P. Sci.

1. P. Sci. Unit 9 Chapter 4 Atoms

2. Atomic Structure – timeline • Ancient Greece - Democritus proposed the atom – a tiny solid particle that could not be subdivided. • 1904 – J.J. Thomson – discovered that atoms contained small, negatively charged particles called electrons.

3. 1911 – Ernest Rutherford – proposed that the atom had two parts – the nucleus in the center (most of the mass) surrounded by the electrons. 1913 – Niels Bohr – hypothesized that electrons traveled in fixed orbits around the atom’s nucleus.

4. 1913 – James Chadwick – concluded that the nucleus contained positive protons and neutral neutrons. 1926 – Erwin Schrodinger – developed the quantum mechanical model – which is based on the wavelike properties of the electron. (not a particle – leads to quantum physics)

5. 1927 – Werner Heisenberg – (the Heisenberg uncertainty Principle) described that it is impossible to know precisely both an electron’s position and path at a given time. Led to the electron cloud theory.

6. Atoms • The smallest particle that has the properties of an element.

7. Dalton’s Atomic Theory • Every element is made of tiny, unique, particles called atoms that cannot be subdivided. • Atoms of the same element are exactly alike. • Atoms of different elements can join to form molecules

8. Parts of an Atom • Nucleus – small, dense center of an atom made up of 2 subatomic particles that are almost identical in size and mass. • Protons – have a positive charge • Neutrons – have no charge

9. Parts of an Atom cont. • Electrons – are tiny particles that have very little mass that moves around the outside of the nucleus. These particles are negatively charged and form a “cloud” around the nucleus.

10. The number of protons an atom has is unique for each element.

11. Atomic Charge • Atoms have no overall charge because the protons (+) cancel out the electrons (-). Helium 2 protons - +2 2 neutrons - 0 2 electrons --2 total charge 0

12. Protons • positive (+) charge • Found in the nucleus • # of protons = atomic # • The number of protons identify the element (atomic #)

13. Neutrons • no charge • Found in the nucleus • Along with protons makes up atomic mass • protons and neutrons are made up of quarks – which three quarks – determines whether it becomes a proton or a neutron.

14. Electrons • negative (–) charge • travel in orbitals (or energy levels) around the nucleus. (electron cloud) • valence electrons - the # of electrons in the outer shell = oxidation #

15. Unit of measure for atomic particles is Atomic mass unit (amu) protons and neutrons = about 1 amu (electrons are about the size of 1 quark)

16. Chemical symbols • The one or two letter abbreviation of the element name.

17. Mass Number or Atomic Mass • the sum of the number of protons and the number of neutrons in the nucleus of an atom. • # of neutrons = mass # - atomic # Neutrons Protons +

18. Average atomic mass • the weighted - average mass of the mixture of all an atoms isotopes. The average atomic mass is close to the mass of its most abundant isotope.

19. Isotopes • Atoms of the same element that have a different # of neutrons. (identified by the element name followed by the mass # ) • ex. C-12, C-14, B-10, B-11) Carbon 14 = 8 neutrons Carbon 12 = 6 neutrons

20. The End For now