Exam Introduction of Environmental Sciences Week 4 PDF

Exam introduction of environmental sciences week 4 Contents Ecology................................................................................................................... 3 Block 1...........................................................................................................

Exam introduction of environmental sciences week 4 Contents Ecology................................................................................................................... 3 Block 1................................................................................................................. 3 What is environmental sciences......................................................................... 3 Origin environmental sciences........................................................................... 3 Environmental awareness.................................................................................. 4 Environmental pollution..................................................................................... 5 Solutions to pollutions....................................................................................... 6 Block 2................................................................................................................. 8 What is ecology................................................................................................. 8 History of life on earth........................................................................................ 9 The ecosystem................................................................................................ 11 Block 3............................................................................................................... 14 What is waste.................................................................................................. 14 Classification of waste..................................................................................... 15 Amount of waste............................................................................................. 15 Impact of waste............................................................................................... 16 Waste management........................................................................................ 16 Legislation...................................................................................................... 21 Block 4............................................................................................................... 22 Plants............................................................................................................. 22 Animals.......................................................................................................... 26 Chemistry.............................................................................................................. 30 Block 1............................................................................................................... 30 Molarity.......................................................................................................... 30 Mass concentration......................................................................................... 31 Ppm/ppb......................................................................................................... 31 Dilution........................................................................................................... 32 Block 2............................................................................................................... 33 1  State of matter................................................................................................ 33 Intermolecular forces...................................................................................... 33 Bond polarity................................................................................................... 36 Molecular polarity........................................................................................... 36 Block 3............................................................................................................... 37 Ion-dipole forces............................................................................................. 37 Dipole-dipole forces........................................................................................ 38 London dispersion forces................................................................................. 39 Hydrogen bonding........................................................................................... 41 Comparison.................................................................................................... 42 Decision tree intermolecular forces.................................................................. 42 Block 4............................................................................................................... 