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Flashcards by Annie Loizides, updated more than 1 year ago
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Created by Annie Loizides
almost 7 years ago
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| Question | Answer |
| What are all substances made from? | Tiny particles called atoms. An atom is the smallest part of an element that can exist |
| What do elements contain? | Only one type of atom |
| What does the periodic table list? | All the chemical elements with 8 main groups each containing elements with similar chemical properties. |
| What do the symbols in the periodic table represent? | Atoms. e.g. O represents an atom of oxygen and Na represents an atom of sodium. |
| What do compounds contain? | More than one type of element |
| What are all atoms made of? | A tiny central nucleus with electrons orbiting around it. |
| What do chemical equations show? | The reactants and the products in a reaction |
| What is useful about symbol equations? | To see how much of each substance is involved in a reaction. e.g. calcium carbonate decomposes on heating: CaCO3-----CaO+CO2 |
| What is a balanced equation? | There is the same number of each type of atom on both sides of the equation. This is important as atoms cannot be created or destroyed in a chem. reaction. |
| The law of conservation of mass | No new atoms are created or destroyed: the total mass of reactants=total mass of products |
| When can the law of conservation of mass altered? | Reactions with gases. When the reactions are carried out in open containers, such as test tubes or conical flasks. |
| What is an aqueous solution? | Substances dissolved in water. |
| What is a mixture composed of? | 2 or more substances that are not chemically combined together |
| Can mixtures be separated ? | Yes-by physical means, such as filtration, crystallisation and simple distillation> |
| Compounds | -They have a fixed composition (the ratio of elements present is always the same in any particular compounds) -Chemical reactions must be used to separate the elements in a compound -There are chemical bonds between atoms of the different elements in the compound. |
| Mixtures | -Mixtures have no fixed composition (the properties vary depending on the amount of each substance mixed together) -The different elements or compounds in a mixture can be separated again more easily (physical means) -There are no chemical bonds between atoms of the different substances in a mixture. |
| Physical means to achieve separation: | -Filtration -Crystallisation -chromatography -distillation |
| Filtration | Separates substances that are insoluble in a particular solvent from those that are soluble in the solvent - e.g. separating a mixture of sand, salt (sodium chloride, and water) The sand collected on the filter paper can then be washed with distilled water to remove any salt solution left. the wet sand is finally dried in a warm oven to evaporate any water off and leave dry sand. |
| Crystallisation | To obtain a sample of pure salt from the salt solution following filtration, you would need to separate the sodium chloride in the solution from the water. This can be done by evaporating the water from the sodium chloride solution. The best way is by heating it in an evaporating dish on a water bath. Heating should be stopped when crystallisation occurs. This is whn small crystals first appear around the edge of the solution or when crystals appear in a drop of solution extracted from the dish with a glass rod. The rest of the water is left to evap. |
| Distillation | Crystallisation separates a soluble solid from a solvent but sometimes the solvent needs to be collected itself instead of just evaporating into the air. A solution is heated and boiled to evaporate the solvent. The vapour given off then enters a condenser. Here the hot vapour is cooled and condensed back into a liquid for collection in a receiving vessel. Any dissolved solids will remain in the heated flask. |
| Why is fractional distillation effective? | It separates miscible liquids, using a fractionating column. The separation is possible because of the different boiling points of the liquids in the mixture |
| Why does Fractional distillation differ from distillation? | Fractional distillation differs from distillation only in that it separates a mixture into a number of different parts, called fractions. |
| DEscribe how fractional distillation works? | A tall column is fitted above the mixture, with several condensers coming off at different heights. The column is hot at the bottom and cool at the top. Substances with high boiling points condense at the bottom and substances with low boiling points condense at the top. Like distillation, fractional distillation works because the different substances in the mixture have different boiling points. |
| What is chromatography? | Chromatography can be used to separate mixtures of coloured compounds. Mixtures that are suitable for separation by chromatography include inks, dyes and colouring agents in food. |
| Describe how chromatography works? | Simple chromatography is carried out on paper. A spot of the mixture is placed near the bottom of a piece of chromatography paper and the paper is then placed upright in a suitable solvent, eg water. As the solvent soaks up the paper, it carries the mixtures with it. Different components of the mixture will move at different rates. This separates the mixture out. |
| What was the earliest idea about the history of the atom? | The word atom comes from atomos, an ancient Greek word meaning indivisible. The Greek philosopher Demokritos (460-370 BCE) maintained that all matter could be divided and sub-divided into smaller and smaller units, and eventually there would be a tiny particle that could not be divided any further - an atom. |
