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2: Homework Solutions

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    Elements and Atomic Structure

    (1) The electron weighs the least. The protons and neutrons are found in the nucleus.

    (2) Argon because it has more electrons and some of those electrons occupy the larger higher energy 3rd shell.

    (3) a. Z = 8; O; atomic oxygen b. Z = 27; Co; cobalt c. Z = 33; As; arsenic d. Z = 59; Pr; praseodymium e. Z = 90; Th; thorium

    (4) a. 9 b. 12 c. 53 d. 29 e. 14

    (5) a. P b. Ir c. Mo d. Be e. Es

    (6) The elements lower in the column because they have more electrons and some of those electrons occupy larger higher energy shells.

    (7) The number of protons determines the identity of an atom. The number of electrons can be lost or gained to form an ion of the same element. Isotopes are atoms of the same element with the same number of protons (same Z) and a different number of neutrons (different A).

    (8) A = mass number = # p + #n which is different from the atomic number = Z = # p only.

    (9) Isotopes are atoms of the same element with the same number of protons (same Z) and a different number of neutrons (different A).

    (10) carbon-11: Z = 6; 6 protons, 5 neutrons; 6 electrons; A = 11

    carbon-12: Z = 6; 6 protons, 6 neutrons; 6 electrons; A = 12

    carbon-13: Z = 6; 6 protons, 7 neutrons; 6 electrons; A = 13

    carbon-14: Z = 6; 6 protons, 8 neutrons; 6 electrons; A = 14

    (11) All isotopes of nitrogen have the same atomic number (Z = 7). Yes, all isotopes of the same element have the same Z.

    (12) Within a group, the smallest elements are at the top and the largest are at the bottom.

    (13) Both C-12 and C-14 have atomic numbers of 6, but the mass number for C-12 is only 12 while the mass number of C-14 is 14. C-14 has two more neutrons than C-12. The average atomic mass of carbon is closer to C-12 indicating it is the most abundant isotope.

    (14) 20984Po

    Periodic Table of Elements

    (15) Column 1 is the alkali metals. Column 2 is the alkaline earth metals. Columns 3 - 12 are the transition metals.

    (16) Column 17 is the halogens. Column 18 is the Noble gases.

    (17) The transition metals can exist in more than one charge state. They have variable charge.

    (18) a) C

    b) P

    c) P

    d) P

    e) C

    (19) metal: Mn; U

    metalloid: Si

    non-metal: B, P

    (20) Using the given clues, determine the identity of the following elements:

    a) Sc

    b) He

    c) B

    d) At

    e) Bi

    (21) a) 7 b) 3 c) 5 d) 2 e) 4

    (22) Alkali metals have only 1 valence electron. Noble gases have 8 valence electrons.

    Additionl Questions

    23. 2.69 × 107 Na atoms (Note: The diameter of each atom is twice the radius.)

    24. 2.18 x 1010 Os atoms

    25. NaF sodium fluoride; NaBr sodium bromide; NaI sodium iodide

    26. MgS magnesium sulfide; MgSe magnesium selenide


    2: Homework Solutions is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.

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