Periodic Table Arrangement

• Organizing objects by sorting them into piles based on similar properties makes them easier to find, similar to organizing elements.

Developing a Periodic Table

• Dimitri Mendeleev, in 1869, aimed to classify elements by studying their physical properties (density, color, melting point, atomic mass) and chemical properties (how elements react).
• Mendeleev arranged elements by increasing atomic masses and noted repeating patterns in their properties.
• Mendeleev grouped elements with similar properties in the same column, creating a table resembling sorted objects with shared characteristics.

Patterns in Properties

• The term "periodic" refers to a repeating pattern.
• Melting point, boiling point, and reactivity exhibited repeating patterns in Mendeleev's table.
• When Mendeleev arranged elements by atomic mass, gaps appeared, leading him to predict the discovery of new elements with properties similar to those in the same columns, which later proved true.

Changes to Mendeleev's Table

• Mendeleev's table allowed scientists to link known element properties to their table position, but some elements appeared misplaced.
• Mendeleev believed atomic masses of some elements were incorrect, leading to their misplacement. For instance, tellurium was placed before iodine despite having a greater atomic mass because iodine's properties resembled fluorine and chlorine more closely.

The Importance of Atomic Number

• In the early 1900s, Henry Moseley resolved Mendeleev's table issues by arranging elements by increasing atomic number instead of atomic mass.
• Atomic number is the number of protons in an atom's nucleus. Arranging by atomic number grouped elements with similar properties.

Today's Periodic Table

• Element properties can be identified by their placement on the periodic table, which is organized into columns, rows, and blocks based on property patterns.
• Each element key includes the chemical symbol, atomic number, atomic mass, and a symbol indicating its state of matter at room temperature.
• A group (column) contains elements with similar chemical properties and reaction patterns.
• Periods (rows) show elements with atomic numbers increasing by one from left to right, altering their physical and chemical properties.

Metals, Nonmetals, and Metalloids

• Metals occupy nearly three-fourths of the periodic table, located on the left side and in the middle.
• Metals are shiny and conduct thermal energy and electricity.
• Nonmetals, except for hydrogen, are on the right side, often existing as gases and not conducting thermal energy or electricity.
• Metalloids lie between metals and nonmetals, exhibiting properties of both.

Physical Properties of Metals

• Metals are shiny, can be drawn into wires (ductility), hammered into sheets (malleability), and conduct electricity and thermal energy.
• Luster is the ability of a metal to reflect light.
• Ductility is the ability to be pulled into thin wires.
• Malleability is the ability of a substance to be hammered or rolled into sheets.
• Metals usually have high density, strength, boiling, and melting points, and are solid at room temperature (except mercury).

Chemical Properties of Metals

• Chemical properties of metals can vary, but metals in the same group often share similar chemical properties.
• Gold and other group 11 elements are unreactive.

Group 1: Alkali Metals

• Group 1 elements are called alkali metals: lithium, sodium, potassium, rubidium, cesium, and francium.
• Alkali metals are highly reactive and are found in compounds in nature and must be stored to prevent contact with oxygen and water vapor.
• Alkali metals are silvery, soft enough to cut, and have low densities.

Group 2: Alkaline Earth Metals

• Group 2 elements are called alkaline earth metals: beryllium, magnesium, calcium, strontium, barium, and radium.
• Alkaline earth metals react quickly, but not as quickly as alkali metals and also do not occur naturally in pure form.
• Alkaline earth metals are soft, silvery, and have low densities, but higher than alkali metals.

Groups 3-12: Transition Elements

• Groups 3-12 contain transition elements, located in the center and at the bottom of the periodic table.
• Transition elements are all metals with higher melting points, greater strength, and higher densities than alkali and alkaline earth metals.
• Transition elements react slowly with oxygen and some can exist as free elements (pure form).
• Transition elements, like iron, make good building materials due to their high densities, strength, and resistance to corrosion.
• Copper, silver, nickel, and gold are used in coins, jewelry, electrical wires, and industrial uses.
• Main-block transition elements form colorful compounds used in paints, pigments, and gemstones.

Lanthanide and Actinide Series

• Lanthanide and actinide series are the two rows of transition elements at the bottom.
• Lanthanide series elements are used to make strong magnets.
• Plutonium, an actinide series element, is used as fuel in nuclear reactors.

Patterns in Properties of Metals

• Metallic properties (luster, malleability, conductivity) generally increase from right to left across a period. Elements on the far right have no metallic properties.
• Metallic properties increase as you move down a group.

The Elements of Life

• Oxygen, carbon, hydrogen, and nitrogen make up over 96% of body mass.
• Phosphorus and sulfur are also common elements in the body.
• These six nonmetal elements form compounds in proteins, fats, nucleic acids, and other large molecules in living things.

Nonmetals in Groups 14-16

• Groups 14-16 include metals, nonmetals, and metalloids with similar chemical properties but different physical properties.
• Carbon is the only nonmetal in group 14 and is a solid that exists in different forms and makes up compounds in living things.
• Nitrogen (gas) and phosphorus (solid) are the only nonmetals in group 15.
• Group 16 contains three nonmetals: Oxygen (gas), and sulfur and selenium (solids).

Group 17: The Halogens

• Halogens are group 17 elements that react with metals to form salts, such as chlorine reacting with sodium to form sodium chloride (table salt).
• Halogens react readily with other elements, including nonmetals, and only occur naturally in compounds, not as free elements.
• Halogens become less reactive as you move down the group.

Group 18: The Noble Gases

• Group 18 elements are noble gases: helium, neon, argon, krypton, xenon, and radon.
• Noble gases only react under special laboratory conditions and were undiscovered when Mendeleev created his table.

Hydrogen

• Hydrogen is the element with the smallest atomic mass and is the most common element in the universe.
• Hydrogen is usually classified as a nonmetal due to properties like being a gas at room temperature.
• However, it also shares properties with alkali metals, such as conducting electricity in liquid form, and reacts like an alkali metal in some reactions.

Metalloids

• Metalloids are elements between metals and nonmetals with properties of both, including boron, silicon, germanium, arsenic, antimony, tellurium, polonium, and astatine.
• Metalloids are located between the metals and nonmetals on the periodic table.
• Silicon is the most abundant metalloid in the universe.

Semiconductors

• Semiconductors conduct electricity at high temperatures but not at low temperatures.
• At high temperatures, semiconductors act like metals and at lower temperatures they act like nonmetals.
• Pure silicon and germanium are used in making semiconductor devices.

Properties and Uses of Metalloids

• Boron is present in water softeners and laundry products and glows green in fireworks.
• Silicon compounds make up sand, clay, and many rocks and minerals.