43 Extern of a reaction.......................................................................................... 43 Chemical equilibrium...................................................................................... 43 Equilibrium constant....................................................................................... 45 Block 5.............................................................................................................. 46 Le Chatelier’s principle.................................................................................... 46 Changing concentration................................................................................... 47 Changing volume and pressure........................................................................ 47 Changing temperature..................................................................................... 48 2 Ecology Block 1 What is environmental sciences Environment → circumstances or conditions that surround us, affect us and interact with us (humans): - Physical - Biological - Technological - Social - Cultural Science → a process for producing knowledge methodically and logically. It helps us understand the world and discover new valuable thing (medicines, energy sources, technology) you can see a scientific process in figure 1 Figure 1 Environmental science → systematic study of our environment and our place in it. It is a human-oriented science and it believes that nature can exist without humans, but that humans cannot exist without nature Origin environmental sciences Human development agricultural revolution industrial revolution Resulted in: depletion / exhaustion of sources pollution of the environment 3 Environmental awareness Report by the Club of Rome “Limits to Growth” (Meadows, 1972) Growth will be limited Resources will be depleted Pollution crisis predicted And just think: Did these predictions prove to be correct? Is it true that there are climate effects, caused by human action? Environmental awareness resulted in for instance: Habitat conservation Search for renewable energy Waste Hierarchy: Lansink's Ladder Sustainable development Remediation of polluted soil, water, air etc. SDG’s (sustainable development goals) The waste hierarchy (figure 2) Figure 2 4 sustainable development Definition → Development that meets the needs of the present without compromising the ability of future generations to meet their own needs. Sustainability quantified: the ecological footprint A measure of human impact on the ‘physical’ world Based on the idea that an ‘area’ can be used, disturbed or is needed for recovery only once for a certain group and a certain period It represents the land area necessary tot sustain current levels of resource consumption and [waste] discharge by a person or a group of people. SDQ’s: people, planet, profit Resulted in for instance: Figure 3 People: peace, (gender) equality for everyone, no poverty, access to health care and education, food and water. Economy: sustainable growth, clean energy, sustainable cities and industries Planet: climate, clean water and soil Environmental pollution Sources of harmful emissions industry/commercial establishments energy production [non-renewable] agriculture domestic/households transport types of harmful emissions industry/commercial establishments Chemicals, noise, dust, radiation, waste (residues).... 5  energy production [non-renewable] CO2, NOx, smog, radioactive wastes, heat Agriculture CH4, N2O, nutrients, NH3, pesticides, plastics in soil and water, light domestic/households Batteries, chemicals, CO2, noise, waste... transport Exhaust fumes Compartments of pollution Water Air Soil Ecology humans animals Figure 4 plants effects of pollution Plastics (example) Global warming Human health Biodiversity loss Figure 5 Solutions to pollutions 1. Remediation → end-of-pipe solutions 2. Process changes → front-of-pipe solutions 3. Sustainable solutions → no-pipe 6  4. Policies → law, regulations, fines Remediation use of the polluted compartment; toxicological effects; price to clean up/ reduce waste; need for the product/compound producing the waste; available technologies; policies. Process changes Change or optimize production processes: Reduce e.g. Concentrate washing-liquids so smaller bottles can be used Re-use e.g. re-use plastic cups at festivals, reuse irrigation water from green houses Recycle e.g. plastics, batteries, cans, glass, … sustainable solutions Real no-pipe solutions are very difficult. Switch to a complete different process. E.g. switch from coal to solar for energy production Improve existing process E.g. re-arranging production process into two separate process cycles: one cycle works with biodegradable compounds. Any waste can be released to the environment; one cycle works with toxic / non-biodegradable compounds. They must be kept inside the production process. 