11. a. List the elements used to form the products in the following list: i. sodium chloride
ii. sodium sulfide iii. potassium oxide iv. barium sulfide v. calcium oxide vi. magnesium chloride
b. Use the periodic table to write the chemical formula for each of the products listed in a. Use the criss-cross method to help you.
Writing chemical formulae – covalent bonding
To write the chemical formula of a covalent compound, it is important to remember that elements share electrons to achieve a full shell in a covalent bond. The periodic table can be used to find out the number of bonds that an element needs to form in a covalent compound.
Fig. 19.11 shows the combining powers of each group of elements in the periodic table. You can see that carbon has a combining power of 4. This means carbon needs to form four bonds.
1 H
Li 2 30 4 321 Be
Na Mg K Ca Rb Sr Cs Ba Fr
Ra B Al
Sc Y
La Ac
Ti Zr Hf Rf Db Sg Bh Hs Mt Ds Rg Cn
V
Nb Ta
Cr Mo W
Mn Tc Re
Fe Ru Os
Co Rh Ir
Ni Pd Pt
Cu Ag Au
: Fig. 19.11 Combining power of element groups in the periodic table
For example, when carbon bonds with another element, it needs to create four bonds with that element. Oxygen has a combining power of two.
? TEST TUBE
12. Use the periodic table to write the chemical formula for the following compounds: a. water (compound of oxygen and hydrogen) b. methane (compound of carbon and hydrogen) c. ammonia (compound of nitrogen and hydrogen) d. hydrogen sulfide (compound of hydrogen and sulfur) e. carbon tetrafluoride (compound of carbon and fluorine)