Wednesday, May 6, 2020

Chemical Earth Notes free essay sample

The living and non-living components of the Earth contain mixtures. Identify the difference between elements, compounds and mixtures in terms of particle theory. An mixture is an impure substance that is, a pure substance contaminated with small amounts of one or more other substances. An element is a pure substance which cannot be separated into other simpler substances. A compound is a pure substance which can be decomposed into simpler substances e. g. elements. Identify that the biosphere, lithosphere, hydrosphere and atmosphere contain examples of mixtures of elements and compounds. The biosphere consists of atmosphere, lithosphere and hydrosphere. The atmosphere contains mixture of gases, and mainly the mixture of nitrogen, oxygen and argon and contains small amounts of gaseous compounds e. g. water, carbon dioxide, nitrogen dioxide, sulphur dioxide and carbon monoxide. The lithosphere contains an extremely diverse variety of mixtures: rocks: compounds of silicon, oxygen, and many metals sand: mainly silicon dioxide and fine dirt soils: clays, aluminium, silicon, oxygen, metals and decomposing animal and vegetable matter mineral ores: oxides, sulphides, carbonates, sulfates, chlorides coal, oil and natural gas: mixtures of compounds or carbon formed from decayed plant and animal matter Elements: iron, gold, silver, copper The hydrosphere major component is the compound water with small quantities of elements such as oxygen and nitroge n and compounds such as carbon dioxide, sodium, calcium and magnesium chloride and sulphates. We will write a custom essay sample on Chemical Earth Notes or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page Apart from dissolved oxygen and nitrogen the mixtures of the hydrosphere contain only compounds. Identify and describe procedures that can be used to separate naturally occurring mixtures of: solids of different sizes, solids and liquids, dissolved solids in liquids, liquids and gases. Separation of solids of different sizes: Solids of different sizes can be separated by sieving Separation of solids and liquids: Solids and liquids can be separated by filtration e. g. sand from sea-water. Sedimentation is also a process of separation, decantation (pouring the liquid off and leaving the solid at the bottom undisturbed) can be done after this. Separation of issolved solids in liquid: evaporation is a method used so that the solid is left while the liquid is evaporated. Separation of liquids: distillation can be used, it is the process in which a solution or mixture of liquids is boiled with vapour formed by being condensed back to a liquid in a different part of the apparatus, and thus separating. Fractional distillation can also be used if the boiling points of two liquids are clo se together. Separation of gases: Gases are generally separated by using either differences in boiling points or differences in solubilities in liquids such as water. Identify the industrial separation processes used on a mixture obtained from the biosphere, lithosphere, hydrosphere or atmosphere and use the evidence available to: identify the properties of the mixture used in its separation identify the products of separation and their uses discuss issues associated with wastes from the processes used Separation of solids of different sizes: Solids of different sizes can be separated by sieving, separation of solids and liquids through sedimentation or decantation. Separation of dissolved solids in liquid by evaporating, separation of liquids with distillation or fractional distillation, separation of gases by using either differences in boiling points or differences in solubilities in liquids such as water. When separating salt water, that is sodium chloride (NaCl) and water (H2O), this will result in normal drinking water and table salt. 2. Although most elements are found in combinations on Earth, some elements are found uncombined Explain the relationship between the reactivity of an element and the likelihood of its existing as an uncombined element. The lower the elements reactivity the lower it is prone to react to another element, and this is because it only needs a minimum amount of electrons to become stable, meaning that it is already quite stable but not perfectly leading it not being that reactive and therefore staying as an uncombined element. Account for the uses of metals and nonmetals in terms of their physical properties. The common uses for metals such as iron, aluminium, copper and lead are for building materials, cars, planes, trains, machinery, electrical wiring, domestic appliances and household goods. It is the physical properties of the metals that most often determine which metal will be used for a particular product. The physical properties most commonly involved are melting point, density, electrical conductivity, hardness and tensile strength. The major uses of non-metals are as compounds. Wide ranges of compounds of non-metals are used in fuels, fertilisers, building materials, furniture, plastics, synthetic fibres, drugs, pesticides, paints, detergents, adhesives and cosmetics. Analyse information from secondary sources to distinguish the physical properties of metals and non-metals. Physical properties for Metals: Good electrical conductors and heat conductors. * Malleable can be beaten into thin sheets. * Ductile can be stretched into wire. * Possess metallic lustre * Opaque as thin sheet. * Solid at room temperature (except Hg). Physical Properties for Non-metals: * Poor conductors of heat and electricity. * Brittle if a solid. * Not ductile. * Do not possess metallic lustre * Transparent as a thin sheet. * Solids, liquids or gases at room temperature. Periodic Table: Semi-metals Semi-metals Non-metals Non-metals Naturally the substances that are liquids at room temperature (25 degrees) are mercury and bromine. The substances that are naturally gases at room temperature are oxygen, nitrogen, hydrogen, helium, neon, argon, krypton, xenon, radon, fluorine and chlorine. The rest are solids. 3. Elements in Earth materials are present mostly as compounds because of interactions at the atomic level. Identify that matter is made of particles that are continuously moving and interacting. All matter is made up of small particles. In solids, these particles are packed closely together in an orderly array. These cause solids to have definite shapes and to be relatively hard. In solids the particles vibrate slightly. In liquids, the particles are arranged in a much less orderly fashion than in solids and they move about much more freely. Particles in liquids possess more motion—more kinetic energy, we say—and the forces between neighbouring particles are comparatively weaker than in solids. The motion of particles in liquids is not confined to vibration as in solids, but also involves random translation from one place to another in the bulk of the liquid as shown. In gases, the particles are much further apart than in solids or liquids, and they are in very rapid random motion. The particles are so far apart and moving so rapidly that there are no significant forces between them. Describe