The Atom & Subatomic Particles

What we knew by 1932: amu (or 1 amu) 0 neutron 1 n amu (or 1 amu) +1 proton 1 p or 1 H amu (or 0 amu) electron 0 e Relative Mass Relative Charge

Location of Subatomic Particles electrons located outside nucleus electrons located outside nucleus protons & neutrons located inside nucleus protons & neutrons located inside nucleus

Atomic Number  atomic number: = size of nuclear charge = size of nuclear charge = number of protons in nucleus = number of protons in nucleus determines identity of element determines identity of element gives order to PT gives order to PT  For neutral atoms: atomic number = # protons = # electrons

Mass Number = # protons + # neutrons # protons + # neutrons

Isotopes atoms of same element can have different mass numbers # protons must be the same so … # protons must be the same so … # neutrons must be different # neutrons must be different

Dalton’s theory must be modified: the atom is divisible the atom is divisible presence of subatomic particles presence of subatomic particles atoms of same element can be different atoms of same element can be different isotopes have different # neutrons isotopes have different # neutrons

Notation 12 C 6 left superscript is mass numberleft superscript is mass number left subscript is atomic numberleft subscript is atomic number

Notation 12 C 6 12 = # protons + neutrons 6 = # protons 6 = # protons 12 – 6 = 6 neutrons How many neutrons in this atom?

17 O 8 Mass number is ? Atomic number is ? # of neutrons is ? # of electrons in atom is? – 8 8 = 9

Mass number is ? Atomic number is ? # of neutrons is ? # of electrons in atom is? 15 N – 7 7 = 8

Mass number is ? Atomic number is ? # of neutrons is ? # of electrons in atom is? F – 9 =

Other Notations C-12 # after symbol is mass number!  must look up atomic number

What’s the difference between H-1, H-2, and H-3?  All H’s have 1 proton 1 proton, so it must have ? neutrons H-1: mass # = 1 1 proton, ? neutrons H-2: mass # = 2 1 proton, so it must have ? neutrons H-3: mass # =

Consider U-234, U-235, & U-238  What’s the atomic number of U?  How many protons in U?  How many neutrons in U-234?  How many neutrons in U-235?  How many neutrons in U-238?  How many electrons in U? – 92 = – 92 = – 92 =

How many neutrons in Po-217?  What’s the atomic number?  How many protons?  So the neutrons are … – 84 = 133 neutrons!

IONS IONS = atoms that gained or lost electrons  protons and electrons aren't = anymore, so ions are not neutral they carry a charge (+/-)

IONS  Charge of ion: = # protons minus # electrons = # protons minus # electrons (subtract the electrons since are negative)

IONS  If atom loses electrons, it has more (+) protons than (-) electrons What kind of ion is it? What kind of ion is it?  If atom gains electrons, it has more (-) electrons than (+) protons What kind of ion is it? What kind of ion is it?positive negative

Charge of Ions  Ion charge: right superscript Cl -1 a chloride ion with a charge of -1 Na +1 a sodium ion with a charge of +1 O -2 an oxygen ion with a charge of -2 If no right superscript, it’s understood to be zero and therefore a neutral atom

Putting it all together  How many protons, neutrons, & electrons in each of the following 23 Na Mg S Zn F N p, 12 n, 10 e 12 p, 13 n, 10 e 16 p, 18 n, 18 e 9 p, 10 n, 10 e 30 p, 34 n, 28 e 7 p, 6 n, 10 e Lost 1 e - Got 2 e- Got 1 e- Lost 2 e- Got 3 e-

What is an amu? atomic mass unit atomic mass unit amu  1/12 the mass of the C-12 atom amu  1/12 the mass of the C-12 atom