Exam Review: Atomic Theory and Structure

Atomic Structure

SC.912.P.8.3

History of

Atomic Theory

Scientific knowledge builds on past research and

experimentation.

The atomic theory has changed over time as new

technologies have become available and new evidence

uncovered..

Watch the video for a quick review of atomic theory.

Democritus - 400 B.C.

Democritus, a philosopher in ancient Greece, began the
search for a description of matter. He questioned whether
matter could be divided into smaller and smaller pieces
forever until eventually the smallest possible piece would
be obtained. He believe that the samples possible piece of
matter was indivisible.

​Democritus named the smallest piece of matter “atomos” meaning “indivisible” or “not to be cut”. To Democritus, atoms were small, hard particles that were all made of the same material, but were formed into different shapes and sizes.

Multiple Choice

Who used the word "atomos" to decsribe the uncuttable (indivisible) atom.

• Democritus

• Thomson

• Bohr

• Dalton

John Dalton - 1803

In the early 1800s, the English Chemist John Dalton performed a number
of experiments that eventually lead to the acceptance of the idea of atoms.
Dalton model is called the Billiard Ball model. He theorized that:

1.

All matter is made of tiny, indivisible particles called atoms.

2.

Atoms of the same element are identical. Atoms of different elements
are different.

3.

Atoms of different elements combine in simple whole number ratios
to form compounds.

4.

In chemical reactions atoms are combined, separated, or rearranged.

Although much of Dalton’s theory still stands today, we now know that it wasn’t 100%
accurate. For example, atoms can be divided because they are made of subatomic particles called
protons, neutrons, and electrons (which are made of even smaller quarks). We also know that
isotopes exist so atoms of the same element are not identical.

Multiple Choice

Which one of these is Dalton's Model?

Multiple Choice

All of the following of Dalton's theories were correct EXCEPT - 

• All atoms are identical.

• All matter is made of atoms.

• Chemical reactions rearrange atoms.

• Compounds contain different atoms.

J.J. Thompson 1897

In 1897, the English scientist named J.J.Thompson
provided the first hint that an atom is made of even smaller
particles. He discovered the presence of a negative
particle in the atom - the electron.

J.J. Thompson discovered the electron by observing the
behavior of a cathode ray in a vacuum tube. Since the
rays were deflected by a positive charge, Thompson,
determined that the ray was composed of negatively
charged particles.

​He proposed a model of the atom that is
sometimes called the “Plum Pudding” model. His theory
was that atoms are made from a positively charged
substance with negatively charged electrons scattered
about. Like raisins in a pudding or chocolate chips in a
cookie.

Multiple Choice

Which one of these is Thompson's Model?

Multiple Choice

Who discovered electrons?

• Rutherford

• Bohr

• J.J. Thompson

• Democritus

Multiple Choice

Which experiment was performed by J. J. Thomson in 1897?

• Oil Drop Experiment

• Gold Foil Experiment

• Wave  Experiment

• Cathode Ray Experiment

Multiple Choice

Which subatomic particle was discovered as a result of the cathode ray experiment?

• proton

• neutron

• electron

• nucleus

Ernest Rutherford, 1908

In 1908, the English physicist Ernest
Rutherford performed an experiment using
positively charged particles fired at gold foil.
Through his experiment, he proved that
atoms are not a “pudding” filled with a
positively charged materials. He theorized
that atoms have a small,dense positively
charged center, which the called the
nucleus. He said that nucleus is tiny
compared to the atom as a whole, because
the atom is mostly open space! He
concluded that the negatively charged
particles are scattered outside the nucleus.

Multiple Choice

Ernest Rutherford discovered that the atom was mostly _________________ and has a _______________ charged nucleus.

• empty space, positively

• empty space, negatively

• full of protons, positively

• full of neutrons, negatively

Multiple Choice

Who performed the Gold Foil Experiment?

• J. J. Thomson

• Ernest Rutherford

• Neils Bohr

• John Dalton

Multiple Choice

Which of the following were outcomes of the Gold Foil Experiment?  

• Electrons occupy different energy levels orbiting the nucleus.

• Electrons are negatively charged subatomic particles.

• Electrons orbit the empty space around the dense positive nucleus.

