science 3

• The periodic table is a chart that organizes all the known chemical elements.
• Elements are listed based on

  their atomic number, which is

  the number of protons in an

  atom's nucleus.
• This arrangement reveals a pattern - elements with similar chemical properties tend to fall in the same vertical columns, called groups
• The table also has horizontal rows, called periods , which show trends in element properties as you move across the table .
• • The periodic table is a fundamental tool in chemistry, allowing scientists to predict element behaviors, understand how they react with each other, and design new materials.
• •In 1869, Dmitri Mendeleev is credited with creating the framework for the modern periodic table.
• The concept of atomic number (number of protons) came later and refined the organization of the table by Henry Moseley in 1913.
• • Elements are fundamental building blocks of matter
• •Groups: There are 18 groups (sometimes called columns) in the periodic table.
• Elements within a group tend to have similar chemical properties because they have the same number of valence electrons, the electrons in the outermost shell of an atom.
• • Periods: There are 7 periods (sometimes called rows) in the periodic table.
• • Metals: Metals are generally found on the left side of the periodic table.
• Metals are shiny, malleable (can be hammered into thin sheets), ductile (can be drawn into wires), and good conductors of heat and electricity.
• •Nonmetals: Nonmetals are generally found on the upper right side of the periodic table
• Nonmetals are often brittle, poor conductors of heat and electricity, and may exist as solids, liquids, or gases at room temperature
• Metalloids are elements that have properties of both metals and nonmetals.
• metalloids

  They are located along a diagonal line separating the metals from the nonmetals on the periodic table
• The alkali metals are the elements in Group 1 (IA) of the periodic table
• The alkali metals are very reactive metals that readily lose one electron to form a cation with a +1 charge.
• The alkaline earth metals are the elements in Group 2 (IIA) of the periodic table.
• The alkaline earth metals are moderately reactive metals that tend to lose two electrons to form a cation with a +2 charge.
• The halogens are the elements in Group 17 (VIIA) of the periodic table.
• The halogens are very reactive nonmetals that readily gain one electron to form an anion with a -1 charge.
• •Noble Gases: The noble gases are the elements in Group 18 (VIIIA) of the periodic table.
• The noble gases are unreactive gases because their outer electron shells are full.
• The lanthanides are a series of 15 metallic elements following lanthanum (La) that are placed at the bottom of the periodic table. These elements share similar properties because they fill the 4f electron subshell.
• The actinides are a series of 15 metallic elements following actinium (Ac) that are placed at the bottom of the periodic table. These elements share similar properties because they fill the 5f electron subshell.
• • Electron configuration refers to the arrangement of electrons around the nucleus of an atom.
• electron configuration

  •It describes which energy levels (orbitals or shells) the electrons occupy.
• Electron configuration is typically written using a notation that specifies the energy level (orbital) and the number of electrons in that level.
• • Number (n): Represents the energy level or shell (e.g., n = 1, 2, 3, etc.).
• Letter (s, p, d, f): Represents the subshell within an energy level. Each energy level can have multiple subshells with different shapes. (s, p, d, and f are the common subshell types)
• Superscript (x): Represents the number of electrons in that specific subshell.
• • s subshell: This subshell can hold a maximum of 2 electrons. It's the simplest subshell and is located closest to the nucleus.
• p subshell: can hold a maximum of 6 electrons. It has three orbitals with slightly different shapes . Each orbital can hold a maximum of 2 electrons .
• The d subshell can hold a maximum of 10 electrons . It has five orbitals with more complex shapes . Similar to the p subshell, each orbital can hold a maximum of 2 electrons .
• The f subshell can hold a maximum of 14 electrons. It has seven orbitals with even more complex shapes.