Atomic Theory

What is an atom Definition? How does an atom differ from an element? How does a compound differ from an element? What holds the atoms together in an element or compound?

answers Atom – basic unit of matter, contains all of the properties of the larger structures Element - Substance containing only one type of atom Compound – Substance containing at least two different types of atoms Elements and compounds are held together by chemical bonds (electrons)

Properties Which two parts of an atom are located in the nucleus? How are electrons held in an atom? Why do the electrons stay attached and not float off into space? What is an atom called that has gained or lost at least one electron? How does this change its properties? What is an atom called that has gained or lost at least one neutron? How does this chamge its properties?

answers Protons and neutrons Electron orbitals (electron cloud). Held to the nucleus by electro-magnetic force (opposite charges) Ion (affects charge/ interaction with other atoms) Isotope (affects weight/ radioactive decay)

Chemical bonds How do atoms stay connected to form larger structures? What makes up a chemical bond? There is a special name for the electrons used in bonding, what are they called? 3 types of Bonds Ionic Bonds Covalent Bonds Metallic Bonds

Ionic Bonds Electrons are transferred from one atom to another causing oppositely charged atoms. The opposite charges cause an electrical attraction between the two atoms. Occurs between Metals and Non-Metals (gases) Weak bonds: easily broken, but quick to reform Can make multiple bonds to form networks, no limit on number of bonds

                                                      

Covalent Bonds Occurs when two atoms share electrons. Only occurs in non-metals (all gases) Strong bonds: not easily broken, used to store energy Usually non-charged, however unequal sharing can cause slight positive or negative charges (polar) Can form multiple bonds, but number is determined by amount of valence electrons. Can over lap bonds to form double or triple strength.

Electronegativity Term used to refer to how strong an atom can attract electrons. Gases typically have a higher affinity for electrons, so they can pull electrons away from metals. (think rust/ iron oxide) If the electronegativity is close (less than 1.2) than the atoms will share electrons (covalent). If the electronegativity is high (more than 1.8), electrons will transfer forming ionic bonds

Metallic Bonds Similar to covalent bonds, electrons are shared. However the bonding occurs at the lower energy levels (D). This allows multiple energy levels to overlap, creating very strong bonds. Only occurs between two metals

Transfer of electrons Sharing of electrons Weak bonds Strong Bonds Ionic Bonds Covalent Bonds Transfer of electrons Sharing of electrons Weak bonds Strong Bonds Metal and non-metal Two non-metals Enegativity 1.8 or more Enegativity 1.2 or less Examples: Examples: NaCl, CaO, MgF2 CO2, F2, P4S10

Identify MgF2 CaO N2O3 Li3N C6H12O6