Periodic Table Trends and Electron Configuration

How are elements organized in the Periodic Table?

Organization by Atomic Number

-The atomic number of an element is the number of protons in the nucleus

-The periodic table is arranged in order of increasing atomic number from left to right and top to bottom

-This arrangement ensures that elements with similar chemical properties appear in columns called groups/families

Electron Arrangement (Electron Configuration)

-Electrons are arranged in energy levels or shells around the nucleus

-Bohr models are a simple way to visualize this: Elections move in discrete orbits (shells) around the nucleus

-The number of electrons in the outermost electron shell determine an elements chemical properties 

Periods on the Periodic Table

-Rows on the periodic table are called “periods”

-All elements in a period have the same number of electron shells 

Columns/Groups 

-Columns are called groups/families

-Elements in the same group have the same number of ve-, so they have similar chemical behavior 

Atomic Radius

Definition: The distance between the nucleus and the outermost electron

Trend across →Decreases

-More protons → higher effective nuclear charge → pulls electrons closer

-Number of energy levels stays the same → no extra shielding

Trend down a group →Increases

-More energy levels (shells) →electrons are farther from the nucleus

-Shielding increases → outer electrons less tightly held

Ionization Energy

Definition: The energy need to remove an electron from an atom 

Trend across a period → Increases 

-Electrons are tightly held

Trend down a group →Decreases

-Outer electrons are farther from the nucleus (more shells, easier to remove)

Electronegativity

Definition: The ability of an atom to attract electrons in a bond

Trend across → Increases

-More protons → stronger pull on shared electrons

Trend down a group →Decreases

-More shells → outer electrons become farther →weaker pull