7 Policies Laws o concerning pollution of groundwater, water & air ▪ (chemical, temperature, bacterial) o concerning effects on nature (disturbance, killing) Subsidies o when you use cleaner technologies o when you recycle Fines o when you cause a pollution o when you use less clean technologies Block 2 What is ecology Ecosystem Earth = a closed system Ecology → It is the study of the interactions between organisms (biotic) and nonliving parts of the environment (abiotic). These interactions happen at different scales Cell (cell biology and microbiology) Individual Population Community Ecosystem Biosphere Figure 6 8  Examples of methodologies Fieldwork to gather data Labwork to measure nitrogen content of leafs Mathematical spatial modelling to test (or) generate hypothesis about mechanisms behind observed patterns Remote sensing (aerial photography) to validate the outcomes of models Figure 7 History of life on earth "Clock analogy (or "snowball Earth") tracks the origin of the Earth to the present day (figure 8) Key events 4.5 billion years ago: Formation of the planet Earth 3.8 billion years ago: Beginning of biology with the origin of single-celled organisms floating in the ocean, the prokaryotes Figure 8 2.7 billion years ago: O2 by cyanobacteria, photosynthetic organisms (the air was mostly CO2 and nitrogen, O2 was their waste) 2.3 billion years ago: O2 starts building up in the atmosphere with the origin of other organisms, the eukaryotes – e.g. algae, seaweed 570 million years ago: O3 layer & the diversification of organisms Sudden appearance of fossils resembling modern phyla provides the first evidence of predator-prey interactions 530 million years ago: Animals take their first steps on land 9  13 million years ago: Extinction of other genus Homo. Homo sapiens is the only surviving human species. Macroevolution Macroevolution started with the origin of life (3.7-4.0 billion years) Evolutionary change at or above species level over a long period This was possible because of chemical and physical processes on early Earth -> evidence can be found on a variety of fields Rise and fall Rise and fall of dominant groups because of: Continental drift (p. 225) Natural disasters (p. 226) Adaptive radiations (p. 228) The evolution of diversely adapted species from a common ancestor upon introduction to new environmental conditions Evolution is not goal orientated New forms arise from existing ones. Those that are most adapted to the existing environment do best. Gradual modification, but always of the already existing basis. Life on Earth will always adapt to the conditions. If one species fades away, others will take over. - > e.g. development of mammals after the extinction of dinosaurs "It is not the strongest of the species that survives, nor the most intelligent; it is the one most adaptable to change." - Charles Darwin – Figure 9 10 The ecosystem What is an ecosystem A natural unit consisting of : All plants, animals, and micro-organisms (biotic factors) in an area functioning Together with all the non-living physical (abiotic) factors of the environment An ecosystem is described by: Energy flow Carbon flow Nutrient cycles (NEXT CLASS) Zonation (= structure) Energy flow Productivity through the ecosystem J m-2 day-1 or kg ha-1 yr-1 Law of thermodynamics (p. 497) ▪ Energy is neither gained nor lost (1st law) ▪ Every energy transformation results in a reduction of free energy (2nd law) In an ecosystem, the next level gets energy (production) from The warmth of the sun Figure 10 Eating (consuming) the previous level Every trophic level energy is lost (2nd law) (see fig. 4.111 and p. 477) In an ecosystem we distinguish between Primary and secondary production: 11  Primary production Plants, algae, bacteria, phytoplankton Net primary productivity (NPP) = o Gross primary productivity (GPP) - respiratory heat (R) NPP depends on available nutrients, water, temperature, light In an ecosystem we distinguish between: Secondary production Herbivores, carnivores, decomposers Net secondary productivity (NSP) = o Gross secondary productivity (GSP) - respiratory heat (R) NSP depends on primary production, competition, energy efficiency The main limiting environmental factors for primary production in terrestrial systems: (see 4.127 on p. 498) and p. 480 ▪ Temperature ▪ Moisture ▪ Nutrients (locally) Example Actual evapotranspiration can represent the contrast between wet and dry climates Figure 11 Transfer efficiency Consumption efficiency Percentage of total productivity available at one tropic level that is actually consumed by higher trophic level Assimilation efficiency The efficiency with which the consumer extracts energy from the food across the gut wall, they excrete waste 12  Production efficiency The efficiency with which the consumer incorporates food energy into secondary production (biomass) Carbon flow: conservation of mass Figure 12 The fate of matter in the community Producers, consumers, and decomposers Producers Produce organic material o Photosynthesis → plants, algae, phytoplankton