1. Warm Up– Monday, September 8th Honors- Turn in your lab report over Lab #1 All- Grab a Ch. 3.3 Notes packet from cart, answer these questions on the front. 1.Decide whether each of the following statements concerning atoms is true or false. a)All of the particles in the nucleus of an atom are charged. b)The atom is best described as a uniform sphere of matter in which electrons are embedded. c)The mass of the nucleus is only a very small fraction of the mass of the entire atom. d)The size of the nucleus is only a very small fraction of the total size of the atom. e)The number of neutrons in an atom must equal the number of electrons.

2. Modern Atomic Theory Atom – smallest unit of an element that retains the properties of that element. 1)Atoms are composed of two regions and three subatomic particles. a)Nucleus - positively charged region located at the center of the atom.

3. Very small compared to the total size of the atom. (marble = size of nucleus / football field = size of atom) Composed of two particles 1. Proton = Positive particle 2. Neutron = Neutral particle Almost all mass is located in nucleus (extremely dense) Nucleus held together by strong nuclear forces.

4. b) Electron Cloud – Mostly empty space Gives atom its size Contains tiny negatively charged particles called electrons. 2)Atoms are very small in size. So small use picometers (1x10 -12 m) Atomic radii range from 40 to 270 pm

7. 3) Atoms have very small masses. Example: mass of oxygen atom 2.6 x 10 -23 g. atomic mass unit (amu) 1 amu = 1.66 x 10 -27 g = 1/12 the mass of a carbon-12 atom. atoms have masses from 1-300 amu’s

8. Comparison of Subatomic Particles ParticleLocationRelative ChargeMass Proton Nucleus+1 approx. 1 amu Neutron Nucleus0approx. 1 amu ElectronElectron Cloud.0005 amu ≈ 0 amu

9. 4) Atoms are electrically neutral. Although an atom contains charged particles, the atom overall is neutral. A proton and an electron have the same amount of charge just opposite in sign. Number of protons = number of electrons.

10. Atomic Number and Mass Number Atomic Number (Z) – –number of protons in the nucleus of atom of a particular element. –whole number listed on the periodic table. Mass Number (A) – – number of protons and neutrons in nucleus of an atom. – do not confuse with decimal number listed on periodic table.

12. Representing Atoms There are two different ways to represent atoms. Symbol Notation –

13. Hyphen-Notation Consists of name of element and a number. –Example: chlorine – 37 Number after name is the mass number. Sample Problem: Determine the number of protons, neutrons, and electrons for a bromine-80 atom.

14. One Minute Paper You have one minute to answer these two questions concerning today’s lesson. –What was the most important thing you learned? –What is still confusing?