Understanding the Periodic Table

• The periodic table displays chemical elements in a tabular format, arranged by atomic number, electron configuration, and recurring chemical properties.
• Elements are arranged by ascending atomic number, representing the number of protons in an atom's nucleus.
• As of 2024, the standard periodic table includes 118 elements.

Organization

• The periodic table features rows called periods and columns called groups.
• Elements within the same group share similar chemical traits due to having the same number of valence electrons.
• Periods are horizontal rows where elements have the same number of electron shells.
• Elements transition from having metallic to non-metallic properties moving from left to right across a period.

Groups

• Groups, or columns, are numbered 1-18 from the left to the right.
• Elements in the same group commonly show similar chemical behavior.

Main Groups

• These include Groups 1, 2, and 13-18.
• Group 1 elements (excluding hydrogen) are alkali metals, which are highly reactive.
• Group 2 elements are alkaline earth metals, known for their reactivity.
• Group 17 contains halogens, which are very reactive nonmetals.
• Group 18 is composed of noble gasses, notable for being very unreactive (inert).

Transition Metals

• Occupy Groups 3-12
• Transition metals show variable valency and create colored compounds.
• They are effective conductors of heat and electricity.

Lanthanides and Actinides

• They appear as separate rows at the bottom of the periodic table.
• Lanthanides (elements 57-71) are also known as rare earth elements.
• Actinides (elements 89-103) are radioactive.

Blocks

• Elements are sorted into blocks according to their electron configurations.
• s-block: Includes Groups 1 and 2 (alkali and alkaline earth metals).
• p-block: Includes Groups 13-18.
• d-block: Includes Groups 3-12 (transition metals).
• f-block: Consists of lanthanides and actinides.

Metals, Nonmetals, and Metalloids

• Metals are usually shiny, conduct heat and electricity well, and are malleable and ductile.
• Nonmetals typically do not conduct heat and electricity well and can be brittle.
• Metalloids (or semimetals) possess properties in between those of metals and nonmetals.

Periodic Trends

• Element characteristics change predictably across the periodic table.

Atomic Radius

• Atomic radius often decreases from the left to the right across a period because of increasing nuclear charge.
• Atomic radius goes up down a group as more electron shells are added.

Ionization Energy

• Ionization energy is the amount of energy needed to remove an electron from an atom.
• Ionization energy usually increases from the left to the right across a period because of increasing nuclear charge.
• Ionization energy goes down a group because the outermost electrons are farther away from the nucleus.

Electronegativity

• Electronegativity measures how well an atom attracts electrons in a bond.
• Electronegativity usually increases from the left to the right across a period.
• Electronegativity decreases going down a group.

Electron Affinity

• Electron affinity measures the energy change when an electron is added to a neutral atom.
• Electron affinity typically increases (becomes more negative) from the left to the right across a period.
• Electron affinity often decreases (becomes less negative) down a group.

Chemical Properties

• Valence electrons determine chemical properties.
• Elements in the same group have similar valence electron arrangements, giving them similar chemical traits.
• Metal reactivity goes up down a group (e.g., alkali metals).
• Nonmetal reactivity goes down a group (e.g., halogens).

Notable Elements

• Hydrogen (H) is the simplest and most common element in the universe.
• Oxygen (O) is needed for breathing and combustion.
• Carbon (C) is present in all organic substances.
• Silicon (Si) is a semiconductor used in electronics.
• Iron (Fe) is a strong metal used in building.
• Gold (Au) is a valuable metal that resists corrosion.
• Uranium (U) is a radioactive element used in nuclear energy.

Isotopes

• Isotopes are versions of an element that have the same number of protons, but a different number of neutrons.
• Isotopes have the same atomic number but different mass numbers.
• The traits of isotopes are generally alike, though their masses differ.

Ions

• Ions are atoms or molecules that gain or lose electrons, leading to an electrical charge.
• Cations are positive ions that form when electrons are lost.
• Anions are negative ions that form when electrons are gained.
• Ionic compounds result from the attraction between cations and anions.

Compounds

• Compounds are created when two or more elements are chemically bonded.
• Chemical formulas show the types and numbers of atoms in a compound.
• Molecular compounds form when atoms share electrons (covalent bonds).
• Ionic compounds form when electrons are transferred between atoms (ionic bonds).

Allotropes

• Allotropes are different structural forms of the same element.
• Examples include diamond and graphite for carbon, and oxygen (O2) and ozone (O3) for oxygen.

Development of the Periodic Table

• Döbereiner's Triads (early 1800s) grouped elements with similar traits into triads.
• Newlands' Law of Octaves (1865) ordered elements by atomic weight, noting that properties recurred for every eighth element.
• Mendeleev's Periodic Table (1869) arranged elements by atomic weight and predicted undiscovered elements.
• Moseley's discovery of atomic number (1913) led to the current arrangement of the periodic table.