Chemical Bonding PDF

Chemical Bonding Ionic Bond Covalent Bond Metallic Bond Octet Rule Stability refers to the strength to stand or a resistance to chemical change or physical disintegration. Stability in atoms involve the possession of eight (8) electrons in its outermost energy level or valenc...

Chemical Bonding Ionic Bond Covalent Bond Metallic Bond Octet Rule Stability refers to the strength to stand or a resistance to chemical change or physical disintegration. Stability in atoms involve the possession of eight (8) electrons in its outermost energy level or valence electrons. As stated by the octet rule proposed by Gilbert Newton Lewis, atoms of all elements to become stable, need to have 8 Valence Electrons The configuration of electrons and valence electrons are highly important in the study of chemical bonding. Electron configuration refers to the distribution of electrons at different positions in an atom. Valence electrons are the electrons occupying the highest energy level in an atom. Sometimes called the outermost electrons, the valence electrons are the ones actually involved in chemical bonding. Lewis Electron Dot Structure (LEDS) A system known as LEDS, proposed by Gilbert N. Lewis, is used to emphasize the atom’s valence electrons. It is a shorthand method which consists of a symbol of the element surrounded by dots. The symbol represents the nucleus of the atom; while the dots represent the valence electrons of the atom. Lewis Electron Dot Structure (LEDS) 1. Write the chemical symbol of the atom. 2. Determine the column or group where an atom belongs in the periodic table or write down its electron configuration to find out the atom’s number of valence electrons. 3. Draw the dots that will correspond to the number of atom’s valence electrons. Distribute the dots evenly. Ionic Bond Elements react with one another forming new substances called compounds. A compound is different both in its physical and chemical aspects from the original atom or element to which it come from. The compound are bound together by a strong attractive force called chemical bond. A type of chemical bond formed when there is transfer of electrons from one atom to another is called an ionic bond. Ionic Bond The compound formed is an ionic compound. This type of bond involves the gaining and losing of electrons. In doing so, the atom becomes a charged particle and will now be called ion. An atom that loses an electron becomes positively charged ion called cation; and the one that gains electron becomes negatively charged ion called anion. Formation of Ionic Compounds Ionic bond formation always involves a bonding between a metal and a nonmetal. When a metal bonded together chemically with a nonmetal, the resulting compound is a salt. The energy needed to remove an electron from the neutral atom is known as ionization energy. Ionization energy generally increases from left to right of the periodic table. Formation of Ionic Compounds Electrons are being transferred. The transfer is made possible as the electron affinity is met. Electron affinity is a measure of how much energy is released when an electron is gained by a certain atom. Its trend generally increases across period and decreases as you go down the group. Formation of Ionic Compounds Since ions are opposite in charge, they attract each other forming a chemical bond known as ionic bond. This type of bond normally formed by attraction of a metal to a nonmetal. It is a bond common to representative elements or those in Groups 1A, 2A and 3A and the elements in Groups 6A and 7A. The compound formed by this bonding is known as ionic compound. Chemical Formulas & Name of Ionic Compounds Ionic compounds are compounds composed of ions or charged particles. They are generally solid at room temperature and have high boiling and melting points. Ionic compounds are poor conductors of electricity but when dissolved in water, these compounds conduct electricity since ions are free to move and carry the charge. Chemical Formulas & Name of Ionic Compounds 1. Write the symbol of the cation first followed by the anion. 2. Write down the ion’s respective charges. 3. Put them together using the crisscross method. The crisscross method is done by writing the charge value of the first ion as subscript of the second ion and vice versa. Drop the positive and negative signs. Chemical Formulas & Name of Ionic Compounds 4. Lastly, reduce the subscripts when possible to the greatest common factor. The previously mentioned compounds are called binary compounds, since they involve only two elements. There are also compounds that contain three different elements. These compounds are called ternary compounds. Most of these compounds consist of metallic cation and a polyatomic anion. Naming Binary and Ternary Compounds For binary compounds, one should name the cation first. Then name the anion changing its suffix to –ide. Meanwhile, to name ternary compounds, one just need to name the cation first, followed by the name of the polyatomic ion. The stock system uses the Roman numeral to describe an ion’s charge. It is enclosed in parenthesis and placed immediately after the metal name. Important Ions and Ionic Compounds Ions are necessary to plants and animals for them to perform