Chemistry Unit 2 Study Guide
Atoms and the Periodic Table
History of Atomic Models
Key Terms:
Continuous Theory of Matter- the theory that matter could be sub-divided without end.
Particle Theory of Matter- the theory that matter is made up of definite particles that cannot be
divided infinitely.
Atoms- The smallest particle of matter capable of chemical interactions.
John Dalton- developed the first experimental atomic model in 1803.
Law of Definite Composition- compounds are formed of elements combined in specific ratios that
are unique for that compound.
Law of Conservation of Matter- matter can neither be created nor destroyed, it only changes form.
Element- a substance made up of all the same kind of atom.
Compound- a substance made up of atoms of two or more elements combined in simple, whole
number ratios.
Joseph J. Thompson- discovered the electron and developed the “plum pudding” model of the
atom.
Plum Pudding model- Atoms are a uniform positive charge with negatively charged electrons
floating in them.
Ernest Rutherford- discovered the nucleus and the proton. Developed the nuclear model of the
atom.
Nucleus- the dense, positively charged, center of an atom composed of protons and neutrons.
Nuclear model- the atom is mostly empty space with a small, dense, positively charged nucleus.
James Chadwick- discovered the neutron.
Atomic number- the number of protons in an atom.
Mass number (atomic mass)- the total number of protons and neutrons in an atom.
Niels Bohr- developed the theory that electrons in an atom exist in specific energy levels outside the
nucleus called principal energy levels. His model was called the planetary model.
Planetary model- electrond orbit the nucleus in distinct energy levels like planets around the sun.
Quantized- when something has separate, discrete values. We call the current model of the atom the
quantum model because the energy levels are quantized, that is, the atom has separate energy levels with distinct energy
values.
Principal energy level- a region around the nucleus containing a specified group of electrons in
sublevels and orbitals.
Ground state- An atom’s lowest energy state.
Louise de Broglie- developed the theory of wave-particle duality.
Wave-particle duality- all matter displays both particle and wave-like properties, including electrons.
Werner Heisenburg- developed the Heisenburg Uncertainty Principle.
Heisenburg Uncertainty Principle - it is impossible to measure simultaneously the position in
space and the energy (or momentum) of an orbiting electron.
Quantum Model- an atomic model that describes the electron’s energy precisely while describing its
location as probability.
Orbital- a 3-dimensional region of probable position where electrons are likely to be found.
You should know:
1) You should know all the key terms listed above. That is, you should be able to explain in
your own words what the term means.
2) If it is a person, you should know what they discovered or what theory they developed and
how that changed the current understanding of the atom
You should be able to:
1) Give a history of our current understanding of the atom. That is, you should be able to
explain, in order, each of the models and what discovery led to a revision of the theory.
Electron Configuration
Key Terms:
Quantum Numbers- each electron has four quantum numbers that give it a specific
address within the atom represented by the letters n, l, m and ms.
Principal Quantum Number (n)- the principle energy level in which the electron resides.
An electron’s “n” is determined by the row of the periodic table in which the element is located.
Electron shell- the set of orbitals within the same principle energy level (n).
Azimuthal Quantum Number (l- a lowercase letter L), describes the sublevels of each
principle energy level.
Sublevels- symmetrical shapes that surround the nucleus represented by the letters s, p, d,
and f.
Subshell- the set of orbitals that have the same n and l values.
Magnetic Quantum Number (m)- Describes the spatial orientation of the orbitals within
an atom
Electron Spin Quantum Number (ms)- describes the “spin” of the electrons in an orbital.
s sublevel- the simplest of all sublevels, it contains only one orbital with a sphere shape. It
has an l value of 0
p sublevel- there are three orbitals in the p sublevel arranged around the x, y, and z axis. It
has an l value of 1
d sublevel- there are five orbitals in the d sublevel. Their shapes are more complex and they
have an l value of 2
f sublevel- there are seven orbitals in the f sublevel. It has the most complex shape and an l
value of 3.
Electron configuration- the way an atom’s electrons are distributed among its orbitals.
Pauli Exclusion Principle- each orbital can hold at most 2 electrons.
Hund’s Rule- for like orbitals, the lowest energy is achieved when the number of electrons
with the same spin is the greatest. (Or, electrons won’t pair up unless they have to!)
Octet- when an atom has eight electrons in its outermost shell. This is very stable
configuration.
You should know:
1) All the key terms listed above. That is, you should be able to explain in your own
words what the term means.