o Chemosynthesis → bacteria Consumers Eat organic material o Primary consumers → consume Figure 13 plants or algae o Secondary consumers → consume herbivores Decomposers Break down organic material o Mainly bacteria and fungi Human interruptions: toxins Release of synthetics previously unknown to nature Persist for long periods in an ecosystem Big problem is that they become more concentrated in successive trophic levels = biological magnification 13  Because biomass is lower at higher levels Examples: PCB’s, pesticides like DDT Block 3 What is waste Definition Basel convention Substances or objects which are disposed of or are intended to be disposed of or are required to be disposed of by the provisions of the law United Nations Wastes are materials that are not prime products (that is products produced for the market) for which the generator has no further use in terms of his/her own purposes of production, transformation or consumption, and of which he/she wants to dispose. Disposal means: Any operation which may lead to resource recovery, recycling, reclamation, direct re-use or alternative uses (Annex IVB of the Basel convention) Types of waste Solid waste waste in solid forms domestic, commercial and industrial wastes Examples: plastics, styrofoam containers, bottles, cans, papers, scrap iron, and other trash Figure 14 Liquid Waste wastes in liquid form Examples: domestic washings, chemicals, oils, waste water from ponds, manufacturing industries and other sources 14 Classification of waste ▪ According to systematics United Nations and EU CLP guideline ▪ CLP = classification, labelling and packaging Figure 15 Amount of waste Figure 16 Figure 17 15 Impact of waste Routes are coupled to air, water, soil, ecology. Figure 18 Figure 19 Waste management Why waste management ▪ Conserves resources & energy ▪ Reduces soil, water & air pollution ▪ Saves landfill space ▪ Waste = resource In nature there is no waste, so re-use all building blocks more Figure 20 Cradle to cradle design Product components are recyclable or biodegradable Extended Producer Responsibility (EPR) or Product Stewardship Reduction ▪ Preferred method: prevent the generation of waste ▪ Manufacturer ▪ decrease materials/energy used during manufacturing ▪ decrease material/energy used during distribution 16  ▪ Consumer ▪ purchase items with minimal packaging ▪ avoid disposable products ▪ includes e.g. backyard composting Re-use ▪ Prolonging a product’s usable lifetime, to use it more often ▪ Repairing items, selling them or donating them to charity ▪ Using durable rather than disposable items (i.e. reusable shopping bags, metal spoons) ▪ Preferable to recycling because item does not need to be collected/reprocessed Recycle Waste treatment facility: plastic separation Figure 21 Figure 22 Composting: Figure 23 17 Figure 24 Factors that hinder re-use and recycling ▪ The market prices of almost all products do not include the harmful environmental and health costs associated with producing, using, and discarding them (external costs). ▪ The economic playing field is uneven, because in most countries, resource-extracting industries receive more government tax breaks and subsidies than reuse and recycling industries. ▪ The demand, and thus the price paid, for recycled materials fluctuates, mostly because buying goods made with recycled materials is not a priority for most governments, businesses, and individuals. ▪ No or wrong waste separation by households and/or companies Ways to encourage re-use and recycling ▪ Increase subsidies and tax breaks for re-using and recycling materials and decrease subsidies and tax breaks for making items from virgin resources. ▪ Increase use of the fee-per-bag waste collection system and encourage or require government purchases of recycled products to help increase demand for and lower prices of these products. 18  ▪ Pass laws requiring companies to take back and recycle/re-use packaging and electronic waste. ▪ Citizens can pressure governments to require product labeling that lists recycled content of products and the types and amounts of any hazardous materials. Waste is resource Waste does not exist We have residues that can be re-used as a resource Circular economy Figure 25 19 Disposal - Only if re-use and recycling are not possible ▪ Waste is ‘burned’ to produce energy ▪ Different techniques available: With / without oxygen Different temperatures Figure 26 Different pressures ▪ Preferred to landfilling – reduces bulk of municipal waste with about 90% and provides energy Incineration ▪ Waste is burned but NO energy is produced ▪ Preferred to landfilling – reduces municipal waste with about 90% Figure 27 ▪ Downsides: Some items may be difficult to burn or cause potentially harmful emissions Strict regulatory restrictions and high environmental and economic costs Landfill ▪ Strict regulatory restrictions and high environmental and economic costs ▪ Items barely decompose in a modern landfill ▪ Landfills face capacity