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Elements as Building BlocksAs you probably saw, the periodic table is organized like a big grid.The elementsare placed in specific locations because of the way they look

and act. If you have ever looked at a grid, you know that there are rows (leftto right) and columns (up and down). The periodic table has rows andcolumns, and they each mean something different.

You've got Your Periods...Even though they skip some squares inbetween, all of the rows go left to right.When you look at a periodic table, each of

the rows is considered to be adifferent period (Get it? Like PERIODictable.). In the periodic table, elements havesomething in common if they are in thesame row. All of the elements in a periodhave the same number ofatomic orbitals.Every element in the top row (the first period) has one orbital foritselectrons. All of the elements in the second row (the second period) havetwo orbitals for their electrons. It goes down the periodic table like that. At

this time, the maximum number of electron orbitals or electron shells forany element is seven.

...and Your GroupsNow you know about periods. The periodictable also has a special name for itscolumns. When a column goes from top tobottom, it's called agroup. The elements in

a group have the same number of electronsin their outerorbital. Those outer electronsare also called valence electrons. They arethe ones involved in chemical bonds withother elements.

Every element in the first column (group one) has one electron in its outershell. Every element in the second column (group two) has two electrons inthe outer shell. As you keep counting the columns, you'll know how many

electrons are in the outer shell. There are some exceptions to the orderwhen you look at thetransition elements, but you get the general idea.

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Transition elements start to add electrons to the second-to-last shell.

Two at the TopHydrogen (H) and helium (He) are special

elements.Hydrogencan have the talents

and electrons of two groups: one and seven.

To scientists, hydrogen is sometimes

missing an electron, and sometimes has an

extra one.Heliumis different from all of the

other elements. It can only have two

electrons in its outer shell. Even though it

only has two, it is still grouped with elementsthat have eight (i.e., noble gases). Thenoble gasesand helium are all

"happy," because their outermost electron shell is full. The elements in the

center section are called transition elements. They have special electron

rules too.

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