1. 4.2 The Structure of an Atom This 45-foot-tall steel sculpture is made of 10 tons of steel. If a proton had the same mass as the sculpture, then an electron would have a mass of about 5 kilograms.

2. 4.2 The Structure of an Atom What are three subatomic particles? Properties of Subatomic Particles Protons, electrons, and neutrons are subatomic particles. Notes

3. 4.2 The Structure of an Atom Protons - Rutherford said the # of positive charges varies in an element - positively charged subatomic particle - found in the nucleus of an atom - each proton is assigned a charge of 1+ - each nucleus must contain at least one proton Properties of Subatomic Particles Notes

4. 4.2 The Structure of an Atom Electrons - Detected by Thomson - negatively charged subatomic particle - found in the space outside the nucleus - each electron has a charge of 1  Properties of Subatomic Particles Notes

5. 4.2 The Structure of an Atom Neutrons - 1932 James Chadwick showed that neutrons exist - neutral subatomic particle that is found in the nucleus - mass almost exactly equal to that of a proton Properties of Subatomic Particles Notes

6. 4.2 The Structure of an Atom What properties can be used to compare protons, electrons, and neutrons? Comparing Subatomic Particles Protons, electrons, and neutrons can be distinguished by mass, charge, and location in an atom.

7. 4.2 The Structure of an Atom Everything scientists know about subatomic particles is based on how the particles behave in experiments. Scientists still do not have an instrument that can show the inside of an atom. Comparing Subatomic Particles

8. 4.2 The Structure of an Atom Comparison between protons, electrons, and neutrons. Protons and neutrons have almost the same mass About 2000 electrons equal the mass of one proton. An electron has a charge that is equal in size to, but the opposite of, the charge of a proton. Neutrons have no charge. Protons and neutrons are found in the nucleus. Electrons are found in the space outside the nucleus. Notes

9. 4.2 The Structure of an Atom How are atoms of one element different from atoms of other elements? Atomic Number and Mass Number Atoms of different elements have different numbers of protons.

10. 4.2 The Structure of an Atom Atomic Number and Mass Number Atomic Number Indicates the number of protons in an atom All atoms of any given element have the same atomic # Atoms on periodic table are neutral each positive charge in an atom is balanced by a negative charge Atomic # also equals the number of electrons Notes

11. 4.2 The Structure of an Atom Atomic Number and Mass Number Mass Number - the sum of the protons and neutrons in the nucleus - to calculate # of neutrons - subtract the mass # of the atom and its atomic # - Atomic Mass number - average mass of 1 atom of an element - most averages will have a decimal Notes

12. 4.2 The Structure of an Atom Symbols Find the –number of protons –number of neutrons –number of electrons –Atomic number –Mass number –Atomic Mass Number –Number of neutrons + protons = 9 = 10 = 9 = 19 + = 18.98 = 19 18.98 9 F

13. 4.2 The Structure of an Atom Symbols Find the –number of protons –number of neutrons –number of electrons –Atomic number –Mass number –Atomic Mass Number –Number of protons + neutrons Na 22.98 11 11 11 11 23 22.98 23 12

14. 4.2 The Structure of an Atom Symbols Find the –number of protons –number of neutrons –number of electrons –Atomic number –Mass number –Atomic Mass Number –Number of protons + neutrons 39.09 19 = 19 = 20 = 19 = 39 = 39.09 = 39 K

15. 4.2 The Structure of an Atom CPS clicker ON Quiz Find the 1. number of protons 2. number of neutrons 3. number of electrons 4. Atomic number 5. Mass number 6. Atomic Mass Number 7. Number of protons + neutrons 8. Charge of a proton (spell answer) 9. Charge of a neutron (spell answer) 10. Charge of an electron (spell answer) Ar 39.948 18

16. 4.2 The Structure of an Atom What is the difference between two isotopes of the same element? Isotopes Isotopes of an element - same atomic number (protons) - different mass numbers - different numbers of neutrons Notes

17. 4.2 The Structure of an Atom Notes Isotopes - atoms of the same element (protons) that have different numbers of neutrons and different mass numbers. To distinguish one isotope from another, the isotopes are referred by their mass numbers. For example, oxygen has 3 isotopes: oxygen-16, oxygen-17, and oxygen-18. All three oxygen isotopes can react with hydrogen to form water or combine with iron to form rust.

18. 4.2 The Structure of an Atom Isotopes With most elements, it is hard to notice any differences in the physical or chemical properties of their isotopes. Hydrogen is an exception. Hydrogen-1 has no neutrons. (Almost all hydrogen is hydrogen-1.) Hydrogen-2 has one neutron, and hydrogen-3 has two neutrons. Because a hydrogen-1 atom has only one proton, adding a neutron doubles its mass.

19. 4.2 The Structure of an Atom Isotopes Water that contains hydrogen-2 atoms in place of hydrogen-1 atoms is called heavy water. Hydrogen- 2 atoms have twice the mass of hydrogen-1 atoms, so the properties of heavy water are different from the properties of ordinary water.

20. 4.2 The Structure of an Atom Assessment Questions 1.In which way do isotopes of an element differ? a.number of electrons in the atom b.number of protons in the atom c.number of neutrons in the atom d.net charge of the atom

21. 4.2 The Structure of an Atom Assessment Questions 1.In which way do isotopes of an element differ? a.number of electrons in the atom b.number of protons in the atom c.number of neutrons in the atom d.net charge of the atom ANS:C

22. 4.2 The Structure of an Atom Assessment Questions 1.Of the three subatomic particles that form the atom, the one with the smallest mass is the neutron. True False

23. 4.2 The Structure of an Atom Assessment Questions 1.Of the three subatomic particles that form the atom, the one with the smallest mass is the neutron. True False ANS:F, electron