restrictions ▪ NIMBY syndrome (not in my backyard) Figure 28 20 Figure 29 Legislation EU Figure 30 21 Block 4 Plants Nutrients from environment Uptake of essential elements Require essential elements to complete their life cycle Derive most of their organic mass from the CO2 of the air Depend on soil for water and nutrients More than 50 chemical elements have been identified in plants Not all of these are essential to plants Essential element The element that is required for a plant to complete its life cycle Figure 31 Taken from the soil Cations (e.g. Ca2+, Mg2+) bind to negatively charged soil particles this prevents them from leaching out of the soil through percolating groundwater Anions (e.g. Cl-, NO3-) do not bind with soil particles and can be lost from the soil by leaching Mechanism of nutrient uptake 22  Figure 32 Interaction with environment Plant nutrition interactions Plant nutrition often involves relationships with other organisms (symbiosis) Different forms are Mutualism: ▪ With bacteria in the rhizosphere ▪ With bacteria in nodules ▪ With fungi in mycorrhizae Commensalism with bacteria Parasitism between plants Predation of insects Mycorrhizae are mutualistic associations of fungi and roots Mycorrhizal relationships are common and might have helped plants to first colonize land Two types of mycorrhizae: 1. Ectomycorrhizae 2. Arbuscular mycorrhizae 23 Figure 33 Plant interactions: commensalism with bacteria Figure 34 Responses to environment Plants, being rooted to the ground, must respond to environmental changes that come their way For example: bending of a seedling toward light begins with sensing the direction, quantity, and colour of the light Plants have cellular receptors that detect changes in their environment 24  Can detect internal and external signals Such as: Light = phototropism Hormones Gravity = gravitropism Touch Figure 35 Wounding or stress Receptors: wounding or stress Environmental stresses have a potentially adverse effect on survival, growth, and reproduction Stresses can be Abiotic stresses Include drought, flooding, salt stress, heat stress, and cold stress Biotic stresses Include bacterial infections and predatory animals Plant responses Are often hormones such as (FYI): Auxin Cytokinin Gibberellin Brassinosteroids Abscisic acid (ABA) Ethylene Figure 36 25  Many different responses. Examples: Drought ▪ slowing leaf growth ▪ reducing the exposed surface area ▪ closing stomata → reduction of transpiration Salt stress Produce organic compound that keeps water potential of cell lower than of environment Cold stress Figure 37 Change lipid composition of the cell membrane Animals interactions with environment: homeostasis Many different animal body plans have evolved over time as a result of environmental challenges Physical laws impose constraints on these animal sizes and shapes Resistance (streamlining) Strength (bones) Force (muscles) Exchange of substances Exchange of substances occurs as substances dissolved in the aqueous medium diffuse and are transported across the cell membranes Single-celled protists living in water have a sufficient surface area of the plasma membrane to service its entire volume of cytoplasm 26  Multicellular organisms with a sac body plan have body walls that are only two cells thick, facilitating the diffusion of materials More complex organisms have highly folded internal surfaces for exchanging materials Combined with a complex body plan, complex organisms can maintain a relatively stable internal environment in a variable environment Coordination and control maintenance internal environment Animals manage their internal environment by regulating or conforming to the external environment Regulator: uses internal control mechanisms to a moderate internal change in the face of external, environmental fluctuation How is this called? -> homeostasis Conformer: allows its internal condition to varying with certain external changes Figure 38 Homeostasis Organisms use homeostasis to maintain a “steady state” or internal balance regardless of external environment In humans, body temperature, blood pH, and glucose concentration are each maintained at a constant level Fluctuations above or below a set point serve as a stimulus. These are detected by a sensor and trigger a response The response returns the variable to the set point (negative feedback) Thermoregulation is the process by which animals maintain an internal temperature within a tolerable range: 27  Endothermic animals generate heat by metabolism birds and mammals are endotherms active at a greater range of external temperatures more energetically expensive Ectothermic animals gain heat from external sources; ectotherms include most invertebrates, amphibians, fishes and non-avian reptiles tolerate greater variation in internal temperature behaviour General Based on physiological systems and processes Is the nervous system’s response to a stimulus Is carried out by the muscular or the hormonal system