1. Aim: What is an atom? DO NOW: Identify X, Y, and Z as a mixture, compound or element. DRAW IMAGE

2. The Atom 1) The atom is the basic unit of matter. 2) Each element is composed of atoms that have different subatomic particles than another element 3) An element is the simplest form of matter that has unique set of properties. 4) An element cannot be broken down into simpler substances 5) Compounds decompose

3. Atomic Structure A) Nucleus 1)Proton 2)Neutron B) Cloud 3) Electron

4. The Three Fundamental Subatomic Particles NameSymbolChargeMass (amu) Mass (g)Location Protonp+p+ 1+1.0071.673 x 10 -24 Nucleus Neutronn0n0 01.0091.675 x 10 -24 Nucleus electrone-e- 1-5.486 x 10 -28 9.109 x 10 -28 Outside nucleus

5. Nucleus 1) It contains most of the mass of the atom; it is very dense 2) It has a positive charge (nuclear charge)

6. Proton Atomic # counts protons only Atomic mass or mass # is both neutron and proton Proton has a positive charge The number of protons is called the nuclear charge

7. Proton cont. In a neutral atom, the number of electrons = number of protons The protons “hold the electrons in the atoms” The mass of the proton is based on the mass of the carbon atom (carbon is very easy to purify) The mass of a proton is 1/12 the mass of carbon-12 (atomic mass unit) a.m.u. The number of protons in an atom is specific to only that element, each element has its own specific number of protons.

8. Neutron Has no charge; neutral Has a mass of 1 atomic mass unit; the neutrons along with the protons are responsible for all of the mass of the atom. Neutrons have a force that combines the protons together, keeping the nucleus stable, called the binding energy.

9. Isotopes Atoms of the same element (same number of protons) that have differing numbers of neutrons are called isotopes. Isotopes of an element have: Differing Atomic mass # Differing # of neutrons Isotopes have the same atomic # but different mass # Changing the number of neutrons does not affect the chemical reactivity of the element.

10. Isotopes Same element Same chemical properties Second one is radioactive

11. Sample Problems 1. Lithium has 3 protons and 4 neutron. What is the mass number? 2. An atom has a mass number of 9 and has 5 neutrons. How many protons does it have?