The+nature+of+covalenting+bonding+&+Predicting+the+formula+of+covalent+bonds

~ A **__COVALENT BOND__** is the **intramolecular** bond which involves the equal //**sharing of electrons**//.

> **e.g.** diatomic molecules ​ H 2 ,O 2 or covalent compounds CO 2, H 2 O, CH 4 > > > __**OCTET RULE**__ explains that atoms in column 14 to 17 in the P.T. tend to form covalent bonds so they will > have //**8** valence electrons// in their valence shells. ( from Chemistry 11 extbook P176 ) > > > > Shared electrons in the F-F covalent bond in order to have 8 electrons for each F. > The shared electrons will form a strong covalent bond.
 * It is formed when two //**nonmetal elements**// combine.
 * The 2 non-metallic elements have relatively //**high**// electroneagivity.
 * Hence, electrons are shared and covalent bonds are **//stronger//** than ionic bonds.


 * ~** __**COVALENT BONDS**__ are **//VERY STRONG//**.

** But **, it is very tempting to say that covalent compounds have high //melting temperature//!

O 2 = － 218℃ F 2 = －220℃
 * e.g.** CH 4= －182℃

//**intermolecular bonds**//.
 * ~** Covalent compounds have __ **// low melting temperature //** __ since when the compounds are melting, the bonds broken are the

Two kinds of //**intermolecular bonds**// are **//London Forces & Dipole-Dipole Forces//**.

Comparing forces :

(# - intramolecular bonds ﹕ - intramolecular bonds)
 * Covalent bonds** # ﹥ Ionic bonds # ﹕﹥﹥H-bond﹕﹥**Dipole-Dipole force** ﹕= **London Forces**﹕


 * London Forces** and **Dipole-Dipole Forces** are really **weak** and **require less energy to break**.


 * Some exeptions**: the covalent compounds have **//__network of covalent bonds__//** will have extremely **high melting points**.


 * **e.g.** C(diamond)= about 3550℃ BN(boron nitride)= about 3000℃




 * ~ Predicting the formula of covalent compounds : **


 * # of electrons the element will be shared = **the valence of the atom**
 * use the //**criss-cross**// method to predict the compound formula (criss-cross the valence of the atoms)

**e.g.** **1** Nitrogen & Hydrogen (ignore the ion charges)

This means ...... N has 3 electrons to share H has 1 electrons to share


 * e.g. 2** Fluorine & Oxygen

This means F has 1 electron to share O has 2 electrons to share

*The table of the **valence** of the atom.

Li Be B **//C N O F//** 1 2 3 **//4 3 2 1//** Na Mg Al Si **//P S Cl//** 1 2 3 4 //**3 2 1**// K Ca Ga Ge As Se //**Br**// 1 2 3 4 3 2 **//1//** Rb Sr In Sn Sb Te **//I//** 1 2 3 4 3 2 //**1**// Cs Ba TI Pb Bi Po **//At//** 1 2 3 4 3 2 **//1//** (the bold Italic parts are the non-metals)

H N O F Cl Br I When these elements form covalent compounds, they will form diatomic compounds by themselves, e.g. N 2, O 2 , Cl 2......
 * The **magic seven**


 * References:**

chemistry 11 textbook Mr. Standring's notes http://a0.att.hudong.com/08/14/300000678340127140140554307_950.jpg