Element Builder
Vocabulary: atom, atomic number, electron, electron dot diagram, element, energy level, ion,
isotope, mass number, neutron, nucleus, periodic table, proton, radioactive, valence electrons
An isotope is an alternative form of an element. Each isotope of an element has the same
number of protons, but a different number of neutrons. The isotope is represented by the atomic
symbol and mass number. Some isotopes are stable, while others are radioactive, which
means the atoms decay over time and emit radiation.
A. What are the stable isotopes of carbon? ___________________________________
B. What are the stable isotopes of nitrogen? __________________________________
C. List two radioactive isotopes of oxygen: ___________________________________
Use the Gizmo to answer the following questions.
D. How many electrons are in a neutral atom of lithium? ___________
E. How many neutrons are in an atom of Mg-25? ___________
F. What is the mass number of an atom with 5 protons and 7 neutrons? ___________
G. An ion is a charged atom. How many electrons are in O2-? ___________
H. How many electrons are in Mg2+? ___________
Question: How are electrons arranged around the nucleus of an atom?
Add electrons to your atom until you have used all the available electrons. How are the
electrons arranged?
Electrons are arranged in orbits called energy levels, shown in the Gizmo.
A. How many electrons can fit in the first energy level? ___________
B. How many electrons can fit in the second energy level? ___________
C. How many electrons can fit in the third energy level? ___________
The electrons in the outermost orbit, called valence electrons, help to create chemical bonds.
Create a lithium atom (3 protons, 4 neutrons, 3 electrons).
How many valence electrons are in a neutral lithium atom? ___________
Turn on Show electron dot diagram. The valence electrons of an atom are shown in an
electron dot diagram. Each dot represents a valence electron.
Draw the electron dot diagram for neutral lithium: ___________
Turn off Show electron dot diagram. Use the Gizmo to create a neutral atom of each of the
following elements. Draw an electron dot diagram for each. When you are finished, turn on
Show electron dot diagram and check your answers.
H
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
Draw diagrams: Create an electron dot diagram for each of the elements below. Use the Gizmo
to help you do this. To check your work, turn on Show electron dot diagram.
H
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
Ar
What do the elements in each column of the periodic table have in common?
Ionic Bonds
Vocabulary: chemical family, electron affinity, ion, ionic bond, metal, nonmetal, octet rule, shell,
valence electron
Each atom consists of a central nucleus and several shells that contain electrons. The
outermost electrons are called valence electrons. (Inner electrons are not shown.)
How many valence electrons does each atom have?
Sodium: ______
Chlorine: ______
Elements can be classified as metals and nonmetals. Metals do not hold on to their valence
electrons very tightly, while nonmetals hold their electrons tightly. Electron affinity is a
measure of how tightly the valence electrons are held.
A. Try pulling an electron away from each atom. Based on this experiment, which atom
is a metal? ____________________ Which is a nonmetal? ____________________
B. Try moving an electron from the metal to the nonmetal. What happens? __________
Introduction: Some of the particles that make up atoms have an electrical charge. Electrons
are negatively charged, while protons are positively charged. Particles with opposite charges
(+ and –) attract, while particles with the same charge (+ and + or – and –) repel.
Question: What happens when atoms gain or lose electrons?
Electrons move around the nucleus of atoms in specific shells, shown by the rings around the
atoms in the Gizmo. The first ring holds two electrons, and the second holds eight. (Electrons in
the inner rings are not shown; you can assume these rings are full.)
I.
Observe the sodium and chlorine atoms. Assuming that the inner rings are full of
electrons, how many electrons are there total in each atom?
Sodium: ____________________
Chlorine: ___________________
J. Each atom is neutrally charged, which means that each atom has the same number
of protons and electrons. Based on this, how many protons are in each atom?
Sodium: ____________________
Chlorine: ___________________
Most atoms are stable with a configuration of eight valence electrons. This is known as the
octet rule. How many valence electrons does each atom have?
Sodium: ____________________
Chlorine: ___________________
2. Form a bond: Each electron has a charge of 1–, and each proton has a charge of 1+. You
can calculate the charge of an atom by subtracting the number of protons from the number
of electrons. Move an electron from the sodium to the chlorine atom.
A. What are the charges of each atom now?
Sodium: _____
Chlorine: _____
Turn on Show charge to check. These charged atoms are called ions.
B. Is each ion stable? Explain.
Click Check in the lower right corner of the Gizmo to check.
3. Think and discuss: Why is there an attraction between the two ions in this chemical bond?
Question: How are ionic compounds formed?
1. Observe: Look at the red lithium atom and the blue oxygen atom. Recall that most atoms
are stable when their outermost ring has eight electrons. (Some atoms, such as lithium and
beryllium, are stable when their outermost ring has two electrons.)
