CHEMICAL BONDING • COVALENT BONDS • IONIC BONDS • METALLIC BONDS Metallic Bonds • How atoms are held together in solid metals. • Metals hold onto their valence electrons very weakly. • Think of them as positive ions floating in a sea of electrons. Sea of Electrons • Electrons are free to move through the solid. They are shared with all the bonded atoms of the metal. + + + + + + + + + + + + Characteristic of Metallic Bonds • High electrical and thermal conductivity • Malleable, ductile, high luster. • Great amount of heat needed to break these bonds. IONIC BONDING When an atom of a nonmetal takes one or more electrons from an atom of a metal, both atoms end up with eight valence electrons IONIC BONDING IS THE COMPOUND AN IONIC COMPOUND? METAL NONMETAL SUBSCRIPTS IONIC BOND FORMATION IONIC BONDING ION – any atom with more or less electrons that it is supposed to have* *Remember that the number of electrons is supposed to be equal to the number of Protons if the atom has a neutral charge IONIC BONDING Metals will tend to lose electrons and become POSITIVE CATIONS Normal sodium atom loses one electron to become sodium ion IONIC BONDING +1 Na is called a sodium ion The +1 symbol means it has lost one electron IONIC BONDING Nonmetals will tend to gain electrons and become NEGATIVE ANIONS Normal chlorine atom gains an electron to become a chloride ion IONIC BONDING Cl-1 is called a chloride ion The -1 symbol means it has gained one electron Properties of Ionic Compounds • Hard, brittle solids. • Stronger bond than covalent bond. • Most dissolve in water • Conduct electricity when dissolved in water. • High melting/ boiling pointsbecause of strong forces between ions. Crystalline structure The POSITIVE CATIONS stick to the NEGATIVE ANIONS, like a magnet. + + - - + + + - + - + - + - + COVALENT BOND FORMATION When one nonmetal shares one or more electrons with an atom of another nonmetal so both atoms end up with eight valence electrons COVALENT BONDING IS THE COMPOUND A COVALENT COMPOUND? NONMETAL NONMETAL YES since it is made of only nonmetal elements Polar Bonds • When two different atoms are connected, the electrons may not be shared equally. • This is a polar covalent bond. pages.uoregon.edu Nonpolar Bonds • When the atoms in a bond are the same, the electrons are shared equally. • This is a nonpolar covalent bond. 800mainstreet.com Characteristics of Covalent Bonds • Represented by Lewis structures • Strong bond but weaker than Ionic bonds • Low melting points & boiling points • Most do not dissolve in water • Do not conduct electricity. • Usually in a gas state at room temperature Covalent bonds • Monatomic: contains one atom • Diatomic: contains two atoms • Polyatomic: contains more than one atom. Diatomic Molecules Br.I.N.Cl.H.O.F Bromine (Br2), Iodine (I2), Nitrogen (N2), Chlorine (Cl2), Hydrogen (H2), Oxygen (O2), Fluorine (F2) You must have these memorized!!!! Octet Rule • Octet rule: atoms tend to gain, lose, or share electrons until they are surrounded by 8 valence electrons (4 electron pairs). • Exceptions: • Hydrogen forms bonds in which it is surrounded by only two electrons. • Boron tends to form bonds in which it is surrounded by 6 electrons. • Main group elements in period 3 and up can form bonds with expanded valance shells. Lewis structure rules • 1.Write the element symbol. Around the symbol, draw dots—one for each valence electron. • 2. The dots should be spread over four sides. Dots are not paired until all sides have at least one dot. • 3. It does not matter on which side dots are placed. Example- Hydrogen can be drawn in four ways: Lewis structure rules • 4. The number of valence electrons is equal to the group number for groups 1 and 2. In groups 13 to 18, subtract 10 and that is the number of valence electrons. Multiple bonds in Lewis Structures • Molecules containing carbon (C), nitrogen (N), and/or oxygen (O) may form multiple bonds. • The need for multiple bonds becomes obvious if there are not enough valence electrons to complete octets by adding unshared electron pairs. Double bonds • Produced by sharing two pairs of electrons between two atoms. Triple Bonds • Produced by sharing three pairs of electrons between two atoms. Hybridization of orbitals • The mixing of two or more atomic orbitals of similar energies on the same atom to produce new hybrid atomic orbitals of equal energies • Example: Methane (CH4) • The s and p orbitals have different shapes. • Orbitals join together to form four new orbitals called sp3. MOLECULAR SHAPES OF COVALENT COMPOUNDS VSepR tHEORY What Vsepr means Since electrons do not like each other, because of their negative charges, they orient themselves as far apart as possible, from each other. This leads to molecules having specific shapes. Things to remember •Atoms bond to form an Octet (8 outer electrons/full outer energy level) •Do NOT forget all electron pairs, including unshared electron pairs!!! Linear EXAMPLE: BeF2 •The central atom is represented by A and the atoms bonded to the central atom are B. •The molecule AB2 is linear •Bond Angle = 180° Trigonal Planar EXAMPLE: GaF3 •The molecule AB3 makes an equilateral triangle. •Bond Angle = 120° Tetrahedral EXAMPLE: CH4 •The molecule AB4 makes the shape of a tetrahedral (kind of looks like a pyramid). •Bond Angle = 109.5°