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Chapter 3: Atoms & Moles
Essential Questions:
1. What is an atom?
2. What particles make up an atom?
3. Where are the particles that make up an atom?
4. What are the different types of electromagnetic radiation?
Section 1: Substances are made of Atoms
Objectives:
1. State the three laws that support the existence of atoms.
2. List the five principles of John Dalton's atomic theory.
The __________ of ________________ ________________ states that two samples of a given
compound are made of the same elements in exactly the same proportions by mass regardless of the sizes or
sources of the samples. For example, every sample of sodium chloride (table salt) is made of 39.35%
sodium and 60.66% chlorine by mass.
Once chemists started sharing data for their laboratory experiments, they realized that in all chemical
reactions conducted with careful measurements the mass of the reacting system does not change. The
___________ of ____________________ of ____________ states that the mass of the reactants in a
reaction equals the mass of the products. This is further evidence that matter is composed of atoms, since
atoms would not be destroyed in a chemical reaction.
As chemists continued to experiment with the synthesis of different compounds, they discovered that
different compounds could be created with different proportions of atoms in a compound were discovered.
Chemists discovered that if two or more different compounds are composed of the same elements, the ratio
of the masses of the second element is always a ratio of small whole numbers. This example illustrates the
________ of ____________ __________________.
Dalton's Atomic Theory
1. All matter is composed of extremely small particles called ______________, which cannot be
________________, created, or __________________.
2. Atoms of a given element are ___________________ in their physical and _______________
properties.
3. Atoms of different elements differ in their ______________________ and _______________
properties.
4. Atoms of different elements combine in ______________, whole number ____________ to form
_____________________.
5. In chemical reactions, atoms are ________________, separated, or ___________________ but
never __________________, destroyed, or _____________________.
Review Questions:
1. What is the atomic theory?
2. According to Dalton, what is the difference between an element and a compound?
3. Which of Dalton's 5 principles still apply to the structure of an atom?
Section 2: Structure of Atoms
Objectives:
1. Describe the evidence for the existence of electrons, protons, and neutrons, and describe the
properties of these subatomic particles.
2. Discuss atoms of different elements in terms of their numbers of electrons, protons, and
neutrons, and define the terms atomic number and mass number.
3. Define isotope and determine the number of particles in the nucleus of an isotope.
Subatomic Particles:
The _______________ was discovered using cathode rays. English physicist, J.J. Thomson pumped
most of the air out of a glass tube and applied a voltage to two metal plates, called ______________, which
were placed at opposite ends of the tubes. The _____________ was attached to the positive terminal, so it
has a positive charge. The other electrode, called a ________________ had a negative charge because it is
attached to the negative terminal of the voltage source. The glowing beam that originated at the cathode and
struck the anode was made of negatively-charged particles, called ____________________.
The Rutherford ______________ ___________________ experiment showed that the nucleus of an
atom consists of a dense, positively-charged ___________________. The _______________ of an atom has
all of the _______________ charge, but only a very small fraction of the ______________ of the atom. By
measuring the numbers of alpha particles that were deflected and the angles of deflection, scientists
calculated the ______________ of the nucleus to be less than ______________ of the radius of the whole
atom.
The positively-charged particles that repelled the alpha particles in the gold foil experiments that
compose the nucleus of an atom are called __________________. The charge of a _____________ was
calculated to be exactly equal, but opposite in sign to the charge of an ________________.
James Chadwick discovered a particle that carried no electrical charge, named _____________,
which are part of the atomic nucleus.
Coulomb's Law states that the
closer two charges are, the
_______________ the force
between them.
Atomic number and Mass number:
The number of protons that an atom has is known as the atom's _______________ ____________.
The ________________ __________________ also reveals the number of _______________ in a neutral
atom. For example, gold has an atomic number of 79, so there are 79 protons in the nucleus of gold and
there are also 79 electrons around the nucleus of every gold atom. The _____________
_________________ is the total number of particles in the nucleus of an atom. Since the nucleus contains
_________________ and ___________________, the mass number is the sum of the number of protons and
neutrons. You can use the mass number to calculate the number of ________________ by subtracting the
atomic number from the _____________ _________________. Unlike the atomic number, which is the
same for all atoms of a given element, the mass number can vary among different _________________.
Review Questions:
1. Describe the differences between electrons, protons, and neutrons.
2. Calculate the atomic number and mass number of an isotope that has 56 electrons and 82 neutrons.
3. Why must there be an attractive force to explain the existence of stable nuclei?
Section 3: Electron Configuration
Objectives:
1. Compare the Rutherford, Bohr, and quantum models of an atom.
2. Explain how the wavelengths of light emitted by an atom provide information about the
electron energy levels.
