Happy Mole Day! Mole day is celebrated every October 23rd between 6:02 in the morning and 6:02 in the evening. Scientists celebrate mole day because the mole is the SI base unit for the amount of a substance. The number of particles in 1 mole of any substance is 6.022 X 1023, which is Avogadro’s number. We will learn more about the mole in section 3.4 as we begin counting atoms…

Just How Big is a Mole? Avogadro's number of pennies placed side by side would stretch for more than 1 million light years! This amount of pennies would also be good enough to repay the debt of United States of America 86 million times!

He was only tense to the 23rd. Mole Day Riddles… What do you call a 10th grade chemistry student? A sophmole What does Avogadro put in his hot chocolate? Marsh-mole-ows! Why did Avogadro stop going to a chiropractor on October 24th? He was only tense to the 23rd.

Wednesday, Oct. 23rd: “A” Day Thursday, Oct Wednesday, Oct. 23rd: “A” Day Thursday, Oct. 24th: “B” Day Agenda Happy Mole Day! Homework Questions? (pg 78: #1-8) Sec. 3.1 Quiz: “Substances are Made of Atoms” Begin Sec. 3.2: “Structure of Atoms” KWL Activity J.J. Thomson, cathode rays, electrons, Ernest Rutherford , gold foil experiment, nucleus, protons, neutrons, Coulomb’s law Homework: Concept Review and KWL

Ch. 2 Tests “Matter and Energy” Class Average Score (out of 60) Average Percentage 2A 48.52 80.87 % 4A 51.93 86.55 % 1B 52.00 86.67 % 3B 53.32 88.87 %

Sec. 3.1 Quiz “Substances are Made of Atoms” I thought the quiz for this section was a little tricky, so we’re going to go through some of it together as a review… You’re welcome! 

Atomic Structure KWL Activity KWL stands for: “K”: What I KNOW or think I know “W”: What I WANT to know “L”: What I LEARNED Take a few minutes to write down at least 5 each in the “K” and “W” sections of the KWL graphic organizer before we begin Section 3.2: “Structure of Atoms Keep this handy because you’ll complete the “L” section as we work through the chapter…

Sec. 3.2: “Structure of Atoms” Scientists discovered that atoms CAN be broken down into smaller parts called subatomic particles. The 3 types of subatomic particles that are most important in chemistry are: Electrons Protons Neutrons

Electrons Were Discovered by Using Cathode Rays J.J. Thomson was studying electricity, not atomic structure, when he discovered electrons. He pumped the air out of a sealed glass tube and attached electrodes to each end. Anode: positive electrode Cathode: negative electrode A glowing beam came out of the cathode. He called the beam a “cathode ray”. The glass tube is known as a cathode ray tube (CRT)

An Electron has a Negative Charge Thomson reasoned that the ray was negatively charged since it was coming from the cathode. He placed a magnet by the tube and saw the ray deflected. He placed a small paddle wheel in the path of the ray and saw the wheel turn, showing that something with mass was hitting the wheel. Thomson concluded that the ray was made of negatively charged particles that have mass. Thomson called these particles electrons.

J.J. Thomson Discovered Electrons Electron: a subatomic particle that has a negative charge.

There Must be Other Subatomic Particles Too… Scientists began to look for more subatomic particles for 2 reasons: Since electrons have a negative charge but atoms have no charge, there must be other subatomic particles that have a positive charge to balance out the electron’s negative charge. The mass of an atom is much larger than the mass of an electron, so there must be other subatomic particles in the atom.

Thomson’s Plum Pudding Model J.J. Thomson proposed that electrons were embedded in a ball of positive charge. Thomson called this model the “plum pudding model”.

Ernest Rutherford’s Gold Foil Experiment

Rutherford Discovered the Nucleus Rutherford directed a beam of positively charged alpha particles at a thin foil of gold. Most of the particles passed straight through the foil, but a few were deflected, some even backwards. Only a very concentrated positive charge in a tiny space within the gold atom could possibly repel the fast-moving alpha particles enough to reverse their direction. The mass of this tiny, positively charged region must be larger than the mass of the alpha particle or it would simply have been knocked out of the way.

Rutherford Discovered the Nucleus Rutherford hypothesized that atoms are mostly empty space except for the dense center, or nucleus. Nucleus: an atom’s central region, which is made up of protons and neutrons. The nucleus has all of the positive charge, nearly all of the mass, but only a very small fraction of the volume of the atom.

Protons are in the Nucleus The positively charged particles in the nucleus were called protons. Proton: a subatomic particle that has a positive charge and that is found in the nucleus of an atom; the number of protons of the nucleus is the atomic number, which determines the identity of an element. A proton’s mass is about 2,000 times that of an electron!!

There Must be Something Else… Because an atom’s mass is greater than the sum of its protons and electrons, scientists began looking for another subatomic particle… Protons + Electrons = Mass of Atom

James Chadwick Discovered Neutrons Neutron: a subatomic particle that has no charge and that is found in the nucleus of an atom. A neutron has about the same mass as a proton.

Coulomb’s Law Coulomb’s law: the closer two charges are, the greater the force between them. (Think of magnets) Also, the larger the two charges are, the greater the force between them.

Why is the Nucleus Stable? If the nucleus is made up of positively charged protons and neutrons with no charge, why doesn’t the force of repulsion push the protons apart and make the nucleus unstable? THE STRONG FORCE!

The Strong Force A fundamental force of nature, the strong force, overcomes the repulsive forces between positively charged protons in the nucleus. All atoms that have more than 1 proton also have neutrons to help stabilize the nucleus.

We’ll finish section 3.2 next time… Homework Not only have we covered a lot today, we didn’t finish this section, so there’s NO HOMEWORK for today! However, please use this time to work on the concept review and/or your KWL We’ll finish section 3.2 next time…