Chemistry Regents Study Guide
Topic 1: The Atom
I. Different Atom Models
a. Dalton’s Model
i. Elements have atoms.
ii. Atoms of an element are the same.
iii. Compounds are formed from combinations of atoms.
b. Rutherford Experiment – Gold Foil
i. What is the experiment?
1. Alpha (positive) particles were shot at gold foil.
2. Most of the particles passed through the foil
3. Only a small amount of the particles were deflected
ii. Atoms are mostly empty space because most of the particles passed
through the foil
iii. Small, dense, positively charged nucleus because only a small amount of
the particles were deflected
c. Bohr Model
i. Added that the nucleus is surrounded by electrons in circular orbits
d. Wave-Mechanical Model
i. What we use now!
ii. Electrons move in an “electron cloud”
iii. “Orbitals” are areas where an electron is most likely to be found
II. Structure of an Atom
a. Subatomic particles
i. Protons: positive charge and 1 amu (mass)
ii. Neutrons: neutral charge and 1 amu (mass)
iii. Electrons: negative charge and 0 amu (mass)
b. Nucleus: made up of protons & neutrons
c. Atomic mass = # of protons + # of neutrons
d. Atomic number = # of protons
i. Changing the number of protons changes the atom into a different element
e. The number of protons = number of electrons of a neutral atom
f. Ground state: all electrons are at their lowest possible energy level
i. Electron configuration shows the number of electrons in each energy level
1. Example: 2-8-7
a. There are 2 electrons in the first energy level, 8 electrons in
the second energy level, and 7 electrons in the third level.
g. Excited state: when an electron gains energy, it moves to a higher energy level
, i. When an electron returns from a higher energy state to a lower energy
state, it releases energy (in the form of light).
ii. This creates the bright line spectrum.
h. Valence Electrons: the outermost electrons
i. All elements in the same Group on the Periodic Table have the same # of
valence electrons
ii. # of Valence electrons determines chemical properties
iii. Atoms with a filled valence level (8 electrons) are stable.
1. H and He are exceptions: they only have 2 valence electrons
2. Atoms form bonds to fill their valence energy level.
3. Noble gasses (Group 18) all have 8 valence electrons, so they are
unreactive.
i. Isotopes: Same element, same # of protons, different # of neutrons (which means
they will have different mass).
i. Same atomic number (protons), different atomic mass (protons + neutrons)
j. The average atomic mass = weighted average of its naturally occurring
isotopes
i. Average atomic mass = (mass 1)(% as decimal) + (mass 2)(% as decimal)
Topic 2: Nuclear Chemistry
I. Each Isotope has a specific mode and rate of decay – Table N
a. Rate of decay is called half-life.
i. Half-life is a constant that doesn’t change.
ii. Half-life = measure of time it takes one half of something to decay.
iii. It will never decay to completely zero.
II. Most atoms are stable, but some atoms have unstable nuclei.
a. Stability depends on the ratio of protons to neutrons
i. Stable isotopes have a 1:1 ratio
b. Most radioactive isotopes have twice as many neutrons as protons
c. All elements higher than 83 are radioactive.
III. Transmutation
a. Transmutation = a change in an atom’s nucleus to make it a new element
i. Artificial: needs additional energy to make it happen
1. Will always have 2 reactants (on the left of the arrow)
2. Examples:
ii. Natural: occurs naturally without added energy
1. Will always have 1 reactant and 2 products
2. Examples:
b. Table O
i. Shows the different radioactive particles that can be released
ii. Top number = charge. Bottom number = mass
Topic 1: The Atom
I. Different Atom Models
a. Dalton’s Model
i. Elements have atoms.
ii. Atoms of an element are the same.
iii. Compounds are formed from combinations of atoms.
b. Rutherford Experiment – Gold Foil
i. What is the experiment?
1. Alpha (positive) particles were shot at gold foil.
2. Most of the particles passed through the foil
3. Only a small amount of the particles were deflected
ii. Atoms are mostly empty space because most of the particles passed
through the foil
iii. Small, dense, positively charged nucleus because only a small amount of
the particles were deflected
c. Bohr Model
i. Added that the nucleus is surrounded by electrons in circular orbits
d. Wave-Mechanical Model
i. What we use now!
ii. Electrons move in an “electron cloud”
iii. “Orbitals” are areas where an electron is most likely to be found
II. Structure of an Atom
a. Subatomic particles
i. Protons: positive charge and 1 amu (mass)
ii. Neutrons: neutral charge and 1 amu (mass)
iii. Electrons: negative charge and 0 amu (mass)
b. Nucleus: made up of protons & neutrons
c. Atomic mass = # of protons + # of neutrons
d. Atomic number = # of protons
i. Changing the number of protons changes the atom into a different element
e. The number of protons = number of electrons of a neutral atom
f. Ground state: all electrons are at their lowest possible energy level
i. Electron configuration shows the number of electrons in each energy level
1. Example: 2-8-7
a. There are 2 electrons in the first energy level, 8 electrons in
the second energy level, and 7 electrons in the third level.
g. Excited state: when an electron gains energy, it moves to a higher energy level
, i. When an electron returns from a higher energy state to a lower energy
state, it releases energy (in the form of light).
ii. This creates the bright line spectrum.
h. Valence Electrons: the outermost electrons
i. All elements in the same Group on the Periodic Table have the same # of
valence electrons
ii. # of Valence electrons determines chemical properties
iii. Atoms with a filled valence level (8 electrons) are stable.
1. H and He are exceptions: they only have 2 valence electrons
2. Atoms form bonds to fill their valence energy level.
3. Noble gasses (Group 18) all have 8 valence electrons, so they are
unreactive.
i. Isotopes: Same element, same # of protons, different # of neutrons (which means
they will have different mass).
i. Same atomic number (protons), different atomic mass (protons + neutrons)
j. The average atomic mass = weighted average of its naturally occurring
isotopes
i. Average atomic mass = (mass 1)(% as decimal) + (mass 2)(% as decimal)
Topic 2: Nuclear Chemistry
I. Each Isotope has a specific mode and rate of decay – Table N
a. Rate of decay is called half-life.
i. Half-life is a constant that doesn’t change.
ii. Half-life = measure of time it takes one half of something to decay.
iii. It will never decay to completely zero.
II. Most atoms are stable, but some atoms have unstable nuclei.
a. Stability depends on the ratio of protons to neutrons
i. Stable isotopes have a 1:1 ratio
b. Most radioactive isotopes have twice as many neutrons as protons
c. All elements higher than 83 are radioactive.
III. Transmutation
a. Transmutation = a change in an atom’s nucleus to make it a new element
i. Artificial: needs additional energy to make it happen
1. Will always have 2 reactants (on the left of the arrow)
2. Examples:
ii. Natural: occurs naturally without added energy
1. Will always have 1 reactant and 2 products
2. Examples:
b. Table O
i. Shows the different radioactive particles that can be released
ii. Top number = charge. Bottom number = mass
