9th grade · Science · Unit 7 of 28
Electrons & Compounds
Why atoms bond and what they make
What your child practices
How valence electrons decide whether atoms gain, lose or share electrons, ionic and covalent compounds, and reading simple chemical formulas.
New York State Learning Standards learning standard: HS-PS1-1; HS-PS1-2 · how outer electrons explain bonding and the outcome of simple reactions
How we explain it
Children can open this short lesson before they practice.
- 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
Electrons & Compounds in New York
In the New York State Learning Standards, this is unit 7 of 28 in 9th grade Science, after Atoms & Electrons and before Chemical Change.
Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.
Sample questions
A taste of this unit. In the app, questions change every time and get easier or harder to match your child.
Question 1
What does the formula CO₂ tell you?
- Two carbon atoms and one oxygen atom
- One carbon atom and two oxygen atoms are in each molecule.
- Carbon dioxide is an element
- 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 2
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.
Question 3
Which pair would most likely form a covalent compound?
- carbon and oxygen
- sodium and chlorine
- potassium and bromine
- calcium and oxygen
carbon and oxygen
Hint: Two non-metals usually share electrons.
Question 4
What charge does an ion of a Group 2 element (like calcium) usually have?
- +2
- −2
- 0
- +1
+2
Hint: Group 2 elements lose their 2 valence electrons.
Question 5
Ionic compounds usually have high melting points because…
- they are very light
- they have no bonds
- the attraction between ions is strong
- they are always gases
the attraction between ions is strong
Hint: A lot of energy is needed to pull the ions apart.
Question 6
Ionic or covalent? Sort each compound.
Sort into: ⚡ Ionic · 🤝 Covalent
- 🧂NaCl (table salt)
- 🧴NH₃ (ammonia)
- ⚗️MgO (magnesium oxide)
- 🧪KBr (potassium bromide)
- 🔥CH₄ (methane)
- 🌫️CO₂ (carbon dioxide)
- 🧊CaCl₂ (calcium chloride)
- 💧H₂O (water)
⚡ Ionic: NaCl (table salt), MgO (magnesium oxide), KBr (potassium bromide), CaCl₂ (calcium chloride) · 🤝 Covalent: NH₃ (ammonia), CH₄ (methane), CO₂ (carbon dioxide), H₂O (water)
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).