Chemistry Review for Final 3: Periodic Trends and Ions

Hydrogen (H) and Helium (He) are the only exceptions- They have 2 in the first shell (orbital).

• 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.

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

• 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.

• 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.

• 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.

• 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.

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

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

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

• There are some exceptions to this rule.

• 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.

• 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.