The Size of an Atom

​Unit 4
The Periodic Table
and Periodic Law

​Lesson 3 -
Periodic Trends

Essential Questions

• What are the period and group trends of different properties?

• How are period and group trends in atomic radii related to electron

configuration?

Periodic Trends
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Atomic Radius

• Atomic size is a periodic trend
influenced by electron configuration.

• For metals, atomic radius is half the distance between adjacent nuclei in a crystal of the element.

Periodic Trends
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Atomic Radius

• For elements that occur as molecules, the atomic radius is half the distance between nuclei of identical atoms that are chemically bonded together.

Periodic Trends
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Fill in the Blank

For many nonmetal elements, the atomic radius is defined as ____the distance between the nuclei of identical atoms that are chemically bonded together.

Atomic Radius

•Atomic radius generally decreases from left to right, caused by increasing
positive charge in the nucleus.

•Valence electrons are not shielded from the increasing nuclear charge because no additional electrons come between the nucleus and the valence electrons.

•Atomic radius generally increases as you move down a group.

•The outermost orbital size increases down a group, making the atom larger.

Periodic Trends
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Fill in the Blank

Atomic radii generally ________as you move down a group.

Fill in the Blank

In general, there is a/an ________ atomic radii as you move from left to right across a period.

Atomic Radius

Periodic Trends
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Multiple Select

Which factors explain why atomic radii generally increase when moving down a group?

Multiple select question.

• added principal energy levels are farther from the nucleus

• electrons in inner orbitals shield the outer electrons from the nucleus

• increased density decreases the size of all subatomic particles

• electrons expand as the pull of the nucleus decreases

• increased distance of valence electrons from the nucleus offsets the pull of increased nuclear charge

Atomic Radius

Periodic Trends
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Go to your ConnectED resources to play Animation: Atomic Radii.

Multiple Select

Which are reasons for atomic radii decreasing across a period?

Multiple select question.

• no additional electrons come between the valence electrons and the nucleus

• more protons are added to the nucleus

• no new energy levels are added

• increased force on the electrons decreases their size

• more neutrons are added to the nucleus

Ionic Radius

•An ion is an atom or bonded group of atoms with a positive or negative charge.

•When atoms lose electrons and form positively charged ions, they always become smaller for two reasons:

1.

The loss of a valence electron can leave an empty outer orbital, resulting in a smaller radius.

2.

Electrostatic repulsion decreases allowing the electrons to be pulled closer to the nucleus.

Periodic Trends
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Fill in the Blank

An atom or group of bonded atoms that has a positive or negative charge is called a/an___ .

Ionic Radius

•When atoms gain electrons, they can become larger, because the addition of an electron increases electrostatic repulsion.

Periodic Trends
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Ionic Radius

Periodic Trends
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•The ionic radii of positive ions generally decrease from left to right.

•The ionic radii of negative ions generally decrease from left to right, beginning with group 15 or 16.

•Both positive and negative ions increase in size moving down a group.

Multiple Choice

Which type of ions increase in size moving down a group?

• positive

• negative

• both positive and negative

• metallic

Ionic Radius

Periodic Trends
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Ionization Energy

•Ionization energy is defined as the energy required to remove an electron from a gaseous atom.

•The energy required to remove the first electron is called the first ionization energy.

Periodic Trends
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Fill in the Blank

__________ ______ is defined as the energy required to remove an electron from a gaseous atom.

Ionization Energy

Periodic Trends
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Ionization Energy

•Removing the second electron requires more energy, and is called the second ionization energy.

•Each successive ionization requires more energy, but it is not a steady increase.

Periodic Trends
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Ionization Energy

•First ionization energy increases from left to right across a period.

•First ionization energy decreases down a group because atomic size increases and less energy is required to remove an electron farther from the nucleus.

Periodic Trends
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Multiple Select

Which of the following are reasons that first ionization energy decreases down a group because and less energy is required to remove an electron farther from the nucleus.

• atomic size increases

• less energy is required to remove an electron farther from the nucleus

• atomic size decreases

• more energy is required to remove an electron farther from the nucleus

Ionization Energy

Periodic Trends
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•The ionization at which the large increase in energy occurs is related to the number of valence electrons.

•The octet rule states that atoms tend to gain, lose or share electrons in order to acquire a full set of eight valence electrons.

•The octet rule is useful for predicting what types of ions an element is likely to form.

Electronegativity

Periodic Trends
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•The electronegativity of an element indicates its relative ability to attract electrons in a chemical bond.

•Electronegativity decreases down a group and increases left to right across a period.

Multiple Choice

True or False: The electronegativity of an element indicates its relative ability to attract electrons in a chemical bond.

• True

• False