The Atom Subatomic Particles What we knew by

The Atom & Subatomic Particles

What we knew by 1932: electron proton neutron Relative Charge Relative Mass 0 e -1 0. 0005486 amu (or 0 amu) or 1 H +1 1. 0073 amu (or 1 amu) 0 1. 0087 amu (or 1 amu) -1 1 p 1 1 1 n 0

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

Atomic Number atomic number: = 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 12 C 6 • left superscript is mass number • left subscript is atomic number

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

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

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

19 F Mass number is ? 19 Atomic number is ? 9 # of neutrons is ? 19 – 9 = 10 # of electrons in atom is? 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 0 1 proton, so it must have ? H-3: neutrons mass # = 3 1 proton, so it must have ? neutrons 1 2

Consider U-234, U-235, & U-238 What’s the atomic number of U? How many protons in U? 92 92 How many neutrons in U-234? 234 – 92 = 142 How many neutrons in U-235? 235 – 92 = 143 How many neutrons in U-238? 238 – 92 = 146 How many electrons in U? 92

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

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

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+1 1 Lost 1 e- 11 p, 12 n, 10 e 34 S-2 16 Got 2 e- 16 p, 18 n, 18 e Lost 2 64 Zn+2 Lost 2 30 ee 12 p, 13 n, 10 e 30 p, 34 n, 28 e 25 Mg+2 12 Got 1 e 9 p, 10 n, 10 e 19 F-1 9 Got 3 e 7 p, 6 n, 10 e 13 N-3 7

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