Atomic Structure and Atomic Models

Comprehensive question-and-answer flashcards covering atomic theory history, subatomic structure, Bohr's model, the periodic table, and quantum chromodynamics.

What is an atom defined as in the lecture notes?

An atom is the smallest unit of matter that retains the chemical properties of an element, is stable, and serves as the basic building block of matter.

What are the two main structural portions of an atom?

The Nucleus (Nuclear Portion) and the Electron Cloud (Extranuclear Portion, Electron Orbital Shell).

What percentage of an atom's mass is located in the nucleus?

99.9%

How is the nucleus described in terms of its physical properties and charge?

It is described as small, dense, and positively-charged.

What is the atomic number of Gold as stated in the notes?

79

What did Democritus propose in the Ancient Greek Model (c. 400 BCE)?

He believed that all matter is composed of small, indivisible particles called atoms, derived from the word atomos meaning uncuttable.

What were the four essences and four substances in Aristotle's 4 Element Theory?

Essences: Cold, Hot, Wet, Dry. Substances: Earth, Water, Fire, Air.

What was John Dalton's 1803 atomic model called, and what was its significance?

It was called the Hook & Eye Affair Model, and it was the 1st scientific based model.

How did John Dalton describe atoms and their combination into molecules?

He stated that atoms are solid indivisible spheres, atoms of the same element have the same shape, and atoms combine to form molecules with their hooks and eyes.

Which atomic model was proposed by Joseph John Thomson in 1897, and what subatomic particle did he discover?

The Plum Pudding Model; he discovered the electron.

How did Joseph John Thomson describe the structure of an atom?

He stated that the atom is a positively charged sphere with negatively charged electrons embedded within, like raisins in a pudding.

What model did Ernest Rutherford propose in 1911, and what did he discover?

The Nuclear Model; he discovered the Nucleus.

How did Ernest Rutherford describe the atom and the nucleus?

He described the atom as mostly empty space, and the nucleus as a dense, positively-charged, centrally-located particle.

What was Niels Bohr's 1913 atomic model called, and how did it describe electron orbits?

The Mini-solar System Model; it stated that electrons orbit the nucleus in fixed energy levels (shells; quantized orbits).

Why is Bohr's Mini-solar System Model significant in radiologic physics?

It is the most useful model to describe x-ray interaction with atoms.

What is an electron transition according to Niels Bohr's model?

It occurs when outer shell electrons transfer to an inner shell by emitting energy if the inner shell becomes vacated.

What is an electron cascade?

A series of multiple electron transitions occurring one after another.

What is the maximum number of orbital shells an atom can have, and how are they designated?

There is a maximum of 7 orbital shells (based on the 7 Periods of the Periodic Table), named from K-shell to Q-shell ($n=1$ to $n=7$).

What does the Octet Rule state regarding the valence shell in Bohr's model?

The outermost shell (valence shell) can only handle 8 electrons (based on the 8 Groups of the Periodic Table).

Who created the first Periodic Table of Elements in 1869, and on what parameter was it based?

Dmitri Mendeleev, based on atomic mass.

Who improved the Periodic Table of Elements in 1913, and on what parameter was it based?

Henry Moseley, based on atomic number.

What do the periods and groups of the Periodic Table represent in terms of atomic structure?

Periods (horizontal rows) are equivalent to the shell numbers, and Groups (vertical columns) are equivalent to the valence electrons of the atom.

What is the Quantum Chromodynamics (QCD) Model (1970s - Present), and what does it focus on?

It is the standard model of particle physics that focuses on the internal structures of protons and neutrons.

According to the Quantum Chromodynamics (QCD) Model, what components make up protons and neutrons, and what force binds the nucleus?

Protons and neutrons are made of quarks (such as Up-type and Down-type) held by gluons, and the model explains the strong force that binds the nucleus together.