Bonding and Naming Chapter 6

Chemical Bonds & Stability Chemical Bond: force that holds two atoms together Valence electrons are the electrons involved in bonding What are the most unreactive elements on the Periodic Table? How many valence electrons do they contain? Lack of reactivity is a result of having a full set of valence electrons in the outermost orbital that creates a stable atom. Atoms will lose, gain, or share electrons in order to obtain a full set of valence electrons and achieve stability.

Formation of Ions Cation: positively charged ion Formed by loss of electrons Typically formed by metals Charge of ion is equal to the number of valence electrons lost by atom Example: Ca will lose 2 valence electrons forming an ion with a +2 charge Ca2+ Example: K will lose 1 valence electron forming an ion with a +1 charge K1+

Formation of Ions Anion: negatively charged ion Formed by gaining of electrons Typically formed by nonmetals Charge of ion is equal to the number of valence electrons gained by atom Example: Cl will gain 1 electron (for a total of 8 valence electrons) forming an ion with a -1 charge Cl- Example: O will gain 2 electrons forming an ion with a -2 charge O2-

Positive and negative ions are attracted to each other Crystal Lattices Positive and negative ions are attracted to each other Charged ions will surround each other and pack together as closely as possible to form an electrically neutral lattice. Ions cluster in ratios that result in a net charge of zero. (Remember: Matter is neutral so positive & negative charges have to be present in equal amounts.)

Types of bonds 3 major types: Ionic Covalent Metallic

Ionic Bonds Form because electrons are transferred from one atom to another. The transfer of electrons results in formation of anions and cations that are attracted to each other. Ionic bonds are formed between metals and nonmetals.

Properties of Ionic Compounds High MP and BP Ionic bonds relatively strong, require large amounts of energy to break apart Color related to structure Hard, rigid, and brittle solids Due to strong attractive forces holding ions in place Conductivity Nonconductors of electricity as solids Conduct electricity when dissolved in H2O (electrolyte)

Examples of Ionic Compounds Table Salt (NaCl) Road Salt (CaCl2) Rust (Fe2O3)

Covalent bonds Covalent bonds are formed when atoms share their valence electrons. Covalent bonds are formed between 2 nonmetals.

Properties of Covalent Molecules Low melting and boiling points Soft and brittle solids Do not conduct electricity, even if dissolved in water.

Examples of Covalent Molecules Sugar, C6H12O6 Water, H2O Isopropyl (Rubbing) alcohol, C3H7OH

Metallic Bonds Lattice formed by metal atoms Do not share electrons or form ions Outer energy levels of atoms overlap Electron Sea Model: all metal atoms in metallic solid contribute valence e- to form “sea” of electrons

Properties of Metals Melting points vary greatly Malleable and ductile Generally durable Good conductors (heat and electricity) Luster Hardness and strength (increase w. # of delocalized e-)

Writing Ionic Compound Formulas All ionic compounds have a net charge of zero because matter is neutral. Use subscripts to indicate the quantity of each ion required to bond to result in a neutral compound. Example: Na and Br Na will form +1 ion to achieve stability Br will form -1 ion to achieve stability Opposites attract to form a neutral ionic compound NaBr

Writing Ionic Compound Formulas Example: K and O K will form +1 ion to achieve stability O will form -2 ion to achieve stability Opposites attract to form a neutral ionic compound K2O Polyatomic Ions: formed from covalently bonded nonmetals by contain extra electrons or fewer than the required number of electrons giving the ion a charge (see list) To write a formula, put the polyatomic ion in parentheses before using a subscript to tell how many you need. Examples: Ca(NO3)2 and Na2SO4

Rules for Naming Ionic Compounds There are two general types of compounds Binary compounds compounds formed by only two different elements. There are three different types of binary compounds: Binary Salts Binary Acids Binary Molecular Compounds

Rules for Naming Ionic Compounds Ternary Compounds Contain a polyatomic ion. Polyatomic ion A group of atoms covalently bonded that possess an overall charge. These ions act as a unit and form ionic compounds. There are three different types of ternary compounds Bases Ternary Acids Ternary Salts

