Atomic & Molecular Models PDF

Atomic & Mole cu lar M o d e ls Lesson 1 Medicine (Pathway Programme) Chemistry Module  Lesso n Outcomes Identify and describe the basic parts of an atom based on atomic models. Describe the steps involved in the scientific method. Identi...

Atomic & Mole cu lar M o d e ls Lesson 1 Medicine (Pathway Programme) Chemistry Module  Lesso n Outcomes Identify and describe the basic parts of an atom based on atomic models. Describe the steps involved in the scientific method. Identify and differentiate between the three states of matter (solid, liquid, gas) and describe their respective properties Perform basic measurements and unit conversions accurately and understand their significance in a chemical context. Introduction to Atomic Theory Atomic theory provides the foundation for understanding the nature of matter. The concept of atoms has evolved from philosophical ideas in ancient Greece to modern scientific understanding. Atoms are the smallest units of matter that retain the properties of an element, and they combine to form molecules and compounds.  Atomic Theory 01 Dalton's Atomic Theory (1803) John Dalton proposed the first scientific atomic theory based on experimental evidence. Postulates of Dalton's Atomic Theory: Bölünmez –Elements are made of small, indivisible particles called atoms. –Atoms of the same element are identical in mass and properties, while atoms of different elements differ. –Atoms combine in simple whole-number ratios to form compounds. John Dalton –Chemical reactions involve the rearrangement of atoms, but atoms are neither created nor destroyed.  Limitations of Dalton’s Theory While groundbreaking, Dalton's theory had limitations that were later addressed by more advanced models. Dalton could not explain: Electron –The existence of subatomic particles (protons, Proton neutrons, electrons). –The phenomenon of isotopes (atoms of the same element with different masses due to varying neutron numbers). Neutron –The internal structure of atoms, which led to further research into atomic models.  Atomic Theory 02 Thomson’s Plum Pudding Model (1904) J.J. Thomson's discovery of the electron through cathode ray experiments led to the Plum Pudding Model. In this model: –The atom is a sphere of positive charge with electron negatively charged electrons scattered within, resembling plums in a pudding. –This model provided the first insight into the existence of subatomic particles, but it failed J.J. Thomson's Plum Pudding to explain the nucleus. Model of the Atom  Atomic Theory 03 Rutherford's Nuclear Model (1911) Ernest Rutherford conducted the Gold Foil Experiment to test Thomson's model. Results of the experiment: –Most alpha particles passed through the foil, but some were deflected, indicating the presence of a dense, positively charged nucleus. Conclusions: –Atoms are mostly empty space with a small, dense nuclei containing protons. Electrons orbit the nucleus. Limitations of Rutherford's Model Although Rutherford's model introduced the concept of a nucleus, it had its limitations: –It could not explain why electrons, which electron are negatively charged, did not collapse into the positively charged nucleus. –It also did not describe the energy levels of electrons, which were later addressed nucleus by Bohr's model. Ernest Rutherford’s Nuclear Model of the Atom  Atomic Theory 04 Bohr's Model (1913) Niels Bohr proposed the idea of quantised energy levels to address the stability of the atom. Key Postulates of Bohr's Model: –Electrons orbit the nucleus in fixed energy levels or shells without radiating energy. –Electrons can move between these energy levels by absorbing or emitting energy in the form of light. Success: Bohr's model successfully explained the spectral lines of hydrogen.  Quantum Mechanical Model (1926) The quantum mechanical model, developed through the work of Schrödinger and others, describes electrons in terms of probability distributions. Instead of fixed orbits, electrons exist in regions called orbitals, where the probability of finding an electron is highest. The model is based on Schrödinger's wave equation, which provides a mathematical framework for predicting electron behavior.  Heisenberg's Uncertainty Principle Werner Heisenberg introduced the uncertainty principle, a key concept in quantum mechanics. The principle states that it is impossible to know both the exact position and momentum of an electron at the same time. This principle challenged classical mechanics and introduced the concept of probabilistic behaviour at the atomic level. Molecular Models: Ball-and-Stick Ball-and-stick models represent atoms as spheres (balls) and bonds as sticks connecting them. These models are useful for visualising molecular geometry and bond angles. 