The Atom & Subatomic Particles

1. The Atom & Subatomic Particles

2. atomic number: • = size of nuclear charge • = number of protons in nucleus • determines identity of element • used to give order to periodic table • For neutral atoms: • atomic number = number of electrons Atomic Number

3. What is an atom?

4. Number of Protons = Number of Electrons Number of Protons = Atomic Number Atomic Mass = Protons + Neutrons

5. Relative Charge Relative Mass Electron, 0e -1 .0005486 amu (or 0 amu)‏ -1 Proton, 1p or 1H +1 1.0073 amu (or 1 amu)‏ 1 1 Neutron, 1n 0 1.0087 amu (or 1 amu)‏ 0 What we knew by 1932:

6. Location of Subatomic Particles • Electrons located outside nucleus • Protons & neutrons located inside nucleus • Protons & neutrons = nucleons

7. atoms of same element with different # neutrons (mass # is different) • # protons stays same! (atomic # is same) • Dalton’s theory modified in number of important ways: • the atom is divisible (protons, neutrons, electrons) • atoms of same element can be different (different # neutrons) Isotopes

8. Mass number = # protons + # neutrons Mass Number

9. 12C Notation 6 • left superscript is mass number • left subscript is atomic number

10. 12 = # protons + neutrons 6 = # protons 12C Notation 6 How many neutrons in this atom? 12 – 6 = 6 neutrons

11. 17 8 17 – 8 = 9 8 17O Mass number is ? Atomic number is ? # of neutrons is ? # of electrons in atom is? 8

12. 15 N 15 7 7 15 – 7 = 8 7 Mass number is ? Atomic number is ? # of neutrons is ? # of electrons in atom is?

13. 19 F 19 9 19 – 9 = 10 9 Mass number is ? Atomic number is ? # of neutrons is ? # of electrons in atom is?

14. Might also see: C-12 • number following symbol is mass number! • Need to look up atomic number Other Notations

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

16. 92 • 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? Consider U-234, U-235, & U-238 92 234 – 92 = 142 235 – 92 = 143 238 – 92 = 146 92

17. 84 • What’s the atomic number? • How many protons? • So the neutrons are … How many neutrons in Po-217? 84 217 – 84 = 133 neutrons!

18. Atoms: electrically neutral so ... # electrons = # protons • IONS = atoms that gained or lost electrons • protons and electrons aren't = anymore, so ions are not neutral they carry a charge (+/-)‏ IONS

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

20. positive negative • If atom loses electrons, it has more positive charge than negative • What kind of ion is it? • If atom gains electrons, it has more negative charge than positive • What kind of ion is it? IONS

21. 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 Charge of Ions

22. Lost 1 Got 2 1 16 p, 18 n, 18 e 11 p, 12 n, 10 e Lost 2 Lost 2 30 p, 34 n, 28 e • How many protons, neutrons, & electrons in each of the following 23Na+1 Putting it all together 34S-2 16 25Mg+2 64Zn+2 12 30 12 p, 13 n, 10 e

23. equal to the atomic mass unit • amu  1/12 the mass of the C-12 atom • C-12 is used as the reference for atomic mass What is an amu?

24. Atomic mass is relative • 1st H-1 used as standard: • 1 atom of H = 1 amu • next O-16 used as standard: • O combines with many elements • 1 atom of O = 16 amu's • Now C-12 is the standard: • 1 atom of C-12 has a mass of exactly 12 amu's Atomic Weight or Mass