Grade 9 Electrons & Compounds worksheet
from Gradelings · Name: ______________________
How to explain it
- Atoms gain, lose or share electrons to get a full outer shell.
- Metals lose electrons and non-metals gain them to form ionic compounds, like sodium chloride.
- Non-metals share electrons to form covalent compounds, like water (H₂O).
Example: Which pair most likely forms an ionic compound: carbon and oxygen, or potassium and chlorine? Ionic compounds form between a metal and a non-metal. Potassium is a metal; chlorine is a non-metal. Answer: potassium and chlorine
Question 1
Which pair would most likely form a covalent compound?
- calcium and oxygen
- sodium and chlorine
- potassium and bromine
- carbon and oxygen
carbon and oxygen
Hint: Two non-metals usually share electrons.
Question 2
Which type of bond forms when electrons are transferred from a metal to a non-metal?
- physical
- ionic
- covalent
- nuclear
ionic
Hint: In ionic compounds, positive and negative ions attract each other.
Question 3
A salt crystal such as NaCl conducts electricity when dissolved in water because…
- the electrons are destroyed
- the atoms melt
- the ions are free to move and carry charge
- the water turns into metal
the ions are free to move and carry charge
Hint: Free-moving ions can carry current in solution.
Question 4
Magnesium has 2 valence electrons and chlorine needs 1 more. What is the formula of magnesium chloride?
- Mg₂Cl₂
- MgCl
- MgCl₂
- Mg₂Cl
MgCl₂
Hint: Each magnesium atom gives up 2 electrons, and each chlorine takes 1, so one Mg needs two Cl.
Question 5
What does the formula CO₂ tell you?
- One carbon atom and two oxygen atoms are in each molecule.
- Carbon dioxide is an element
- Two carbon atoms and one oxygen atom
- Carbon is an oxygen ion
One carbon atom and two oxygen atoms are in each molecule.
Hint: The small number (subscript) after a symbol says how many atoms.
Question 6
Why is oxygen's formula in water H₂O, with two hydrogens?
- Oxygen needs two more electrons, and each hydrogen shares one.
- Water has no bonds.
- Hydrogen is a noble gas.
- Oxygen has two protons.
Oxygen needs two more electrons, and each hydrogen shares one.
Hint: Oxygen has 6 valence electrons and needs 2 more, so it shares with two hydrogen atoms.
Question 7
What charge does an ion of a Group 2 element (like calcium) usually have?
- +1
- 0
- −2
- +2
+2
Hint: Group 2 elements lose their 2 valence electrons.
Question 8
Ionic or covalent? Sort each compound.
Sort into: ⚡ Ionic · 🤝 Covalent
- 🧊CaCl₂ (calcium chloride)
- 🧴NH₃ (ammonia)
- 🧪KBr (potassium bromide)
- 🔥CH₄ (methane)
- ⚗️MgO (magnesium oxide)
- 💧H₂O (water)
- 🧂NaCl (table salt)
- 🌫️CO₂ (carbon dioxide)
⚡ Ionic: CaCl₂ (calcium chloride), KBr (potassium bromide), MgO (magnesium oxide), NaCl (table salt) · 🤝 Covalent: NH₃ (ammonia), CH₄ (methane), H₂O (water), CO₂ (carbon dioxide)
Hint: Ionic compounds are usually a metal plus a non-metal (like NaCl). Covalent compounds are usually two or more non-metals sharing electrons (like H₂O).
Question 9
Table salt (NaCl) is made of…
- sodium and chlorine joined by ionic bonds
- carbon and hydrogen
- two gases sharing electrons
- metals only
sodium and chlorine joined by ionic bonds
Hint: Sodium gives an electron to chlorine, and the ions attract.
Question 10
Why does sodium (1 valence electron) form a positive ion?
- It shares its electrons equally.
- It loses its protons.
- It loses its one outer electron to reach a stable, full outer shell.
- It gains seven electrons.
It loses its one outer electron to reach a stable, full outer shell.
Hint: Losing one electron leaves sodium with a full second shell and a charge of +1.
Answer key
- 1. carbon and oxygen
- 2. ionic
- 3. the ions are free to move and carry charge
- 4. MgCl₂
- 5. One carbon atom and two oxygen atoms are in each molecule.
- 6. Oxygen needs two more electrons, and each hydrogen shares one.
- 7. +2
- 8. ⚡ Ionic: CaCl₂ (calcium chloride), KBr (potassium bromide), MgO (magnesium oxide), NaCl (table salt) · 🤝 Covalent: NH₃ (ammonia), CH₄ (methane), H₂O (water), CO₂ (carbon dioxide)
- 9. sodium and chlorine joined by ionic bonds
- 10. It loses its one outer electron to reach a stable, full outer shell.
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