Year 9 Science · Unit 2 · Lesson 06
Foundation Worksheet
Learning Goals
Fill the gap
Choose the correct word from the word bank. Each word is used once. Two words will not be used.
Electrons are arranged in energy around the nucleus of an atom. The outermost shell is called the shell. Atoms that have a outer shell, like the gases helium, neon and argon, are very and rarely react. Atoms without a full outer shell are : they gain, lose or share electrons to become stable. The way an atom’s electrons are spread across its shells is called its electron , for example 2,8,1 for sodium.
True or false? Fix the false ones
Circle T or F. If a statement is false, correct it on the line.
The first electron shell can hold up to 8 electrons.
Correct it:
Noble gases are generally unreactive under ordinary conditions, associated with their full outer shells.
Correct it:
Sodium (2,8,1) has 1 valence electron, which it can lose to become stable.
Correct it:
An atom with a full outer shell is highly reactive and bonds quickly with other atoms.
Correct it:
1. Complete the table. The first row is done for you.
| Element (atomic number) | Configuration | Valence electrons |
|---|---|---|
| Lithium (3) | 2,1 | 1 |
| Helium (2) | ||
| Nitrogen (7) | ||
| Aluminium (13) | ||
| Chlorine (17) |
Sort it: what will this atom do?
Each chip is the electron configuration of an atom. Write it in the correct box. Hint: count the electrons in the last shell.
Loses electrons
Gains electrons
Full shell: generally low reactivity
2. Welders use argon (2,8,8) as a shield gas to keep air away from hot metal. Explain why argon is suitable, and why sodium (2,8,1) would be completely unsuitable for this job.
Scenario: a teacher demonstration
Behind a safety screen, a teacher dropped a small piece of lithium, sodium and potassium, each about the size of a grain of rice, into three troughs of water. The class timed how long each piece took to react completely and disappear. Table 1 shows sample class results.
| Metal | Configuration | Time to disappear (s) | Observed |
|---|---|---|---|
| Lithium | 2,1 | 62 | Fizzed |
| Sodium | 2,8,1 | 14 | Melted, whizzed about |
| Potassium | 2,8,8,1 | 4 | Lilac flame |
Source: stopwatch times, in whole seconds.
3. Look at the electron configurations. What do all three metals have in common, and what is different about them?
4. Describe the association in Table 1 between number of shells and observed reaction time. Predict how rubidium (2,8,18,8,1), the next metal down Group 1, might behave in water from this trend. Explain why this table does not show that shell number alone causes the reaction rate.
5. Party balloons may contain helium (atomic number 2); some old airships used hydrogen (atomic number 1). Hydrogen gas is H2: two atoms share a pair of electrons. When ignited in oxygen, hydrogen reacts to form water, releasing energy overall as bonds are rearranged. Compare the fire risk of helium and hydrogen. Use the electron configurations of separate atoms, distinguish them from H2 molecules, and explain why an incomplete atomic shell alone does not explain combustion.