1. 23.1 Atomic structure The Rutherford scattering experiment  In 1911, Ernest Rutherford carried out the famous Rutherford scattering experiment to explore the internal structure of an atom.

2. 23.1 Atomic structure detector  radiation source gold foil vacuum lead screen beam of  particle zinc sulphide screen The experimental setup

3. 23.1 Atomic structure Result of the experiment most  particles pass straight through the gold foil. some  particles are scattered by an angle.  radiation source gold foil very few  particles are bounced back.

4. 23.1 Atomic structure The Rutherford’s atomic model nucleus It is mostly empty space. It consists of a tiny nucleus with all positive charges and most of the mass of the atom. Video: Gravitational analogue of scattering experiment

5. 23.1 Atomic structure Structure of an atom  Protons and neutrons are called nucleons, bound together by strong nuclear force.  They have about the same mass. Nucleus proton (positively charged) neutron (not charged)

6. 23.1 Atomic structure Electron  orbits around the nucleus.  carries negative charges.  has mass much smaller than that of a proton or a neutron.

7. 23.1 Atomic structure Comparison between protons, neutrons and electrons Particles inside an atom Relative mass Relative charge proton1+1 neutron10 electronnegligible  1

8. 23.1 Atomic structure Atomic number and mass number  Atomic number (Z) or proton number = number of protons in a nucleus Different elements have different atomic numbers.  Mass number (A) or nucleon number = number of nucleons in a nucleus = number of protons (Z) + number of neutrons (N) A = Z + N

9. 23.1 Atomic structure  Nuclide – an element having specific values of Z and A  Symbolic notation for a nuclide X:  For example, a helium nuclide with atomic number 2 and mass number 4:  A nuclide can also be represented by its name followed by its mass number: helium-4 or He-4

10. 23.1 Atomic structure Isotopes  Isotopes – nuclides with the same atomic number Z but different mass numbers A Why do isotopes have different mass numbers?  They have different numbers of neutrons.  Radioisotopes – isotopes that are radioactive

11. 23.1 Atomic structure The isotopes of hydrogen proton neutron radioisotope of hydrogen

12. 23.1 Atomic structure That’s the end of Section 23.1 Check Point Key Ideas Previous Page Section 23.2 Exit