Section 5.2 The Modern Periodic Table

Mendeleev created his periodic table before the discovery of protons (arranged his according to atomic weight and properties). Henry Moseley arranged the elements by increasing atomic number in the modern periodic table. This resulted in a periodic pattern of properties.

The Modern Periodic Table There are 7 rows on the periodic table. Rows are called periods. The number of elements in a period varies because of the number of orbitals. As you move down into a different row you add an energy level (or ring) around the nucleus.

Each column is called a group (or family). There are 18 groups. Elements within a group have similar properties. Properties of elements repeat in a predictable way when atomic numbers are used to arrange elements into groups. Elements in a group have similar electron configurations (all end the same).

This pattern of repeating properties is called the Periodic Law. An element’s electron configuration determines its chemical properties. This pattern of repeating properties is called the Periodic Law. Most periodic tables give at least 4 key pieces of information for each element. 1. The name 2. The symbol 3. The atomic number 4. The atomic mass

Atomic mass is a value that depends on the distribution of an element’s isotopes in nature and the masses of those isotopes. Units = amu (atomic mass units) The mass in grams of an atom is extremely small and not very useful. Matter contains trillions of atoms. Scientist chose one isotope to serve as a standard- carbon. They gave 12 atomic mass units to the carbon-12 atom (6 protons, 6 neutrons). Now an amu is 1/12 the mass of a carbon-12 atom.

Classes of Elements There are 3 ways to classify elements. By the elements state of matter-solid, liquid, or gas (at room temperature). - solids- black, liquids- blue(purple), and gasses- red. Divided into two groups based on whether they occur naturally or are synthetic (man made). -1-92 occur naturally (all but 2-Tc and Pm). These are written in solid colors. -93 on are synthetic (written in white and outlined in black).

Puts the elements into categories based on their properties (also called regions). - These regions are metals, nonmetals and metalloids. The 3 Regions (Classifications)-using Fig. 7 p.133 Metals- Represented by blue boxes. Majority of elements on the periodic table.

Properties of Metals Good conductors of heat and electricity. Solids at room temperature (except Hg) Malleable (most) Most are ductile. The left side are extremely reactive. As you move right across the metals they become less reactive. Lustrous Higher boiling points.

Properties of Nonmetals Represented by the yellow boxes. Poor conductors of heat and electricity. Low boiling points (b.p.). Can be gases at room temperature (why low b.p.). Solids are usually brittle (shatter or crumble). Vary in chemical properties as well as physical. 1 liquid element- Bromine Some are very reactive- group 17- halogens. Some are unreactive- group 18- Noble gasses.

Properties of Metalloids Green boxes on periodic table (8 total) Properties fall between metals and nonmetals. Ability to conduct electricity but varies with temperature. Si and Ge are good insulators at low temps. and good conductors at high temps.

Properties Vary Across a Period As you go left to right across a period on the periodic table the elements become less metallic and more nonmetallic in their properties. The most reactive metals are on the left side-Group 1A (alkali metals). The most reactive nonmetals are in Group 17 or 7A (halogens).

Transition Metals The transition metals are elements that form a bridge between the left and right side of the periodic table (between the s and p blocks). They fill the d and f orbitals. The lanthanide and actinide series are also known as the inner transition metals. These are the two rows below the periodic table. Many of these elements have similar properties even though they are not in the same groups.

Section 5.3 Representative Groups Valence Electrons: Electrons in the highest energy level (furthest ring from the nucleus). Play a key role in chemical reactions. Are the electrons involved in bonding. Only come from the s and p orbitals. Maximum number is 8. Elements in groups have similar properties because they have the same number of valence electrons.

Group 1 Alkali Metals Group 1 (or 1A) metals are the most reactive metals because they have 1 valence electron. They increase in reactivity as you go down the group. Lithium is the least reactive and Cesium and Francium are the most reactive. Sodium and potassium have to be stored in oil because they react with the oxygen and water vapor in air. Cesium has to be stored in a glass tube filled with argon because it reacts with water temperatures as low as -115˚C.

