Lewis Dot Structures of Covalent Compounds

Atoms are made up of protons, neutrons, and electrons. The

protons and neutrons are located at the center of the atom,

the nucleus. These electrons can be divided into core

electrons and valence electrons. The valence electrons are

the outermost electrons and are the ones involved in

chemical reactions

p+

e-

p+

p+

e-e-

n0

n0

n0

p+

p+

p+p+

n0

n0

e-

e-

e-

e-

e-

e-

e-

The NucleusProtons and neutronsare located in thenucleus (center) of the atom

Electrons Electrons occupy most ofthe volume of an atomThey arrange themselvesin ’shells’ at varyingdistances from the nucleus

Valence electronsThese are the outermost electrons and the ones In chemical reactions

The number of valence electrons varies by element. For the

Main Group elements, the number of valence electrons is

equal to the Group Number that the elements belong to.

For example, Sodium (Na) belongs to Group 1A and therefore

has 1 valence electron.

HLi

KRbCs

NaBeMgCaSrBa

BAlGaInTi

CSiGeSnPb

NPAsSbBi

OSSeTePo

FClBrIAt

HeNeArKrXeRn

Transition metals

IA

IIA IIIA IVA VA VIA VIIA

VIIIA

The Periodic Table

For example, Bromine (Br) belongs to Group VIIA and

therefore has 7 valence electrons. We can represent the

valence electrons of an atom using a Lewis dot symbol, in

which the element symbol is surrounded by dots representing

the valence electrons.

For example, Oxygen has six valence electrons, so its Lewis

dot symbol is:

O

Note the six dots representing the six valence electrons

For example, neon has eight valence electrons, so its Lewis dot symbol is:

NeFor example, carbon has four valence electrons, so its Lewis dot symbol is :

C

How many valence electrons does Potassium (K) have? 1

How many valence electrons does Antimony (Sb) have? 5

How many valence electrons does Phosphorus (P) have? 5

How many valence electrons does Magnesium (Mg) have? 2

HeNeArKrXeRn

VIIIA The Noble Gas elements in Group VIIIA have

either two valence electrons (He) or eight

valence electrons (Ne, Ar, Kr, Xe, and Rn).

extremely stable because they have full

valence shells-

Metallic elements at the left side of the Periodic Table tend to

lose one or more electrons to form positive ions, such as Na+

and Mg2+, each of which has the electron configurationof the

Noble Gas that preceds it.

Nonmetals at the right side of the Periodic Table tend to either

gain electrons to form negative ions such as F-, O2-, and N3- or

to share electrons in covalent bonds.