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Integrated Science Chapter 4 Notes Section 1: Compounds and Molecules 1. Compounds • Elements combine to form compounds example: the elements sodium and chlorine can combine to form table salt • Chemical bond – the attractive force that holds atoms or ions together When two or more elements bond to form a compound, the properties of the compound are different from the properties of the elements that formed the compound • A compound always has the same chemical formula example: the formula for water is always H2O, if the formula is different the compound is not water • Chemical structure shows the bonding within a compound Chemical structure – the arrangement of bonded atoms or ions within a substance Bond length – the average distance between the nuclei of two bonded atoms Bond angle – the angle formed by two bonds to the same atom • Different structures give compound different properties Compound with network structure are strong solids Some networks are made of bonded ions ♦ Recall that ions are charged particles and that unlike charges attract 2. Molecules • Some compounds are made of molecules molecule – the smallest unit of substance that exhibits all of the properties characteristic of that substance ♦ example: sugar is composed of molecules of C12H22O11 that are weakly attracted to each other • Different molecules have different strengths of attraction between molecules The molecules of a solid have the strongest attractive force, followed by liquids, and then gases which have the weakest attractive force Section 2: Ionic and Covalent Bonding 1. Three different bonds describe the way atoms bond most substances • Atoms bond when the valence electrons interact • Generally, atoms join to form bonds so that each atom has a full outermost energy level 2. Ionic Bonds • Ionic bond – a bond formed by the attraction between oppositely charged ions Ions are formed by an atom either gives up an electron or electrons or when an atom accepts an electron or electrons In general, metals will give up electrons and nonmetals will accept electrons • Ionic compound are in the form of networks, not molecules • When melted or dissolved in water, ionic compound conduct electricity 3. Metallic bond – a bond formed by the attraction between positively charged metal ions and the electrons around them 4. Covalent bonds • Covalent bond – a bond formed when atoms share one or more pairs of electrons • Covalent bonds are often formed between two or more nonmetals Nonmetals will share pairs of electrons to gain the noble gas configuration Equal sharing of electrons result in the formation of nonpolar covalent bonds Unequal sharing of electrons result in the formation of polar covalent bond 5. Polyatomic ions • Polyatomic ion – an ion made of two or more atoms that are covalently bonded and that act like a single ion • Typically the polyatomic ion consists of nonmetals • There are many polyatomic ions (refer to page 121) • In a chemical formula, parentheses group the atoms of the polyatomic ion Section 3: Compound Names and Formulas 1. Naming Ionic Compounds • Names of ionic compounds include the ions of which they are composed Usually, the cation (positive ion) is just like the name of the element from which it is formed ♦ Because transition metals can form several cations with different charges, a Roman numeral is used to show the cations’s charge ♦ Example: iron oxide can have two formulas, FeO or Fe2O3, so FeO is iron (II) oxide and Fe2O3 is iron (III) oxide Usually, the root of the name of the element that forms the anion plus the suffix ide is used in the name of the ionic compound ♦ Example: NaCl, is name sodium chloride. Sodium forms the cation in this compound and chlorine forms the anion 2. Writing Formula for Ionic Compounds • Use the criss-cross method to determine the formula for an ionic compound Example: calcium chloride ♦ We know that calcium (Ca) will give up two electrons to become the cation Ca+2, and that chlorine (Cl) will accept one electron to become the anion Cl-1 ♦ Remember, the compound that is formed must have no charge, that is the positive charges equal the negative charges ♦ To determine the formula for calcium chloride write the cation and anion side-by-side, then draw an arrow from the charge number or the anion down over so that it is below the cation and draw and arrow from the charge number of the cation over and below the anion. ♦ These numbers will tell you the number of cations and anions that are in the formula Ca+2 Cl-1 CaCl2 Ca1 Cl2 ♦ So, the formula for calcium chloride is CaCl2 3. Naming Covalent Compounds • Numerical prefixes are used to name covalent compounds of two elements Example: CO2 is called carbon dioxide Common numerical prefixes: prefix value mono one di two tri three tetra four 4. Chemical formulas for covalent compounds • Empirical formula – the simplest chemical formula of a compound that tells the smallest wholenumber ratio of atoms in the compound Different covalent compound can have the same empirical formula ♦ example : formaldehyde and acetic acid have the same empirical formula--CH2O, but they are totally different substances ♦ ♦ ♦ To distinguish between formaldehyde and acetic acid we must write their molecular formulas Molecular formula – a chemical formula that reports the actual numbers of atoms in one molecule of a compound The molecular formula for formaldehyde is CH2O and the molecular formula for acetic acid is C2H4O2 Section 4: Organic and Biochemical Compound 1. Organic Compounds • Organic compound – any covalently bonded compound that contains carbon • When a compound is made of only carbon and hydrogen atoms it is called a hydrocarbon Alkanes are hydrocarbons that have only single covalent bonds ♦ Example: methane, CH4, is the simplest alkane, and has a structure like this: Alkenes have double carbon-carbon bonds ♦ Example: ethylene, C2H4, is the simplest alkene, and has a structure like this: Alcohols are organic compound that are made of oxygen as well as carbon and hydrogen. ♦ Alcohols have hydroxyl, or OH-, groups ♦ Example: methanol, CH3OH, is the simplest alcohol, and has a structure like this: 2. Polymers • Polymer – a large organic molecule made of many smaller bonded units Some polymers are natural (example: rubber), and some are manmade (example: polyethylene) The elasticity of a polymer is determined by its structure ♦ A polymer string is flexible but not elastic, that is, it will not regain its shape once it is deformed (example: a soft-drink bottle) ♦ A polymer net is elastic, it will regain its original shape after being deformed (example: a rubber band) 3. Biochemical Compounds • Biochemical compound – any organic compound that has an important role in living things • Some biochemicals: Carbohydrates – organic compound that are made of carbon, hydrogen, and oxygen and that provide nutrients to the cells of living things Proteins – a biological polymer made of bonded amino acids Amino acid – any one of 20 different naturally occurring organic molecules that combine to form proteins
