Chemical Bonds and Compounds

Bonding The Statue of Liberty What is the statue made of? Why is it green if it is made of copper? If pennies are made of copper, why are most of them not green? Bonds

Some matter around us is made of uncombined elements (copper, sulfur, oxygen, and other pure elements) copper sulfur oxygen Statue of Liberty is green because of a compound

formed when copper (Cu), sulfur (S), and oxygen (O) combine chemically (copper sulfate) Bonds The new compound formed now has its own properties Compounds no longer have the properties of the individual elements that make the compound Example Sodium chloride or salt (NaCl) has its

own properties .but as individual elements, the properties are different. Sodium (Na) Chlorine (Cl) Soft, silvery metal that reacts violently with water Greenish-yellow gas that is poisonous Formulas

Chemical Formula Shows the elements that a compound is composed of and the exact number of atoms of each element NaCl = 1 atom of sodium and 1 atom of chlorine H2O = 2 atoms of hydrogen and 1 atom of oxygen *subscript written below subscript *no subscript = 1 atom of an element Practice Familiar Name Sand

Chemical Name Silicon dioxide Formula SiO Element ____________ silicon Number of atoms ______ 1 Element ____________ oxygen Number of atoms ______ 1 Water

Hydrogen oxide H2O hydrogen Element ____________ Number of atoms ______ 2 Element ____________ oxygen Number of atoms ______ 1 Atomic Stability Compounds form because they are

more stable than the individual atoms alone Noble gases are unusually stable and very rarely form compounds ..why??? Atomic Stability They have a filled and stable outer energy level (8 electrons) 1 This is known as the octet rule

1 8 2 3 7 4 6 5 Argon

Valence electrons = 8 The Octet Rule States that atoms of elements gain, lose, or share electrons in order to have 8 electrons in their outer shell Goal is to achieve the stability of the noble gases (which already have 8 electrons in their outer shell, with exception of helium which has 2)

Atomic Stability Chemically stable When outer energy level is complete Atom is stable when outer energy level has 8 electrons (except H and He which need two electrons to be stable) Helium Energy Levels Is an atom of hydrogen stable? No Why not?

It only has 1 electron and needs 1 more to fill its outer energy level and become stable Hydrogen will be more stable when it forms a compound with another element Energy Levels Is an atom of helium stable? Yes Why? It has a full outer energy level (stable) - Helium rarely forms compounds because it already is stable

- Elements in groups 13-17 are short of electrons in their outer energy levels, therefore they easily form compounds to have stable outer energy levels of 8 electrons (Lewis structures practice) Ionic Bonding Goal for bonding: To achieve stability!! Sodium loses one electron and chlorine gains one electron to become stable New inner energy level of sodium becomes the stable outer energy level by losing the single electron

it had in its outer energy level Ions Charged particle that has more or less electrons than protons Cation = Positive ion (loses electrons) Anion = Negative ion (gains electrons)

Ions - Sodium (Na) loses 1 electron and becomes positively charged with a charge of 1+ (cation) - Chlorine (Cl) gains 1 electron and becomes negatively charged with a charge of 1- (anion) Na Cl - Compound NaCl is stable and has a neutral charge because positive and negative charges of

the ions cancel each other Ionic Bonds What keeps the ions together? Force of attraction between the opposite charges of the ions. Does a compound have a charge? No because the charges of the ions must cancel each other (compound is

neutral or have a zero charge) Ionic Bonds In an ionic bond, metals and nonmetals bond Elements that bond ionically are usually across from each other in the Periodic Table http://www.wisc-online.com/

objects/index_tj.asp? objID=GCH2204 Ionic Compounds Covalent Compounds Contain positive and negative ions (Na+Cl-) Exist as neutral molecules (C6H12O2) Solids suchs as table salt (NaCl(s))

Solids, liquids,or gases (C6H12O6(s), H2O(l), CO2(g)) High melting and boiling points Lower melting and boiling points (i.e., often exist as a liquid or gas at room temperature) Strong force of attraction between particles Relatively weak force

of attraction between molecules Separate into charged particles in water to give a solution that conducts electricity Remain as same molecule in water and will not conduct electricity

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