qualitatively the energy levels of electrons in atoms. Electrons in an atom exist in discrete energy levels which we call first, second, third and so on. Each of these energy levels can only accommodate certain amount of electrons. The first level only holds 2 electrons and second hold eight, the nth energy level is calculated by the formula 2n2 electrons. Describe atoms in terms of mass number and atomic number. Atoms are made up of electrons, neutrons and protons. The protons and neutrons stay in nucleus and the electrons orbit around them. The atomic number is described by the number of protons in the nucleus. The atomic mass number is the number of protons + neutrons in the nucleus of the atom. Describe the formation of ionic compounds in terms of the attraction of ions of opposite charge. Ionic compounds are formed because an atom that is not stable tends to give away a certain amount of electrons to become stable while the other electron needs to gain some to become stable. These two atoms give and accept, leading them to become an ion. Therefore there are strong electrostatic forces holding the ions together as ionic compounds. Describe molecules as particles which can move independently of each other. Particles are packed closely together in an orderly array in solids. In liquids they are arranged in a much less orderly fashion than in solids, and they move more freely, and in gases the particles are much further apart than in solids or liquids and are in a very rapid motion gaining more kinetic energy leading to the particles moving independently. As the particles move faster and further in distance the significant forces between them diminish. Distinguish between molecules containing one atom (the noble gases) and molecules with more than one atom. All elements wish to have a noble gas configuration that is to become stable. Elements in group 1 lose 1 electron to become a stable. Group tend to lose 2 electrons, Group 4 elements either lose 4 or gain 4 electrons. Describe the formation of covalent molecules in terms of sharing of electrons. Covalent bonds are formed between pairs of atoms that both need to form noble gas configuration. This is done by creating a covalent bond, and sharing the needed amount of electrons, satisfying and stabilising both atoms. . Energy is required to extract elements from their naturally occurring source Identify the differences between physical and chemical change in terms of rearrangement of particles. Changing the state of a substance, changing the physical appearance, dissolving the solid in a liquid and separating mixtures do not require any new substance to be formed. A change in which no new substances are formed is called a physical change. On the other hand, when change in which at least a new substance is formed, e. g. heating green copper carbonate to form a black solid and colourless gas, is a chemical change. Summarise the differences between the boiling and electrolysis of water as an example of the difference between physical and chemical change. The processes boiling water and electrolysing water are two very different things. Eletrocysing the water causes it to produce two new substances, hydrogen and oxygen gases whereas the boiling of water just converts it from liquid to vapour. The electrolysis of water is also very difficult to reverse and hence the difference between physical and chemical change is portrayed through these two processes. Analyse and present information to model the boiling of water and the electrolysis of water tracing the movements of and changes in arrangements of molecule. When boiling the water just changes its’ state from liquid to vapour, and the amount of vapour is equal to the amount of water, therefore there are no new substances made and there isn’t any rearrangement of particles. However, in electrolysis the particles are rearranged into hydrogen and oxygen gases, hence creating a chemical change. Explain that the amount of energy needed to separate atoms in a compound is an indication of the strength of the attraction, or bond, between them. The amount of energy that is required is directly proportionate to the strength of the attraction or bond, the energy it takes to separate atoms in a compound indicates the strength of the bond. The stronger the bond is the more energy it will take to separate. 5. The properties of elements and compounds are determined by their bonding and structure Identify differences between physical and chemical properties of elements, compounds and mixtures. Elements cannot be separated into simpler substance, and the physical properties of metals and non-metals are different. Compound is homogenous and is a pure substance that can be decomposed into simpler substances that is, elements. Compounds are at least two different atoms bonded together, therefore when separated the chemical properties are different. Mixture is an impure substance that is contaminated with small amounts of one or more other substances, physical separation techniques can separate the impurities from the purities. Distinguish between metallic, ionic and covalent bonds. Covalent bonds are between non-metals and consists of 2 or more atoms sharing electrons. A metallic bonding is between metals and aims to sustain a noble gas configuration. Ionic bonds are between both non-metals and metals where one atom gives or receives electrons from each other to become stable. Identify common elements that exist as molecules or as covalent lattices. Phosphorus and sulfur exist as covalent P4 and S8 molecules respectively. H2, F2, Cl2, O2 and N2 are diatomic gases and Br2 is a diatomic liquid while I2 is a diatomic. Describe metals as three dimensional lattices of ions in a sea of electrons. Metals are three dimensional lattices of cations in a sea of delocalised electrons and it is the attraction between the positive and negative metal ions. Describe the physical properties used to classify compounds as ionic, covalent molecular or covalent network. The physical properties to classify compounds as: Ionic are: High melting point No solid conductivity No liquid conductivity Flexible and brittle Covalent Molecular: No conductivity Soft and brittle Low melting points Covalent network has: High melting points No conductivity Hard and brittle Describe ionic compounds in terms of repeating three-dimensional lattices of ions. Ionic compounds are in the form of repeating three-dimensional lattices of ions, formed by the transferral of electrons. The positively and negatively charged ions are joined by electrostatic attraction. Choose resources and process information from secondary sources to construct and discuss the limitations of models of ionic lattices, covalent molecules and covalent and metallic lattices. The main limitations of models of ionic lattices is that sometimes the indicative features only applies a minor amount of elements or does not include all the necessary features and is predicted. The model does not apply to all ionic compounds, it only explains a small amount of ionic compounds. These limitations are similar to covalent molecules and metallic lattices.

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