• Electrons move in wave patterns around the nucleus

Multiple Choice

Which model was created after the discovery of the nucleus?

• Dalton's

• Rutherford's

• Quantum Mechanical

• Plum Pudding

Niels Bohr, 1913

In 1913, the Danish scientist Niels Bohr proposed an improvement. He built on the concept that the mass of an atom is contained mostly in the nucleus. He also theorized that electrons move in definite orbits around the nucleus, much like
planets circle the sun. These orbits, or energy levels, are located at certain distances from the nucleus. Bohr's model is referred to as the planetary model.

Bohr observed the atoms could absorb energy and jump to a higher orbit and emit energy when they fall back to a lower orbit. This energy can be observed as colored light if the energy is within the visible range.

In class, we saw this phenomenon by putting metal ion solutions in the flame and observing colored flames.

Multiple Choice

Proposed that electrons move around the nucleus in specific layers, or shells.

• Bohr

• Rutherford

• Chadwick

• Thomson

Multiple Choice

Which model was proposed by Neils Bohr?

• Planetary Model

• Plum Pudding Model

• Quantum Mechanical Model

• Solid Ball Model

Multiple Choice

What does the Bohr model suggest?

• Atoms are small, hard, indivisible objects. 

• That protons in the nucleus are attracted to electrons in the electron clouds. 

• That electrons travel around the nucleus of an atom in orbits or definite paths.

Multiple Choice

Light is emitted when electrons

• move from one atom to another.

• collide with one another, releasing energy.

• move from a lower energy level to a higher energy level.

• move from a higher energy level to a lower energy level.

Multiple Choice

What evidence led Niels Bohr to believe that electrons occupy specific energy levels in atoms?

• Excited electrons emit colored light at every possible wavelength.

• Excited electrons emit colored light at only certain wavelengths.

• Electrons emit colored light only when in an excited state.

• Electrons emit colored light only when in ground state.

Modern Electron Cloud Theory - 20th Century

Scientists: Schrodinger, Heisenberg, Einstein, and many others

According to today’s atomic theory, electrons do not orbit the nucleus in neat plant-like orbits
but move at high speeds in an electron cloud around the nucleus. These clouds represent a high probability of finding an electron. Electron clouds have distinct shapes and energies. An electron’s location depends upon how much energy the electron has.

Multiple Choice

What does an orbital represent?

• the limits of the electron location

• the probability of the electron location

• the circular path that an electron travels around the nucleus

• the minimum distance between the electron and the nucleus

Multiple Choice

Whose created this atom model?

• Dalton

• Thomson

• Rutherford

• Bohr

• Heisenberg and Schrodinger

Multiple Choice

John Dalton, JJ Thomson, Niels Bohr, Ernest Rutherford, James Chadwick, Erwin Schrodinger, and Louis de Broglie, and several other scientists contributed to the body of knowledge known as atomic theory. What do the changes made to atomic theory and the evolution of this body of knowledge demonstrate about the scientific process?

• Experimentation is key to yielding valid results

• Scientists need to replicate prior experiments to validate their findings.

• Theories change as new information becomes available

• Competition and financial gain drive scientific inquiry

Multiple Choice

How did each model of the atom help to develop the atomic theory? 

• Each model provided opinions that were added.

• Each model showed different properties of the same structure. 

• Each model showed new particles that had been discovered.

• Each model built upon the other to show new particles or properties of previously discovered particles. 

Match

Match the following

Dalton

JJ Thomson

Rutherford

Bohr

• Dalton

• JJ Thomson

• Rutherford

• Bohr

Mass Number (A)

The mass number is the number of protons plus the number of neutrons in
an atom’s nucleus. This carbon atom has 6 protons and 6 neutrons so it has a
mass number of 12.

You can use atomic number (protons) and mass number (protons + neutrons) to calculate the number of neutrons in an atom: Mass # - Atomic # = # of neutrons.

Mass number (A)

Ions

Ions are atoms which have lost or gained electrons.

Ions are formed because atoms want to have 8 electrons. This is known as the
octet rule. Atoms are more stable when they have a full outer shell.

Metals lose electrons to form positive cations.

Nonmetals gain electrons to form negative anions.

Hotspot

Atoms in which periodic table column will form 2+ ions?