1. Answer Key
Ch. 11 Review Sheet

2. 1. What is an atom?
The smallest particle in which an element can be divided and still be the same substance

3. 2. What particle did J. J. Thomson discover?
The electron

4. 3. Where are electrons most likely to be found?
Electron Clouds

5. 4. What did Dalton believe?
All substances are made of atoms
Atoms cannot be divided, created, or destroyed
Atoms join with other atoms to make new substances
Atoms of the same element are alike and atoms of different elements are different

6. 5. What is the plum-pudding model? What did the plums represent?
J.J. Thomson’s atomic model
Plums represented electrons

7. 84 (mass # = protons + neutrons)
6. What is the mass number of the element with 36 protons, 36 electrons, and 48 neutrons?
(mass # = protons + neutrons)

8. 7. What part of an element has the least mass?
Electron

9. 8. How did Democritus describe atoms?
Small, hard particles that could not be divided; atoms were made of a single material that could be formed into different shapes and sizes.

10. 9. If hydrogen-1 has one proton, how many protons does hydrogen-2 have?

11. 10. How many atoms does a penny have?
2 x 10 22

12. Atoms of the same element that have different numbers of neutrons.
11. What are isotopes?
Atoms of the same element that have different numbers of neutrons.

13. 12. What are radioactive isotopes?
Atoms that have an unstable nucleus that will change over time.

14. Negatively charged particle in an atom
13. What is an electron?
Negatively charged particle in an atom

15. Positively charged particle in the nucleus of an atom
14. What is a proton?
Positively charged particle in the nucleus of an atom

16. A particle with no charge found in the nucleus of an atom
15. What is a neutron?
A particle with no charge found in the nucleus of an atom

17. 16. What is the atomic number?
Number of protons in the nucleus of an atom; it’s also the number of electrons in a neutral atom

18. Weighted average of all the occurring isotopes of an element
What is the atomic mass?
Weighted average of all the occurring isotopes of an element

19. Region in an atom where electrons are likely to be found
18. Define electron cloud.
Region in an atom where electrons are likely to be found

20. A charged particle that forms when an atom loses or gains electrons
19. Define ion.
A charged particle that forms when an atom loses or gains electrons

21. 20. What is a gravitational force?
Force of attraction between two objects

22. 21. What is a weak force?
Force in the nucleus of an unstable atom that allows the nucleus to change.

23. 22. Define atomic mass unit
Unit of mass that describes the mass of an atom or molecule
(SI Unit)

24. 23. What is a strong force?
Force that occurs in the nucleus in order to keep protons from repelling each other.

25. 24. Calculate the number of neutrons in chlorine-37.
Mass #- atomic #
37-17 = 20

26. 25. What is the difference between atomic mass & atomic number?
Atomic mass is weighted average of isotopes of an element; atomic number is the number of protons in an atom of an element.