Study Guide for Development of the Atomic Theory and the Atom
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Name one experiment that was important in the development of the atomic theory? What did it help
discover?
What is the difference between an atom and a molecule?
How many elements are there?
Explain how the atomic theory has changed as scientists have discovered new information about the
atom.
What error did Thomson find in Dalton’s atomic theory? (Thomson discovered that atoms are made of
smaller parts.)
What is the name of Thomson’s model of the atom? (the plum-pudding model)
Democritus thought that matter is composed of atoms.
Dalton based his theory on observations of how elements combine.
Thomson discovered electrons in atoms.
Rutherford discovered that atoms are mostly empty space with a dense, positive nucleus.
Bohr proposed that electrons are located in levels at certain distances from the nucleus.
The electron-cloud model represents the current atomic theory.
A(n) electron is a particle with a negative electric charge.
The nucleus is where most of an atom’s mass is located.
What did Dalton do in developing his theory that Democritus did not do? (He performed experiments and
drew conclusions from them to develop his theory.)
What discovery demonstrated that atoms are mostly empty space? (Rutherford’s gold-foil experiment, in
which Rutherford observed that most of the positively charged particles that he aimed at a piece of gold
foil went straight through.)
What refinements did Bohr make to Rutherford’s proposed atomic theory? (Bohr suggested that
electrons could move around the nucleus only in certain paths. They could jump from path to path, but
not stay between the paths.
Describe the size of an atom.
Name the parts of an atom.
Describe the relationship between numbers of protons and neutrons and atomic number.
Describe the forces within an atom.
Name the two kinds of particles that can be found in the nucleus. (Protons and neutrons can be found in
the nucleus.)
What is an atom’s mass number equal to? (The total number of protons and neutrons in that atom.)
Atoms are extremely small. Ordinary-sized objects are made up of very large numbers of atoms.
Atoms consist of a nucleus, which has protons, and usually neutrons, and electrons, located in electron
clouds around the nucleus.
The number of protons in the nucleus of an atom is that atom’s atomic number. All atoms of an element
have the same atomic number.
The mass number of an atom is the sum of the atom’s neutrons and protons.
Which particle has no electric charge? (Neutrons)
Protons have a positive charge.
All atoms of the same element contain the same number of protons.
Neutrons have no electrical charge.
The mass number of an element is the number of protons and neutrons in the nucleus.
The discovery of the electron proved that the atom is not indivisible.
Study Guide for the Periodic Table
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Describe how Mendeleev arranged elements in the first periodic table. (First, he wrote the names and
properties of the elements on cards. Then, he arranged his cards by different properties, such as density,
appearance, and melting point. Then, he arranged the elements in order of increasing atomic mass. When
he did so, a pattern appeared.)
Explain how elements are arranged in the modern periodic table. (Elements are arranged by atomic
number and in 18 columns called groups, or families, and 7 rows called periods. )
Compare metals, nonmetals, and metalloids based on their properties and on their location in the
periodic table. (Metals tend to be shiny, malleable, ductile, good conductors, and most are solid at room
temperature. Nonmetals are not malleable or ductile, not shiny, and are poor conductors of thermal
energy and electric current. Metalloids have properties of both metals and nonmetals.)
What does malleable mean? (Malleable means the metal can be flattened and rolled into thin sheets.)
What does ductile mean? (Ductile means the metal can be drawn into thin wires.)
Metalloids can also be called semiconductors.
Describe the difference between a period and a group. (Groups are the columns of the periodic table.
Elements in the same group often have similar chemical and physical properties. Periods are the rows of
the periodic table.)
Mendeleev developed the first periodic table by listing the elements in order of increasing atomic mass.
He used his table to predict that elements with certain properties would be discovered later.
Properties of elements repeat in a regular, or periodic, pattern.
Moseley rearranged the elements in order of increasing atomic number.
Elements in the periodic table are classified as metals, nonmetals, and metalloids.
Each element has a chemical symbol. If it has one letter, it is capitalized. If it has more than one letter,
the first letter is capitalized and the rest are lowercase.
A horizontal row of elements is called a period.
A vertical column of elements is called a group or family.
Explain why elements in a group often have similar properties. (The properties of the elements in a group
are similar because the atoms of the elements have the same number of electrons in their outer energy
level. Atoms will often take, give, or share electrons with other atoms in order to have a complete set of
electrons in their outer energy level. Elements whose atoms undergo such processes are called reactive
and can combine to form compounds.)
Describe the properties of the elements in the groups of the periodic table. (USE YOUR PERIODIC TABLE
FOLDABLE TO STUDY THIS.)
Why is hydrogen set off by itself in the periodic table? (Its properties do not match the properties of any
one group.)