Name:
Date:
Biology Honors
Activity: Drawing Atomic and Molecular Models
Objective: The purpose of this activity is to introduce students to common methods of drawing atoms and
molecules. Students will also review electron configurations and covalent bonding.
Procedure: Complete each of the problems below.
Part 1: Drawing Atomic Models
1.
When drawing atoms, indicate the number of protons and neutrons in the nucleus and draw the electrons
in their shells. See the example below. Use the periodic table of the elements to help you determine the
number of protons, neutrons, and electrons.
Instructions for drawing atoms:
#1 Determine number of protons (atomic number) and put in nucleus
#2 Determine number of neutrons (atomic mass – atomic number) and put in nucleus. If it is not already
done so you will first need to round the atomic mass to the nearest whole number
#3 For a neutral atom, place same number of electrons in energy shells as there are protons in the
nucleus. Fill inner shells first and move outward. The first three energy levels fill with 2, 8, and 18
electrons respectively. However, a shell does NOT need to be full before you move to the next level.
Use your periodic table to help decide where the electrons go.
Example: Draw a Fluorine atom.
#1 atomic number is 9 – so there are 9 protons
#2 subtract atomic mass from atomic number: 19 – 9 = 10
There are 10 neutrons in the nucleus.
Note: neutron number does not always equal proton number
#3 number of electrons = number of protons for a neutral
atom. There are 9 electrons, 2 go in the first shell, and 7 go in
the next shell. For shell levels 2 and greater put electrons at
cardinal points clockwise going N, E, S, W and pair up
electrons.
2. Make a drawing of these atoms in the space provided. Each of these elements has an important biological
role, which we will discuss later. Answer the questions that follow.
a) Hydrogen
c) Nitrogen
e) Sodium
b) Carbon
d) Oxygen
f)
Phosphorus
Name:
g) Sulfur
Date:
Biology Honors
h) Potassium
i)
Calcium
3. Write the number of valence electrons for each atom above in the space next to your drawing.
Part 2: Drawing Molecular Models
4. A molecular model shows how the various atoms are bonded. A typical molecular model shows
all the bonds in the molecule as individual lines. You need to remember that each line
represents a pair of shared electrons. For example, this is a model of methane (CH4). In the case
of methane, notice that H can form one covalent bond because it only has one empty spot in its
valence shell. Carbon on the other hand can form four covalent bonds because it has four empty
spots in its valence shell:
5. Let’s focus on hydrogen first.
a) How many valence electrons does H have?
How many covalent bonds can H form?
b) In nature, hydrogen exists as the gaseous molecule H2, with the two
hydrogen atoms sharing one pair of electrons. Draw this molecule:
6. Now focus on carbon. Carbon is probably the most important element in biological molecules. Let’s see why.
a) How many valence electrons does C have?
How many covalent bonds can C form?
b) The simplest carbon compound if methane, CH4. Draw this molecule:
7. Now focus on oxygen.
a) How many valence electrons does O have?
How many covalent bonds can O form?
b) Oxygen is an element found in water along with hydrogen. Water’s
chemical formula is H2O. Draw the water molecule to the right:
8. Now focus on nitrogen.
a) How many valence electrons does N have?
How many covalent bonds can N form?
b) Ammonia (NH3) is a common biological waste product. Draw an
ammonia molecule to the right:
9. Draw a molecule of carbon dioxide, CO2. Note that double covalent bonds
exist between the atoms
10. Draw a molecule of formaldehyde, H2CO, in the space to the right.