Atoms in Combination: The Chemical Bond Chapter 10 PDF

Atoms in Combination: The Chemical Bond chapter 10- part one Atoms bind together in chemical reaction by rearrangement of electrons.  Electrons Shells and chemical bonding The atoms is mostly empty space, with a tiny, dense nucleus surrounded by sw...

Atoms in Combination: The Chemical Bond chapter 10- part one Atoms bind together in chemical reaction by rearrangement of electrons.  Electrons Shells and chemical bonding The atoms is mostly empty space, with a tiny, dense nucleus surrounded by swift electrons. Whatever holds two atoms together thus involves primarily those outer electrons. They are given special name of valence electrons, the number of electrons in an atom’s outermost shell is called its valence. Electrons Shells and chemical bonding The most stable arrangement of electrons- the electron configuration of lowest energy is a completely filled outer shell. The atoms with a total of 2, 10 , 18, or 36 electrons have filled orbits and very stable configurations= inert gases( noble gases) Periodic Table of Elements  Electrons Shells and chemical bonding Every object in nature tries to reach a state of lowest energy, and atoms are no exception. For example: if you put a ball on top of a hill, it will tend to roll down to the bottom, creating a system of lower gravitational potential energy. In the same way, when two or more atoms come together the electrons tend to rearrange themselves to minimize the chemical potential energy of the entire system.  Electrons Shells and chemical bonding Chemical bonds result from any redistribution of electrons that leads to a more stable configuration between two or more atoms especially that of a filled electron shell. Most atoms adopt one of three simple strategies to achieve a filled shell: They give away electrons Accept electrons Share electrons. If the bond formation takes place spontaneously, without outside intervention, energy will be released in the reaction.  Types of chemical bonds Three principal kinds of chemical bonds- ionic, metallic, and covalent, all of which involve redistributing electrons between atoms. In addition, three types of attractions- polarization, van der waals interactions, and hydrogen bonding, result from shifts of electrons within their atoms or groups of atoms.  Ionic Bonds Chemical bonds in which the electrical force between two oppositely charged ions holds the atoms together. Ionic bonds often form as one atom gives up an electron while another receives it. Ionic Bonds Ionic Bonds Ionic Bonds: The 12th element, magnesium, donates two electrons to oxygen, to form magnesium oxide. Ionic Bonds: Ionic bonding of three Atoms Calcium chloride, CaCl2 Calcium ions have the formula Ca2+. Chloride ions have the formula Cl-. You need to show two chloride ions, because two chloride ions are needed to balance the charge on a calcium ion. Ionic Bonds have the following properties... High melting and boiling points Very poor electrical conductivity as a solid. But very good when molten or dissolved. Soluble in polar solvents (e.g. water) Metallic Bonds Electrons are redistributed so that they are shared by many atoms. For example, sodium metal, is made up entirely of individual sodium atoms. All of these atoms begin with 11 electrons, but they release 1 to achieve the more stable 10-electron configuration. Metallic Bonds The extra electrons move away from their parent atoms to float around the metal, forming a kind of sea of negative charge. In the negative electron sea, the positive sodium ions adopt a regular crystal structure  Metallic Bonds Metallic bonding, in which a bond is created by the sharing of electrons among several metal atoms Metallic Bonds have the following properties... High melting and boiling points Very good electrical and thermal conductivity. Poor Solubility Shiny luster Examples; alloys: brass, bronze, and steel alloys Covalent Bonds In which well-defined clusters of neighboring atoms , called molecules, share electrons These strongly bonded groups may consist of any where from two to many millions of atoms. Covalent Bonds The simplest covalently bonded molecules contain two atoms of the same element, such as the diatomic gases hydrogen( H2), nitrogen( N2), and oxygen( O2) Covalent Bonds Examples of gas molecules that have a nonpolar covalent bond Covalent Bonds The most fascinating of all covalently bonded elements is carbon, the basis of all life on earth. Carbon, with two electrons in its inner shell and four in its outer shell, presents a classic case of a half-filled shell. Carbon-based molecules may adopt almost any shape, such as nylon (a), and cholesterol (b) To help protect y our priv acy , PowerPoint has block ed automatic download of this picture. Covalent bond A single bond( H-H) forms when one electron from each atom is shared, while a To help protect y our priv acy , PowerPoint has block ed automatic download of this picture. double bond ( O=O) results when two electrons from each atom are shared between one another. Covalent bond By forming bonds among several adjacent carbons atoms, you can make rings, long chains, branching structures, planes and three-dimensional frameworks of carbon in almost any imaginable shape. So, important is the study of carbon-based molecules that chemists have given it a special name: Organic Chemistry Polarization and hydrogen bonds In many molecules, the electrical forces are such that, although the molecule by itself is electrically neutral, one part of the molecule has more positive or negative charge than another. In water( for example) the electrons tend to spend more time around the oxygen atoms than around the hydrogens.  Polarization and hydrogen bonds This uneven electron distribution has the effect of making the oxygen side of the water molecule more negatively charged, and the two” Mikey Mouse ears” of the hydrogen atom more positively charged.  