Short answers worksheet grade 8 Short Answer 1. How was Bohr s theory of atomic structure similar to the current theory? 2. How was Bohr s theory of atomic structure different form the current theory? 3. Describe the difference between atomic number and atomic mass. 4. How are protons in the nucleus of an atom able to stay close to one another even though they have the same charge? 5. Compare protons and neutrons. 6. Put the following atomic models in the proper sequence: Rutherford s model, electron-cloud model, plum-pudding model, Bohr s model.
7.Is it possible to have carbon atoms with different numbers of protons? Explain. 8. How is the atomic mass of an element calculated? 9. How do isotopes differ from one another? 10. State the periodic law, which is the basis for the periodic table. 11. Explain why hydrogen is unique. 12. What are three characteristics of metals? 13. How would you describe boron? 14. What are three characteristics of nonmetals? 15. What is sodium chloride and what is it used for?
16. Name three properties of a crystal lattice. 17. How might an atom of oxygen fill its outermost energy level? 18. What are the three types of chemical bonds? 19. List three properties of ionic compounds. 20. List three properties of substances that have covalent bonds. 21. What are three properties of metals that are a result of metallic bonding? ----------- ----------- ----------- ----------- WITH MY BEST WISHES
Short answers worksheet grade 8 Answer Section SHORT ANSWER 1. ANS: Bohr s theory and the current theory both have electrons traveling in orbits around a central nucleus. 2. ANS: In Bohr s theory, the electrons move only in definite paths. Current atomic theory expresses the position of electrons in terms of the probability that electrons will be found in regions of the atom called electron clouds. 3. ANS: The atomic number is the number of protons in an atom. Atomic mass is the sum of the number of protons and neutrons in an atom of a particular isotope. 4. ANS: Protons can stay close to one another inside the nucleus of an atom due to the strong force. Although the electromagnetic force causes particles with the same charge to repel each other, the strong force is greater than the electromagnetic force at close distances. 5. ANS: Protons are positively charged particles in the nucleus of an atom. Neutrons are particles in the nucleus of an atom that have no charge. 6. ANS: plum-pudding model, Rutherford s model, Bohr s model, electron-cloud model 7. ANS: No. All atoms of an element have the same atomic number, the number of protons in the nucleus of an atom. 8. ANS: by taking a weighted average of the mass numbers of the isotopes of that element 9. ANS: in the number of neutrons they have 10. ANS: Answers will vary. Sample answer: The periodic law states that chemical and physical properties of elements are periodic, repeating functions of the elements atomic numbers. This is why elements in vertical groups of the periodic table share similar properties. 11. ANS: Answers will vary. Sample answer: The properties of hydrogen do not match the properties of any single group.
12. ANS: Answers will vary. Sample answer. Most metals are solid at room temperature, have few electrons in their outer energy level, and are shiny. Other possible answers: Most metals are ductile, good conductors of electric current and thermal energy, and are malleable. 13. ANS: Answers will vary. Sample answer: Boron is a metalloid that is almost as hard as a diamond, but is also very brittle. At high temperatures, it is a good conductor of electric current. 14. ANS: Answers will vary. Sample answer: Atoms of nonmetals have an almost complete set of electrons in their outer level. Nonmetals are not malleable or ductile. Other possible answers: Nonmetals are not shiny and are poor conductors of thermal energy and electric current. 15. ANS: Sodium chloride is table salt. It is used to flavor food. 16. ANS: brittleness, high melting point, high boiling point 17. ANS: An atom of oxygen has six valence electrons. In order to fill its outermost energy level, oxygen must gain two electrons or share two electrons with other atoms. 18. ANS: ionic, covalent, metallic 19. ANS: brittleness, high melting points, high boiling points 20. ANS: low melting points, low boiling points, brittle in solid state. 21. ANS: ability to conduct electricity, ability to be reshaped, ability to bend without breaking.