unit 5 periodic table

antoine lavoisier

• Compiled a list of 23 known elements in the 1790s.

• Known as the Father of Modern Chemistry.

john newlands

• Introduced the Law of Octaves in 1864, noting repeating patterns every 8th element.

• Worked with 70 known elements but did not account for all.

dimitri Mendeleev

• Created the first periodic table in 1869, arranging elements by atomic mass.

• Left blank spaces and predicted properties of undiscovered elements.

henry moseley

• Established the concept of atomic number in 1913, organizing elements by increasing atomic number.

periodic table organization

• Periods: Horizontal rows.

• Groups: Vertical columns (1-18, newer system; older system: A/B).

• Representative Elements: Elements in the s and p blocks (Main Group).

periodic law

• When elements are arranged by increasing atomic number, there is a periodic repetition of chemical and physical properties.

inert gases (noble gases)

He,Ne,Ar,Kr- chemically inert

inner transition metals

rare earth metals, 2 series below the main table

solids

most elements

liquid

Br and Hg

gases

H,N,O,F,Cl and all noble gases

metals

• Properties: Ductile, malleable, lustrous, good conductors, high melting points and density.

• Majority solid at room temperature (exception: Hg).

nonmetals

• Properties: Dull, low melting points and density, poor conductors (good insulators).

metalloids

• Elements: B, Si, Ge, As, Sb, Te, Po, At.

• Have intermediate properties.

• Examples: Si used in semiconductor chips, Ge in solar cells.

valence electrons

• Increase from left to right.

• Remain the same from top to bottom.

octet rule

• Atoms tend to gain, lose, or share electrons until surrounded by eight valence electrons.

• An octet consists of eight electrons stabilizing the atom (similar to noble gases).

atomic radius trends

• Defined as the distance of an atom to its neighboring atom.

• Decreases across a period (left to right).

• Increases down a group (top to bottom).