Types of bonding Ionic bonds Covalent bonds Metallic bonds Chemical bonding Why do atoms bond They lower the potential energy between the charged particles that compose atoms A chemical bond forms when the potential energy of the bonded atoms is less than the potential energy of the separate atoms Nuclear to nucleus repulsions Electron to electron repulsions Nucleus to electron attractions Metal and non metal ionic bond electrons transferred Nonmetal and nonmetal covalent bond electrons share Metal and metal metallic bond electrons pooled When a metal atom loses electrons it becomes a cation When a nonmetal atom gains electrons becomes Nonmetal atoms have relatively high ionization energies so it is dif cult to remove electrons from them When nonmetals bond together it is better in terms of potential energy for the atoms is to share valence electrons Shared electrons hold the atoms together attracting nuclei of both atoms Relatively low ionization energy of metals allows them to lose electrons easily Metal atoms releasing their valence electrons to be shared as a pool by all the atoms or ions in the metal Organization of metal cation islands in sea of electrons Electrons delocalized throughout metal structure Metallic bonding vs properties of metals Delocalized electrons are able to move through metallic crystal metallic solids conduct electricity Heating will cause the metal ions to vibrate faster and will therefore make it more dif cult for the electrons to travel through the crystal as temperature increases the electrical conductivity of metal decreases Metallic solids conduct heat well Metallic solids re ect light Metallic solids are malleable and ductile Metals generally high melting points and boiling points Valence electrons are most important I bonding Valence electrons and bonding Lewis bonding theory Or electron dot structures Emphasizes valence electrons to explain bonding Allows to draw models called Lewis structures Lewis structures predict molecular stability shape size and polarity Atoms bond because it results in a more stable electron con guration Transfer or share electrons All atoms obtain an outer shell with eight electrons Octet rule Some exceptions Determining the number of valence electrons in an atom The column number on the periodic table is the number of valence electrons 1A Li 1e 2A Be 2e Lewis structure of atoms The valence electrons are represented as dots surrounding symbol of element Example Lewis structure for arsenic As is in column 5A therefore has 5 valence electrons Lewis structure of ions Cations have Lewis symbols without valence electrons Anions have Lewis structure with eight valence electrons Octet rule When atoms bond they tend to gain or lose or share electrons to result in eight valence electrons Noble gas con guration Ns2 np6 Exceptions He two valence elections duet H Li Be B attain an electron con guration like He Expanded offers for elements in period 3 or below Using empty valence d orbitals Lewis theory and ionic bonding Electrons are transferred until metal loses all its valence electrons and nonmetal achieves octet Lewis theory of covalent bonding Single covalent bonds Share their valence electrons with other atoms Shared electrons count towards each atom s octet Bonding pairs Lone pairs or no bonding pairs 2 atoms share one pair of electrons One atom may use more than one single bond to ll octet Double covalent bond Four electrons Triple covalent bonds Six electrons Predicting power of Lewis theory Covalent compounds molecular compounds compounds of non metals Hydrogen and halogens are all diatomic molecules Oxygen forms two single bonds or a double bond Reminder Covalent bonding vs properties or covalent compounds Attractions between atoms are directional Covalently bonded compounds will be found as individual molecules Covalent compounds are made of individual molecule units Melting and boiling points of molecular compounds are very low Covalent compounds are found in all three states at room temp Molecular compounds do not conduct electricity in solid or liquid state Molecular acids conduct electricity when dissolved in water but not in the solid or liquid state due to them being ionized by the water The more electrons two atoms share the stronger the bond should be Bond strength is measured by how much energy is needed to break the bond The more electrons two atoms share the shorter the bond should be Bond length is determined by measuring the distance between nuclei of bonded atoms Polar covalent bonding Covalent bonding between unlike atoms results in unequal sharing of the electrons Result is polar covalent bond One atom pulls the electrons in the bond closer to its side One end of the bond has large electron density than other When comparing bonds to like atoms Bond polarity Most bonds have some degree of sharing and some degree of ion formation to them Bonds are covalent if the amount of electron transfer is not enough for material to display classic properties of ionic compounds Bonds are polar covalent if the sharing is not the same enough to produce a dipole in the bond Electronegativity The ability of an atom to attract bonding electrons to itself Increases across period Decreases down group F is the most electronegative element Fr is the least electronegative element Noble gases are not assigned values Opposite of atomic size trend The larger the difference in electro negativity the more polar the bond Electro negativity difference and bond type If difference in electro negativity between bonded atoms is 0 the bonds is pure covalent If difference is 0 1 to 0 4 non polar covalent 0 5 to 1 9 polar covalent 2 0 or higher ionic Bond polarity Bond dipole moments Dipole moment is a measure of bond polarity Dipole moment is a particle with a and end Directly proportional to size of the partial charges and directly proportional to the distance between them Dipole moment q r Measured in Debeyes D More elections two atoms share and larger two atoms are the larger the dipole moment 1 Do not need to know percent ionic Haracter Lewis structures of molecules Lewis theory predicts that atoms will be most stable when they have their octet of valence electrons Does not require that atoms have same number of lone pair electrons they had before bonding Send atoms commonly violate octet rule Lewis structures C 4 bonds 0 lone N 3 bonds 1 lone O 2 bonds 2 lone pairs H and Halogen 1 bond Be 2 bonds and 0 lone B 3 bond 0 lone Ex