Section Review Answers Chapter 4 Section 1 1. Everything in the ...

Section Review AnswersChapter 4Section 11. Everything in the universe is made up of indivisibleunits called atoms.2. Elements are made of tiny, unique particlescalled atoms. Atoms cannot be divided. Atoms ofthe same element are identical. Atoms of differentelements can join to form molecules.3. Dalton had experimental evidence to support histheory, while Democritus did not.4. In Thomson’s model, electrons are embeddedin a sphere of positive charge. In Rutherford’smodel, positive charge is concentrated in thenucleus (the dense core of the atom), and electronssurround the nucleus.5. a. Because air was removed from the tube, thebeam of negative particles observed by Thomsonmost likely came from the atoms of the cathode.This suggests that atoms are made up of smallerunits, including negative charges.b. The observation that positive particles weredeflected at large angles suggested that positivecharge is concentrated at the center of the atom,in the nucleus.6. No, the atom is not indivisible. It is made up ofsmaller parts, such as the electron.Section 21. The proton is positive, the electron is negative,and the neutron is neutral. Protons and neutrons

are found in the nucleus and are massive(m = 1.67 _ 10–27 kg) compared to the electrons(m = 9.11 _ 10–31 kg), which are found outsidethe nucleus.2. Atomic number is the number of protons only.The number of electrons equals the numberof protons in a neutral atom. Mass number isthe total number of protons and neutrons. Thenumber of neutrons is found by subtracting theatomic number from the mass number.3. The proton defines the element because eachelement always has the same number of protons,while the number of neutrons and electrons canvary.4. Atoms of the same element can have differentmasses because they can have different numbersof neutrons. These “versions” of each element arecalled isotopes.5. a. 14 – 6 = 8b. 15 – 7 = 8c. 35 – 16 = 19d. 45 – 20 = 256. The unified atomic mass unit (u)7. Avogadro’s constant is 6.022 _ 1023/mol. Itis the number of particles in one mole of asubstance.8. a. 54.94 g/mol Mnb. 112.41 g/mol Cdc. 74.92 g/mol Asd. 87.62 g/mol Sr9. Yes. The atom is normally neutral becausethe protons and electrons are balanced. If an

3. When an electron jumps between levels, theatom either gains or loses energy in the formof photons.4. The third energy level can hold 18 electrons:2 in the s orbital, 2 in each of 3 p orbitals (for6 total), and 2 in each of 5 d orbitals (for 10total).5. Each rung of the ladder represents an energylevel. Electrons can be only on the rungs, notbetween rungs. A ladder is not a good modelfor an atom because electrons exist in threedimensionalorbitals.6. In Bohr’s model, the electrons travel alongfixed paths. In the modern model, electronsbehave more like waves on a string than likeparticles.7. Nitrogen has 7 electrons, so there are 2 inthe first level and 5 in the second level. Thus,nitrogen has 5 valence electrons.End of chapter Review AnswersUsing Key Terms2. In the nucleus, a silicon atomhas 14 protons, and it usually has14 neutrons. A silicon atom has14 electrons, four of which arevalence electrons.3. Atomic number tells the numberof protons in the atom. All atomsof the same element have thesame number of protons, so theyhave the same atomic number.The mass number is the totalnumber of protons and neutrons

in an atom. The number of neutronscan vary, so the mass numbercan vary among atoms of thesame element. These differentatoms are called isotopes.4. The molar mass is the mass ofone mole, or 6.022 _ 1023 particles,of the element.5. An orbital is a region in the atomwhere there is a high probabilityof finding electrons.Understanding Key Ideas6. a7. b8. d9. c10. a11. b12. b13. cMath Skills27. 1.5 g Fe _ 1 mol Fe/55.85 g Fe = 0.027 mol Fe28. 15.1 mol Al _ 26.98 g Al/1 mol Al = 407 g Al