3. List the four quantum numbers and describe their significance.
4. Write the electron configuration of an atom by using the Pauli Exclusion Principle and the
aufbau principle.
Atomic Models:
Thomson’s Plum Pudding Model
Characteristics:
-
Electrons are ____________-charged particles
-
Electrons are like the __________ in the pudding
-
The rest of the atom is a ____________-charged cloud
Rutherford’s Model
Characteristics:
-
Atom is mostly ______________ space
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Nucleus has most of the ____________, but not much
____________.
Bohr Model
Characteristics:
-
Electrons live in _____________ energy levels
-
When electrons absorb energy, they move to _________
energy states
-
When electrons release energy, it is in the form of _________
Electrons act like both particles and _____________. Thomson’s experiments demonstrated that
electrons act like ____________ that have mass. In 1924, Louis de Broglie pointed out that the behavior of
electrons according to Bohr’s model was similar to the behavior of _________________. De Broglie
suggested that _______________ could be considered waves confined to the space around a nucleus. As
waves, electrons could have only certain _______________ which correspond to the specific energy levels.
The present-day model of the atom takes into account both the particle and wave properties of electrons. In
this model, electrons are located in _____________, regions around a nucleus that correspond to specific
energy levels. Orbitals are regions where ____________ are likely to be found.
In 1913, Bohr showed that hydrogen’s line-emission spectrum could be explained by assuming that
the hydrogen atom’s electron can be in any one of a number of distinct energy levels.
•
An electron can move from a low energy level to a high energy level by absorbing
___________________.
•
Electrons at a higher energy level are ____________ and can move to a lower energy level
by ____________ energy. This energy is released as _________ that has a specific
wavelength.
•
Each different move from a particular energy level to a lower energy level will release light
of a different ________________.
Quantum Numbers:
The present-day model of the atom is also known as the _________ _________. To define
the region in which electrons can be found, scientists have assigned four quantum numbers that specify the
properties of the electrons. A _______________ ____________ is a number that specifies the properties of
electrons.
•
The _____________ quantum number, symbolized by n, indicates the main ____________
___________ occupied by the electron.
•
•
Values of n are positive integers, such as 1, 2, 3, and 4.
•
As n increases, the electron’s distance from the nucleus and the electron’s energy increases.
The main energy levels can be divided into sublevels. These sublevels are represented by the
_________ ___________ quantum number, l.
•
This quantum number indicates the __________ or type of orbital that corresponds to a
particular sublevel.
•
A letter code is used for this quantum number.
•
•
l = 0 corresponds to an s
•
l = 2 to a d orbital
orbital
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l = 3 to an f orbital
l = 1 to a p orbital
•
The ___________ quantum number, symbolized by m, is a subset of the l quantum number.
•
It also indicates the numbers and _____________ of orbitals around the nucleus.
•
The number of orbitals includes
•
one s orbital
•
five d orbitals
•
three p orbitals
•
seven f orbitals
The ________ quantum number, indicates the orientation of an electron’s magnetic field relative to
an outside magnetic field. A single orbital can hold a maximum of ________ electrons, which must have
opposite spins. The ____________ ____________ principle states that two particles of a certain class
cannot be in the exact same energy state. This means that that no two electrons in the same atom can have
the same four _____________ _______________. The arrangement of electrons in an atom is usually
shown by writing an _____________ _______________. The _________ principle states that electrons fill
orbitals that have the lowest energy first. Aufbau is the German word for “________ ____.” The smaller the
____________ quantum number, the lower the energy. Within an energy level, the __________ the l
quantum number, the lower the energy. So, the order in which the _________ are filled matches the order of
energies.
Based on the quantum model of the atom, the
arrangement of the electrons around the
nucleus can be shown by the nucleus’s
electron configuration.
Example: fluorine has 9 electrons.
Its electron configuration is written as
1s22s22p5.
Two electrons are in the 1s orbital, two
electrons are in the 2s orbital, and five
electrons are in the 2p orbitals.
Review Questions:
1. How does the Bohr model differ from Rutherford’s model?
2. What happens when an electron moves from the excited state to the ground state?
3. Why do electrons fill the 3s orbital before the 3d orbital?
Section 4: Counting Atoms
Objectives:
1. Compare the mass quantities and units for atomic mass with those for molar mass
2. Define mole, and explain why this unit is used to count atoms.
3. Calculate either mass with molar mass or number with Avogadro’s number given an amount in
moles