Chemistry Basics Fact Sheet
Basic General Chemistry
Matter is composed of elements, the simplest forms into which matter can be broken
down using ordinary chemical techniques. Examples are hydrogen (H), carbon (C),
oxygen (O), etc.
Atoms are the smallest units of elements, and are in turn composed of
o Protons (positively charged)
o Electrons (negatively charged)
o Neutrons (not charged, neutral)
o In all atoms, the number of protons = the number of electrons.
The nucleus is the core of an atom. Protons plus (usually) neutrons are found there.
Atoms of an element always have the same number of protons, but sometimes have
different numbers of neutrons. For example, carbon always has 6 protons, but can have
6, 7 or 8 neutrons. Variants such as these are called isotopes. Some isotopes are
radioactive, and have been extensively used as tracers to elucidate complex biochemical
The electrons orbit the nucleus in electron shells. For biology, we need only consider
the first 3 shells. They have maximum electron carrying capacities:
o 1 (inner) shell: 2 electrons max
o 2 (further from the nucleus): 8 max
o 3 : 8 max
Atoms with full outer (valence) shells are unreactive, for example helium (safe for
Atoms with incomplete outer shells are reactive, for example hydrogen (unsafe for
balloons). Reactive atoms will transfer or share electrons with other atoms, forming
o Ionic bonds result from electron transfer from one atom to another.
Na (sodium) can lose an electron to Cl (chlorine).
Both elements are now ions (atoms or molecules that have gained or
lost one or more electrons): Na and Cl . Their opposite charges hold
them together. This is known as an ionic bond.
o Covalent bond result from electron sharing. For example, two hydrogen
atoms will share a pair of valence (outer shell) electrons to form 2 .
Covalent bonds can be either
1 Non-polar. When electrons are equally shared, due to both atoms
having equal or nearly equal attraction for electrons. Carbon (C) and
hydrogen (H) are about equal in electron attraction, so C-H bonds are
Polar. When electrons are unequally shared, due to one atom having
a much greater attraction for electrons than the other. The shared
electrons are more frequently found near the stronger attracting
atom, creating small differences in charge distribution, or poles.
Oxygen and nitrogen are the two most important strong electron
attractors in biochemistry. Bonds such as O—H, N—H, C—N, C—O,
etc., are polar.
Water, H2O, is a polar compound, due to the stronger attraction for electrons of