Pre-Test
Q&A	Physical Science Series: Chemical Bonding

Instruction 1-5

Connection Among the Location in the Table, the Atomic Number, and Mass | How to Identify Metals, Semimetals, Nonmetals, and Halogens | How to Identify Alkaline Metals, Alkaline Earth Metals, and Transition Metals | Lanthanide, Actinide, Transactinide, and Transuranium Elements | Ionization Energy, Electronegativity, Relative Sizes | How Many Electrons Can Bond? | Size and Mass | Location and Quantum Electron Configuration | Summary

Ionization Energy
http://www.shodor.org/chemviz/ionization/students/background.html

The amount of energy required to pull an electron off a neutral atom is the ionization energy. Since each successive shell for the electrons is larger than the previous one, the electrons in the shells further from the nucleus require less energy to be pulled off. In other words, the larger the shell number or the further down in the periodic table, the lower the ionization energy.

As we go from left to right on the periodic table, there are more and more protons in the nucleus. The greater number of protons pulls stronger at the valence electrons (the electrons in the outer most shell). This causes an increase in the ionization energy.

To summarize, moving down the table causes a decrease in the ionization energy. Moving to the right causes an increase in the ionization energy. See the figure for the trend.

Electronegativity
http://en.wikipedia.org/wiki/Electronegativity

Electronegativity is the measure of how easy it is to place another electron in the neutral atom. It is almost the opposite of ionization energy, except that some elements don’t accept another electron and it becomes impossible to measure a value. As the shells get larger, it is harder to put an electron in the atom.

As more protons get added to the nucleus, the easier it is to add an electron. The noble gases don’t want to get another electron, so it is almost impossible to put an extra one in the atom.

To summarize, moving down the table causes a decrease in electronegativity. Moving to the right causes an increase in electronegativity. The arrows in the figure show increasing electronegativity.

Atom Size
http://www.historyoftheuniverse.com/atomsize.html

The atom size is based on the distance between two atoms. One method uses the distance between atoms that are bonded; another method uses the distance between atoms of the element in a solid. Since the atom is incredibly small, scientists use small units to measure the size of an atom, either Angstroms (Å, 1 x 10^–10 m), nanometers (nm, 1 x 10^–9 m), or picometers (pm, 1 x 10^–12 m). When an atom gains or loses electrons (it becomes an ion), the size also changes. The size of the atoms increases when moving down a group (column). This is because there are electrons added to the next larger shell. The size of the atoms decreases when moving from left to right (along a period). This is because there are more protons in the nucleus that pull on the electrons. The pull increases, the electrons get closer and the size decreases.

To summarize, moving down the table causes an increase in the size of the atoms. Moving to the right causes a decrease in the size of the atoms. The arrows in the figure show increasing atomic radius.

for Students, Parents and Teachers

Now let's do Practice Exercise 1-5 (top). 

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