Periodic Trends

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• What is the radius of a circle?

• What would the atomic radius be?

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l. Atomic RadiusA. The electron cloud surrounding a

nucleus is based on probability and does not have a clearly defined edge

B. Defined by how closely an atom lies to a neighboring atom

ll. Atomic Radius Across a Period

A. Atomic radius generally decreases in size as you move left to right across the period

1. Increasing positive charge in the nucleus pulls the electrons of the same energy level in.

Why?

What is this force called?

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• What happens to the radius as you go down a column? Why?

• What keeps the additional protons from drawing the electrons closer?

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lll. Atomic Radius Down a Group

A. Atomic radius increases as you move down a group1. Orbital size increases as you move down a group

with increasing energy level

2. Larger orbitals means that outer electrons are farther from the nucleus. This increased distance offsets the greater pull of the increased nuclear charge.

3. As additional orbitals between the nucleus and the outer electrons are occupied, the inner electrons shield the outer electrons from the pull of the nucleus this is called shielding.

Shielding The inner electrons shield the outer electrons from feeling the pull of the nucleus

Question Time• How do you define the atomic radius

since the electron cloud does not have a clearly defined edge?

• What happens to the atomic radius as you move left to right? Why?

• What happens to atomic radius as you move down a group? Why?

• What is shielding?

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• An- prefix (Anarchy) vs Cat- prefix

• An = without Cat = with

• Anodes are without what?

• Cathodes are with what?

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lV. Cation and AnionA. An ion is a positively or negatively

charged atom that gains or loses an electron.

B. A cation loses electrons and produces a positive charge

C. An anion gains electrons and produces a negative charge

Cations are attracted to cathodes. What is the charge of a cation?

Anions are attracted to anodes. What is the charge of an anode?

16 protons

18 electrons

Anion

S2- Sulfur Anion

12 protons

10 electrons

Cation

Mg2+ Magnesium Cation

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• What happens to the atomic radius of cations? Why?

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V. Ionic Radius - CationsA. Groups 1A, 2A, 3A, and other metals tend to lose

electrons and form cations.

B. When atoms lose electrons they become smaller

1. The electron lost will be a valence electron leaving a completely empty outer orbital

2. Electrostatic repulsion between fewer number of remaining electrons decreases, allowing them to be pulled closer to the nucleus

These atoms lost electrons and became smaller cations.

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• What happens to the atomic radius of anions? Why?

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Vl. Ionic Radius - AnionsA. Group 5A, 6A, and 7A tend to gain

electrons and form anionsB. When atoms gain electrons and form

negatively charged ions, they become larger. 1. The addition of an electron to an atom

increases the electrostatic repulsion between the atom’s outer electrons forcing them farther apart resulting in a larger radius.

These atoms gained electrons and became larger anions

Question Time• What is an ion?• What is a cation and an anion?• What happens to the size of the atom

when it becomes a cation? Why?• What happens to the size of the atom

when it becomes an anion? Why?

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End for today!

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• What could ionization energy mean?

• How do atoms become ions?

• Which atoms are more likely to become ions (by removing electrons)? Do they have a high or low ionization energy?

Vll. Ionization EnergyA. The energy required

to remove an electron from a gaseous atom

B. Indication of how strongly an atom’s nucleus holds onto its valence electron

C. Groups 1A, 2A, and 3A tend to have low ionization energies because they want to lose electrons.

Vlll. Ionization Energy Trends –

Across a PeriodA. Ionization energy increases as you

move left to right1. Across a period electrons are added to

the same energy level (same distance away from the nucleus), yet the nuclear charge is increasing across a period increasing the attraction to the electrons.Why would ionization energy increase?

lX. Ionization Energy Trends – Down a Group

A. Ionization energy decreases as you move down a group1. Down a group electrons are added to a

higher energy level (farther distance away from the nucleus), making it easier to remove an electron

What happens to the ionization energy as you go down a column? Why?

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• What does every atom want?

• What are the two exceptions?

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X. Octet RuleA. Sodium atom 1s22s22p63s1

B. Sodium ion 1s22s22p6 (Sodium atom lost 1 electron)

C. Neon 1s22s22p6

D. Sodium ion has the same electron configuration as neon

E. Octet rule states that atoms gain, lose, or share electrons to acquire a full set of eight valence electrons (to be like a noble gas)

Xl. ElectronegativityA. Indicates an element’s ability to

attract electrons in a chemical bondB. fluorine (F) is the most

electronegative elementC. Cesium (Cs) and francium (Fr)are

the least electronegativeD. Noble gases do not tend to have an

electronegativity number since they tend not to form compounds

Where is there going to be a high amount of electronegativity? Why?

Xll. Trends with Electronegativity

A. Electronegativity increases as you move left-to-right across a period1. As you go left to right, the nuclear

charge increases, more strongly attracting electrons

A. Electronegativity decreases as you move down a group1. Electrons get further away from the

positive nucleus

Question Time• What is ionization energy?• What is the trend in ionization energy as you

move left to right? Down a group?• What is the octet rule? What elements do

atoms want to be like?• What is electronegativity?• What are the trends in electronegativity?• What is the most electronegative element?

What is the least?• Why do noble gases tend not to have an

electronegativity value?• What is the difference between ionization

energy and electronegativity?