Atomic Structure & Theory

Atomic structure and the history of

the Atomic Theory

Atoms

• An atom is the smallest particle into which an element can be divided and still be the same substance.

• An element is a substance made of only one kind of atom

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​What is an atom?

​The building blocks of matter

​What are atoms made of?

​Atomic Structure

• Atoms are made of smaller particles called sub-atomic particles

• These particles are protons, neutrons and electrons

• Protons and neutrons form the nucleus at the center of the atom

• The electrons orbit around the nucleus

​The mass and charge of sub-atomic particles

​Sub-atomic Particles

• Protons are positively charged particles that has a mass of 1u

• Neutrons carry no electric charge and have the same mass as a proton (1u)

• Electrons are negatively charged particles and have almost zero mass

Multiple Choice

The smallest particle into which an element can be divided and still be the same element is a(n)

• proton

• neutron

• electron

• atom

Multiple Choice

Which subatomic particle has a positive charge?

• proton

• nuetron

• electron

• atom

Multiple Choice

Which subatomic particle has a negative charge?

• proton

• neutron

• electron

• atom

Multiple Select

Which TWO of the following subatomic particles are inside the nucleus?

• protons

• electrons

• neutrons

• There are no subatomic particles in the nucleus of an atom.

• The number of protons in the nucleus of an atom is the atomic number of that atom

• ​The number of protons distinguishes the atoms of one element or from the atoms of another

What is the Atomic Number of an atom?

​Describing an atom: Atomic Number

• The combined number of protons and neutrons in an atom's nucleus is its atomic mass (also called mass number)

• Atoms of an element always has the same number of protons, but they sometimes have a different number of neutrons

• These atoms are called isotopes

​What is atomic mass?

​Describing atoms: Atomic mass

Multiple Choice

The number of which subatomic particle determines the element of an atom (if it's carbon, oxygen, nitrogen, etc.)?

• proton

• neutron

• electron

• Subatomic particles do no determine the element of an atom.

Multiple Choice

What is the mass number defined as?

• the number of protons

• the number of protons and neutrons

• the number of neutrons

• the number of protons and electrons

Scientific theories of what an atom looks like has been through many changes throughout history. From Democritus in ancient Greece to Erwin Schrodinger, as new discoveries are made, the Atomic Theory has been updated.

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History of Atomic Theory

In ancient times, people believed that matter was made of various combinations of earth, wind, water and fire.

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​Matter made from earth's elements

​Ancient Ideas of Matter

• First recorded idea of matter being made of tiny particles

• Democritus called these particles "the atomos", which means indivisible in Greek

• He believed that atoms were hard, solid spheres with hooks that attached to other atoms

​Ancient Greek atoms

​Democritus

• First scientific explanation of an atom

• Theorized (correctly) that all atoms of an element would be identical to each other but different from atoms of all other elements

• Believed that atoms were spheres of solid matter

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​Solid Sphere Model

​John Dalton

• Discovered the negatively charged electron

• Believed that atoms were made of positively charged matter and the electrons were mixed throughout the atom (like fruit in a fruit-cake)

• Commonly referred to as the "Plum Pudding Model"

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​Plum Pudding Model

​J.J. Thomson

​J.J. Thomson's experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons.

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J.J. Thomson's cathcode experiment

Nuclear Model

Ernest Rutherford

• Discovered that atoms had a very small but dense nucleus that was positively charged and the electrons orbited around the nucleus

• Also discovered that atoms were made mostly of empty space

• Commonly referred to as the "Nuclear Model"

​Rutherford's gold foil experiment showed that the atom is mostly empty space with a tiny, dense, positively-charged nucleus. This led Rutherford to propose the nuclear model, in which an atom consists of a very small, positively charged nucleus surrounded by the negatively charged electrons.

Rutherford's gold foil experiment

• Discovered that electrons had different amounts of energy, depending on how far away they were from the nucleus.

• Theorized the existence of "electron shells" with different energy levels where electrons could be found

• Commonly referred to as the Bohr Model or Planetary Model

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Planetary Model/Bohr Model

​Neils Bohr

• Theorized that electrons did not exist on fixed shells or energy levels

• Represented electrons as being in an electron cloud surrounding the nucleus

• First model that accurately account for the Heisenburg Principle

• Commonly referred to as the Electron Cloud Model

​Electron Cloud Model

​Erwin Schrodinger

Multiple Choice

An atom's overall charge is ________.

• positive 

• depends

• neutral 

• negative 

Multiple Choice

What scientist is best known for his "Plum Pudding" model of the atom?

• J.J. Tomson

• Ernest Rutherford

• John Dalton

• Democritus

Multiple Choice

J.J. Thomson provided evidence that an atom...

• is the smallest particle of matter

• contains negatively charged particles

• has an overall negative charge

• has an overall positive charge

Multiple Choice

Rutherford's gold foil experiment provided evidence that...

• negative and positive charges are spread evenly throughout the atom.

• alpha particles have a positive charge.

• gold is not a dense as previously thought.

• there is a dense positively charged nucleus at the center of an atom.

Multiple Choice

Ernst Rutherford discovered which part of the atom through the use of gold foil?

• Proton

• Neutron

• Electron

• Orbitals

Multiple Choice

What scientist is best known for his "Plum Pudding" model of the atom?

• J.J. Thomson

• Ernest Rutherford

• John Dalton

• Democritus

Multiple Choice

Place the following scientists in order, from earliest to latest: 
Rutherford, Dalton, Bohr, Thomson

• Dalton, Rutherford, Bohr, Thomson

• Thomson, Dalton, Rutherford, Bohr

• Dalton, Thomson, Rutherford, Bohr

• Bohr, Dalton, Rutherford, Thomson

Multiple Choice

Who came up with the model of an atom pictured?

• J.J. Thompson

• Ernest Rutherford

• Neils Bohr

• James Chadwick