High Viscosities
Why does group 4A elements tend to form covalent bonds rather than ionic bonds? 
Actually, both are same. Both can form in liquid state at room temperature. Both alcohol molecules and water molecules contain H and O . Both are compounds ,different types of atoms. Both are formed from covalent bonds and non metals. For further explanation water molecules hold hydroxyl groups that can form hydrogen bonds with water molecules and with alcohol molecules. And alcohol molecules can form hydrogen bonds with other alcohol molecules such as with water. As alcohol form hydrogen bonds with water and tend to be relatively soluble in water. The hydroxyl group is referred to as a hydrophilic group, because it forms hydrogen bonds with water and increase the solubility of an alcohol in water.
The difference in electronegativity determines the type of chemical bonding between atoms. Metals and nonmetals often have a large difference in electronegativity, and tend to form ionic bonds, while nonmetals bonded to nonmetals tend to have smaller electronegativities and tend to form covalent bonds.
form
Covalent bonds involve sharing of electrons.
The process called "hydrogenation" adds chemical bonds within the oil to decrease the number of double carbon bonds, changing the fat from unsaturated (fewer hydrogen bonds) to saturated (more hydrogen bonds).Saturated fats tend to be solids.
Hydrogen bonding between molecules occurs between water molecules. These are types of dipole-dipole interactions. Hydrogen bonds between hydrogens eg H2 are covalent as are the bonds between hydrogen and carbon atoms. Hydrogens have a mid range electronegativity so they tend to form covalent bonding.
they tend to have strond bonds
Why does group 4A elements tend to form covalent bonds rather than ionic bonds? 
denser liquids tend to have more viscosity
A metal bonding with non-metals tend to form ionic bonds, a non-metal that bonds with another non-metal tend to form covalent bonds.
unsaturated fats
Carbons almost always form covalent bonds.
Actually, both are same. Both can form in liquid state at room temperature. Both alcohol molecules and water molecules contain H and O . Both are compounds ,different types of atoms. Both are formed from covalent bonds and non metals. For further explanation water molecules hold hydroxyl groups that can form hydrogen bonds with water molecules and with alcohol molecules. And alcohol molecules can form hydrogen bonds with other alcohol molecules such as with water. As alcohol form hydrogen bonds with water and tend to be relatively soluble in water. The hydroxyl group is referred to as a hydrophilic group, because it forms hydrogen bonds with water and increase the solubility of an alcohol in water.
Carbon will almost always form bonds with other carbon atoms, and that is part of what makes it such a useful element.
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Water is highly cohesive. Its molecules tend to resist increases in their motion. When water is heated, some of the energy is used to disturb the hydrogen bonds between neighboring molecules.