Simply: Distance from the nucleus to the valence electrons. More officially: “half the distance...

Simply: Distance from the nucleus to the valence electrons.

More officially: “half the distance between the nuclei in a molecule consisting of identical atoms”

The size of the atoms DECREASES from left to right across a period.

WHY? The nucleus is gaining more protons to become larger and more strongly positive. The stronger nuclear stronger nuclear charge charge attracts the electrons and draws the cloud towards the nucleus.

Period #2

The size of the atoms DECREASES from bottom to top of a group.

WHY? There are fewer energy levels at the top of the periodic table. The pull of the nucleus is shieldedshielded as more energy levels are added.

1A

Use your periodic table and knowledge of atomic radius to answer the following multiple choice questions.

1. Which of the following atoms will have the smallest radius?

a. Tin b. Strontium c. Selenium d. Arsenic

2. Which of the following atoms will have a larger radius than calcium?

a. Aluminum b. Copper c. Potassium d. None

3. In magnesium oxide, MgO, the smaller atom is:

a. Magnesium b. Oxide c. Neither

Check your answers. Do you have questions?

1. Which of the following atoms will have the smallest radius?


2. Which of the following atoms will have a larger radius than calcium?


3. In magnesium oxide, MgO, the smaller atom is:


Cations form by losing electrons to become stable. As electrons are lost, the atom becomes smaller. Therefore,

cations are smaller than their corresponding neutral atomscations are smaller than their corresponding neutral atoms.

• Draw the orbital diagram for neutral potassium.

• Draw the orbital diagram for the potassium cation.

• Compare your drawings. Does the trend make sense?

Anions form by gaining electrons to become stable. As electrons are added, the atom becomes larger. Therefore,

anions are bigger than their corresponding neutral anions are bigger than their corresponding neutral atoms.atoms.

• Draw the orbital diagram for sulfur.

• Draw the orbital diagram for the sulfide ion.

• Does the trend make sense?

Energy required to remove an electron from an atom.

Based on what you know about the octet rule, which atoms might WANT to have electrons removed? Which ones might NOT WANT to have electrons removed?

The IE INCREASES from left to right across a period.

WHY? The nucleus is gaining more protons to become larger and more strongly positive. The nucleus holds tightly to the electrons. Therefore, HIGH ENERGY is needed to remove an electron.

WHY? There are fewer energy levels at the top of the periodic table. The pull of the positive nucleus is NOT shielded by few energy levels. At the bottom of the table, the pull of the nucleus IS SHIELDED by the many energy levels. Therefore, LOW ENERGY is needed to remove an electron from a large atom.

The ionization energy of elements INCREASES from bottom to top of a group.

Use your periodic table and knowledge of ionization energy to answer the following multiple choice questions.

1. Which of the following atoms will have the smallest IE?


2. Which of the following atoms will have a larger IE than calcium?


3. In magnesium oxide, the atom with the smallest ionization energy is:


Check your answers. Do you have questions?

1. Which of the following atoms will have the smallest IE?


2. Which of the following atoms will have a larger IE than calcium?


3. In magnesium oxide, the atom with the smallest ionization energy is:


You have learned about ionization energy already, but there is more to the story...

1st Ionization Energy - energy required to remove the first electron from an atom

2nd Ionization Energy - energy required to remove the second electron from an atom

3rd Ionization Energy - energy required to remove the third electron from an atom

The pattern on the periodic table requires more thought for predicting 2nd and 3rd IEs

Example: Aluminum

Draw the orbital diagram for Al.

•1st IE = 580 kJ/mol (removes the highest energy electron – the lone 3p)

•2nd IE = 1815 kJ/mol (removes the next highest energy electron – a 3s)

•3rd IE = 2740 kJ/mol (removes the 3rd highest energy electron – the final 3s)

•4th IE = 11,600 kJ/mol (removes a “core electron” or a non-valence shell electron – WILL NOT OCCUR)

2nd Ionization Energy - energy required to remove the second electron from an atom

Compare the 2nd ionization energy of Mg with the 2nd ionization energy Na.

• Thought process:

•Magnesium needs to lose two electrons to become stable, and sodium needs to lose one electron to become stable.

•Who will require more energy to take the second electron?

• Answer: Sodium is STABLE after losing one electron, and it will require LOTS of energy to remove a second.

The ability of an atom to draw electrons from another atom closer to itself when in a chemical bond.

The EN INCREASES from left to right across a period.

WHY? The nucleus is gaining more protons to become larger and more strongly positive. The nucleus holds tightly to the electrons. Therefore, the strong nucleus is able to draw the bonding electrons closer.

WHY? There are fewer energy levels at the top of the periodic table. The pull of the positive nucleus is NOT shielded by few energy levels. At the bottom of the table, the pull of the nucleus IS SHIELDED by the many energy levels. Therefore, the shielded nucleus is unable to draw the bonding electrons closer.

The electronegativity of elements INCREASES from bottom to top of a group.

Notice: Noble gases have NO electronegativity since they do not form bonds.

1. Which of the following has the greatest electronegativity?

a. Nitrogen b. Bismuth c. Silicon d. Neon

2. In water, H2O, which atom is holding the bonding electrons closest to itself?

a. Hydrogen b. Oxygen c. Neither

Answer the following questions using your periodic table and understanding of EN.

1. Which of the following has the greatest electronegativity?

a. Nitrogen b. Bismuth c. Silicon d. Neon

2. In water, H2O, which atom is holding the bonding electrons closest to itself?

a. Hydrogen b. Oxygen c. Neither

Check your answers. Do you have questions before we move on to ionic radius?

Applications of Periodic Trends

• Let’s look at 5-3 Review & Reinforcement.– Which ATOM has the larger atomic radius?– Which ION has the smaller atomic radius?– Which atom or ion has the larger ionization

energy?– Question 33 - Why is there such a large jump in

ionization energy between the second and third ionization energies for magnesium?

More Applications of Trends• Let’s look at 5-3 Practice Problems.

– 1-5 Answers– Question 6: Which is largest: a K atom, a K+1

ion, or an Rb atom?– Question 7: Which of the following is the

largest: a Cl atom, a Cl- ion, or a Br atom?– Question 8: Which of the following is the

smallest: a Li atom, a Li1+ ion, or a Na atom?– Question 9: Which of the following is the

largest: a Te2- ion, an I- ion, or an Xe atom?

Sample Discussion Question

• Which is the smaller atom: oxygen or nitrogen? Why?

• Which atom has higher ionization energy: fluorine or chlorine? Why?

Simply: Distance from the nucleus to the valence electrons. More officially: “half the distance...

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