1. Chapter 11 Introduction to atoms
Welcome Back! Tonight we are going to dive into learning about the development of the Atomic Theory and the parts of the atom. We will also take time to look at different versions of the atom in the forms of isotopes and ions and how the atom is manipulated to create these types of particles. Tonight, we will focus on the Atomic Theory.
Introduction to atoms

2. Development of the Atomic Theory
Atoms are small particles that are made up of even smaller particles, which determine the properties of the atom.
First thing we need to know is that atoms are small particles and they are made of even smaller particles, these smaller particles are what determine the properties of the atom.

3. Beginning of the Atomic Theory
Around 440 BCE, Greek philosopher Democritus first proposed the idea of a particle that could not be cut any smaller. He called this particle atomos, meaning uncuttable or indivisable.
Aristotle, also a Greek philosopher, disagreed with Democritus. He did not believe that such an indivisible particle existed.
It turned out that Democritus was right. Atoms do exist.
An atom is defined as the smallest particle into which an element can be divided and still be the same substance.
The first atomic theory was developed about 440 BCE, by the Greek philosopher Democritus first proposed the idea of a particle that could not be cut any smaller. He called this particle atomos, which means uncuttable or indivisible. Aristotle who is also a Greek philosopher, he disagreed with Democritus, he did not believe that such an indivisible particle existed. It turned out that Democritus was right. Atoms do exist! An atom is defined as the smallest particle into which an element can be divided and still be the same substance. Let’s now look at how this theory continues to be developed.

4. Dalton’s atom theory Based on Experiments
John Dalton, a British chemist and teacher, first proposed his atomic theory in 1803.
Dalton’s Atomic Theory
All Substances are made of atoms
Atoms are small particles that cannot be created, destroyed, or divided
Atoms of the same element are exactly alike
Atoms join with other atoms to make new substances
John Dalton: is a British chemist and teacher who first proposed his atomic theory is Dalton created what we now know as the Modern Atomic Theory, the parts of his atomic theory include: All substances are made of atoms, Atoms are small particles that cannot be created, destroyed, or divided, atoms of the same element are exactly alike, and atoms join with other atoms to make new substances. This modern atomic theory is the basis for everything we know about the atom today, there are parts of it that have been adapted and modified to create a better understanding of the structure of the atom.

5. Thomson’s discovery of electrons
In 1897, J.J. Thomson, a British scientist, showed that a part of Dalton’s Atomic Theory was incorrect.
Thomson showed that there were even smaller particles inside the atom, disproving Dalton’s idea that atoms could not be divided into smaller pets.
Thomson actually had discovered the presence of a negative particle inside the atom. This particle was called an electron.
Thomson believed that electrons were distributed throughout the whole atom.
In 1897, JJ Thomson a British scientist, showed that part of Dalton’s Atomic Theory was incorrect. Thomason determined a good representation of the atom was a cake with raising or plums being evenly distributed throughout, his model is often referred to as the “Plum Pudding Model” or the Chocolate Chip Cookie model. Though this model Thomson showed that there were even smaller particles inside the atom, disproving Dalton’s idea that atoms could not be divided into smaller pets. Thomson actually had discovered the presence of a negative particle inside the atom which he surmised would be the plums or chocolate chips in the positive dough. This particle was called an electron. Thomson believed that electrons (chips) were distributed through the whole atom.

6. Rutherford’s atomic shooting gallery
In 1909, Ernest Rutherford, a student of Thomson’s, further revised the atomic theory.
Rutherford proposed that the atom was mostly empty space with a tiny part made of highly dense matter.
He believed that in the center of the atom was an extremely dense, positively charged center which he called the nucleus.
In 1909, Ernest Rutherford, a student of Thomson’s further revised the Modern Atomic Theory. Rutherford performed what refer to as the gold foil experiment where he set up a fluorescent screen gallery that had a thin gold foil placed in the center, he then had an alpha particle emitter that was shot at the gold foil. He noticed that some particles were deflected while some particles were able to pass right though. This lead Rutherford to propose that the atom was mostly empty space with a tiny part made of highly dense positive matter. He believed that in the center of the atom was an extremely dense, positively charged center that he called and we still refer to today as the nucleus.

7. Where are the electrons
In 1913, a Danish scientist, Niels Bohr proposed that electrons move around the nucleus in set paths that he called energy levels.
Bohr believed that the electrons traveled in set paths and had the ability to change energy levels. This was known as the Bohr Model
Now we know a little bit about the discovery of the nucleus, but what about those electrons that Thomson found, we know that they are not evenly distributed throughout and we know that the atom is mostly made of empty space, so where are the electrons. In 1913, a Danish scientist, Niels Bohr proposed that electrons move around the nucleus in set paths that he called energy levels. Bohr said that this motion was similar to the way that planets orbit the sun in the solar system. Bohr believed that the electrons traveled in set paths and had the ability to change energy levels. We refer to this as the Bohr Model, you will often see the Bohr Model and we will be using this a lot when we start bonding atoms.

