The Atom Subatomic Particles Atomic Number atomic number

The Atom & Subatomic Particles

Atomic Number atomic number: equal to size of nuclear charge equal to number protons determines identity element determines order on periodic table for neutral atoms: # of protons equals # of electrons

What is an atom composed of?

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

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

Isotopes atoms of same element: different # neutrons (mass # is different) # protons stays same! (atomic # is same) How Dalton’s theory was modified: 1. 2. atom is divisible (protons, neutrons, electrons) atoms of same element can be different (different # neutrons)

Mass Number mass number is equal to: # protons added to # 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 (mass #) - 6 (atomic #) 6 neutrons

17 O 8 mass number is ? 17 atomic number is ? 8 # of neutrons is ? 17 – 8 = 9 # of electrons in atom is? 8

15 N 7 mass number is ? 15 atomic number is ? 7 # of neutrons is ? 15 – 7 = 8 # of electrons in atom is? 7

Other Notations might also see: F-19 number following symbol is mass number! need to look up atomic number 19 F

What’s the difference between H-1, H-2, and H-3? All H’s must have 1 proton H-1: mass # = 1 1 proton, 0 neutrons H-2: mass # = 2 1 proton, 1 neutrons H-3: mass # = 3 1 proton, 2 neutrons

Consider U-234, U-235, & U-238 what’s the atomic number of U? 92 how many protons in U? 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

IONS atoms: electrically neutral so. . . # electrons EQUAL # protons IONS are atoms that gained or lost electrons protons & electrons ARE NOT equal anymore, so ions are not neutral they carry a charge (+/-)

IONS to calculate charge of ion: # protons minus # electrons

IONS If atom loses electrons, it has more positive charge than negative (#p+ > #e-) what is sign of ion formed? positive If atom gains electrons, it has more negative charge than positive (#e- > #p+) negative what is sign of ion formed ?

Charge of Ions Ion charge written as 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 11 lost 1 e- 11 p, 12 n, 10 e 25 Mg+2 12 lost 2 e- 12 p, 13 n, 10 e- 34 S-2 16 gain 2 e- 16 p, 18 n, 18 e 64 Zn+2 30 lost 2 e- 30 p, 34 n, 28 e-

What is an amu? atomic mass unit amu 1/12 mass of C-12 atom C-12: used as reference for atomic mass