Elements, molecules and cells (wk1)

Question 1

Describe elements in living matter (6)

Answer 1

-Smallest unit of an element is the atom
-Every atom consists of a nucleus and surrounding electrons
-The nucleus contains protons which carry positive electric charge and neutrons that have no electronic charge
-Exception is H (hydrogen), which has a single proton in its nucleus
-Electrons orbit the nucleus and carry a negative charge of equal absolute value to the protons
-26 elements are known to make up living organisms – the most abundant are: hydrogen, carbon, nitrogen, oxygen, phosphorus, sulphur (these 6 occupy more than 97% of the mass of biological substances)

Question 2

The processes that facilitate the formation of molecules and compounds
-Atoms form chemical bonds to make molecules

Answer 2

-Atoms form chemical bonds to make molecules – Atoms can form bonds with atoms of the same or different elements. A bond is formed when atoms share electrons. The bond formed when 2 atoms share electrons is a covalent bond. If each atom contributes one electron, a single bond is formed, for 2 electrons, double bond etc. The number of bonds an atom can form is determined by the distribution of electrons in it’s atomic orbitals (electronic structure).

Question 3

The processes that facilitate the formation of molecules and compounds
-Molecules and compounds

Answer 3

-Molecules and compounds – Atoms are joined by covalent bonds to form molecules e.g. 2 hydrogen atoms connected by a single bond form a hydrogen molecule. If molecules of a substance exist of atoms belonging to 2 elements, it’s a compound. Organic compounds contain carbon, inorganic compounds do not e.g. water.

Question 4

The processes that facilitate the formation of molecules and compounds
-Ions and Radicals

Answer 4

-Ions and Radicals – Molecules are electrically neutral. Compounds take the form of ions (carry electrical charge). Some atoms are more stable with more electrons than protons and so the ion carries a negative charge (anion). When atoms carry less electrons than protons, there is a positive charge (cation). When a molecule or ion has an unpaired electron, it is known as radical. A molecule in a biological fluid can be easily converted into an ion through the exchange of one of more hydrogen cations (H+) with its surroundings.

Question 5

The processes that facilitate the formation of molecules and compounds
-Polarity and miscibility

Answer 5

-Polarity and miscibility – Polarity describes whether and what degree a substance is polar and affects the physical property of miscibility (the ability to mix with other substances). It is done through: polar substances tend to mix with polar substances, nonpolar substances tend to mix with nonpolar substances and a polar substance and a nonpolar substance do not readily mix with each other.