Elements as Building Blocks

Elements as Building Blocks The periodic table is organized like a big grid. Each element is placed in a specific location because of its atomic structure. As with any grid, the periodic table has rows (left to right) and columns (up and down). Each row and column has specific characteristics. For example, beryllium (Be) and magnesium (Mg) are found in column two and share certain similarities while potassium (K) and calcium (Ca) from row four share different characteristics. You've got Your Periods... Periodic Table showing Periods Even though they skip some squares in between, all of the rows read left to right. When you look at the periodic table, each row is called a period (Get it? Like PERIODic table.). All of the elements in a period have the same number of atomic orbitals. For example, every element in the top row (the first period) has one orbital for its electrons. All of the elements in the second row (the second period) have two orbitals for their electrons. As you move down the table, every row adds an orbital. At this time, there is a maximum of seven electron orbitals. ...and Your Groups Periodic Table showing Groups Now you know about periods going left to right. The periodic table also has a special name for its vertical columns. Each column is called a group. The elements in each group have the same number of electrons in the outer orbital. Those outer electrons are also called valence electrons. They are the electrons involved in chemical bonds with other elements. Every element in the first column (group one) has one electron in its outer shell. Every element in the second column (group two) has two electrons in the outer shell. As you keep counting the columns, you'll know how many electrons are in the outer shell. There are exceptions to the order when you look at the transition elements, but you get the general idea. Transition elements add electrons to the second-to-last orbital. For example, nitrogen (N) has the atomic number seven. The atomic number tells you there are seven electrons in a neutral atom of nitrogen. How many electrons are in its outer orbital? Nitrogen is in the fifteenth column, labelled 'Group VA'. The 'V' is the Roman numeral for five and represents the number of electrons in the outer orbital. All of that information tells you there are two electrons in the first orbital and five in the second (2-5). Phosphorus (P) is also in Group VA which means it also has five electrons in its outer orbital. However, because the atomic number for phosphorus is fifteen, the electron configuration is 2-8-5. Two at the Top Periodic Table showing hydrogen and helium Hydrogen (H) and helium (He) are special elements. Hydrogen can have the electron traits of two groups: one and seven. For chemists, hydrogen is sometimes missing an electron like the members of group IA, and sometimes has an extra one as in group VIIA. When you study acids and bases you will regularly work with hydrogen cations (H+). A hydride is a hydrogen anion and has an extra electron (H-). Helium (He) is different from all of the other elements. It is very stable with only two electrons in its outer orbital (valence shell). Even though it only has two, it is still grouped with the noble gases that have eight electrons in their outermost orbitals. The noble gases and helium are all "happy," because their valence shell is full. Families Stick Together Different elements behave in similar ways We just covered the columns and rows of the periodic table. There are also other, less specific, groups of elements. These groups are all over the table. Scientists group these families of elements by their chemical properties. Each family reacts in a different way with the outside world. Metals behave differently than gases, and there are even different types of metals. Some elements don't react, while others are very reactive, and some are good conductors of electricity. The columns of the periodic table are often used to define families. The noble gases are all located in the far right column of the table. That column is labeled Group Zero. Other families can be made of elements in a series. A good example of a series of elements is the transition metal family. The thing to remember is that a family of elements can be found in several ways. You need to run tests and study the elements to determine their properties. Only after that testing can you determine what family an element belongs in. Examples of Families - Alkali Metals - Alkaline Earth Metals - Transition Metals - Halogen Gases - Noble Gases Examples of Physical Properties - Density - Boiling Point - Melting Point - Conductivity - Heat Capacity Examples of Chemical Properties - Valence - Reactivity - Radioactivity Halogens on the Right Halogens on the Periodic Table In the second column from the right side of the periodic table, you will find Group Seventeen (Group XVII). This column is the home of the halogen family of elements. Who is in this family? The elements included are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). What Makes Them Similar? When you look at our descriptions of the elements fluorine and chlorine, you will see that they both have seven electrons in their outer shell. That seven-electron trait applies to all of the halogens. They are all just one electron shy of having full shells. Because they are so close to being happy, they have the trait of combining with many different elements. They are very reactive. You will often find them bonding with metals and elements from Group One of the