Part 1: Atom Basics. Week 1: Atoms. Part 2: A Short History of Atomic Theory

Transcription

1 Part 1: Atom Basics Week 1: Atoms Part 2: A Short History of Atomic Theory

2 Part 1: Atom Basics

3 Part 1: Atom Basics / Objectives After this lesson I can define an atom & its three parts. distinguish the terms element and atom. recall the charge, mass, symbol and location of all three sub atomic particles. describe the nucleus and give an analogy for its size compared to the rest of the atom. recall that the nucleus is held together by the strong nuclear force.

4 Atoms and Elements Atoms are the smallest fundamental unit of matter. They are made of three parts: Protons, Neutrons, and Electrons An element is the type or identity of an atom and is determined by the number of protons the atom has. All atoms are 1 of the 118 elements on the periodic table. Examples: 1 proton = hydrogen 8 protons = oxygen 26 protons = iron. 92 protons = uranium The number of protons an element has is often referred to as it s atomic number. Protons are found in the Nucleus (the center of the atom) they are positively charged and have a mass of 1 a.m.u (atomic mass unit). Protons sometimes go by the symbol p + or H +

5 Practice Problems: Atoms and Elements Directions: Give the name or symbol for the elements below 1) Atom with 55 protons 2) Element that has 22 protons 3) Atom with 19 protons 4) Element that has 112 protons. 5) Atom with 89 protons Directions: State the number of protons for the given element 1) Carbon 2) Sulfur 3) Fe 4) Copper 5) Gold 6) Bh

6 Neutrons Hydrogen atoms contain just 1 proton. All the other elements have neutrons as well. Neutrons are also found in the nucleus and have a mass of 1 a.mu. Unlike protons, they do not have a charge. Neutrons use the symbol n Electrons are outside the nucleus, are negatively charged, and have a mass so small, (.0002 a.mu.) we often say their mass is negligible. Electrons have the symbol e - In summary, Atoms are made up of only three parts called subatomic particles: protons, neutrons, and electrons.

7 Model of the Nucleus Image Credit: nscl.msu.edu

8 The Nucleus is much, much, smaller than what is picture here Image Credit:

9 Videos! Show Video 1: What is an atom? Show Video 2: Just How Small is an Atom?

10 The Nucleus The Nucleus contains virtually all of the atom s mass. This is because the protons & neutrons each have a mass of 1 a.m.u, while electrons have a negligible mass. Despite having virtually all of the atom's mass, the Nucleus takes up virtually none of the atom s volume. To put it in numbers, the Nucleus has: 99.99% an atom s mass 00.01% an atom s volume (it s 10,000+ times smaller than the atom as a whole) These facts are easy to memorize but difficult to visualize. Some of the analogies on the next slide will help, as will the links at the end of the section.

11 The Nucleus The Nucleus is the center of the atom, tightly packed with protons and neutrons. Students often question how the protons can be packed together inside the nucleus, after all, don t the positive charges on the protons repel one another? The strong nuclear force is what prevents the positive charges on the protons from splitting the nucleus apart. In other words it s what holds the nucleus together.

12 Analogies for the Nucleus a pencil eraser on the pitchers mound of a big league ball park. The park represents the entire atom, but the very small nucleus is the pencil eraser. If an atom were the size of the Ford Field, the nucleus would only be the size of a small marble. However, the mass of that marble would be roughly 230,000,000,000 pounds.

13 Videos! Show Video 3: CCC Episode 1 - The Nucleus

14 Part 1 Additional Resources & Links Youtube video What is an Atom? TedED: Just How Small is an Atom? Crash Course Chemistry Episode 1 Note: at about 7:30 in the video Hank starts talking about concepts that we are not covering. Quizziz Review (use code )

15 Part 2: A Short History of Atomic Theory

16 Part 2: A Short History of Atomic Theory / Objectives After this lesson I can summarize how our model of the atom has changed over the last 2,500 years as a result of experimentation and new evidence. draw a picture of the Greek atom. draw a picture of the Plum Pudding model of the atom and label the parts draw a picture of the Rutherford model of the atom and label the parts. draw a picture of the Bohr model of the atom and label the parts.

17 History of Atomic Theory Overview The idea of atoms dates back thousands of years to ancient Greeks. Atomic Theory, like all scientific theories, is about building upon the observations and experiments of others. As such, many people of have made contributions to atomic theory. Dozens of people are noteworthy with most living within the last 100 years or so. We are going to look at 4 people who made major revisions to our model of the atom: Democritus JJ Thompson Ernest Rutherford Niels Bohr

18 ~400 B.C.E.: Democritus s Atom Democritus was a Greek philosopher who first came up with the idea of atoms. He thought of atoms as indivisible, solid, and spherical. Democritus was NOT a scientist. In fact, science as we define today did not even exist back then. He came up with the idea of atoms simply by thinking about what happens if you keep cutting an object. He reasoned that if you keep cutting or dividing an object sooner or later you would get to a point where it could not be cut or divided any further. Atomos in Greek means that which cannot be split

19 Democritus s Model of the Atom Image Credit:

20 JJ Thompson discovers the electron JJ Thompson was a scientist who discovered electrons through experiments he did with cathode ray tubes. He also discovered that these negatively charged particles were 2,000 times less massive than the atom. Like many scientific discoveries, this lead to more questions. Since we knew atoms where neutral overall, how did the positive and negative charges balanced each other out? Thompson reasoned that atoms were a lot like plumb pudding, which was a popular desert at the time. He thought that the negatively charged electrons (plums) were spread throughout a positively charged spherical mass (pudding) To use a desert you are more familiar with, he thought atoms were like chocolate chip cookies. The chocolate chips were the electrons and the cookie dough was a positively charged mass

21 JJ s Plumb Pudding Model Image Credit: & Wikipedia

22 1907 Ernest Rutherford Discovers the Nucleus Ernest Rutherford s gold foil experiment is perhaps the most famous experiment in the history of chemistry; it is part of the reason why Rutherford got an element named after him. Rutherford discovered that atoms have a dense, positively charged center, or nucleus, but for the most part were empty space. This lead to JJ s plumb pudding model being revised to the nucleus centered model of the atom. Also known as the Rutherford model of the atom. Our picture of the atom was still not complete though. This is because Rutherford did not have a clear picture for what the electrons were doing and neutrons had still not been discovered yet.

23 Rutherford s Nucleus Centered Model of the atom Image Credit: Wikipedia

24 1913 Niels Bohr Proposes a New Model to Explain the Electrons While Rutherford showed that the electrons of an atom were outside the nucleus, he was not able to explain the behavior of those electrons. What Bohr did was explain the behavior of electrons based on existing observations and mathematics. He hypothesized that: Electrons travel around the nucleus in fixed orbits These orbits were regions outside the nucleus where the electrons were allowed to be. For his contribution to atomic theory Bohr received a Nobel prize and eventually had a element named after him. Later scientists and physicists would build upon his ideas. To this day, our understanding and model of the electrons continues to evolve.

25 Bohr Model of atom Image Credit:

26 Bohr Model of the Atom After the Discovery of Neutrons Image Credit: Encyclopedia Britannica

27 Part 2 Additional Resources & Links Tyler Dewitt s YouTube Video: Model of the Atom Timeline Crash Course Chemistry Episode 37: History of Atomic Chemistry TedED: 2,400 year search for the Atom YouTube Video.

28 Week 1 Review Links Quizlet Review