General Structure of the Periodic Table

As stated last section, the periodic table organizes the elements according to general patterns of similarity. Below is a very small image of the periodic table. It is basically unreadable in terms of specific information, but it allows us to easily look at the periodic tables structure general trends.

The vertical columns of the periodic table (marked by yellow stripes in the figure) are called groups. The horizontal rows are called periods. There are 18 groups and 7 periods. In discussing the periodic table from here on out we will use the terms group and period. Down a group means moving from top to bottom; across a period means moving from left to right.

Reading the Periodic Table: Carbon

To describe the information contained within each individual box we will use a specific example: carbon.

Element Name

The purpose of the element name is obvious. However, many Periodic Tables do not include element names. For those situations you must memorize the symbols that accord to each element name.

Element Symbol

Each element has a specific one or two letter symbol that is used interchangeably with its name. These should be memorized. Most of the time, symbols quite clearly accord to the name of the element they represent, as C accords to carbon. Occasional, however, an element's name and symbol have little relation. For example, the symbol for mercury is Hg.

Atomic Number

As you move across a period the atomic number increases. Similarly, as you move down a group the atomic number increases. In this way, the atomic number represents exactly where in the periodic table an element stands.

More importantly, and the reason why the ordering of the elements according to atomic number yields elements in groups with similar chemical and physical properties, the atomic number is the same as the number of protons in the nucleus of an atom of an element, and also the same as the number of electrons surrounding the nucleus in a neutral state. Carbon, for example, has six protons and six electrons. (Protons and electrons will be discussed in more detail in the Atomic Structure SparkNote)

(atomicmass) Atomic Mass

Along with protons, an atom also contains neutrons in its nucleus. The atomic mass (also called atomic weight) of an element is the combined number of protons and neutrons in the nucleus.

Atoms of particular elements generally have different "versions," meaning that elements have atoms with different numbers of neutrons in their nucleus. These different versions are called isotopes. The atomic weight displayed is actually the weighted average of the mass numbers of the various isotopes. The atomic weight for Carbon is 12.01 because around 99% of all carbon is the carbon-12 isotope.

Simple Periodic Trends

Atomic Number

The Atomic number increases from the top left to the bottom right. It ascends sequentially across each period.

Atomic Weight

Weight The atomic weight of the elements generally increases as you move down a group and across a period. Hydrogen, at the top left of the table, is the lightest element. The unnamed element 112 is the heaviest. There are some instances when this rule does not hold true, however. For instance, because it has a high percentage of isotopes with many neutrons, the atomic weight of tellurium (Te) is higher than that for iodine (I), even though iodine has a higher atomic number.

Types of Elements

Elements can be organized by group or period, but they also can be placed into three distinct groups: metals, semi-metals, and non-metals.

Metals

Metals are the pink section on the left side of . Metals are generally lustrous solids, often deformable (though mercury (Hg) is a liquid at room temperature). Metals are highly conducive to both heat and electricity.

Nonmetals

Nonmetals are the blue boxes on the upper right hand of the periodic table. More than half of the non-metals are gaseous at normal temperatures.

Semimetals

Semimetals are the green boxes on the periodic table. As their transitory name and placement on the periodic table suggest, they exist in between the distinctions of metals and nonmetals.

Metals and Nonmetals

Most chemical compounds are formed by the interactions between metals and non- metals.

Further Periodic Trends

Beyond those trends described here, there are a number of further periodic trends such as atomic size, ionization energy, electron affinity, and electronegativity. We will discuss these trends in the atomic structure SparkNote, since we must have a better understanding of atomic structure before getting into their specifics.