Polarization and hydrogen bonds Atom clusters of this type, with a positive and negative end, are called polar molecules. The electrons of an atom or molecule brought near a polar molecule such as water will tend to be pushed away from the negative side and shifted toward the positive side. This subtle electron shift called polarization.  Polarization and hydrogen bonds One of the most important consequences of forces due to polarization is the ability of water to dissolve many materials. Water, made up of strongly polar molecules, exerts forces that make it easier for ions such as Na+ & Cl- to dissolve. A process related to the forces of polarization leads to the Hydrogen bond.  Polarization and hydrogen bonds Hydrogen bond: a weak bond that may form after a hydrogen atom links to an atom of certain other elements( oxygen or nitrogen) by a covalent bond. Hydrogen bonds are common in virtually all biological substances, from everyday materials such as wood, plastics, silk, and candle wax, to the complex structures of every cell in your body. Hydrogen bonds in every living thing link the two sides of the DNA double helix together.  Van der Waals Forces Another forces between molecules, called the van der Waals forces, results from the polarization of electrically neutral atoms or molecules that are not themselves polar. For example, an electron in one atom will be repelled by the electrons, but attracted to the nucleus, of an adjacent atom. The net result of these forces exerted on the electron may be a temporary shift of the electron.  Van der Waals Forces The sum of attractive forces wins out over repulsive forces and weak bonds are formed. This weak force that binds two atoms or molecules together is called the van der waals force. Within each sheet of a piece of clay, atoms are held together by strong ionic and covalent bonds. One sheet is held to another, however by comparatively weak van der waals forces. Van der Waals Forces Graphite, a form of carbon that serves as the “lead” in your pencil, contains layers of carbon atoms strongly linked to each other by covalent bonds, these layers are held to each other by van der waals bonds.  Van der Waals Forces Many other examples of van der waals forces can be seen in everyday life. Layers of talcum powder ( ‫)مسحوق بودرة‬ Layers of lead pencil Layers of graphite Candle wax, Vaseline and other petroleum products. States of Matters Matter exists in four states: solid, liquid, gas and plasma. Plasmas are only found in the coronae and cores of stars. The state of matter is determined by the strength of the bonds between the atoms that makes up matter. Thus, is proportional to the temperature or the amount of energy contained by the matter. Gases A gas is any collection of atoms or molecules that expands to take the shape of and fill the volume available in its container. Most common gases, including those that form our atmosphere, are invisible, but the force of a gust of wind is proof that matter is involved. Gases The individual particles that comprise a gas may be isolated atoms such as helium or neon, or small molecules such as nitrogen( N2) or carbon dixiode(CO2). Plasma At extreme temperatures like those of the Sun, high-energy collisions between atoms may strip off electrons, creating a Plasma, in which positive nuclei move about in a sea of electrons. Plasmas, are efficient conductors of electricity and, because they are gaslike, can be confined in a strong magnetic field or” magnetic bottle” Plasma Plasmas are the least familiar state of matter to us, yet more that 99.9% of all the visible mass in the universe exists in this form. Several planets, including the earth, have regions of thin plasma in their outer atmospheres. Plasma is an ionized gas and the fourth state of Matter Atoms are normally electrically neutral, consisting of identical numbers of positively charged protons and negatively charged electrons. In a plasma some of the electrons have been separated from their atoms and are free to wander. Liquids Any collection of atoms or molecules that has no fixed shape but maintains its volume is called a liquid. Attractive forces between individual atoms or molecules hold the liquid together. At the surface of the liquid, these attractive forces act to prevent atoms or molecules from escaping. Liquids In effect, they pull the surface in, giving rise to surface tension. Solids Include all materials that possess a more or less fixed shape and volume. In all solid materials the chemical bonds are both strong and directional.  Solids: adopts several quite different kinds of atomic structures. In Crystals, groups of atoms occur in a regularly repeating sequence, the same atom or atoms appearing over and over again in a predictable way. A crystal structure can be described by first determining the size and shape of the tiny boxlike unit that repeats, then recording the exact type and position of every atom that appears in the box  Solids: adopts several quite different kinds of atomic structures. In Crystals, groups of atoms occur in a regularly repeating sequence, the same atom or atoms appearing over and over again in a predictable way. A crystal structure can be described by first determining the size and shape of the tiny boxlike unit that repeats, then recording the exact type and position of every atom that appears in the box Solids: Crystals Common crystals include grains of sand and salt, computer chips, gemstones, metals, and alloys. Most ceramics, a broad class of hard, durable solids that includes bricks, concrete, pottery, porcelain, teeth and bones and most rocks and minerals.  Glasses In contrast to crystals, are solids with predictable local environments for most atoms, but no long-range order to atomic structure. In most common windows and bottle glasses, for example, silicon and oxygen atoms form a strong three-dimensional framework. Glasses have no regularly stacked boxes of structure. Solids: crystal & glass