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9th grade · Science · Unit 4 of 10

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.

Arizona Academic Standards learning standard: HS.P1U1.1; HS.P1U1.2 · how outer electrons explain bonding and chemical reactions

How we explain it

Children can open this short lesson before they practice.

  1. Atoms gain, lose or share electrons to get a full outer shell.
  2. Metals lose electrons and non-metals gain them to form ionic compounds, like sodium chloride.
  3. 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 Arizona

In the Arizona Academic Standards, this is unit 4 of 10 in 9th grade Science, after Atoms & Electrons and before Photosynthesis & Respiration.

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.

Source: Arizona Department of Education

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    Ionic or covalent? Sort each compound.

    Sort into: ⚡ Ionic · 🤝 Covalent

    • ⚗️MgO (magnesium oxide)
    • 💧H₂O (water)
    • 🧪KBr (potassium bromide)
    • 🧂NaCl (table salt)
    • 🧴NH₃ (ammonia)
    • 🔥CH₄ (methane)
    • 🧊CaCl₂ (calcium chloride)
    • 🌫️CO₂ (carbon dioxide)

  2. Question 2

    Why does sodium (1 valence electron) form a positive ion?

    • It loses its one outer electron to reach a stable, full outer shell.
    • It shares its electrons equally.
    • It gains seven electrons.
    • It loses its protons.

  3. Question 3

    Which pair would most likely form a covalent compound?

    • sodium and chlorine
    • potassium and bromine
    • calcium and oxygen
    • carbon and oxygen

  4. Question 4

    What is the chemical formula of water?

    • H₂O₂
    • H₂O
    • HO₂
    • H₂

  5. Question 5

    What charge does an ion of a Group 2 element (like calcium) usually have?

    • +2
    • −2
    • 0
    • +1

  6. Question 6

    Why do noble gases like neon rarely form compounds?

    • They have no electrons.
    • Their outer shells are already full, so they have little reason to gain, lose or share electrons.
    • They are all liquids.
    • They are all radioactive.

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