Is governed by complex interactions between genetic and environmental factors Behavior helps an animal to ▪ Obtain food ▪ Find a partner for reproduction ▪ Maintain homeostasis Why? 1. Individual survival 2. Reproductive success Behaviour can affect fitness by influencing: Foraging behaviour 28  Mating choice Fitness → Evolutionary success (best adapted to environment, most offspring) Foraging behavior Includes recognizing, searching for, capturing and eating food items Natural selection refines behaviours that enhance the efficiency of feeding Optimal foraging model views foraging behaviour as a compromise between the benefits of nutrition and costs of obtaining food The costs of obtaining food include: ▪ energy expenditure ▪ the risk of being eaten while foraging Natural selection should favour foraging behaviour that minimizes the costs and maximizes the benefits Optimal foraging model: Figure 39 29 Chemistry Block 1 Molarity Back to basics: Mole = 6.022x1023 elementary entities (Avogadro’s number) H2O = molecular substance; 1 mole = 6.022x1023 molecules of water Pb = metal; 1 mole = 6.022x1023 atoms of lead NaCl = mineral; 1 mole = 6.022x1023 units of an Na+ and Cl- ion Molar mass Mass of an atom/molecule/mineral formula is expressed in atomic mass units (amu) Mass of a mole of substance = same number as amu, but now in gram Mass 1 molecule = 18 amu; mass 1 mole water = 18 g 𝑚 Relation mass-mole: 𝑛 = 𝑚𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠 m = Mass(g) n = number of mole (mol) molar mass (g/mol) molarity Express composition of mixtures: concentrations Concentration of solutions: solvent (largest amount), medium in which solute (least amount) is dispersed Molarity = number of moles of solute per litre of solution 𝑚𝑜𝑙 𝑠𝑜𝑙𝑢𝑡𝑒 𝑛 𝑀𝑜𝑙𝑎𝑟𝑖𝑡𝑦 = →𝑀=𝑉 𝐿 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 M = molarity (mol/L) n = number of mole (mol) V = volume (L) 30  Concentration often symbolised by square brackets: [NaCl] = 0.20 mol/L Mass concentration Mass percentage Used in solid mixtures and solutions 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑐𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡 𝑖𝑛 𝑚𝑖𝑥𝑡𝑢𝑟𝑒/𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 𝑀𝑎𝑠𝑠 % 𝑜𝑓 𝑐𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡 = × 100% 𝑡𝑜𝑡𝑎𝑙 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑚𝑖𝑥𝑡𝑢𝑟𝑒/𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 𝑚𝑐𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡 % 𝑚⁄𝑚 = × 100% 𝑚𝑚𝑖𝑥𝑡𝑢𝑟𝑒 30 g sodium chloride + 100 g water, mix; mass percentage sodium chloride = {30/(100+30)} *100% = 23% m/m Ppm/ppb Ppm Used in solutions (sometimes in gas mixtures = ppmV) For very diluted solutions Mg/l ppm = parts per million (mass concentration, NOT molarity) 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑐𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡 𝑖𝑛 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 𝑝𝑝𝑚 𝑜𝑓 𝑐𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡 = × 106 𝑡𝑜𝑡𝑎𝑙 𝑚𝑎𝑠𝑠𝐴 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 𝑚𝑠𝑜𝑙𝑢𝑡𝑒 𝑝𝑝𝑚𝑠𝑜𝑙𝑢𝑡𝑒 = × 106 𝑚𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 If water is solvent: 1 L water= 1 kg water= 106 mg of water Dilute solutions in water: solute hardly adds to density, so still 1 L solution = 1 kg In that case, equations changes to 𝑚𝑔 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑒 𝑖𝑛 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 𝑝𝑝𝑚 𝑜𝑓 𝑐𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡 = 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 𝑖𝑛 𝑙𝑖𝑡𝑒𝑟𝑠 𝑚𝑠𝑜𝑙𝑢𝑡𝑒 (mg) 𝑝𝑝𝑚𝑠𝑜𝑙𝑢𝑡𝑒 = 𝑉𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 (L) 31 Ppb For EVEN MORE DILUTED solutions: ppb = parts per billion 𝑚𝑠𝑜𝑙𝑢𝑡𝑒 (𝛍𝐠) 𝑝𝑝𝑏𝑠𝑜𝑙𝑢𝑡𝑒 = 𝑉𝑠𝑜𝑙𝑢𝑡𝑒 (L) Unless mentioned differently, we assume solutions are dilute for ppm and ppb calculations μg/L Dilution Change the concentration of a solution by adding extra solvent: dilution Adding extra solvent changes the VOLUME, NOT the AMOUNT of solute in the solution (n and m of solute stay the same) Calculations related to dilutions: 𝐶1 × 𝑉1 = 𝐶2 × 𝑉2 C1 = concentration original solution C2 = concentration diluted solution V1 = volume original solution V2 = volume diluted solution Concentration unit (molarity, mass concentration, etc.) and volume unit (L, mL etc.) can be anything, but have to be the same for solution 1 and solution 2 for the calculation to work Sometimes we don’t dilute but increase concentration, e.g. by evaporating solvent from the solution: same equation applies 32 Block 2 State of matter We know compounds can exist in different phases or state of matter. Mostly this is in the gas state, the liquid state and the solid state. Here you see the different states visualised on a molecular level Intermolecular forces Attraction-repulsion between molecules Forces between “molecules” : electrical in origin mutual attraction of unlike charges, or mutual repulsion of like charges weaker than ionic or covalent bonds You know that atoms in a molecule are held together by covalent bonds, which are shared electron pairs. We call those intramolecular forces. Ions within a mineral are held together by electrostatic attraction. The atoms within a metal are held together by electrons moving between atoms in the atomic arrangement of the metal. 