C HEMICAL B ONDS Chapter 6

I NTRODUCTION There are Three Types of Bonds: 1. Ionic Bonds – bond between a metal and a nonmetal 2. Covalent Bonds – bond between two nonmetals 3. Metallic Bonds – bond between two metals

I ONIC B ONDING Chapter 6.1

I. S TABLE E LECTRON C ONFIGURATIONS A. When the highest occupied energy level of an atom is filled with electrons, the atom is stable and not likely to react. What element group does this sound like? B. Chemical properties depend on the number of valance electrons - How can we find valence electrons easily??? A. Electron Dot Diagram – model of an element where each dot represents a valence electron

II. I ONIC B ONDS - Elements with 8 valence electrons tend to be unreactive or stable. - Unreactive – they do not chemically combine with other substances! A. Transfer of Electrons – some elements achieve stable electron configurations through the transfer of electrons between atoms. - Example: Salt

II. I ONIC B ONDS CONT’D B. Formation of Ions 1. When an atom gains or loses and electron, the number of protons no longer equals the number of electrons – THE ATOM BECOMES CHARGED! 2. Ion – an atom that has a positive or negative charge 1. Lose an electron – positive charge  cation Metal Example: Na Gain an electron – negative charge  anion Nonmetal Example: Cl 1-

II. I ONIC B ONDS CONT’D C. Formation of Ionic Bonds 1. Positive and Negatives Attract! 2. Chemical Bond – the force that holds atoms or ions together as a unit. 3. Ionic Bond – Force the holds cations and anions together when electrons are transferred. D. Ionization Energy – the amount of energy used to remove an electron 1. The lower the energy the easier it is to remove the electron and visa versa

III. I ONIC C OMPOUNDS *** A chemical formula for an ionic compound tells you the ratio of the ions in the compound. A. Crystal Lattices Attraction keeps ions in fixed positions with repeating patterns. Crystals – solid particle whose atoms are arranged in a lattice structure (repeating pattern) B. Properties of Ionic Compounds VERY STONG BONDS! 1. High melting point 2. When solid, a poor conductor of electrical current 3. When melted or dissolved, a great conductor of electrical current

C OVALENT B ONDING Chapter 6.2

I NTRODUCTION R EVIEW There are Three Types of Bonds: 1. Ionic Bonds – bond between a metal and a nonmetal 2. Covalent Bonds – bond between two nonmetals 3. Metallic Bonds – bond between two metals

I. C OVALENT B ONDS Nonmetals tend to have a high ionization energy – making it easier to SHARE electrons instead of TRANSFERING A. Sharing Electrons 1. Covalent Bond – is chemical bond in which two atoms share a pair of valence electrons 2. Single Bond – when two atoms share one pair of electrons

I. C OVALENT B ONDS CONT’D A. Sharing Electrons B. Molecules of Elements - The attraction between the electron of the first atom to the proton of the second atom keeps the atoms held together and visa versa 1. Molecule – a neutral group of atoms that are joined together by one or more covalent bonds. 2. Diatomic Molecules – two of the same elements bonded (H 2, Br 2, I 2, N 2, Cl 2, O 2, F 2 ) C. Multiple Covalent Bonds 1. Single Bond - between two atoms one pair of electrons is shared 2. Double Bond - between two atoms two pairs of electrons are shared 3. Triple Bond - between two atoms three pairs of electrons are shared

I. C OVALENT B ONDS CONT’D A. Sharing Electrons B. Molecules of Elements C. Multiple Covalent Bonds D. Types of Covalent Bonds 1. Polar Covalent Bonds 2. Nonpolar Covalent Bonds

II. U NEQUAL SHARING OF E LECTRONS - The type of atom in a molecule and its shape are factors that determine whether a molecule is polar or nonpolar. Elements to the right of the periodic table and the top of the group have the greatest attraction for electrons. This creates an unequal sharing of electrons. A. Polar Covalent Bonds – a covalent bond where electrons are not shared equally. - The atom with the greater attraction for electrons has a partial negative charge  δ – - The atom with the lesser attraction for electrons has a partial positive charge  δ +

II. U NEQUAL SHARING OF E LECTRONS CONT’D A. Polar Covalent Bonds – a covalent bond where electrons are not shared equally. B. Nonpolar Molecules - a covalent bond where electrons are shared equally.

III. A TTRACTION B ETWEEN M OLECULES A. Covalent bonds are weaker than ionic bonds B. Attraction between polar molecules are stronger than attraction between nonpolar molecules.

W HEN THE DIFFERENCE BETWEEN THE ELECTRONEGATIVITIES OF THE ELEMENTS IN A COMPOUND IS RELATIVELY LARGE, THE COMPOUND IS BEST CLASSIFIED AS IONIC. W HEN THE ELECTRONEGATIVITIES OF THE ELEMENTS IN A COMPOUND ARE ABOUT THE SAME, THE ATOMS SHARE ELECTRONS, AND THE SUBSTANCE IS COVALENT.

T HE S TRUCTURE OF M ETALS Chapter 6.4

I NTRODUCTION R EVIEW There are Three Types of Bonds: 1. Ionic Bonds – bond between a metal and a nonmetal 2. Covalent Bonds – bond between two nonmetals 3. Metallic Bonds – bond between two metals

I. M ETALLIC B ONDS Review: Metals become stable by losing electrons. Where do the electrons go if there is not a nonmetal to accept them? In metals, valence electrons are free moving among the atoms. Metal atoms become cations surrounded by a pool of shared electrons Metallic Bonds – attraction between a metal cation to the shared electrons that surround it. The cations in a metal form a lattice that is held in place by strong metallic bonds between the cations and the surrounding valence electrons The number of electrons does not change  Metals are neutral

I. M ETALLIC B ONDS CONT’D Some metallic bonds are stronger than others The more valence electrons the strong the bond Alkali metals tend to have very weak bonds b/c of the lower number of valence electrons  we can cut them with a butter knife (very soft = weak bonds) Transition metals have move valence electrons  harder with high melting points Tungsten is the filament in light bulbs.

II. E XPLAINING P ROPERTIES OF M ETALS The mobility of electrons within a metal lattice explain some of the properties of metals. Conduct Electric Current Malleability Electrical Current – flow of charged particles Lattice of metals is flexible unlike the lattice of ionic bonds Metal ions are able to shift Does not shatter b/c it is still held together by the ion attraction

III. A LLOYS o Alloy – a mixture of two or more elements, one must be a metal o Have properties of metals o Scientist can design alloys with specific properties by varying the types and amounts of elements in the alloy. A. Copper Alloys o Copper is very soft, but when mixed together with tin it makes bronze and brass  the metals become much harder and stronger.

III. A LLOYS A. Copper Alloys B. Steel Alloys o 1900s considered the age of steel due to the demand for bridges, skyscrapers, and automobiles. o Contains iron and small amounts of carbon. o The carbon fills in the iron lattice to make it stronger. o Type of steel depends on the percentage of iron and carbon used. o Would the steel used for the cables of a bridge be the same kind of steel used in the towers of a bridge? C. Other Alloys o Airplanes must be large, but light and thin.

N AMING C OMPOUNDS AND W RITING F ORMULAS Chapter 6.3