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Atomic Structure

Learn about subatomic particles and atomic structure in this informative guide. Explore topics such as atomic number, isotopes, ions, and more.

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Atomic Structure

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  1. Atomic Structure Subatomic Particles

  2. Henry Mosley - 1913 • Mosley used the cathode ray tube in a slightly different way. • Substituted a denser material in place of the glass and was able to get even higher radiation  X- Rays

  3. He tried 30 different metal targets!

  4. Atomic Number - 1913 • Mosley tried 30 different elements as “STOPPERS.” • Found that the greater the atomic weight of the “stopper,” the shorter the wavelength of the x-rays.

  5. What does any good scientist do? PLOTS THE DATA! • Moseley tried plotting the wavelength of the x-ray vs. the atomic mass of the stopper. Not so nice… • Then he tried correlating the wavelength of the x-ray with an integer, n. Got a very pretty graph.

  6. Mosley’s integer was the atomic number!

  7. Atomic Number • Size of nuclear charge. • Atomic number = # protons in nucleus. • Determines the identity of the element. • Used to order the periodic table. • For neutral atoms • atomic number (#p) = number of electrons.

  8. Henry Mosley Killed in WWI at the age of 28.

  9. What we knew by 1932: -1 1 1 0

  10. What is an a.m.u.? • atomic mass unit • Defined as 1/12th the mass of the C-12 atom • C-12 is used as the reference for atomic masses. • One atom of C-12 has a mass of exactly 12 amu Relative Mass

  11. Location of Subatomic Particles • Electrons located outside nucleus. • Protons & neutrons located inside nucleus. • Protons and neutrons combined are called: nucleons

  12. Mass Number • Mass number = # protons+# neutrons • Always a whole number (no decimals) • Mass number can be estimated from the atomic mass by rounding to the nearest integer. • REMEMBER: Only the # neutrons can vary for any given element. The number of protons must remain the same – it identifies the element!

  13. Isotopes • These are atoms of the same element with a different number of neutrons. The protons are the same! • So Dalton’s theory has been modified in a number of important ways. • The atom is divisible. • Atoms of the same element can be different.

  14. Isotopic Notation 12C 6 • The left superscript is the mass number. • The left subscript is the atomic number. • Sometimes both are given; sometimes only the mass number is given. (You can figure out the atomic number from the P.T.)

  15. Notation 12 = no. of protons + neutrons. 6 = no. of protons. 12C 6 How many neutrons in this atom? 12 – 6 = 6 neutrons

  16. 17O Mass number is ? Atomic number is ? # of neutrons is ? # of electrons in atom is? 17 8 8 17 – 8 = 9 8

  17. 15N Mass number is ? Atomic number is ? # of neutrons is ? # of electrons in atom is? 15 7 7 15 – 7 = 8 7

  18. 19F Mass number is ? Atomic number is ? # of neutrons is ? # of electrons in atom is? 19 9 19 – 9 = 10 9

  19. Hyphen Notation • Might also see C-12. The number following the symbol is the mass number! • You have to look up the atomic number.

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

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

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

  23. IONS Charged Particles

  24. IONS • Atoms electrically neutral # of electrons = # of protons • IONS are atoms that have gained or lost electrons. • The protons and electrons don’t balance out anymore, so ions carry a charge.

  25. IONS • Chargeof ion = #protons - #electrons (We subtract the electrons since they’re negative.)

  26. IONS • If the atom loses electrons, it’s going to have more positive charge than negative. What kind of ion is it? • If the atom gains electrons, it’s going to have more negative charge than positive. What kind of ion is it? Positive (cation) Negative (anion)

  27. Charge of Ions • If we want to specify an ion, we write the charge as a 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 oxide ion with a charge of -2. • If there’s no right superscript, it’s understood to be zero and a neutral atom.

  28. Putting it all together • How many protons, neutrons, & electrons in each of the following: 23Na+1 Got 1 Got 2 Lost 1 34S-2 19F-1 16 9 11 16 p, 18 n, 18 e 9 p, 10 n, 10 e 11 p, 12 n, 10 e Got 3 Lost 2 Lost 2 13N-3 64Zn+2 25Mg+2 30 7 12 7 p, 6 n, 10 e 30 p, 34 n, 28 e 12 p, 13 n, 10 e

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