Learning objective 1: I can evaluate different models of atoms and develop a model to describe the scale and proportion of atoms and molecules.

Richard Feynman, a great physicist, said he would save this fact: If all scientific knowledge were to disappear tomorrow except for one fact, what fact would you pick? Richard Feynman, a great physicist, said he would save this fact: All things are made of atoms.

atom The

Subatomic Particle Charge Location Size/Weight Proton Positive (+) Nucleus or “Core” Large/1 au Neutron No Charge (0) Electron Negative (-) Electron Cloud Small/0 au

How many times can you divide something in half? Ancient Greeks were the first known thinkers to try to answer this question. Is matter even made of little pieces (particles)? Aristotle didn’t think so… People have wanted to know for a really long time…

Democritus Used the word “atmos” His theoretical model of the atom…

Except smaller… Smaller… Smaller…

Hey, why is it a sphere? I don’t know.

The world was black and white back then. Why is it grey? I have no idea. The world was black and white back then. Just kidding.

Why didn’t Democritus know? He didn’t do EXPERIMENTS! This didn’t exist yet And, even if it did exist…it isn’t good enough to see atoms

What did Democritus’ model explain? Not much… His theory was that all matter was made of tiny spheres. It explains why we can divide things in half many, many times, but not change the identity of the substance.

Fast forward to this guy… John Dalton He was put in charge of the local school at age 12! In 1808, he published A New System of Chemical Philosophy He had done chemical reactions and measured the amounts of everything that reacted. Through this, he deduced that every substance was not only made of atoms, but consisted of specific numbers of atoms and types of atoms. For example, one chemical would react with an exact amount of another chemical, but no more.

So, he now had a little bit of evidence… But, he was still very wrong about many of his guesses His atom model was still this…

Dalton’s Atomic Theory Elements are made of extremely small particles called atoms. Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties. Atoms cannot be subdivided, created, or destroyed. Atoms of different elements combine in simple whole-number ratios to form chemical compounds. In chemical reactions, atoms are combined, separated, or rearranged. The most important part… Scientist Information Model John Dalton All matter is made of atoms. Atoms are too small to see, indivisible and indestructible. All atoms of a given element are identical.

What did Dalton’s model explain? Why you can break something into pieces but that doesn’t change the identity of that substance.

That’s important, but… How do we get past the idea that everything is just made of little tiny spheres? What are these spheres?!

Ernest Rutherford Some physicists of that time were extremely negative towards scientists in other subjects…for example, when Wolfgang Pauli’s wife left him for a chemist, he said “Had she taken a bullfighter I would have understood, but a chemist…” Rutherford would have agreed. He said “All science is either physics or stamp collecting.” So it’s especially that when he won a Nobel prize, he didn’t win the Nobel prize for physics, he won it for chemistry.

He wasn’t that smart… but apparently he would just work on a problem harder and longer than anyone else Often during lectures he would get so lost in his own equations that he would just give up in the middle and tell the students to work it out for themselves. His colleagues also said that he really wasn’t that good at experimenting either.

Luckily for Rutherford, people had been doing some big time experiments...(finally!) This guy discovered the electron Electrons have a negative charge, but atoms don’t have a charge, so an atom is probably like this!

The important part… Scientist Information Model J.J Thompson Discovered the negative electron, and predicted that there also must be a positive particle (proton) to hold the electrons in place.

What did Thompson’s model explain? How an atom has no charge, but it also contains electrons (so it must have a positive charge— protons!)

Rutherford Hans Geiger Rutherford and the gold foil experiment: He shot super high energy particles at a sheet of gold foil and instead of zooming through, a few bounced back. They were so high energy it was like shooting a cannon ball at a sheet of paper and having some bounce back.

He didn’t know exactly where the electrons were, but he knew there was a positively charged nucleus surrounded by negatively charged electrons. Rutherford Model

The important part… Ernest Rutherford Scientist Information Model Ernest Rutherford Discovered the nucleus of an atom and named the positive particles in the nucleus “protons”. Concluded that electrons are scattered in empty space around the nucleus.

What did Rutherford’s model explain? Why particles couldn’t pass through atoms.

This guy discovered neutrons James Chadwick

The important part… Scientist Information Model James Chadwick Discovered that neutrons were also located in the nucleus of an atoms and that they contain no charge. Neutrons

Niels Bohr suggested that the electrons took up orbits based on their energy level. Bohr Model

The important part… Neils Bohr Scientist Information Model Neils Bohr Concluded that electrons are located in planet-like orbits around the nucleus in certain energy levels. *Explains bonding.

What did Bohr’s model explain? Why atoms are different from one another, and why they bond.

Werner Heisenberg

Werner Heisenberg Electrons don’t orbit like planets. Actually, you can’t be sure where they are and where they are headed!

Heisenberg Uncertainty Principle: we can know the path an electron takes through space, or we can know its location, but it is not possible to know both. Bohr: “If you are not outraged on first hearing about quantum theory, then you didn’t understand what had just been said” Heisenberg, when asked how best to envision an atom, said “Don’t try.”

Schrodinger Model

The important part… Scientist Information Model (Many Scientists!) The Modern Atomic Theory Electrons do not orbit the nucleus in neat planet-like orbits but move at high speeds in an electron cloud around the nucleus. There ARE still energy levels.

What does the modern model explain? Why we can’t accurately measure electron locations.

Subatomic Particle Charge Location Size/Weight Proton Positive (+) Nucleus or “Core” Large/1 au Neutron No Charge (0) Electron Negative (-) Electron Cloud Small/0 au

Schrodinger Model (current model) Electron cloud: electrons are in here somewhere Nucleus with protons and neutrons Schrodinger Model (current model)