CHAPTER 2: ATOMS, MOLECULES AND IONS DALTON's ATOMIC THEORY -matter (element) is composed of indivisible and indestructible particles termed atoms -all atoms of the same element are identical. atoms of different elements are different including different masses
-compounds are formed by the joining of two or more atoms of different elements. A cpd. always has the same relative number and types of atoms (Law of Constant Composition) -in a chem. Rx. atoms are rearranged but are not created or destroyed (Law of Conservation of Mass)
NUCLEAR ATOM -atom is divisible, discovery of negative particle termed electron (β rays) -for atom to be neutral there must be positive particle, proton -most of mass and all of positive charge is in small region termed nucleus -A neutral particle, neutron, must exist to hold nucleus together Summary of early
experiments (Thompson, Rutherford, Millikan) on Atomic Structure
Radioactivity-the spontaneous emission of particles and energy from atomic nuclei
particle amu charge electron.0005486-1 proton 1.0073 +1 neutron 1.0087 0 Atomic Mass Unit (amu) scale. 1amu= 1.66054x10-24 g (both the proton and neutron have masses of 1 amu) A relative mass scale for atoms based on the assigned value of exactly 12 for the mass of 12 C.
ATOMIC NUMBER, Z- the number of protons in the nucleus. (All atoms of the same element have Z in common. For a neutral atom the number of electrons equals Z.) MASS NUMBER, A-The number of protons and neutrons in the nucleus of an atom. Give the
number of protons, neutrons and electrons for the following neutral atoms 12 C, 31 P, 238 U, 235 U A neutral atom contains the same # of electrons as protons ISOTOPES- two atoms of the same element that differ in the number of neutrons in the nucleus. Calc of Av Atomic Weight
Calculate the average atomic mass (atomic weight) of boron from the following data. (see other example) isotope mass %occ 10 B 10.0129 19.91 11 B 11.0093 80.09 Someone pays you and your roommate $100.00 to paint their garage. Calculate your share. Would you like to recalculate your share if
you did 90% of the work? Elements -metals -metalloids (semimetals) -nonmetals
The PERIODIC TABLE organizes the elements into columns (vertical) termed groups or families and rows (horizontal) termed periods. Elements in the same family have similar chemical properties while properties of the elements change greatly across a period. Periodicity (repeating)
Molecular Formulaindicates the actual number and type of atoms in a pure substance Empirical Formulaindicates the relative number and type of atoms in a pure substance Structural Formula - indicates the order of connection of the atoms in a pure substance
Two major types of compounds MOLECULAR COMPOUNDS compounds composed of molecules (non-metals) IONIC COMPOUNDS-a cpd formed by the combination of cations (metals) and anions (non-metals) (electrostatic attraction) CATION-an atom (or group
of atoms) with a positive charge resulting from loss of electron(s) (metals normally form cations) ANION- an atom (or group of atoms) with a negative charge resulting from gain of electron(s) (non-metals normally form anions) MONATOMIC ION- an ion containing a single atom(many in Table 2.4) POLYATOMIC ION - an ion
that contains two or more atoms bonded together (many in Table 2.5) GUIDELINES FOR FORMULATING SIMPLE IONIC COMPOUNDS -Ionic cpds are neutral. The charges of cations and anions balance -Metals lose electrons to form cations (complete loss of valence electrons)
-Non-Metals gain electrons to form anions. The number gained is 8-group num.
VALENCE ELECTRONS - the outermost and most chemically important electrons of an atom. The number of valence electrons (for main group elements) is given by the group number. PREDICT THE FORMULAS OF ALL OF THE IONIC CPDS FORMED USING THE FOLLOWING IONS
CATION ANION Na + Cl - Mg 2+ O 2- Al 3+ 3- PO 4 PROPERTIES OF IONIC COMPOUNDS -solids, lattice -high melting point -conduct electricity in molten state or if dissolved in water, but not in solid ELECTROLYTE- a substance that conducts electricity when molten or
in solution NOMENCLATURE, IONIC -name cation 1 st anion 2 nd -name of main group cations is the same as the name of the element -name of transition metal cation is name of element with charge given as a roman numeral in ( ) -monatomic anions use the
name of the element altered so that it ends in -ide (for example) nitrogen nitride N 3- oxygen oxide O 2- sulfur sulfide S 2- halogen halide X - -names, formulas, and charges of polyatomic ions must be memorized (TABLE 2.5)
Name the following molecular compounds CO 2 CO PF 3 PF 5 NO 2 N 2 O 4
NOMENCLATURE, BINARY MOLECULAR CPDS - elements normally listed in order of GROUP NUM. (except NH 3 CH 4 ) -name of second non-metal altered to end in -ide -number of times of occurrence indicated by the use of a prefix 1 mono 2 di
3 tri 4 tetra 5 penta 6 hexa Names of common acids, H a X are given on page 64 and will be used in Chapter 4.
Examples of names of ionic compounds
Nomenclature, Ionic and Molecular Formulate and name all the ionic compounds formed from: -Name cation 1 st anion 2 nd -name of main group cations is the same as the name of the element -name of transition metal cation is name of element with charge given as a roman numeral in ( ) -monatomic anions use the name of the element altered so that it ends in -ide -names, formulas, and charges of polyatomic ions must be memorized, (TABLE 2.5) cation anion Na + Cl - Mg 2+ O 2- Al 3+ 3- PO 4 NaCl sodium chloride Na 2 O sodium oxide Na 3 PO 4 sodium phosphate MgCl 2 magnesium chloride MgO magnesium oxide Mg 3 (PO 4 ) 2 magnesium phosphate AlCl 3 aluminum chloride
Al 2 O 3 aluminum oxide AlPO 4 aluminum phosphate With transition metals: M + M(I) M 2+ M(II) M 3+ M(III) examples CuClO 4 copper(i) perchlorate Cu(ClO 4 ) 2 copper(ii) perchlorate
Fe(NO 3 ) 2 iron(ii) nitrate Fe(NO 3 ) 3 iron(iii) nitrate Examples of names of binary molecular compounds CO 2 carbon dioxide CO carbon monoxide PF 3 phosphorous trifluoride PF 5 phosphorous pentafluoride NO 2 nitrogen dioxide N 2 O 4 dinitrogen tetroxide