Are there symmetrical and polar molecules

Big Bang HTL 2, textbook

58 Fundamentals of Chemistry Section (2nd year, 3rd semester) Summary Atomic bonds are formed between non-metal atoms. In the case of an atomic bond (= electron pair bond, = covalent bond) the atoms reach a noble gas state by using electrons together. Molecules are created in which the individual atoms are held together by electron pairs. An atom forms as many bonds as it lacks electrons in the noble gas state. Structural formulas can be used to visualize how the atoms in the molecule are connected. In the case of valence line formulas, one also sees the non-binding electron pairs. 4.5.2 Pulling a rope, for atoms polar atomic bond In this chapter we learn that the law of the strongest also applies to atoms. We also learn where the boundaries and transitions between atomic and ionic bonds lie. So far we have described the atomic bond as “brotherly sharing” of electrons. But you can also look at the whole thing from another point of view, namely as a battle for the electrons. Who still remembers electronegativity and what it indicates? Correct, the EN value indicates how strongly an atom attracts binding electrons. Both binding partners actually do not want to share the binding electrons, but prefer to have them all to themselves. Therefore they “pull” on these electrons with a certain force (EN value). The higher the EN value, the more the atom “pulls”. Are both partners now equally strong (same EN values), such as B. with Cl 2, the electrons are also evenly distributed. The bond is non-polar. The binding electrons are located exactly between atom 1 and atom 2. The centers of gravity of the positive and negative charges (the protons and the electrons) coincide, see Fig. 4.28. If 2 equally strong people pull on a rope, nothing happens - no shift. If a partner pulls more strongly on the binding electrons (if it has a higher EN value), the electrons become a little bit Z What is a pole? What do you imagine by the term “dipole”? F43 Fig. 4.27 shifted towards him. The protons in the nucleus, however, remain in place. The centers of gravity of the positive and negative charges no longer coincide. The atom with the higher EN value is a little negatively charged, the atom with the lower EN value a little bit positive. A polar bond is created = a bond with a positive and a negative end or pole. This small partial charge (partial charge) is denoted by d (pronounced "delta") + or d -. Polar molecules: Whether a polar molecule arises as a whole, ie whether it becomes a polar molecule, depends on the spatial structure of the molecule in question. In the case of diatomic molecules, polar molecules are created automatically. Molecules with a positive and a negative pole are called dipoles. (F43) Example: HCl - hydrogen chloride In the case of molecules made up of 3 or more atoms, it depends on whether the molecule is symmetrical or not. If all the centers of gravity of the charge coincide, the overall result is a non-polar molecule. Completely symmetrically arranged polar bonds cancel each other out. Examples: CH 4 methane - symmetrical molecule - no dipole H 2 O water - non-symmetrical molecule - dipole CO 2 carbon dioxide - symmetrical molecule - no dipole The polarity has great effects on solubility and melting and boiling points, see Tab. 4.3. Fig. 4.28: Centers of charge in polar and non-polar bonds Fig. 4.29: HCl - a polar molecule Fig. 4.30: Centers of charge and molecular geometry For testing purposes only - property of the publisher öbv

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