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Science revision (Physics (Equations (Density=mass/volume, Specific latent…
Science revision
Physics
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Hooke's law
a law stating that the strain in a solid is proportional to the stress within the elastic limit of that solid
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Newton's First Law- An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
Newton's Second Law- The acceleration of an object is dependent upon two variables - the net force acting upon the object and the mass of the object.
Newton's Third Law- For every action, there is an equal and opposite reaction.
Energy can be stored in different ways and is transferred by heating, waves, or when a force moves an object. Here are some examples:
Chemical energy stores include fuel, foods, or the chemicals found in batteries. The energy is transferred during chemical reactions.
Kinetic energy stores describe the energy an object has because it is moving.
Gravitational potential energy stores are used to describe the energy stored in an object because of its position, such as an object above the ground.
Elastic potential energy stores describe the energy stored in a springy object when you stretch or squash it.
Thermal energy stores describe the energy a substance has because of its temperature.
Chemistry
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A relitivly small number of substances are made up of only one type of atom. There are called elements.
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The name for each element depends on which language it is spoken in so we have chemical symbols so scientists can understand results from other countries and compare results.
The elements in the periodic table are arranged in columns, called groups. Each group contains elements with similar chemical properties.
The vast majority of substances you come across are not elements. They are made up of different elements and they are called compounds.
Chemical equations show to reactants( the substances you start with) and the products( the substances that have been made) in a reaction.
All atoms are made up of a tiny central nucleus with electrons orbiting around it. The nucleus is made up of protons and neutrons.
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You can add state symbols to a balanced chemical equation. These state symbols are (s) for solids, (l) for liquid, (g) for gas and (aq) for aqueous.
To balance an equation you need the same amount of atoms need to be on each side. During a reaction atoms cannot be created or destroyed, so the total mass of the products formed in a reaction is equal to the total mass of the reactants.
To separate substances you can use the following methods. Filtration, crystallisation, distillation or chromatography
A mixture is made up of two or mode substances ( elements or compounds) that are not chemically combined together.
Filtration is the process of separating a mixture. Its used to separate substances that are insoluble in a particular solvent from those that are soluble in the solvent.
Crystallisation is the process of obtaining a sample of a crystallised substance. You need to hear the solution up using an evaporating dish until crystals start to form and then you leave them for over 24 hours. When many more crystals have formed place them onto a dry paper towel and gently pat the moisture off of them and you have a pure sample of a crystal made from a solution.
Distillation is the process of heating a solution to reach its boiling point so it evaporates. The evaporated liquid goes into a condensing tube and the steam turn back to liquid. The liquid is then collected in a beaker at the end of the condensing tube. Distillation only works if two substances have different boiling point.
Chromatography is separating compounds in a mixture. It works because some compounds in a mixture will separate better than others in the solvent. Chromatography paper is used to keep a record of the separations, the pigments in the colours will separate out onto the paper.
Fractional distillation is the separation of a liquid mixture into fractions differing in boiling points. An example of where fractional distillation is used is for separation crude oil into its many products like tar and petroleum.
History of the atom
He suggested that atoms re-arrange themselves and combine with other atoms in new ways. In many ways, Dalton's ideas are still useful today. For example, they help to visualise elements, compounds and molecules, as well as the models still used to describe the different arrangement and movement of particles in solids, liquids and gases.
At the end of the 1800s, a scientist called J.J.Thomas discovered the electron. This is a tiny negatively charges particle that was found to have a mass 2000 times smaller than the lightest atom
Ten years later Geiger and Marsden were doing an experiment on radioactive particles. They were firing dense, positively charged particles at the thinnest piece of gold foil they could make. They expected the particles to pass straight through the gold atoms but their results shocked them.
The Greeks were the first people to have an idea about atoms and particles however it was not until the 1800s when these ideas became linked to strong experimental evidence when john Dalton put forward his ideas about atoms. His experiments suggested that atoms were like tiny hard spheres. He also suggested that each chemical element had its own atoms that differed from others in their mass. Dalton believed that atoms could not be divided or split. They were the fundamental building blocks of nature.
Thomson proposed a different model of the atom. He said that a tiny negatively charged electrons must be embedded in a cloud of positively charge. He knew that atoms had no overall charge so he had to balance out the positive charge with electrons. He imagines the electrons as bits of plum in a plum pudding. This is how it became known as the plum pudding model.
In 1914 Niels Bohr revised the atomic model again. He noticed that light was given out of atoms when they were heated only had specific amounts of energy. He suggested that electrons must be orbiting the nucleus at a set distance. The light must be given out when excited electrons fall from high to a low energy level. Bohr matched his model to the energy values observed.
Scientists had knowledge of protons but a second sub atomic particle in the nucleus was also proposed to explain the missing mass that had been noticed in atoms. These neutrons must have no charge and have the same mass as a proton. Because neutrons have no charge it was very hard to detect them in experiments. It was not until 1932 when James Chadwick did an experiment that could only be explained by the existence of neutrons
There are three sub atomic particles. They are called protons, neutrons and electrons, Because the atom has an equal amount of protons and electrons there is no overall charge to the atom.
The number of protons in each atom is called the atomic number on the periodic table. The elements are arranged in order of their atomic number.
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Given the atomic number and the mass number you can work out how many protons, neutrons and electrons are in the atom. Number of neutrons=mass number- atomic number.
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In the diagram of the atom the first shell holds two electrons at the most. The second energy level can hold up to eight electrons. Once there are eight electrons in that energy level, the fourth begins to fill up. Every time a new row on the periodic table starts there is an new energy level (or shell).
To save drawing the atom you can use the atoms electronic structure. For example, the sodium atom has an electronic structure of 2,8,1. You start at the lowest energy level recording the numbers in each successive energy level or shell. The number of electrons in each shell are separated by a comma.
Depending on the group the atom will have a certain amount of electrons on its outer shell. In group 1 there is 1 electron on the outer shell in group 2 there are 2 electrons on the outer shell ect.
Elements in group 1 are very reactive where as elements in group 0 are very nonreactive. Group 0 contains gas elements. these are know as the noble gases. When elements in group one react they all give off hydrogen and a metal hydroxide. For example, Lithium+water--> lithium hydroxide+hydrogen.
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During the 19th century, chemists were finding new elements almost every year. They tried to find patterns in the behaviour of the elements but it proved to be very difficult. this would allow them to organise the elements and understand more about chemistry.
John Dalton arranged the elements in order of their atomic weights, which had been measured in various chemical reactions. In 1808 he published a table of elements in his book "A New System of Chemical Philosophy"
In 1864 John Newlands built on Dalton's Idea. He arranged the known elements in order of mass but noticed that the properties of every eighth element seemed similar. He produced a table showing the 'laws of octaves however he assumed that all the elements had been found. He did not take int account that chemists were still discovering new ones.So he filled in his octaves, even though some of his elements were not similar at all
Mendeleev's periodic table cracked the problem. At this time 50 elements had been discovered. He places all of the elements in order of their atomic weights. He found patterns in the elements and he left gaps in the periodic table for elements that had not yet been discovered. When elements were found they fit his pattern and in the spaces he left in the periodic table
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