2) How many orbitals and how many total electrons are each energy level
3) The four components that make up a quantum number.
You should be able to:
1) Write the electron configuration of any atom in a ground-state diagram.
2) Write the summary notation and abbreviated forms of the electron configuration.
3) Write the first two quantum numbers for any given element (n= and l= ).
4) Explain the relationship between the terms electron cloud, electron shell, subshell,
and orbital. (Electron cloud refers to all the electrons in an atom, electron shell to the electrons in a
given energy level, subshell to the electrons in the same sublevel (ex. 3p) and orbital to the specific
region within a sublevel. So Carbon has 6 electrons in its electron cloud, 2 electrons in the 1st electron
shell and 4 electrons in the 2nd shell, with 2 of those electrons in the p subshell and one electron in 2
out of 3 p orbitals.
Element Notations
Key Terms:
Atomic Number (Z)- the number of protons that are in an atom’s nucleus.
Isotopes- When an atom has a number of neutrons unequal to its number of protons.
Mass Number (A)- the number of protons plus the number of neutrons, or atomic mass.
Average Atomic Mass- the mass of an element when all isotopes are average together.
Valence Electrons- Valence electrons are the electrons in the outermost energy level.
Valence electrons are not necessarily the last electrons to fill an orbital. However, they are
the electrons with the highest “n” value, the highest principle quantum number.
Electron Dot Notation- each valence electron is represented as a dot beside the element
symbol. If there are multiple valence electrons, they are put in pairs on the four sides of the
symbol.
You should know:
1) All the key terms listed above. That is, you should be able to explain in your own
words what the term means.
2) The notation used to identify different isotopes.
You should be able to:
1) Write the chemical notation for an isotope.
2) Identify how many protons, neutrons and electrons are in a given isotope.
3) Figure out the number of valence electrons in each element.
4) Write the electron-dot notation for any element.
History of the Periodic Table
Key Terms:
Periodic Table- a table organizing the known elements according to their atomic number.
Dmitri Mendeleev- developed the periodic table
You should know/ be able to explain:
1) The improvements Mendeleev made to the existing arrangements of elements.
2) How Mendeleev’s table differs from the modern periodic table we use today
Periodic Table Trends
Key Terms:
Atomic Radius- the distance from the center of an atom’s nucleus to its outermost energy
level. An atom’s radius is determined by the size of the electron cloud that surrounds it.
Ion- an atom that has lost or gained electrons.
Cation- an atom that loses electrons and becomes positively charged
Anion- an atom that gains extra electrons and becomes negatively charged
Ionization energy- the minimum amount of energy required to remove one electron from
the ground state (lowest energy state) of the gaseous-state atom.
Electron affinity- the energy involved in the addition of an electron to an atom
Electronegativity- the attraction between an atom’s nucleus and its valence electrons. In
other words, it is a measure of how strongly atoms hold onto their electrons.
You should be able to:
1) Explain the trends for atomic radius, ionization energy, electron affinity, and
electronegativity as you move from left to right across the table and top to bottom.
2) Explain what factors affect ionization energy, electron affinity, and electronegativity.
3) Explain how the size of a cation or anion compares to the parent atom
4) Predic for any given element whether the atomic radius, ionization energy, electron
affinity, and electronegativity will be relatively small or large.
Families of the Periodic Table
Key Terms:
Groups (families)- the vertical columns in the periodic table. Elements in the same group
have the same number of electrons in their outer energy level.
Periods- the horizontal rows in the periodic table. Elements in the same period have the
same number of energy levels.
Metals- elements located on the left of the “staircase” of the periodic table.
Non-metals- elements located on the right side of the “staircase” of the periodic table.
Metalloids- elements that are on either side of the “staircase”. They exhibit properties of
both metals and non-metals.
You should be able to:
1) For any element in the periodic table be able to tell the name, symbol, # of protons,
neutrons, and electrons, the energy level and the number of electrons in the outer energy
level as well as determine if it is a metal, non-metal, or metalloid.
2) For each of the families listed, you should be able to identify what column (group #) it is
in, how many valence electrons it has (at least for the first four groups listed), some of the
properties or characteristics of that group and why they have that trait. (e.g. alkaline metals
are highly reactive because they have only one valence electron)
1) Alkali Metals
2) Alkaline Earth Metals
3) Halogens
4) Noble Gases
5) Transition Elements
6) Inner Transition Elements