5.1 Atoms, Bonding, and the Periodic Table

Valence Electrons and Bonding Valence electrons are those electrons that have the highest energy level and are held loosely The number of valence electrons in an atom help to determine properties of the element, including bonding properties

Each element has a specific number of valence electrons, ranging from 1-8 An electron dot diagram includes the symbol for the element surrounded by dots; each dot stands for one valence electron

Chemical Bonds, Stability, and Chemical Reactions Atoms of most elements are more stable when they have 8 valence electrons Atoms usually react in a way that makes each atom more stable – Either the number of valence electrons increases to 8 (or two, in the case of hydrogen) – The atom gives up loosely held valence electrons

A chemical bond is the force of attraction that holds two atoms together as a result of the rearrangement of electrons between them When atoms bond, they will either lose, gain, or share electrons In either of these cases, the change will result in a chemical reaction which will form a new substance

How the Periodic Table Works As the atomic number increase, the number of electrons increases Elements within a group/column, always have the same number of valence electrons Elements within a group have similar properties because they all have the same number of valence electrons in their atoms

Noble Gases-Group 18 Atoms of these elements have 8 valence electrons except for Helium, which has 2 Because these atoms are stable, they do not react easily with other elements so they do not usually form compounds Halogens-Group 17 Contain 7 valence electrons Will gain an electron to give it 8 valence electrons React easily with other elements whose atoms can give up or share electrons

Alkali Metals-Group 1 Have 1 valence electron Alkali metals become more chemically stable by losing their 1 valence electron when forming a chemical bond This property makes alkali metals extremely reactive Other Metals-Groups 2-12 Most have 1,2, or 3 valence electrons React by losing electrons The reactivity of a metal depends on how easily its atoms lose electrons Reactivity of metals decreases from left to right across the periodic table In Groups 1 and 2, reactivity increases from top to bottom

Other Nonmetals Have 4 or more valence electrons Like the halogens, nonmetals become stable when they gain or share enough electrons to have a set of 8 valence electrons Nonmetals combine with metals by gaining electrons Nonmetals combine with nometals by sharing electrons Oxygen and halogens are the most reactive nonmetals Metalloids Have between3-6 electrons They can lose or share electrons when forming bonds Hydrogen Has only 1 valence electrons Reactive element Considered to be a nonmetal