Rules for Naming Ionic Compounds Binary Salts Made up of a metal and a nonmetal. To name this type of compound Name the first element Name the second element but change the ending to “ide” Example: CaS calcium sulfide MgCl2 _______________________________

Rules for Naming Ionic Compounds Binary Acids All acids must begin with hydrogen. If it is a binary acid then the first element is hydrogen and the second is a nonmetal. To name a binary acid: Hydrogen is named “hydro” The second element is named but the ending is changed to “ic” followed by the word “acid” Example: HBr hydrobromic acid HCl ________________________________

Rules for Naming Ionic Compounds Bases All bases end with the hydroxide ion (OH-). To name a base: name the first ion follow with hydroxide. Examples: Al(OH)3 - aluminum hydroxide Na(OH) - ________________________

Rules for Naming Ionic Compounds Ternary salts Generally if the formula ends with a polyatomic ion but does not contain hydroxide (a base) and does not begin with hydrogen (an acid) then it must be a salt. To name a ternary salt: Name the first element Name the polyatomic ion Examples: Na2(SO4) sodium sulfate Ca3(PO4)2 - _______________________________

Rules for Naming Ionic Compounds The Stock or IUPAC Method Transition Metals and a Few Other Metals Have various charges When one of these metals is found in a compound you must use a Roman numeral in the name to indicate the charge. Examples: FeCl3 - iron (III) chloride Sn(SO4) - tin (II) sulfate Cr(PO4) - ____________________________________

Important Terminology Molecules are made up of atoms that are covalently bonded. Therefore, substances that have ionic bonds are not referred to as molecules. Substances with ionic bonds are made up of ions and the particles are referred to as formula units.

Structural Formulas Steps to determine Lewis structures for covalent molecules: Electrons that are shared are written between two atoms. There is always a central atom, unless there are only 2 atoms in the compound. Single bonds are represented by 2 dots or a single dash; double bonds are represented by 4 dots or 2 dashes; and triple bonds are represented by 6 dots or three dashes.

Structural Formulas Electrons (dots) can be moved around the symbol of element in any order but CANNOT go from one element to another ~ if shared, they must stay between atoms! Electrons between atoms are counted as belonging to both atoms. Dot diagram is CORRECT if all atoms have 8 electrons except atoms in Groups 1, 2, and 13. Atoms from Groups 1, 2, 13, and 17 never have double or triple bonds.

Lewis Dot Diagrams for Covalent Compounds - Examples H2O HCl BI3 CCl4

Lewis Dot Diagrams for Covalent Compounds - Examples PO43- NH4+

VSEPR Model Valence Shell Electron Pair Repulsion model All electron pairs around the central atom affect the shape of the molecule. The shape of molecules depends upon the number of both shared and unshared (lone) pairs of electrons around the central atom. Draw the dot diagram for water and label the shared and unshared electron pairs:

VSEPR Model Unshared pairs take up more room than shared pairs and therefore they are important in predicting the shape of the molecule. The shape of a molecule is determined by drawing lines connecting the centers of the atoms in the molecule. There are six (6) shapes that you have to learn.

Molecular shapes 2 – atom linear 3 – atom linear Trigonal planar Tetrahedral Trigonal pyramid Bent

Steps for determining shape Draw the Lewis Dot Diagram. Count up the number of shared and unshared electron pairs around the central atom. Memorize the following chart…

Example Electron Dot Diagram Shared Pairs Unshared (Lone) Pairs Molecular Shape Structural Formula HCl BeI2 AlBr3 CH4 NH3 H2O

Rules for Naming Binary Molecular Compounds Formed between two nonmetals. Since nonmetals can form many different compounds with each other, Greek prefixes are used to show how many atoms of each element are present in the compound. Greek Prefixes: mono - one hexa - six di - two hepta - seven tri - three octa - eight tetra - four nona - nine penta - five deca – ten

Rules for Naming Binary Molecular Compounds Rules similar to those for binary salts EXCEPT If there is more than one atom in the first element, then use the appropriate prefix in front of the name of that element. The second element always has a prefix (use mono if there is only one) and change the ending to “ide.” Examples: CO carbon monoxide P2O5 ________________________________