Atomic Structure Wayne County ublic Schools Wayne ：原子結(jié)構(gòu)韋恩縣公立學校的韋恩

1、atomic structurereview the atom is the smallest unit of an element that has the properties of that element. according to rutherfords nuclear model of the atom, the nucleus is tiny, dense, and positively charged.the rest of the atom, which is made of electrons, is very large compared to the nucleus a

2、nd negatively charged.reviewnucleustiny, dense, positively chargedelectron clouddiffuse, negatively charged10-10 m10-15 mcharge and mass elementary charge (e) = 1.6x10-19 coulombscoulomb (c) = si unit of electric chargecharge can be + or -.for conveniences sake, we write +1 instead of +1.6x10-19 c.a

3、lso write -1 instead of -1.6x10-19 c. masses of atoms are measured in atomic mass units (amu).1 amu = 1/12 mass of carbon-12 atom.1 amu = 1.66x10-24 gramssubatomic particlesproton (p+)location: nucleuscharge: +1mass: 1.007 amuneutron (no)location: nucleuscharge: neutralmass: 1.008 amuelectron (e-)lo

4、cation: electron cloud (outside nucleus)charge: -1mass: 0.0005 amuatomic number (z) atomic number (z) number of p+ in the nucleus. atomic number of oxygen = 8all oxygen atoms have 8 p+.no other type of atom has 8 p+. atomic number of uranium = 92all uranium atoms have 92 p+.no other type of atom has

5、 92 p+.mass number (a) mass number (a) combined number of p+ & no. a = p+ + no number of no = a z what is the mass number of an atom that has 8 p+ and 9 no?answer: 8 p+ + 9 no = 17 how many no are in a titanium atom with a mass number of 48 (z = 22 for titanium)?answer: a z = (48 22) = 26 noatom

6、ic and mass numbers what are the atomic and mass numbers of the following atoms?= protons= neutronsz =a =z =a =z =a =z =a =11122437isotopes isotopes have the same number of p+ but diff. numbers of no.example: all carbon atoms have 6 p+. some carbon atoms have 6 no, and some have 7 no. some carbon at

7、oms have a = 12, and some have a = 13.isotopes three isotopes of oxygen:oxygen - 17o - 17o178oxygen - 18o - 18o188oxygen - 16o - 16o168za8 p+8 no8 p+9 no8 p+10 noaverage atomic mass average atomic mass weighted average of the masses of all atoms in a sample. the atomic mass given on the p.t. is a we

8、ighted average.average atomic mass of neonatomic numberavg. atomic masscalculating average atomic mass the element silicon has three naturally-occurring isotopes:isotopeabundancemass (amu)si-2892.23%27.977si-294.68%28.976si-303.09%29.974 what is the average atomic mass of silicon?calculating average

9、 atomic mass what is the atomic mass of silicon?first convert all percentages to decimals: 92.23% 0.9223 4.68% 0.0468 3.09% 0.0309next multiply the decimals by the masses: 0.9223 x 27.977 amu = 25.80 amu (4 sf) 0.0468 x 28.976 amu = 1.36 amu (3 sf) 0.0309 x 29.974 amu = 0.926 amu (3 sf)now add the r

10、esults: 25.80 + 1.36 + 0.926 = 28.09 amu (2 dec. places)this agrees with the mass given on the periodic table.calculating average atomic mass the element chlorine has two naturally-occurring isotopes:isotopeabundancemass (amu)cl-3575.78%34.969cl-3724.22%36.966 what is the average atomic mass of chlo

11、rine?calculating average atomic mass 0.7578 0.2422x 34.969 amux 36.966 amu= 26.50 amu= 8.953 amu35.45 amucalculating average atomic mass iron has four naturally-occurring isotopes:isotopeabundancemass(amu)fe-545.845%53.940fe-5691.754%55.935fe-572.199%56.935fe-580.282%57.933 what is the average atomic ma