GENERAL CHEMISTRYREN CORNEJO, ECEREN CORNEJO, ECEPROJECTDATEINSTRUCTORSEPTEMBER 16, 2019GENERAL CHEMISTRYATOMS, MOLECULES AND IONSCHAPTER DESCRIPTIONChapter 2 – Atoms, Molecules, and Ionsdiscusses:1.Dalton’s postulates regarding the existenceof the atom2.Atomic mass—its uses and limitations3.The structure of the atom4.The existence of isotopesCHAPTER DESCRIPTIONChapter 2 – Atoms, Molecules, and Ionsdiscusses:5.The periodic table6.Molecules and Ions7.Chemical Formulas8.Naming CompoundsATOMIC THEORYATOMIC THEORYIn 1804, John Dalton proposed the existence of atoms.
ATOMIC THEORYATOMIC THEORYATOMIC THEORYDalton’s postulates can be used to explain threequantitative laws that had been developed shortly beforehe proposed his theory.ATOMIC THEORYThe Law of Conservation of Mass- states that mass is neither created nor destroyed in achemical reaction or physical change.ATOMIC THEORYThe Law of Definite Proportions- states that every chemical compound is made up ofelements in a definite ratio by mass.ATOMIC THEORYThe Law of Multiple Proportions- states that when two or more different compounds areformed from the same elements, the ratio of masses ofeach element in the compounds for a given mass of anyother element is a small whole number.
ATOMIC THEORYCalculate the mass of sodium chloride formed by thecomplete reaction of 10.0 g of sodium with 15.4 g ofchlorine. What law allows this calculation?Calculate the mass of oxygen that will combine with 2.00 gof magnesium if 0.660 g of oxygen reacts with 1.00 g ofmagnesium. What law allows this calculation?ATOMIC THEORYATOMIC NUMBERATOMIC NUMBERWhat makes an atom of one element different from anatom of another element is that the atoms of each elementhave a characteristic number of protons.Indeed, the number of protons in an atom of any particularelement is called that element’satomic number.ATOMIC NUMBERBecause an atom has no net electrical charge, the numberof electrons it contains must equal the number of protons.All atoms of carbon, for example, have six protons and sixelectrons, whereas all atoms of oxygen have eight protonsand eight electrons.ATOMIC NUMBERThus, carbon has atomic number 6, and oxygen hasatomic number 8.The atomic number is shown by the subscript; thesuperscript, called themass number, is the number ofprotons plus neutrons in the atom.
ATOMIC NUMBERAtoms with identical atomic numbers but different massnumbers are called isotopes of one another.ATOMIC NUMBERAtomic masses are so small that an appropriate unit wasdeveloped to report them—an atomic mass unit (amu).The atomic mass of the lightest element, hydrogen, wasoriginally taken to be 1 amu.1࠵?࠵?࠵?=1.66×10−24࠵?.ATOMIC NUMBERThe modern values of the atomic masses are based onthe most common kind of carbon atom, called “carbon-12”and written 12C, as the standard.