Alkaline Earth Metals Are in group 2 (2A) and have 2 valence electrons. They are not as reactive as group 1. The differences in their reactivity is shown by how they react with water. Ca, Sr, and Ba react with cold water. Mg reacts with hot water and Be does not react at all with water.

The chlorophyll in plants contain magnesium. It is involved in the process that uses sunlight to produce sugar in plants. When mixed with other metals it becomes as strong as steel but much lighter. It is used in bike frames and backpacks. Our bodies need calcium to keep our bones and teeth strong. Calcium carbonate is the main ingredient in chalk, limestone, and coral. A plaster cast is made up of the compound calcium sulfate.

The Boron Family It is group 3A or 13 on the periodic table. They have 3 valence electrons and need to lose 3 electrons to become stable. Aluminum is the most abundant metal in the Earth’s crust. Boron is used in laboratory glassware and cookware that can go directly from the oven to the refrigerator. It is put in special glass that does not shatter easily.

The Carbon Family It is group 4A or 14 on the periodic table. It contains 4 valence electrons and needs to gain or lose 4 electrons to become stable. This group is made up of metals (Sn, Pb), metalloids (Si, Ge), and a nonmetal (C). The metallic properties increase as you move down the group. Life would not exist without carbon. Except for water, most of the compounds in your body contain carbon (fats, sugars, proteins, etc.).

Organic chemistry is the branch of chemistry devoted to the element carbon. Silicon is the 2nd most abundant element in the Earth’s crust. It is found in the form of silicon dioxide in quartz rocks, sand, and glass. The clay in pottery contains silicate compounds. Silicon carbide is an extremely hard compound used on saw blades to make them last longer than ordinary steel blades.

The Nitrogen Family Group 5A or 15 on the periodic table. Contains 5 valence electrons and needs to gain 3 electrons to become stable. Made up of 2 nonmetals (N, P), 2 metalloids (As, Sb) and 1 metal (Bi). The elements in this group have a very wide range of physical properties. Nitrogen is the most abundant gas in air.

This nitrogen is used to produce fertilizers; which also contain phosphorus. Phosphorus can exist in different forms with different properties. White phosphorus bursts into flames when it comes into contact with oxygen (really reactive). Red phosphorus is less reactive and is used to make matches ignite.

The Oxygen Family This is group 6A or 16 on the periodic table. It has 6 valence electrons and needs to gain 2 electrons to become stable. This group has 3 nonmetals (O, S, Se) and 2 metalloids (Te, Po). Oxygen is the most abundant element in the Earth’s crust. Oxygen is needed to keep complex life forms alive. It is used to release the energy stored in food.

Is highly flammable and needed for combustion reactions. Can be stored in oxygen tanks as a liquid under pressure. Ozone is a form of oxygen that is used in the upper atmosphere to help absorb harmful radiation emitted by the sun. At the ground level it can irritate your eyes and lungs. Sulfur is found in large natural deposits and was one of the first elements discovered. Most sulfur is in sulfuric acid used in fertilizers.

The Halogens The halogens are in group 7A or 17. They all have 7 valence electrons and need 1 more to become stable like the noble gases. They may have different physical characteristics but they have similar chemical properties. F and Cl are gases, Br is a liquid and I is a solid. They are highly reactive nonmetals. Fluorine is the most reactive in the group. So reactivity decreases down this group. They react easily with most metals.

Noble Gases The noble gases are in group 8A or 18. They have 8 valence electrons and are considered to be stable. They are colorless and odorless. Helium is placed with the noble gases because it acts like a noble gas but it only has 2 valence electrons. All noble gases are used in “neon” lights except for radon. They emit light when a current passes through them.

All groups with the A labels are called the representative elements or main group elements. These are the elements that make up the s and p blocks (orbitals). There are 25 elements essential to the human body. Read pages 146-147. Some elements are harmful to your body such as arsenic, lead, and mercury. Read pages 148-149.