The Atom & Subatomic Particles

What we knew by 1932: 1.0087 amu (or 1 amu) neutron 1n 1.0073 amu +1 neutron 1n 1.0073 amu +1 proton 1p or 1H 0.0005486 amu (or 0 amu) -1 electron 0e Relative Mass Relative Charge -1 1 1

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

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

Mass Number = # protons + # neutrons

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

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

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

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

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

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

F 19 Mass number is ? Atomic number is ? # of neutrons is ? # of electrons in atom is? 19 9 19 – 9 = 10 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 H-1: mass # = 1 1 proton, ? neutrons H-2: mass # = 2 1 1 proton, so it must have ? neutrons H-3: mass # = 3 2 1 proton, so it must have ? neutrons

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 92 234 – 92 = 142 235 – 92 = 143 238 – 92 = 146 92

How many neutrons in Po-217? What’s the atomic number? How many protons? So the neutrons are … 84 84 217 – 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 (subtract the electrons since are negative)

IONS If atom loses electrons, it has more (+) protons than (-) electrons What kind of ion is it? If atom gains electrons, it has more (-) electrons than (+) protons 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 23Na+1 Got 2 e- Lost 1 e- Got 1 e- 34S-2 19F-1 9 1 16 16 p, 18 n, 18 e 9 p, 10 n, 10 e 11 p, 12 n, 10 e Lost 2 e- Lost 2 e- 13N-3 Got 3 e- 25Mg+2 64Zn+2 12 30 7 7 p, 6 n, 10 e 30 p, 34 n, 28 e 12 p, 13 n, 10 e

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