Question

chemistry ch 04&05 - atomic structure (& electrons in atoms) review part b true - false classify each of these statements as always true, at; sometimes true, st; or never true, nt. 11. the atomic number of an element is the sum of the protons and electrons in an atom of that element. 12. the atomic number of an atom is the total number of protons in an atom of that element. 13. an atom of nitrogen has 7 protons and 7 neutrons. 14. relative atomic masses are expressed in amu or u. 15. the number of neutrons in the nucleus can be calculated by subtracting the atomic number from the mass number. part c matching match each description in column b to the correct term in column a column a column b 16. atomic number a. atoms that have the same number of protons but different numbers of neutrons 17. mass number b. weighted average mass of the atoms in a naturally occurring sample of an element 18. isotopes c. equals the number of neutrons plus the number of protons in an atom 19. atomic mass unit (amu) d. 1/12th the mass of a carbon - 12 atom 20. atomic mass e. the number of protons in the nucleus of an atom of an element

Explanation:

Part B

11.

The atomic number is the number of protons only, not the sum of protons and electrons. So it is never true (NT).

12.

By definition, the atomic number of an atom is the total number of protons in an atom of that element. So it is always true (AT).

13.

Most nitrogen - 14 atoms have 7 protons and 7 neutrons, but there are other nitrogen isotopes. So it is sometimes true (ST).

14.

Relative atomic masses are indeed expressed in amu (atomic mass units) or u. So it is always true (AT).

15.

The formula for calculating the number of neutrons $n$ is $n = A - Z$, where $A$ is the mass number and $Z$ is the atomic number. So it is always true (AT).

Part C

16.

The atomic number equals the number of protons in the nucleus of an atom of an element. So it matches with e.

17.

The mass number equals the number of neutrons plus the number of protons in an atom. So it matches with c.

18.

Isotopes are atoms that have the same number of protons but different numbers of neutrons. So it matches with a.

19.

An atomic mass unit (amu) is defined as 1/12th the mass of a carbon - 12 atom. So it matches with d.

20.

The atomic mass is the weighted average mass of the atoms in a naturally occurring sample of an element. So it matches with b.

Answer:

Part B

1. NT
2. AT
3. ST
4. AT
5. AT

Part C

1. e
2. c
3. a
4. d
5. b