1. Particles in the Atom Each element is chemically unique. To understand why they are unique, you need to know the structure of the atom (the smallest particle of an element) and the characteristics of its components.

3. Electrons (-) charge no mass located outside the nucleus Protons (+) charge 1 amulocated inside the nucleus Neutrons no charge 1 amulocated inside the nucleus Particles in the Atom

4. Los electrones (-) coste no masa situado fuera del núcleo Protones (+) coste 1 amuSituado en el interior del núcleo Neutrones sin cargo 1 amuSituado en el interior del núcleo Partículas en el átomo

5. electronsprotonsneutrons Atoms consist of electrons, protons, and neutrons. 1. Electrons and protons have electrical charges that are identical in magnitude but opposite in sign. Relative charges of 1 and +1 are assigned to the electron and proton, respectively. 2. Neutrons have approximately the same mass as protons but no chargethey are electrically neutral. 3. The mass of a proton or a neutron is about 1836 times greater than the mass of an electron. Protons and neutrons constitute the bulk of the mass of the atom. Particles in the Atom Copyright 2007 Pearson Benjamin Cummings. All rights reserved.

6. Discovery of the Neutron James Chadwick bombarded beryllium-9 with alpha particles, carbon-12 atoms were formed, and neutrons were emitted. + + Dorin, Demmin, Gabel, Chemistry The Study of Matter 3rd Edition, page 764 *Walter Boethe

7. Humor Two atoms are walking down the street. One atom says to the other, Hey! I think I lost an electron! The other says, Are you sure?? Yes, Im positive! A neutron walks into a restaurant and orders a couple of drinks. As she is about to leave, she asks the waiter how much she owes. The waiter replies, For you, No Charge!!!

8. Subatomic particles Electron Proton Neutron NameSymbolCharge Relative mass Actual mass (g) e-e- p+p+ nono +1 0 1/1840 1 1 9.11 x 10 -28 1.67 x 10 -24

9. Structure of the Atom There are two regions The nucleus With protons and neutrons –Positive charge –Almost all the mass Electron cloud –Most of the volume of an atom –The region where the electron can be found

10. Subatomic Particles Most of the atoms mass. NUCLEUS ELECTRONS PROTONS NEUTRONS Negative Charge Positive Charge Neutral Charge ATOM QUARKS Atomic Number equals the # of... equal in a neutral atom Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

11. Subatomic Particles Most of the atoms mass. NUCLEUS ELECTRONS PROTONS NEUTRONS Negative Charge Positive Charge Neutral Charge ATOM QUARKS Atomic Number equals the # of... equal in a neutral atom Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

12. Subatomic Particles Quarks –component of protons & neutrons –6 types –3 quarks = 1 proton or 1 neutron He Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

13. Size of an atom Atoms are incredibly tiny. Measured in picometers (10 -12 meters) –Hydrogen atom, 32 pm radius Nucleus tiny compared to atom –Radius of the nucleus near 10 -15 m. –Density near 10 14 g/cm 3 IF the atom was the size of a stadium, the nucleus would be the size of a marble. California WEB

14. Counting the Pieces Atomic Number = number of protons # of protons determines kind of atom Atomic Number = number of electrons in a neutral atom Mass Number = the number of protons + neutrons California WEB 12 6 C 14 6 C 12 6 C Mass Number = A Atomic Number = Z