| What did Dalton suggest? | - substances were made up of atoms that were like tiny, hard spheres. - each chemical element had its own atoms that differed from others in their mass. He said these could not be divided or split. They were the tiny building blocks of nature -all the atoms of a particular element are identical to each other and different from the atoms of other elements -atoms are rearranged in a chemical reaction -compounds are formed when two or more different kinds of atoms join together |
| What did Dalton suggest about chemical reactions? | That atoms rearranged themselves and combined with other atoms in new ways. |
| What did J.J. Thomson discover in the late 1800s? | The electron- a tiny, negatively charged particle. |
| What were JJ THomson's suggestions? | He said that tiny negatively charged particles must be embedded in a cloud of positive charge. He knew that atoms themselves carry no overall charge, so any charges in an atom must balance out-Plum pudding model. |
| How did JJ Thompson's discovery contradict Dalton? | (electron) This showed that the atom contained smaller pieces, whereas Dalton had thought that atoms could not be broken down into anything simpler. |
| Who gave evidence for the nucleus? | Geiger and Marsden students |
| What did the Geiger and Marsden students carry out? | They were doing an experiment with radioactive particles -they were firing dense, positively charges particles (alpha) at a thin piece of gold foil. They expected them to pass through the gold atoms |
| What did Rutherford conclude from the results of Geiger and Marsden? | He said that Thomson's atomic model was not possible. The positive charge must be concentrated at a tiny spot in the centre of the atom, otherwise the large, positive particles fired at the foil could never be repelled back. It was proposed that the electrons must be orbiting around this nucleus, which contains dense positively charged protons. |
| What did Neils Bohr state in 1914? | He noticed that the light given out when atoms were heated only has specific amounts of energy. He suggested that the electrons must be orbiting the nucleus at set distances , in energy levels. The energy must be given when energised electrons fall from high to a low energy level. energy is released. |
| How were neutrons suggested? | SCientists at the time has speculated that there were 2 types of sub-atomic particles inside the nucleus. They had evidence of protons but a second sub-atomic particle in the nucleus was also proposed to explain the missing mass. These neutrons must have no charge and have the same mass as a proton. |
| Why were neutrons difficult to discover? | Neutrons have no charge, so it was difficult to detect them. IN 1932 James Chadwick did an experiment that could only be explained by the existence of the neutrons |
| What does the nucleus contain? | Two types of sub-atomic particle: protons and neutrons |
| What is a third types of sub-atomic particle which orbits the nucleus? | Electrons-tiny particles |
| What charge do protons have? | Positive charge relative charge +1 |
| What charge do neutrons have? | NO charge-neutral |
| What charge do electrons have? | negative charge relative charge -! |
| Where is the mass of an atom concentrated? | IN the nucleus |
| W | The proton and neutron |
| What is the mass of an electron like? | So small-negligible mass can be ignored |
| Why is there no overall charge on any atom? | Atoms contain an equal number of protons and electrons, so carry no overall charge |
| What is the atomic number ? | The number of protons ( and electrons) |
| Why does it help knowing the atomic number of an element? | You also know its number of electrons (as this is equal to the number of protons |
| What is the mass number? | The number of protons+neutrons |
| How can you work out the number of neutrons | Number of neutrons=mass number-atomic number |
| what is an ion? | A charged particle produced by the loss or gains of an electron |
| What happens if an atom loses electrons? | They form positive ions |
| What happens if an atom gains electrons? | It forms a negative ion |
| What are isotopes? | Atoms of the same element with different numbers of neutrons. |
| What does an isotope have? | The same atomic number but different atomic masses |
| What can extra neutrons cause? | They may make the nucleus unstable, so it is radioactive. However, not all isotopes are rad. -they are simply atoms of the same element that have different masses. |
| What may be different about samples of different isotopes? | They have different physical properties. e.g they will have a different density and they may or may not be radioactive. |
| What is always the same about isotopes? | They always have the same chemical properties, because their reactions depend on their electronic structures. Electrons are the same |
| How are electrons arranged? | In shells/ orbits/ energy levels |
| How do the electrons fill up the atom? | They begin by occupying the lowest energy level (closest to the nucleus) |
| Give the e.c for the maximum number of shells/ | 2,8,8... |
| How many electrons do all group 1 elements contain in their outermost shell? | 1 electron |
| How do you work out the electronic configuration? | -Look at the atomic number -Using the number work out how many electrons are needed in each shell -the e.c. is represented by commas e.g. atomic number of 12 2,8,2 |
| What do the chemical properties depend on? | How many electrons it has |
| Describe group 0 elements in the periodic table. | -NOble gases -very unreactive elements -their atoms all have a very stable arrangement of electrons -8 electrons in outer shell , except for helium wiich has 2 |
| What happens after 8 electrons occupy the eighth shell? | The 4th shell starts to fill up |
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