1905891
| Frage | Antworten |
| Early periodic table summary | The chemical elements can be arranged in a periodic table. Within the table, elements with similar properties are placed together in groups. Like other chemists, such as Newlands, Mendeleev listed elements in order of mass, but he realised that he needed to leave gaps for the elements that had not been discovered. |
| Why was Mendeleev's idea accepted? | He left gaps for elements that had yet to be discovered. He predicted the properties of where elements should be. When new elements were discovered they were close to Mendeleev's predictions. |
| The modern periodic summary | The periodic table shows the elements arranged in order of their atomic number. Elements in a group all react in a similar ways because they have the same number of electrons in the outer most shell. |
| Group 1- alkali metals summary | The group 1 elements are also known as the alkali metals. They are very reactive with water, producing alkali solutions and hydrogen gas. Lithium, at the top of the group is less reactive than potassium, nearer the bottom of the group. These elements always react to make compounds in which they form singly charged positive ions. |
| What does reacting and alkali metal + water give you? | metal hydroxide + hydrogen |
| When the alkali metals react, what charge do they form? | They form a metal ion carrying a +1 charge. |
| List some properties of alkali metals. | -they are very soft and can be cut easily with a knife. -they have low densities (lithium, sodium and potassium will float on water). -they react quickly with water - producing a metal hydroxides and hydrogen gas. -their hydroxides dissolve in water to form alkaline solutions. |
| The transition elements summary | The transition elements nearly all have high densities, high melting points and are good conductors. They are less reactive than the alkali metals, and often form colored compounds. The transition elements and their compounds are useful catalysts in the chemical industry. |
| Name some physical properties of the transition metals. | -are good conductors of electricity and energy -are hard and strong -have high densities -have high melting points (with the exception of mercury which is liquid at room temperature |
| The halogens summary | Group 7 elements are also called the halogens. Fluorine, at the top of the group, is the most reactive, while iodine is much less reactive. They react with other non-metals to form compounds which have covalent bonds. With metals they react to form ionic compounds. |
| Name some properties of the halogens. | -they are a group of poisonous non-metals that have coloured vapours -they have low melting and boiling points -they are poor conductors of energy and electricity -their molecules are diatomic (each contain two atoms) |
| Name a reactivity trend in group 7 | At the top of Group 7, has the lowest melting point and lowest boiling point in the group. The melting points and boiling points then increase as you go down the group. |
| Hard water summary | Hard water contains calcium and/or magnesium ions. These react with soap to form scum. Hard water can also produce scale when it is heated. This is a poor conductor of energy, and makes kettles and water heaters less efficient. Hard water is better for teeth and bones than soft water. It may also help reduce heart disease. |
| How does Hard water gain dissolved calcium and magnesium ions to become hard? | These dissolve when river or streams flow over rocks containing calcium and/or magnesium compounds. For example, limestone contains calcium carbonate, CaCO3. Carbonic acid in rainwater reacts with this to produce soluble calcium hydrogencarbonate. |
| Removing hardness summary | Soft water does not contain calcium or magnesium ions. This means it does not produce scum or scale. Temporary hard water can be softened by heating it whereas permanent hard water cannot. Either type of hard water can be softened by adding sodium carbonate or using a water softener which contains a n ion-exchange column. |
| Water treatment summary | Making water fit to drink involves passing it through a filter to remove solids. We then add chlorine to it to kill microbes. Household water filters contain ion-exchange resin to remove metal ions. They also include carbon, and often silver, which discourages the growth of bacteria. |
| What should water made for drinking contain? | It is important that water for drinking should contain only low levels of dissolved substances and microbes. |
| What is the job of a calorimeter? | A simple calorimeter can be used to compare the energy released by different fuels or different foods in a school chemistry lab. |
| What is the formula for calculating the energy released? | Q = mc ΔT Where: Q = the heat energy transferred (joule, J) m = the mass of the liquid being heated (grams, g) c = the specific heat capacity of the liquid (joule per gram degree Celsius, J/g°C) ΔT = the change in temperature of the liquid (degree Celsius, °C) |
| Comparing the energy released by fuels summary | When fuels burn they react with oxygen. This reaction releases energy. The reaction is exothermic. The energy content of foods and fuels can be measured using a calorimeter. |
| Energy transfers in solutions summary | Even a polystyrene cup can be used as a simple calorimeter. We measure the temperature change, then we used the equation Q = mc ΔTto calculate the energy change. |
| Energy level diagram summary | Bond breaking is an endothermic process whereas bond making is exothermic. An energy level diagram shows the difference in energy between reactants and products. In an exothermic reaction the products have less energy that the reactants and the temperature of the surroundings increases. The minimum amount of energy needed to start a reaction is its activation energy. A catalyst offers an alternative reaction pathway with a lower activation energy and speed up the reaction. |
| Show a energy level diagram for an exothermic reaction. | |
| Show an energy level diagram for an endothermic reaction. | |
| Is an endothermic reaction bond breaking? | Yes, energy has to be supplied to break chemical bonds. Energy in taken in from the surroundings. |
| Is an exothermic process bond making? | Yes, when new bonds are formed , energy is released to the surroundings. |
| Bond making and bond breaking. | Bond breaking is endothermic and bond making is exothermic. |
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