Chemical Foundations Notes

Formulas of Compounds 1. Symbols - a.used to represent the element b.first letter is capital, second letter (if necessary) is lower case 2. Subscripts – a.small number to the lower right of the element symbol b.represents the relative composition of each element in a compound or molecule 3. Superscripts – a.small number to the upper right of the symbol/formula b.used to represent the charge of an ion 4. Coefficients – a.big number in front of the formula b.indicates the number of compounds present C = carbonCa = calciumCr = chromium CO 2 = 1 carbon, 2 oxygenBa(NO 3 ) 2 = 1 barium, 2 nitrogen, 6 oxygen Ca +2 NO 3 -1 Br -1 3 CO 2 = 3 carbon dioxide or 3 carbon, 6 oxygen

Modern Concept of the Atom The atom is made of three elementary particles. Protons 1. ____________ charge 2. mass is almost equal to the mass of the ___________ 3. Found in the _____________ 4. Number of protons is __________ to the atomic number Neutrons 1. ____________ charge 2. mass is __________________________ than the proton 3. Found in the _____________ 4. Neutrons act as the glue that holds together the nucleus. - too few or too many neutrons can result in nuclear instability and then radioactivity Electrons 1. ____________ charge 2. mass is ___________________ than the proton 3. Found moving around the nucleus at near the speed of light. - sometimes called _______________________ or ______________________ 4. The Quantum Mechanical Model - currently accepted model of the atom (Chapter 11) - for now we will use the Bohr model, rings of electrons positive neutrons nucleus nucleus equal no or neutral slightly greater negative electron cloud charge cloud 2000 x less

► Atoms are always _____________ ► Isotopes  Atoms with the __________ number of protons but a ______________ number of neutrons  A different number of neutrons results in a different mass.  Mass of individual atoms is determined by only the protons and neutrons, the electrons are too light to be significant. ► Mass Number = __________ + ___________  Isotope notations ► 40 K means that potassium has a mass number of 40 ► Potassium-40 also means a mass number of 40 neutral protons different same neutrons

X = Element symbol Z = Atomic number = # of protons in nucleus = # on periodic table A = Mass number = # of protons + # of neutrons in nucleus Element Symbo l Atomic Number Mass Number Number of Protons Number of Neutrons Number of Electrons Carbon 14 C 6 Chlorine3517 Sodium1112 X A Z Cl Na

Ions When an atom gains or loses an __________________ it takes on a charge and becomes an ion the charge is determined by the #e - (negative charge) when compared to #p + (positive charge) Calcium ions (Ca +2 ) has 20 p + and 18 e - because the calcium atom lost 2 electrons Fluoride ions (F -1 ) has 9 p + and 10 e - because the fluorine atom gained one electron Positive Ions are called _______________ Negative Ions are called _______________ ElementSymbol Atomic Number Mass Number Number of Protons Number of Neutrons Number of Electrons Carbon 14 C +4 6 Chlorine Cl Sodium Na +1 Na Electron Cations Anions