A. How many electrons will the lithium atom give up to become stable? _____________
B. How many electrons does the oxygen atom need to become stable? ____________
C. Can a stable compound be made from these two atoms? Explain why or why not.
___________________________________________________________________
___________________________________________________________________
2. Form bonds: Click Add metal to add another lithium atom, and then transfer electrons from
the lithium to the oxygen. Click Check.
A. Did you make a stable compound? _______
B. Turn on Show formula. What is the formula of this compound? ________________
C. Turn on Show charge. What is the charge of each ion? Li _____ Li _____ O _____
3. Practice: Use the Gizmo to create stable compounds from the combinations given below.
After transferring electrons, arrange the atoms to demonstrate the attraction between
positively charged ions and negatively charged ions. Click Check to check each compound.
Ionic charges
Chemical formula
A. Lithium and fluorine:
Li __
F __
_________________
B. Beryllium and oxygen:
Be __ O __
_________________
C. Magnesium and fluorine:
Mg __ F __
_________________
D. Aluminum and chlorine:
Al __ Cl __
_________________
E. Beryllium and nitrogen:
Be __ N __
_________________
Covalent Bonds
Vocabulary: covalent bond, diatomic molecule, Lewis diagram, molecule, noble gases,
nonmetal, octet rule, shell, valence, valence electron
1. The outermost electrons in each atom are called valence electrons. How many valence
electrons does each fluorine atom have?
2. Click Pause (
What happens?
). Drag an electron from the left atom to the right atom. Click Play.
3. Click Pause, drag an electron from the right atom to the left, and then click Play.
What happens now?
Introduction: The electrons that orbit the nucleus of an atom are arranged into shells. The first
shell contains up to two electrons and the second contains up to eight electrons. Most elements
are stable when they have eight valence electrons—a rule of thumb known as the octet rule.
(Elements with less than five electrons are stable with two valence electrons.)
Question: What happens when atoms share electrons?
4. Predict: Each hydrogen atom has one valence electron, but it needs two electrons to be
stable. How can both hydrogen atoms each achieve a stable configuration?
_________________________________________________________________________
5. Form a bond: Drag the electrons so that they move around both hydrogen atoms. Click Play
to observe them in orbit, and then click Check. You have created a covalent bond.
Congratulations, you have completed a molecule of hydrogen! Because the molecule has
two atoms, it is a diatomic molecule.
6. Draw a diagram: Covalent bonds are shown in Lewis diagrams. In a Lewis diagram, dots
represent unshared valence electrons and dashes represent pairs of shared electrons.
Turn on Show Lewis diagram. What is the Lewis diagram for hydrogen, H2?
H
H
7. Form a bond: Now select Fluorine and create a molecule of fluorine, F2.
What is the Lewis diagram for fluorine, F2?
F
F
Question: How do atoms share more than one pair of electrons?
4. Observe: Like fluorine and most other elements, oxygen atoms are most stable with a full
complement of eight valence electrons.
A. How many valence electrons does each oxygen atom have now? _______________
B. How many more electrons does each oxygen atom need to be stable? ___________
5. Form a bond: Drag electrons back and forth until the molecule of oxygen (O2) is stable. Click
Check to confirm your molecule is stable.
How many pairs of shared electrons are there in a stable molecule of oxygen? __________
6. Draw a diagram: Draw a Lewis diagram of the oxygen molecule in the space below at left.
To check your work, turn on Show Lewis diagram. Draw the correct diagram on the right.
Practice diagram:
O
O
Actual:
O
O
7. Practice: Create covalent bonds and stable molecules for the remaining substances. Draw
Lewis diagrams for each one. (As above, draw the diagram on your own before checking
your work.)
Nitrogen
N
N
H
Ammonia
Chlorine
Cl
H
N
H
Cl
H
Methane
Water
H
O
H
Carbon dioxide
O
C
O
H
C
H
H
Silica
O
Si
O
8. Count: Review the Lewis diagrams you drew on the previous page. Note that each element
tends to form a certain number of chemical bonds. This value is the valence of the element.
For each element in the table below, use the Gizmo to find the number of valence electrons
and the list the valence based on the Lewis diagram. Then find the sum of these numbers.
Element
Symbol
Fluorine
F
Hydrogen
H
Oxygen
O
Nitrogen
N
Chlorine
Cl
Carbon
C
Silicon
Si
# of valence
electrons
Valence
Sum
9. Apply: Selenium has six valence electrons. What is the valence of selenium? ___________
10. Think and discuss: The last column of the periodic table contains the noble gases,
elements that do not easily form chemical bonds.
Why don’t these gases tend to form chemical bonds? __