Chapter 2 - Structure of the Atom

Understanding the atom (atomic level) is essential to the study of radiologic science due to:

• interactions in the x-ray tube that produce x-rays occur at the atomic level.

• interactions between the x-ray photons and the human body also occur at the atomic level.

• x-ray photons exiting the patient interact at the atomic level of the image receptor to create images.

• other areas of study in the radiologic sciences will require a working knowledge of the atom

Who was Leucippus?

an ancient Greek philosopher most often associated with the earliest atomic theory

Who was Democritus of Abdera

• a student and follower of Leucippus, who provided one of the most detailed and elaborate theories

• is credited with expanding on and formalizing the earliest atomic theory

• lived from about 460 BC to about 370 BC

How did Democritus's atomic theory explain the diverse properties of matter in the physical world?

• Democritus believed that these atoms were indestructible and differed in their size, shape, and structure

• he theorized that the nature of the object depended on its atoms

Who was John Dalton?

• the English in the early 1800s

• developed a sound atomic theory based not on philosophical speculation but on scientific evidence.

What did John Dalton’s theory explain?

• that all elements were composed of tiny indivisible and indestructible particles called atoms

• that compounds were formed by molecules and molecules by fixed ratios of each type of constituent atom

• that a chemical reaction was a rearrangement of atoms

Who was Dmitri Mendelee?

• a renowned Russian chemist whom most notably developed the periodic table of elements, by advancing John Dalton’s work

• which demonstrates that elements, arranged in order of increasing atomic mass, have similar chemical properties.

Who was Joseph John “J.J.” Thomson?

• a renowned British physicist

• discovered the electron while studying cathode ray tubes

• developed the “plum pudding model”

Who was Ernest Rutherford?

• a pioneering physicist

• conducted experiments with alpha particles

• proposed a new model of the atom that resembled a tiny version of our solar system

• a student of Joseph John “J.J.” Thomson that advanced his theory

Who was Niel Bohr?

• a 20th-century Danish physicist

• refined Rutherford’s work, bringing us to the theory and model of the atom with which we are most familiar

Niel Bohr’s theory describes the atom as having three fundamental particles (components):

electrons, neutrons, and protons

The quantity of each fundamental particles (electrons, neutrons, and protons) is unique in which way?

to the matter or element it composes

What is the nucleus made up of:

protons and neutrons (nucleons)

Orbiting the nucleus are _____ in defined energy levels and distances from that nucleus

electrons

If the negative charges outnumber the positives, the atom is called:

a negative ion (anion)

If the positive charges outnumber the negatives, the atom is called:

a positive ion (cation)

Electrical charge is a characteristic of:

matter

What energy results from the strong nuclear force that holds the nucleus together?

binding energy

What does binding energy create?

creates a strong attraction in the nucleus, overcoming the natural tendency for like charges to repel

Binding energy is also a measure of the amount of energy necessary to:

split an atom (break it apart)

The electron-binding energy depends on the following:

• how close the electron is to the nucleus

• how many protons are in the atom

The force of attraction between the negatively charged electrons and positively charged protons keeps the electrons:

in orbit

Just as neutrons and protons are held together in the nucleus by nuclear binding energy, the electrons are held in their orbits by:

electron-binding energy

Nuclear binding energy and electron binding energy are key determinate of:

x-ray production

The two types of atomic interactions in the x-ray tube that produce x-rays are:

• characteristic

• bremsstrahlung

Describe what is characteristic interactions:

the removal of orbital electrons from atoms

Describe what is bremsstrahlung interactions?

attraction to the nucleus of the atom and the penetrating strength (energy) of the x-ray photon produced

An atom has defined energy levels, each at a different distance from the nucleus, called:

electron shells

How do the electrons orbit around the nucleus?

three-dimensionally

Which of the following statements is true regarding electron shells in atoms?

the shells fill from the K shell outward; the outermost shells may not fill completely

The limit of electrons can be determined with which formula?

2n², in which n is the shell's number.

Which of the following statements best describes the octet rule (valence shell) and the maximum number of electrons in the outermost shell of an atom?

the outermost shell can hold a maximum of 8 electrons. Octet rule, valance shell

Atoms represent _____ for interaction.

targets

What happens when the atom is more complex?

greater is the opportunity for interaction

Name four elements used in an X-Ray tube?

tungsten, aluminum, copper, nickle

What device was used by Dr. Roentgen that produced the X-Rays?

the cathode tube

How is Power measured?

by Watts

The Periodic table is attributed to who?

Dmitri Mendeleev

The outer most shell of an atom is called?

the valence shell

What is another name for “atomic number”?

• protons

• number of protons an atom contains in its nucleus

What is another name for the “atomic mass number”?

• protons and neutrons (nucleons)

• number of protons and neutrons an atom has in its nucleus

What are Elements?

the simplest forms of substances that compose matter

What is a Chemical symbol?

an abbreviation of the element

What are isotopes?

the same number of protons but a different number of neutrons

What are isotones?

the same number of neutrons but a different number of protons

What are isobars?

a different number of protons but the same total number of protons and neutrons

What are isomers?

the same number of protons and neutrons but different amounts of energy within their nuclei

There are two primary ways atoms bond to form molecules and subsequently more complex structures:

ionic bond and covalent bond.

Ionic bonding:

• is based on the attraction of opposing charges

• one atom gives up an electron and one atom takes an extra electron

• the difference in electrical charge bonds them together

Covalent bonding:

• is based on two atoms sharing electrons that then orbit both nuclei

• an outermost electron from one atom begins to orbit the nucleus of another adjacent atom in addition to its original nucleus

• can be thought of as a figure-8 pattern

Definition of atoms:

• from the Greek word “atomos” meaning indivisible

• the basic building block of matter composed of electrons, protons, and neutrons

Definition of binding energy:

a force of attraction that holds the nucleus of an atom together and hold the electrons in orbit around the nucleus

Definition of a compound:

the combination of elements in definite proportions

Definition of an electron:

• subatomic particle with one unit of negative electrical charge

• mass of 9.109 × 10^-31 kg

Definition of an electron shell:

a defined energy level at a distance from the nucleus within which electrons orbit

Definition of an element:

a substance that cannot be broken down into simpler parts by ordinary chemical means

Definition of a neutron:

• a subatomic particle with no electrical charge

• mass of 1.675 × 10^-27 kg

Definition of a nucleus:

the central core of an atom made up fundamentally of protons and nuetrons

Definition of a proton:

• subatomic particle with one unit of positive electrical charge

• mass of 1.673 × 10^-27 kg

Molecule are:

two or more atoms bonded together