Basic chemistry for biology worksheet



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Each of the following elements is found in living organisms. For each symbol shown, name the element, list the atomic number, the atomic mass, the number of protons, neutrons and electrons.


Symbol Element Atomic # Mass # Protons # Neutrons # Electrons


C Carbon 6 12.011 6 6 6

H Hydrogen 1 1.00797 1 1 1

  • Nitrogen 7 14.0067 7 7 7
  • Oxygen 8 15.9994 8 8 8
  • Phosphorus 15 30.97376 15 15 15

S Sulfur 16 32.06 16 16 16

Na Sodium 11 22.99 11 11 11

Mg Magnesium 12 24.305 12 12 12

Cl Chlorine 17 35.453 17 17 17

K Potassium 19 39.09 19 19 19

Ca Calcium 20 40.08 20 20 20



Atoms normally contain equal numbers of protons and electrons, thus they are electrically (positive / negative /neutral).

An electron is a (negatively / positively) charged particle. So if an atom loses an electron, it will then have an overall (negative /positive) charge.

If an atom were to gain an electron, it would have an overall (negative /positive) charge.

If a hydrogen atom loses its electron, it ends up with a (negative /positive) charge. (This hydrogen ion is often referred to as a proton, as the entire structure of the atom is now simply the proton that is left in its nucleus)

The atomic symbol for magnesium is Mg .

How many protons does a magnesium atom have? 12

How many electrons? 24

How many neutrons? 12

In the space below, draw a magnesium atom. Label the protons, neutrons, and place the electrons in orbitals with the correct number of electrons in each. Remember, the first orbital can take 2 electrons, the second can take 8 and the third can take 8.

Atoms with 1,2 or 3 electrons in their valence shell (the outermost shell) will lose electrons in order to become stable, thus forming positively charged ions. What will happen to the magnesium atom?

In the space below, draw a chlorine atom with the protons, neutrons and electrons correctly placed in orbitals.

Atoms with 6 or 7 electrons in their valence shell will gain electrons in order to become stable, thus forming negatively charged ions. What will happen to the chlorine atom?

If magnesium and chlorine atoms were to come into proximity with each other, what would be the formula of the molecule that would be formed.

For each of the following molecules, list the elements that are present, the number of atoms of each and draw the structure of the molecule.


Molecule Elements Present & of Atoms Structure


H2O NH3 CH4 CO2 CCl4 CHCl3

List the elements contained in each of the following molecules:


Biotin (one of the B-vitamins) C10H16O3N2S

Adenosine Triphosphate (the body’s primary energy carrying compound) C11H18O13N5P3 Chlorophyll (the primary pigment in photosynthesis) C55H68O5N4Mg

Write the formula for the following molecules:


A molecule of sucrose with 12 Carbon atoms, 22 Hydrogen atoms, and 11 Oxygen atoms

A molecule of vitamin B12 with 63 Carbon atoms, 90 Hydrogen atoms, 14 Oxygen atoms, 14 nitrogen atoms, 1 phosphorous atom, and 1 atom of Cobalt

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