33 Intermolecular forces intro Types of intermolecular forces: Ion-Dipole Forces Dipole-dipole forces Van der Waals forces London dispersion forces Hydrogen-bonding forces So here are the different types of forces in between molecules, intermolecular forces, which also includes the interaction between ions and molecules. These forces are weaker than covalent bonds, ionic bonds and metallic bonds, they are easier to break. They influence a lot of properties, for example they determine whether a compounds is a liquid, a solid or a gas. Bond dipole moments Polar covalent bonds N H C Figure 40 A covalent bond is where two atoms have one or more shared electron pairs, keeping them together. Only, these electron pairs are not always shared equally between the two atoms, often one atom pulls harder on the electrons than the other atom, which results in a small charge difference. The atom that pulls hardest on the electrons gets a small negative charge surplus, a partial negative charge. The atom that pulls less hard on the electrons gets a small positive charge surplus, a partial positive charge. So now we have a covalent bond with one slightly positive atom on one end and one slightly negative atom at the other end, we call that a polar covalent bond, like in hydrogen chloride 34 In ionic compounds, one atoms pulls so hard at the shared electrons that the whole electron pair is actually transferred to one atom, then we do not have a covalent bond anymore, now the atoms become ions with a full charge, not a partial charge. Then we have an ionic bond, not a polar covalent bond anymore. If the two atoms on the covalent bond pull equally hard at the shared electron pairs, then we do not get partial charges so we have a nonpolar covalent bond, like in chlorine gas. Electronegativity of elements Figure 41 How hard an atom pulls at the shared electron pair is determined by the electronegativity of the element. Here you see a periodic table with the electronegativities of the most common elements. As you can see, from left to right and from bottom to top, the electronegativity generally increases. That is also why, in for example ionic compounds, most metals on the left have a positive charge (they lose electrons) and e.g. the halogens and oxygen have a negative charge (they gain electrons). 35 Bond polarity Bond dipole moment Figure 42 a difference in electronegativity between C and Cl C-Cl bond has a bond dipole moment, µ The strength of the dipole moment (value of mu and symbolised by the length of the arrow) is determined by both the distance between the two partial charges and the difference in electronegativity. If either of these increase, the dipole moment also increases. Molecular polarity Molecular dipole moment individual bond polarities cancel (sum = 0) the molecule as a whole does not have a dipole moment the molecule is nonpolar Figure 44 Figure 43 36 In molecules we have several bonds, which can all have their own dipole moment. The sum of these bond-dipoles determines whether the molecule as a whole has a dipole moment, or not Figure 45 Figure 46 - individual bond polarities do not cancel molecule has a dipole moment molecule is polar Block 3 Ion-dipole forces Attraction between an ion and the partial charge on the end of a polar molecule (dipole) Figure 47 NaCl dissolved in water, for example. Both the sodium and chloride ions are surrounded by water molecules (which are polar). 37 Dipole-dipole forces electrical interactions between dipoles on neighboring molecules only when molecules are close together in right orientation Figure 48 Depending on the temperature and the geometry of the molecules, rearranging to the most advantageous position is easy or difficult. Figure 49 Dipole moment increases => intermolecular force increases => boiling point increases When molecules have same polarity: smaller molecules have higher dipole- dipole forces What we can see here is that if the dipole moment increases, the boiling point increases too. This is not directly related to the mas of the molecule, because methyl cyanide has the smallest mass but the highest boiling point. 1- when the dipole moment increases, the intermolecular forces increase, it takes more energy-higher temperature to break them apart, so higher boiling point 38 2- … this is Smaller molecules can more easily rotate and take the most advantageous position towards each other (= position with the most intermolecular forces) London dispersion forces Figure 50 Motion of electrons gives a short-lived dipole moment Induces temporary dipoles in neighboring molecules Results in (weak) intermolecular forces Here we see two non-polar molecules. In these molecules, the electrons are symmetrically distributed around the whole molecule. But that is not always the case, electrons can move around, sometimes resulting in an asymmetrical distribution within the molecule. This results in s weak and short-lived molecular dipole moment This weak dipole moment in one molecule can induce (by repelling the electrons) a temporary dipole moment in a neigbouring molecule. The two molecules now attract each other So this results in weak intermolecular forces. 