109.5° Example: The ball-and-stick model of methane (CH₄) shows a tetrahedral structure with 109.5° bond angles. Methane Molecular Models: Space-Filling Space-filling models depict atoms as spheres scaled to their atomic radii, showing how atoms pack together in a molecule. Methane These models help visualise the relative sizes of atoms and the overall molecular structure. Example: Space-filling models of DNA highlight the helical structure and the packing of base pairs.  Let's Review Matter Matter is anything that has mass and takes up space, and it can exist in four states: Solid Liquid Gas Plasma Fixed shape and Fixed volume but Neither fixed Ionised gas volume no fixed shape, shape nor volume where electrons Particles are closely Particles can move Particles move are separated packed and vibrate in around each other. freely and fill the from nuclei place. container. found in stars and lightning.  Phase transitions Melting (Solid to Liquid): Adding energy weakens particle bonds. Freezing (Liquid to Solid): Removing energy strengthens particle bonds. Evaporation/Boiling (Liquid to Gas): As more energy is added, particles at the surface escape into the gas phase (evaporation), and when heating continues throughout, boiling occurs. Condensation (Gas to Liquid): Removing energy causes particles to slow and clump into liquid. Sublimation (Solid to Gas) and Deposition (Gas to Solid): Skipping the liquid phase directly. Ionization (Gas to Plasma) and Recombination (Plasma to Gas): Gaining or losing energy to strip or recombine electrons  The Scientific Method The scientific method is a systematic approach that chemists use to investigate natural phenomena, develop new knowledge, and solve scientific problems. It consists of a sequence of steps that ensures rigorous testing and validation of scientific ideas. Hypothesis Experiment Observation Analysis Theory Conclusion Development 1. Observation Observe a phenomenon, ask questions, or identify a problem to investigate. Example: A chemist observes that a solution changes colour when mixed with a particular reagent. 2. Hypothesis Formation Formulate a tentative explanation (hypothesis) based on observations. Example: The hypothesis might be that the colour change is due to the formation of a new compound in the solution. 3. Experimentation Design and carry out experiments to test the hypothesis, ensuring that only one variable changes at a time to determine the cause of observed effects. Example: Conduct a series of reactions where the reagent is mixed with different chemicals to see if the colour change consistently occurs under specific conditions. 4. Data Collection & Analysis Measure and record data, and use statistical tools to analyse the data for consistency and reliability. Example: Record the concentration, temperature, and time of reaction, as well as any observable changes (colour, gas formation, etc.). Analyse the data to determine trends or patterns. 5. Conclusion: Draw a conclusion based on the experimental results. Does the data support or refute the hypothesis? Example: If the colour change happens only with a specific concentration of the reagent, the conclusion might state that a threshold level of the reagent is necessary for the reaction. 6. Theory Development: prove If the hypothesis is repeatedly validated, it can be developed into a theory. A theory offers a well-substantiated explanation for natural phenomena. Example: The conclusion might lead to a theory about how the reagent interacts with other chemicals to cause the observed colour change. Measurements and Unit conversions mass Temp ligyilm Analytical balance Pipette Thermometer Graduated cylinder In a Balance: Analytical laboratory setting, specialized equipment is used to accurately Measures precise mass. measure fundamental quantities like mass, volume, and temperature. Pipette: Transfers small liquid volumes. Accurate measurements are essential in chemistry for reproducibility Thermometer: Measures temperature. and precision, which can affect the outcome of experiments. UnitCylinder: Graduated conversions Measures liquidare often volume. needed in calculations.  Let's Wrap Up Atomic and molecular models are critical to understanding the structure of matter and chemical behaviour. The evolution of atomic models reflects the scientific process and the importance of evidence in shaping scientific theories. Accurate measurements and unit conversions are essential for successful chemical experiments and reliable results.