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![]() Nitrogen and not the oxygen atom is the central atom in nitrogen dioxide. The nitrogen atom can bond by coordinating a covalent bond, and the charge distribution leads to a negative charge on oxygen. The overall charge on the molecule is 1(+4) + 2(-2) = 0. Nitrogen shows a +4 oxidation state, and each oxygen shows a -2 oxidation state. This is because oxygen is more electronegative, nitrogen is less electronegative than oxygen, and the electronegative element with a negative charge is more stable. In the oxides of nitrogen, nitrogen always shows a positive charge, and oxygen possesses a negative charge. Nitrogen and oxygen readily combine to form various oxides as nitrogen shows variable oxidation states. To explain molecular geometry and bond angles, the most important theory we need to discuss is the VSEPR theory. Molecules forming a covalent bond with different atoms usually are arranged in various forms. Molecules forming a covalent bond with the same atoms with more than two atoms are polyatomic molecules for example, O3, P4, S8. Molecules forming a covalent bond with the same atoms, like homoatomic molecules, are usually arranged linearly for example, H2, I2, Br2, Cl2, F2 etc. A covalent bond is usually formed by sharing electrons, without ions, amorphous solids, and is directional. ![]() An ionic bond is formed by the transfer of electrons, forms ions and is crystalline and non-directional. Ionic and covalent molecules are very different from one another. They can have different bondings, like covalent and ionic. Molecules have atoms bonded around them and occupy space. Compounds have a fixed composition irrespective of the source from which they are prepared, and this follows the law of constant proportion. Molecules that are made of two atoms are binary compounds, while those made of three atoms are tertiary compounds. Molecules can be diatomic, triatomic, or polyatomic and can be made of the same type of atoms or different types of atoms. Water has four electron groups, but only two atoms attached to the central atom so it is bent.Elements that are naturally unstable combine with other elements to gain stability. First draw the Lewis electron dot diagram for water and determine its molecular shape. The first two steps remain the same as the tail-to-head method: 1. Let’s examine this method again for a molecule of water. An alternative method to determine the vector sum of dipole arrows is known as the vector component method. Now superimpose the net molecular dipole arrow onto the molecule. Draw a new line connecting the tail of the first vector. Draw in dipole arrows for all polar covalent bonds, starting the arrow at the more electropositive atom, and ending at the more electronegative atom. Water has four electron groups, but only two atoms attached to the central atom so it is bent. Let’s examine this method for a molecule of water. One method to determine the vector sum of dipole arrows is known as the tail-to-head method. Therefore the molecular polarity is the vector sum of the individual bond dipoles. Each bond’s dipole moment can be treated as a vector quantity, having a magnitude and direction. The overall polarity of molecules with more than one bond is determined from both the polarity of the individual bonds and the shape of the molecule. Table 9.4 Summary of Molecular Shapes Number of Electron Groups on Central Atom When the two electron groups are 180° apart, the atoms attached to those electron groups are also 180° apart, so the overall molecular shape is linear. A molecule whose central atom contains only two electron groups orients those two groups as far apart from each other as possible-180° apart. Remember that a multiple bond counts as only one electron group.Īny molecule with only two atoms is linear. ![]() When applying VSEPR to simple molecules, the first thing to do is to count the number of electron groups around the central atom. There are two types of electron groups: any type of bond-single, double, or triple-and lone electron pairs. VSEPR makes a distinction between electron group geometry, which expresses how electron groups (bonding and nonbonding electron pairs) are arranged, and molecular geometry, which expresses how the atoms in a molecule are arranged. It says that electron pairs, being composed of negatively charged particles, repel each other to get as far away from each other as possible. The basic idea in molecular shapes is called valence shell electron pair repulsion (VSEPR). Small molecules-molecules with a single central atom-have shapes that can be easily predicted. There is an abundance of experimental evidence to that effect-from their physical properties to their chemical reactivity. Determine the polarity of molecules using net molecular dipoles.Determine the shape of simple molecules. ![]()
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