8. Have we found the Electrons?
Austrian physicist Erwin Schrodinger and German physicist Werner Heisenberg showed one aspect of the Bohr-Model was incorrect. They proved that electrons do not travel in set, predictable paths.
The current atomic theory states that the electrons paths are not definite, but there are regions within the atom where the electrons are likely to be.
These likely regions are known as orbitals and together form the electron cloud. This model is known as the electron cloud model.
We now know that electrons move so quickly within the cloud that it is like they are everywhere at once.
Later, Austrian physicist Erwin Schrodinger, yes the one with the cat, and German physicist Werner Heisenberg showed one aspect of the Bohr Model was incorrect. They proved that the electrons do not travel in set predictable paths or orbits. They determined that there were different shapes the electrons made and called these shapes orbitals. The current atomic theory states that the electron paths are not definite, but there are regions within the atom where the electrons are likely to be. These likely regions are known as orbitals and together from the electron cloud. This model is known as the electro cloud model. We now know that electrons move so quickly within the cloud that it like they are everywhere at once. Think of a swarm of gnats buzzing around.

9. The atom
Even though atoms are small, they are made up of particles that are even smaller.
So tonight we are diving into the parts of an atom. Even though atoms are small, they are made up of particles that are even smallere.

10. What is an atom made of? NUCLEUS
Protons are positively charged particles that are found within the nucleus of each atom.
The proton has the second greatest mass of any of the subatomic particles that make up the atom.
Neutrons are also found in the nucleus, but they do not carry any charge. (NEUTRAL)
The nucleus is extremely dense
What is an atom made of? Let’s start with the nucleus. This nucleus is made of protons which are positively charged particles that are found within the nucleus of each atom. The proton has the second greatest mass of any of the subatomic particles that make up the atom. Neutrons are also found in the nucleus, but the do not carry any charge also known as neutral. The nucleus is extremely dense and carries most of the mass of the atom.

11. What is an atom made of? Electron Cloud
Electrons are the negatively charged subatomic particles that are found outside of the nucleus in the electron cloud.
Electrons are the least massive of any of the subatomic particles. It would take electrons to equal the mass of one neutron.
The units for mass of subatomic particles are atomic mass units (amu).
Electrons are not found in the nucleus they are negatively charged subatomic particles that are found outside of the nucleus in the electron cloud. Electrons are the least massive of any of the subatomic particles. It would take 1836 electrons to equal the mass of one neutron. The units for mass of subatomic particles are atomic mass units. Protons have about 1 amu, Neutrons have a mass of about 1 amu as well. Electrons have so little mass that it does not register as an amu.

12. What is an atom made of?
Atoms are neutral. This is because the number of protons is always the same as the number or electrons in an atom.
If an atom loses or gains electrons it is no longer an atom. It is an ion.
If an atom loses an electron it becomes a positive ion (cation), If it gains an electron, it becomes a negative ion (anion).
Atoms are neutral. This is because the number of protons is always the same as the number or electrons in an atom/ If an atom loses or gains electrons it is no longer an atom. It is an ion. If an atom loses an electron it becomes a positive ion (cation) because it is PAWSATIVE! If it gains an electron, it because A NEGATIVE ION or an anion.

13. How do atoms of different elements differ?
There are over 110 elements. There are different elements because there are different atoms.
The atoms different because within the atom there are different numbers of protons (and electrons)
The number of protons within an atom is reflected in the atomic number of the element. All atoms of an element have same atomic number.

14. Isotopes
Isotopes are defined as atoms with the same number of protons, but different numbers of neutrons.
Atoms of isotopes are the same element because they have the same number of protons.
Atoms of isotopes have different masses because they have a different number of neutrons.
Isotopes of an atom share most of the same physical and chemical properties.
Isotopes of an element can be identified by their mas number.
The mass number is the sum of the protons and neutrons found in the nucleus.
The atomic mass of an element is an average of the masses of all natural isotopes of an atom.
To calculate the number of neutrons in an atom, subtract the atomic number from the atomic mass.

15. Forces in atoms There are four basic forces at work within the atom
Gravitational-all objects with mass exert a gravitational pull.
Electromagnetic- all objects with a charge exert an attraction for the opposite charge
Strong-all objects that are in close proximity to one another exert a force on each other, found in the nucleus.
Weak-found in the nucleus, due to the activities of the smallest nuclear particles (bosons) responsible for radioactivity
These four forces work together to give an atom it structure and properties.