Ionic and covalent bonds

Give electrons or share them

1. Ionic and covalent bonds: from zero

2. Metal plus poison gas

Sodium is a soft, reactive metal. Chlorine is a poisonous gas. Together they make table salt.

Pick the right answer

Predict: what holds sodium and chlorine together in table salt?

A. Attraction between a positive ion and a negative ion
B. A pair of electrons shared by the two atoms
C. Nothing: they are only mixed

Explanation

Sodium gives an electron to chlorine, forming a positive sodium ion and a negative chloride ion. The attraction between these opposite ions, the ionic bond, holds table salt together.

3. Ionic bond

Na (2, 8, 1) → $Na+ Na X^{+}$ (2, 8) (loses 1 electron)
Cl (2, 8, 7) → $Cl- Cl X^{-}$ (2, 8, 8) (gains 1 electron)
$Na+ Na X^{+}$ (2, 8) → $Na+ Na X^{+}$ and $Cl- Cl X^{-}$ attract
$Cl- Cl X^{-}$ (2, 8, 8) → $Na+ Na X^{+}$ and $Cl- Cl X^{-}$ attract

Electron transfer in sodium chloride

Ionic bond

The electrostatic attraction between a positive ion and a negative ion, formed by transfer of electrons.

Both ions now have a stable outer level, like a noble gas.

4. Covalent bond

Two chlorine atoms share one pair of electrons in

Cl2 Cl X_{2}

Covalent bond

A bond formed by sharing pairs of electrons between two atoms.

Each chlorine atom has 7 outer electrons and needs one more. Neither gives one away, so they share a pair.

5. Transfer or share?

Sort into groups

Sort each substance by the bond between its atoms.

$MgO MgO$ : magnesium (metal) and oxygen $H2O H X_{2} O$ : hydrogen and oxygen $KBr KBr$ : potassium (metal) and bromine $CH4 CH X_{4}$ : carbon and hydrogen $O2 O X_{2}$ : two oxygen atoms

6. Summary

Ionic bond: one atom gives electrons, the other takes them; the oppositely charged ions attract.
Covalent bond: two atoms share pairs of electrons.
Next: metal atoms bond to each other in a third way, the metallic bond.

Can you explain why sodium and chlorine form ions, but two chlorine atoms share?

Reveal

Atoms	What happens	Bond
Na (2, 8, 1) + Cl (2, 8, 7)	Na gives 1 electron to Cl	Ionic bond
Cl (2, 8, 7) + Cl (2, 8, 7)	Neither gives one away, so they share a pair	Covalent bond

Sodium loses its 1 outer electron and chlorine gains it:

Na+ Na X^{+}

and

Cl- Cl X^{-}

form and attract. Each chlorine atom has 7 outer electrons and needs one more, so two chlorine atoms share a pair.

Concepts in this lesson