periodic table. The elements in the column on the left each have one electron that they like to donate. Sodium Chloride is a Halogen We've just told you how reactive the halogens are. Not all halogens react with the same intensity or enthusiasm. Fluorine is the most reactive and combines with most elements from around the periodic table. Reactivity decreases as you move down the column. As you learn more about the table, you will find this pattern true for other families. As the atomic number increases, the atoms get bigger. Their chemical properties change just a little bit when compared to the element right above them on the table. What is a Halide? The elements we are talking about in this section are called halogens. When a halogen combines with another element, the resulting compound is called a halide. One of the best examples of a halide is sodium chloride (NaCl). Don't think that the halogens always make ionic compounds and salts. Some halides of the world are a part of molecules with covalent bonds. The Noble Gases Inert gases on the periodic table We love the noble gases. Some scientists used to call them the inert gases. It didn't really work because there are a few other gases that are basically inert but not noble gases. Nitrogen (N2) might be considered an inert gas, but it is not a noble gas. The noble gases are another family of elements, and all of them are located in the far right column of the periodic table. For all of you budding chemists, the far right is also known as Group Zero (Group 0) or Group Eighteen (Group XVIII). This family has the happiest elements of all. Why Are They Happy? Using the Bohr description of electron shells, happy atoms have full shells. All of the noble gases have full outer shells with eight electrons. Oh, wait! That's not totally correct. At the top of the noble gases is little helium (He), with a shell that is full with only two electrons. The fact that their outer shells are full means they are quite happy and don't need to react with other elements. In fact, they rarely combine with other elements. That non-reactivity is why they are called inert. Who's in the Family? Neon is one of many inert gases used around you All of the elements in Group Zero are noble gases. The list includes helium, neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). Don't think that, because these elements don't like to react, we don't use them. You will find noble gases all over our world. Neon is used in advertising signs. Argon is used in light bulbs. Helium is used in balloons and to cool things. Xenon is used in headlights for new cars. Because of their chemical properties, these gases are also used in the laboratory to help stabilize reactions that would usually proceed too quickly. When you move down the periodic table, as the atomic numbers increase, the elements become rarer. They are not just rare in nature, but rare as useful elements, too. But Wait, They Do Bond! Some do. As of about 40 years ago, scientists have been able to make some compounds with noble gases. Some have been used in compounds to make explosives, and others just form compounds in a lab. The thing to remember is that they were forced. When going about their natural lives, you will never (well, never say never, because there may be an exception) find the noble gases bonded to other elements. Metal Basics Many metals are in the periodic table We wanted to give you a big overview of metals before we get into details about specific families. Almost 75% of all elements are classified as metals. They are not all like silver (Ag), gold (Au), or platinum (Pt). Those are the very cool and shiny ones. There are other metals like potassium (K) and iridium (Ir) that you might not think about right away. Many Kinds of Metals How many kinds of metals are there? So many. Don't even try to memorize them all. Just remember the ones you might need in class. Here's a quick list: Actinide Metals, Lanthanide Metals, Alkali Metals, Alkaline-Earth Metals, Rare Metals, Rare-Earth Metals, and Transition Metals. Remember, that's the easy list. Lucky for you, the periodic table is excellent at organizing elements, and you will find each of these groups in specific areas of the periodic table. How Do You Identify a Metal? Bronze was one of the first alloys created by humans. What are the characteristics of metals? We've got four traits that will help you identify whether an element is a metal or not: 1. Conduction: Metals are good at conducting electricity. Silver (Ag) and copper (Cu) are some of the most efficient metals and are often used in electronics. 2. Reactivity: Metals are very reactive, some more than others, but most form compounds with other elements quite easily. Sodium (Na) and potassium (K) are some of the most reactive metals. A metal like iron (Fe) forms iron oxide (Fe2O3), which you know as rust. 3. Chemical: It gets a little complex here. Metals usually make positive ions when the compounds are dissolved in solution. Also, their metallic oxides make hydroxides (bases) (OH-), and not acids, when in solution. Think about this example: When sodium chloride (NaCl) is dissolved in water (H2O), it breaks apart into sodium (Na+) and chlorine (Cl-) ions. Do you see how that sodium is the positive ion? Sodium is the metal. It works that way for other metals. Potassium chlorine (KCl) works the same way. When it is dissolved, the potassium ion (K+) is the positive ion. 4. Alloys: Metals are easily combined. Mixtures of many metallic elements are called alloys. Examples of alloys are steel and bronze.