Chemical Bonds Chapter 19 Blue Book Chapter 20 White Book

Oil and Water  Observe the demonstration.  Why do you think the oil didn’t mix with the water?  Why do you think the alcohol did mix with the water?

Combined Elements  Elements combine with other elements to form compounds.  A compound has properties that are different from the elements that made it.

Chemical Formulas  Element symbols are combined into chemical formulas to represent compounds  The chemical formula shows which elements are involved and the exact number of atoms of each element.

Chemical Formulas  Chemical formulas contain element symbols and subscripts.  The subscripts apply to the element that comes before it.  If the element does not have a subscript, there is only 1 atom of that type of element.

Chemical Formula Examples  H 2 O  CH 4  NH 3  C 2 H 5 O 7

Chemical Formulas  Some formulas have parenthesis. Just like you do in math, if there is a subscript outside a parenthesis, the subscript multiplies everything inside the parenthesis.  C 3 (PO 4 ) 4

Why do atoms bond?  Atoms bond to other atoms because the electrons from one atom are attracted to the protons from another atom.  All elements can bond except for the Noble Gases.  The Nobel Gases cannot bond because they have 8 electrons (the maximum) in their outer energy level.

Chemically Stable  An atom is chemically stable if its outer energy level is full.  All elements want to have 8 electrons in its outer energy level (except for Hydrogen which only wants 2).  When an atom gets 8 electrons (or 2 for hydrogen) it will be stable.

Getting Stable  Atoms that do not have full outer levels can lose, gain or share electrons to achieve a full outer shell.  To do this they combine with another atom  Atoms can also combine with multiple atoms to achieve stability

Chemical Bonds  When electrons are shared, lost or gained, the atoms become attracted to each other.  This attraction is called a chemical bond.  A chemical bond is what holds the two atoms together.

Gain or Loss of Electrons  Atoms lose or gain electrons to become stable.  An atom that has lost or gained an electron is called an ion.  An ion has a charge because it has unequal numbers of protons and neutrons.

Ions  When an atom loses an electron, it becomes positively charged  When an atom gains an electron, it becomes negatively charged  The electric force (the force between charged objects) holds the ions together

How many electrons?  To determine how many electrons an element will lose or gain…  Look at the periodic table.  If all elements want to get to 8 or 0, determine if its closer to zero or eight.  If its closer to zero, it will lose and make zero.  If its closer to eight, it will gain and make eight.

Determining Charge  An ions charge is also called its oxidation number.  For every electron the atom loses, the charge goes up by +1  For every electron the atom gains, the charge goes down by -1

Ionic Bond  When two ions combine, it forms an ionic compound.  Occurs between a metal and a nonmetal.  Ionic Bonds produce a neutral compound  A negative ion combines with a positive ion  Sometimes more than two ions must be combined.

Covalent Bonds  When electrons are shared between atoms, it forms a covalent bond.  A covalent bond produces a molecule.  Electrons are always shared in pairs.  If one pair is shared, its called a single bond  If two pairs are shared, it’s a double bond  If three pairs are shared, it’s a triple bond

Polar Molecules  When the electrons are not equally shared it forms a polar molecule  Occurs when one atom is bigger than the other.  A polar molecule has a slightly positive end and a slightly negative end  When the electrons are shared equally, its called a non-polar molecule.

Binary Ionic Compounds  Binary Compounds are compounds made from two different elements.

Writing Formulas  To write the formula for binary ionic compounds, you must look at the oxidation numbers.  The atoms must be combined so that the charge of the compound is neutral.  Simplest way is to find the charge of each element involved, and switch the numbers.

Naming Binary Compounds  The positive element is always written first  The first element’s name stays the same  The ending of the second element is changed to –ide  Oxide  Hydride  Nitride  Chloride

Polyatomic Ions  Polyatomic Ions are ions made from more than one element.  These ions have a charge and are treated like all other ions when writing chemical formulas.  If they have a subscript, put them in parentheses.

Hydrates  An ionic compound that has water chemically attached to it.  Example: NaCl ▪ 7H 2 O

Covalent Molecules  Ionic Compounds have one correct combination for two ions.  Covalent Molecules have multiple (physically) correct combinations.  To distinguish all the molecules made from the same element, prefixes are used.

Prefixes  1 – mono  2 – di  3 – tri  4 – tetra  5 – penta  6 – hexa  7 – hepta  8 – octa

Naming Molecules  The first element gets a prefix if its subscript is bigger than one.  The second element always gets a prefix and its ending gets changed to –ide.