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Section 4-1

A B C D. Section 4.1 Assessment. Who was the first person to propose the idea that matter was not infinitely divisible? A. Aristotle B. Plato C. Dalton D. Democritus. Section 4-1. A B C D. Section 4.1 Assessment. Dalton’s theory also conveniently explained what?

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Section 4-1

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  1. A B C D Section 4.1 Assessment Who was the first person to propose the idea that matter was not infinitely divisible? A.Aristotle B.Plato C.Dalton D.Democritus Section 4-1

  2. A B C D Section 4.1 Assessment Dalton’s theory also conveniently explained what? A.the electron B.the nucleus C.law of conservation of mass D.law of Democritus Section 4-1

  3. A B C D Section 4.2 Assessment Atoms are mostly ____. A.positive B.negative C.solid spheres D.empty space Section 4-2

  4. A B C D Section 4.2 Assessment What are the two fundamental subatomic particles found in the nucleus? A.proton and electron B.proton and neutron C.neutron and electron D.neutron and positron Section 4-2

  5. A B C D Section 4.3 Assessment An unknown element has 19 protons, 19 electrons, and 3 isotopes with 20, 21 and 22 neutrons. What is the element’s atomic number? A.38 B.40 C.19 D.unable to determine Section 4-3

  6. A B C D Section 4.3 Assessment Elements with the same number of protons and differing numbers of neutrons are known as what? A.isotopes B.radioactive C.abundant D.ions Section 4-3

  7. A B C D Section 4.4 Assessment A reaction that changes one element into another is called what? A.chemical reaction B.beta radiation C.nuclear reaction D.physical reaction Section 4-4

  8. A B C D Section 4.4 Assessment Why are radioactive elements rare in nature? A.They do no occur on Earth. B.Most have already decayed to a stable form. C.They take a long time to form. D.They are too hard to detect. Section 4-4

  9. Section 4.1 Early Ideas About Matter Key Concepts • Democritus was the first person to propose the existence of atoms. • According to Democritus, atoms are solid, homogeneous, and indivisible. • Aristotle did not believe in the existence of atoms. • John Dalton’s atomic theory is based on numerous scientific experiments. Study Guide 1

  10. Section 4.2 Defining the Atom Key Concepts • An atom is the smallest particle of an element that maintains the properties of that element. • Electrons have a 1– charge, protons have a 1+ charge, and neutrons have no charge. • An atom consists mostly of empty space surrounding the nucleus. Study Guide 2

  11. Section 4.3 How Atoms Differ Key Concepts • The atomic number of an atom is given by its number of protons. The mass number of an atom is the sum of its neutrons and protons. • atomic number = number of protons = number of electrons • mass number = atomic number + number of neutrons • Atoms of the same element with different numbers of neutrons are called isotopes. • The atomic mass of an element is a weighted average of the masses of all of its naturally occurring isotopes. Study Guide 3

  12. Section 4.4 Unstable Nuclei and Radioactive Decay Key Concepts • Chemical reactions involve changes in the electrons surrounding an atom. Nuclear reactions involve changes in the nucleus of an atom. • There are three types of radiation: alpha (charge of 2+), beta (charge of 1–), and gamma (no charge). • The neutron-to-proton ratio of an atom’s nucleus determines its stability. Study Guide 4

  13. A B C D Whose work led to the modern atomic theory? A.Dalton B.Rutherford C.Einstein D.Aristotle Chapter Assessment 1

  14. A B C D Which particle is not found in the nucleus of an atom? A.neutron B.proton C.gamma ray D.electron Chapter Assessment 2

  15. A B C D Two isotopes of an unknown element have the same number of: A.protons B.neutrons C.electrons D.both A and C Chapter Assessment 3

  16. A B C D Lithium has an atomic mass of 6.941 and two isotopes, one with 6 neutrons and one with 7 neutrons. Which isotope is more abundant? A.6Li B.7Li C.Both isotopes occur equally. D.unable to determine Chapter Assessment 4

  17. A B C D What happens when an element emits radioactive particles? A.It gains energy. B.It gains neutrons. C.It loses stability. D.It loses energy. Chapter Assessment 5

  18. A B C D What is the smallest particle of an element that still retains the properties of that element? A.proton B.atom C.electron D.neutron STP 1

  19. A B C D How many neutrons, protons, and electrons does 12454Xe have? A.124 neutrons, 54 protons, 54 electrons B.70 neutrons, 54 protons, 54 electrons C.124 neutrons, 70 protons, 54 electrons D.70 neutrons, 70 protons, 54 electrons STP 2

  20. A B C D The primary factor in determining an atom's stability is its ratio of neutrons to ____. A.protons B.electrons C.alpha particles D.isotopes STP 3

  21. A B C D What is the densest region of an atom? A.electron cloud B.nucleus C.isotopes D.atomic mass STP 4

  22. A B C D Why are electrons attracted to the cathode in a cathode ray tube? A.The cathode is more stable. B.The cathode has a positive charge. C.The cathode has a negative charge. D.The cathode has no charge. STP 5

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