8.2 Ionic Bonding

Ionic Bonds

• Ionic bonds are made between metal and non-metal atoms

• Electrons are transferred from the metal atom to the non-metal atom

• Metal atoms lose electrons form positive ions called cations.

• Non metal atoms gain electrons form negative ions called anions.

Metals • Metals atoms lose electrons to form positive

ions (an atom that loses or gains electrons) called cations.

E.g., Beryllium (Be) Group 2 Neutral atom Positive ion 4+ P’s 4+ P’s4- E’s 2- E’s0 2+

Valence Electrons

The electrons in the outer shell of an atom, which determines its power to combine with other elements

Non-metals

• Non-metal atoms gain electrons to form negative ions called anions.

E.g., Carbon (Ca) Group 14

Neutral atom Negative ion

6+ P’s 6+ P’s

6- E’s 10- E’s

0 4-

An example of ionic bonding…..

• Let us consider the bonding in the substance sodium chloride.

• Na+ + Cl- Na+Cl- • In this reaction the sodium (Na) atom

loses 1 electron while the chlorine atom accepts the electron in the transfer process.

NaCl

• Thus we can say that sodium chloride is an ionic compound

NaCl

Na+ Sodium ion This charged

atom contains:11+ Protons

+ 10- Electrons- 1

Cl-

Chloride ion

This charged atom contains:

17+ Protons

+ 18- Electrons

+1

Sodium Chloride

• Thus NaCl

• Once these two ions (An atom that has become charged be gaining or losing one or more electrons) have been formed, they will attract each other because of their opposite charges

CaO

• Ca2+ + O2- Ca2+O2-

• In this reaction the calcium (Ca) atom loses 2 electrons while the oxygen (O) atom accepts the two electrons in the transfer process.

Thus we can say that calcium oxide is an ionic compound

Calcium OxideCa2+ Calcium ion O2- Oxide ion 20+ Protons 8+ Protons 18- Electrons 10- Electrons2+ 2-

Once these two ions have been formed, they will attract each other because of their opposite charges.

There is an electrostatic attractive force present (like charges repel and unlike charges attract) that creates the chemical bond in the NaCl and CaO,called an ionic bond.

Let’s try one…..

Magnesium and Fluorine

Metal Non-metal12+ Protons 9+ Protons10- Electrons 10- Electrons2+ 1-

Mg2+ + F1- Mg2+F1-

Chemical name: Magnesium fluoride

Chemical Formula: MgF2

• Group 1 elements form cations with one positive charge.

• Group 2 elements form cations with two positive charges.

• Group 3 elements form cations with three positive charges.

• Group 17 elements form anions with one negative charge.

• Group 16 elements form anions with two negative charges.

• group 15 elements form anions with three negative charges.

Group number on the periodic table indicates the number of electrons the atom will lose or gain.

Figuring out Ionic Charge

• For metals, it‘s the same as thegroup number (the column number).

• For non metals, the charge is equal to whatever number needs to be addedto the group number to get 8. Group 8, (the noble gases), don‘t form ions asthey do not need to gain any electrons to have a full outer shell

More to try……..

Potassium and Sulfur

Aluminium and Chlorine

Aluminum and Oxygen

Calcium and Fluorine

Bonding in Ionic Compounds• According to the ionic electrostatic model, solids such as

NaCl consist of positive and negative ions arranged in a crystal lattice.

• Each ion is attracted to neighbouring ions of opposite charge, and is repelled by ions of like charge; this combination of attractions and repulsions, acting in all directions, causes the ion to be tightly fixed in its own location in the crystal lattice.

Sodium metal reacts with chlorine gas in a violently exothermic reaction to produce NaCl (composed of Na+ and Cl- ions):

2Na(s) + Cl2(g) -> 2NaCl(s)