Periodic Trends and Electronegativity Lesson

Periodic Trends

Atomic Radius, Ionization Energy, Electron Affinity, and Electronegativity

Atomic Radius

• One-half the distance between the nuclei of identical atoms that are bonded together.

• Measure the distance between the nuclei of two identical atoms bonded together and divide the distance by 2.

Atomic Radius

Compare the size of each atom in the picture to the right. Do you notice any trends?

Multiple Choice

Based on the image on the last slide. As you go across a period, does the atomic radius get smaller or larger?

• Smaller

• Larger

• Stays the same

Atomic Radius

• As you go across the period (row) Atomic Radius decreases.

• This is caused by an increasing positive charge in the nucleus.

• Electrons are on the same energy level going across the period, but more protons are pulling electrons in closer. This results in a smaller atomic radius.

Atomic Radius

• As you go down a group (column) Atomic Radius increases

• The number of electron shells increase as you move down the periodic table.

• This results in a larger atomic radius because the nucleus has less pull on the outer shell of electrons.

Multiple Choice

Put these elements in order of INCREASING atomic radius.

Li, O, C, F

• O, C, F, Li

• F, O, C, Li

• Li, C, O, F

• C, F, Li, O

Multiple Choice

Put these elements in order of DECREASING atomic radius.

Ca, Be, Ba, Sr

• Sr, Ba, Be, Ca

• Be, Ca, Sr, Ba

• Ba, Sr, Ca, Be

• Ca, Be, Ba, Sr

Ionization Energy

• The energy required to remove one electron from the outer shell of a neutral atom.

• This is the energy needed to form an ion.

• When ionization energy is high it is harder to remove that electron.

Multiple Choice

Which elements do you think will have a low ionization energy and lose electrons more readily?

• elements that form anions (negative charge)

• Elements that form cations (positive charge)

• Transition metals

Ionization Energy

• Moving across a period, ionization energy increases.

• Group one has a low ionization energy and has a high reactivity

• Group 18 has a high ionization energy and are unreactive.

• Caused by an increasing positive charge in the nucleus, attracting electrons more strongly.

Ionization Energy

• decreases as you move down the periodic table.

• Elements with larger atomic radius have less pull on their electrons in the outer shell and tend to give them up.

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Multiple Choice

Element A has a ionization energy of 419 kJ/mol. What block is it likely in?

• P block

• S block

• D block

• F block

Multiple Choice

Element B has an ionization energy of 1000 kJ/mol. What block is it likely to be in?

• P block

• S block

• F block

• D block

Electron Affinity

• The energy change that occurs when a neutral atom gains an electron.

• energy changes that are more negative have a higher electron affinity.

Multiple Choice

What elements do you expect to have a high electron affinity?

• Elements that form cations

• Elements that form anions

• Transition metals

Electron Affinity

• As you move across the period table, electron affinities generally become more negative.

• There are some exceptions to this rule.

Electronegativity

• Measures the ability of an atom in a chemical compound to attract electrons from another atom in the compound.

• Think about what elements attract electrons.

• The highest value is 4.0 and fluorine is the most electronegative element.

Electronegativity

• Increases as you move across the periodic table.

• Group 1 and 2 metals are the least electronegative elements and tend to lose electrons when forming ions.

• Nitrogen, oxygen, and halogens are the most electronegative and strongly attract electrons when in compounds.

• Decreases or stays the same moving down a group.

Multiple Choice

What elements have the highest Electronegativity?

• Halogens (group 17)

• Alkali Metals (Group 1)

• Alkaline-earth Metals (group 2)

• Noble gases (group 18)