important cellular activities of the body. The body ions, known as electrolytes, are needed for the activation of the nervous system. Important Ions and Ionic Compounds Na+ - controls and regulates bodily fluids K+ - controls and regulates bodily fluids particularly the osmotic balance in the kidneys Ca2+ - component of the bones and teeth; essential for muscle contraction Mg2+ - component of chlorophyll; plays assisting role in metabolic functions Cl- most abundant anion; necessary in gastric juice Important Ions and Ionic Compounds NaNO3 (sodium nitrate) used as meat preservative CaF2 (calcium fluoride) component of toothpaste; helps prevent tooth decay AgBr and AgCl (silver halides) used in the photographic industry to make films for capturing images, light sensitive ingredient used in photographic film NaOH (sodium hydroxide) used in the manufacture of soaps Al2O3 (aluminum oxide) one of the most used compounds in engineering processes like in the making of airplanes due to its light weight Covalent Bond Type of bond that exists between nonmetals. Sharing of electrons Electronegativity is the electron attracting ability of each atom Sharing of electrons in a chemical bonding of nonmetals happens because electronegativity difference between them is equal or less than 1.7 Covalent Bond When two or more nonmetallic elements combine in a covalent bonding, a molecule is formed. Gases like O2, H2, N2, F2, Cl2 and I2 always occur in diatomic molecule. As such they are more stable than single atoms. Their bonding is held together by a bond known as covalent bond. A line is drawn to show the shared electron pair. Covalent Bond Three types of covalent bond exist which depend on the number of shared electron pair. – A single covalent bond, denoted by one short line, is the sharing of one electron pair between two atoms. – A double covalent bond, denoted by two short lines, is the sharing of two electron pairs. – A triple covalent bond, denoted by three short lines, is the sharing of three electron pairs. Covalent Bond Chemical Formulas and Name of Covalent Compounds The shared electron pair, often referred to as bonding pair, is represented by either a pair of dots or a line. The chemical formula reflects the number of atoms in the molecule. In writing the formula, it is important that you draw first the LEDS. Then show the sharing of the pairs of electrons with either single, double or triple lines. Finally, write the formula by placing the more electropositive first followed by the more electronegative element, including the subscript to show the number of atoms in a molecule. Covalent Bond Naming Covalent Compounds To name covalent or molecular compounds, you first have to name the first nonmetal. The second nonmetal is named by changing its suffix with -ide. A prefix such as mono, di, and tri among others is used at the beginning of each element to denote the number of atoms present in the element. 1 mono 6 hexa- 2 di- 7 hepta- 3 tri- 8 octa- 4 tetra- 9 nona- 5 penta- 10 deca- Covalent Bond Molecular Geometry It is the molecular geometry that gives us the general shape of the molecules. The shape depends on the number of bonding pairs present around the central atom and how many of those bonding pairs are participating in a bond. In molecular geometry, the bond length and angles are determined experimentally. A simple procedure known as the valence shell electron pair repulsion (VSEPR) can help predict the geometric shape arrangement of atoms in molecules. The concept of VSEPR is that all the valence shell electron pairs of the central atom are considered. It includes both the pairs that form covalent bonds or the bonding pairs and the pairs that are unshared or the nonbonding pairs known as lone pairs.  Covalent Bond Molecular Geometry  Covalent Bond Molecular Geometry Properties of Ionic and Covalent Compounds Metallic Bonds The third type of chemical bonding is metallic bonding. This type of bond is a bond among metals. As metals lose their outer electrons, metal cations are formed. The electrons from all the metal atoms form a sea of electrons that flow around these metal cations. The electrostatic force that holds the atoms together in metals is called metallic bond. Metallic Bonds Metallic Properties Metallic solids have special properties that separate them from other solids. Majority of elements are metals. Many of them combine with each other to form huge number of metallic compounds. Materials bonded by metallic bonds are good electrical and thermal conductors due to their free valence electrons. Metallic Bonds Metallic Properties Metals have high melting points. This is due to the electrostatic attraction between the lattice of metal cation and the fluid of valence electrons in which they are immersed. The transition elements or those belonging to the d-block of the periodic table have stronger and higher melting points. Metallic Bonds Metallic Properties Metallic compounds are known to be malleable and ductile. Malleability is the ability of metals to be shaped by pressure, either by hammering, rolling into sheets or forging. On the other hand ductility is the ability of metals to be drawn into wires. Luster is another property among metals. Luster is the ability to shine and reflect light.