- An ion is a charged particle formed from an atom or a group of atoms by the loss or gain of electrons
- An ion’s no. of electrons ≠ no. of protons
- Ions that are positively-charged are called cations and those that are negatively-charged are called anions
- Atoms of metals tend to lose valence electrons to attain a noble gas configuration
- Atoms of non-metals tend to gain electrons to attain a noble gas configuration
¶ Describe the relationship between ionic charge and the group number of an element.
- Group I metal atoms lose one electron to form ions with a charge of 1+
Li (2,1)→Li+ (2)Na (2,8,1)→Na+ (2,8)K (2,8,8,1)→K+ (2,8,8)
- Group II metal atoms lose two electron to form ions with a charge of 2+
Be (2,2)→Be2+ (2)Mg (2,8,2)→Mg2+ (2,8)Ca (2,8,8,2)→Ca2+ (2,8,8)
- Group III metal atoms lose three electron to form ions with a charge of 3+
Al (2,8,3)→Al3+ (2,8)
- Group VII non-metal atoms gain one electron to form ions with a charge of 1-
F (2,7)→F− (2,8)Cl (2,8,7)→Cl− (2,8,8)
- Group VI non-metal atoms gain two electrons to form ions with a charge of 2-
O (2,6)→O2− (2,8)S (2,8,6)→S2− (2,8,8)
- Sodium and chlorine react in the ratio if 1:1 to form sodium chloride
- Each sodium atom loses its single valence electron to form a positively charged sodium ion:
Na (2,8,1)→Na+ (2,8)+e−
- Each chlorine atom gains an electron from a sodium atom to form a negatively charged chloride ion:
Cl (2,8,7)+e−→Cl− (2,8,8)
- A strong ionic bond is formed between the oppositely charged Na+ ion and Cl- ion
- Magnesium and chlorine react in the ratio if 1:2 to form magnesium chloride
- Each magnesium atom loses its two valence electron to form a positively charged magnesium ion:
Mg (2,8,2)→Mg2+ (2,8)+2e−
- Each of a pair of chlorine atom gains an electron from a magnesium atom to form a negatively charged chloride ion:
Cl (2,8,7)+e−→Cl− (2,8,8)
- A strong ionic bond is formed between the oppositely charged Mg+ ion and two Cl- ions.
- In general, the number of the non-metal ions in an ionic compound is the charge (group number) of the metal ion in that compound while the number of metal ion in the ionic compound is the charge of the non-metal ion in that compound.
| Metal atom from |
Metal ion |
Non-metal atom from |
Non-metal ion |
Ionic compound formula |
| Group I |
X+ |
Group VII |
T- |
XT |
| Group I |
X+ |
Group VI |
U2- |
X2U |
| Group I |
X+ |
Group V |
V3- |
X3V |
| Group II |
Y2+ |
Group VI |
U2- |
YU |
| Group II |
Y2+ |
Group V |
V3- |
Y2V3 |
| Group III |
Z3+ |
Group VII |
T- |
ZT3 |
| Group III |
Z3+ |
Group VI |
U2- |
Z2U3 |
| Group III |
Z3+ |
Group V |
V3- |
ZV |
¶ Relate the melting/boiling point of ionic compounds to their giant ionic lattice and strong ionic bonds.
- Ionic compounds are hard, crystalline solids at room temperature and pressure
- They have high melting and boiling points
- This is because the ions are held in their fixed positions in a crystal lattice structure by very strong ionic bonds which requires a lot of energy to overcome
- The covalent bond is a strong bond formed by the sharing of electrons between atoms of non-metal elements (usually), between the positive nuclei and negative shared electrons
- A molecule is made up of two or more atoms held together by covalent bonds
- Covalent bonds can be formed between atoms of the same element or atoms of different elements
- A molecule of an element contains atoms of same element covalently bonded together: e.g. Hydrogen (H2), oxygen (O2), chlorine (Cl2)
- A molecule of a compound contains atoms of different elements covalently bonded together: e.g. Water (H2O), carbon dioxide (CO2)
- Each hydrogen atom has one electron in its outer shell
- By sharing electrons, each atom has two electrons in its outer shell
- Each hydrogen atom has gained a stable duplet configuration
- The oxygen atom shares one outer electron with each hydrogen atom (two electrons between both hydrogen atoms)
- Each hydrogen atom shares its outer electron with the oxygen atom
- The oxygen atom achieves an octet electronic configuration
- Each hydrogen atom achieves a duplet electronic configuration
- The sharing of four electrons between oxygen and hydrogen results in the formation of two single covalent bonds, each hydrogen atom is bonded to the oxygen atom by a single covalent bond
- The carbon atom shares four outer electrons with four hydrogen atoms.
- Each hydrogen atom shares its outer electron with the carbon atom.
- The carbon atom achieves an octet electronic configuration.
- Each hydrogen atoms achieves a duplet electronic configuration.
- The sharing of four electrons between a carbon atom and four hydrogen atoms results in the formation of four single covalent bonds, four hydrogen atoms are bonded to one carbon atom by four single covalent bonds.
- The nitrogen atom shares three outer electrons with three hydrogen .atoms.
- Each hydrogen atom shares its outer electron with the nitrogen atom.
- The nitrogen atom achieves an octet electronic configuration.
- Each hydrogen atoms achieves a duplet electronic configuration.
- The sharing of three electrons between a nitrogen atom and three hydrogen atoms results in the formation of three single covalent bonds, three hydrogen atoms are bonded to one nitrogen atom by three single covalent bonds.
- The carbon atom shares four of its outer electrons with two oxygen .atoms.
- Each oxygen atom shares its outer electron with the nitrogen atom.
- The carbon atom achieves an octet electronic configuration.
- Each hydrogen atoms achieves a duplet electronic configuration.
- The sharing of four electrons between a carbon atom and two oxygen atoms results in the formation of two double covalent bonds, two oxygen atoms are bonded to the carbon atom by two double covalent bonds.
- Start by stating the valence electron of each atom
- Thereafter, try to share the electrons between each atom so that they have either two or eight valence electrons
¶ Relate the melting/boiling point of simple covalent substances to their simple molecular structure and weak intermolecular forces.
- Simple covalent substances are held in a simple molecular structure that are held together by weak intermolecular forces of attraction
- Atoms in these molecules are held by strong covalent bonds
- Simple molecular covalent substances are usually liquids or gases at room temperature and pressure (some exceptions: iodine and sulfur are solids at r.t.p.).
- They have low melting and boiling points as the molecules are held together by very weak intermolecular forces of attraction so very little energy is required to overcome this force between the molecules