number of protons in the nucleus of an atom; the periodic table is arranged based on this

average mass of an atom of an element

Rows of elements are arranged horizontally based on increasing atomic number

Columns (up and down); vertical arrangement Elements have similar chemical properties and the same valence electrons

elements that have the same number of valence electrons with similar chemical properties

an expression that states the number and type of atoms present in a molecule of a substance

malleable, ductile, luster (shiny), good conductors of heat and electricity (left side of periodic table)

Elements that are poor conductors of heat and electric current (right side of periodic table)

Elements that share some properties with metals and some properties with non-metals. (located along staircase of the periodic table)

Group 18 and the most unreactive elements on the periodic table

Group 1 - most reactive elements in the periodic table

credited with the creation of the basis for our modern day periodic table

the outermost electron(s)

the characteristics of a substance that can be used to identify the substance and that describes how the substance reacts with other substances resulting in a new substance Ex: acidity, basicity,combustibility, reactivity

a characteristic of matter (such as a size, shape, or state that) can be observed and measured Ex: shape, density, solubility, odor, color, mp, bp, size, state

no new substances formed; reversible Ex: boiling, melting, freezing, evaporation, condensing, breaking of glass, crushing paper, solubility

new substance is formed; irreversible Ex rusting, tarnishing, precipitate, color change, gas given off