by sharing electrons with other non-metals. The reactivity of he halogens decreases going down the group. 4 of 5 Transition Elements Most of the transition elements have high melting and boiling points. They also have a high density. The transition metals are strong and hard, making them useful for making alloys. The transition metals do not react vigorously with oxygen or water, making them useful as structural metals. They have metallic structures with delocalised electrons, making them good electrical and thermal conductors. 5 of 5
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