39 Figure 51 Increase in molecular size/weight => increase in LDP => increase in boiling point Figure 52 Larger contact area between molecules => stronger LDP LDP are always present, also in molecules with dipole-dipole forces etc. Pentane and dimethylpropane have the same molecular formula and weight, but a different boiling point. Pentane is a more linear molecule, creating a bigger surface area for it to interact with other pentane molecules than dimethylpropane, which, being spherical, has less contact area with neighbouring molecules. 40 Hydrogen bonding Dipole-dipole attraction between H of one molecule and lone electron pair of another molecule Conditions: H is attached to O, N or F, and interacts with lone electron pair of another O, N or F Figure 53 So this is a special category of dipole-dipole interaction which is much stronger than conventional dipole-dipole interactions A hydrogen bond is the dipole dipole attraction between a hydrogen in one molecule and a lone electron pair on another molecule Only happens with O, N and F because of the relatively small size and relatively high electronegativity of these atoms. This combination allows H to get very close to electron pair of the other molecule, creating a strong interaction So, the condition for hydrogen bonding to happen is: the hydrogen is attached to an oxygen, nitrogen or fluorine atoms, and the oxygen, nitrogen or fluorine also has to have a lone electron pair to interact with. Water: multiple hydrogen bonds per molecule: high melting and boiling point For such a small molecule, water has a very high melting and boiling point compared to other molecules that size. Hydrogen bonds are very important in our everyday life. They hold the double helix structure of DNA together for example 41 Comparison Figure 54 Decision tree intermolecular forces 42 Block 4 Extern of a reaction N2 (g) + 3H2 (g) → 2NH3 (g) Theoretical yield of combining 1 mol N2 and 3 mol H2: 2 mol NH3 In reality: yield is 0.6 mol NH3, actual yield; 0.7 mol N2 and 2.1 mol H2 remain unreacted Reason: reactions are reversible While N2 (g) + 3H2 (g) → 2NH3 (g) happens, the reaction 2NH3 (g) → N2 (g) + 3H2 (g) also happens When both reactions happen at the same rate: no more net change in concentrations = chemical equilibrium Chemical equilibrium is defined by: Rates of forward (→) and reverse (←) reaction are equal AND Concentrations of reactants and products do not change Chemical equilibrium Reaction of N2O4 gas to NO2 gas When equilibrium state is reached: double arrow N2O4 (g)  2NO2 (g) Equilibrium = dynamic Figure 55 43 Vial filled with N2O4 (colourless) kept frozen: no reaction Let it come to room temperature: N2O4 reacts to NO2 (brown colour) When NO2 is formed, it also starts to react back to N2O4 (reverse reaction). Reverse reaction increases in rate as more NO2 is formed, forward reaction decreases in rate as less N2O4 remains At one point: forward and reverse reaction have the same rate: no more colour change, no more change in concentrations – 1…. 2 - Equilibrium is dynamic: reactions are happening, but does not result in change of concentration Figure 56 Three reaction mixtures Left: only NO2 present in reaction vial, starts to react to form N2O4, at one point equilibrium is reached, then the concentration of the compounds remains the same over time (horizontal line) Middle: Only N2O4 in the vial, reacts to form NO2 until equilibrium is reached Right: mixture of NO2 and N2O4 In all cases equilibrium state is reached, but with different concentrations of N2O4 and NO2 in the vial at equilibrium state. Is there a commonality in all these situations? 44  Equilibrium constant Figure 57 Value of quotient [NO2]2/[N2O4] at equilibrium = equilibrium constant Here we see different mixtures of NO2 and N2O4 with their initial concententrations (the amounts we put together in a reaction vessel) and the concentrations of the compouinds at equilibrium. As you can see, in all reaction mixtures, the only thing that is the same for all equilibria is the value of the quotient [NO2]2/[N2O4] General reaction aA + bB  cC + dD [𝐶]𝑐 [𝐷]𝑑 Equilibrium constant expression 𝐾𝐶 = [𝐴]𝑎[𝐵]𝑏 KC = equilibrium constant (= a value); KC is dimensionless, concentration units NOT added in calculation A, B, C, D = reactants and products a, b, c, d = number of mole in equation [A] etc: concentration at equilibrium [C]c [D]d aA + bB  cC + dD K C = [A]a [B]b KC >> 1 : equilibrium favours products, lies to the right KC