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9th grade · Science · Unit 4 of 7

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.

Minnesota K-12 Academic Standards benchmark: 9C.3.2.1.1; 9C.2.2.1.2 · outer electrons and the outcome of simple reactions, and conservation of atoms

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 Minnesota

In the Minnesota K-12 Academic Standards, this is unit 4 of 7 in 9th grade Science, after Atoms & Electrons and before Electric Current.

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: Minnesota Department of Education (MDE)

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

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

    • −2
    • 0
    • +2
    • +1

  2. Question 2

    What does the formula CO₂ tell you?

    • One carbon atom and two oxygen atoms are in each molecule.
    • Two carbon atoms and one oxygen atom
    • Carbon dioxide is an element
    • Carbon is an oxygen ion

  3. Question 3

    Why is oxygen's formula in water H₂O, with two hydrogens?

    • Hydrogen is a noble gas.
    • Oxygen has two protons.
    • Oxygen needs two more electrons, and each hydrogen shares one.
    • Water has no bonds.

  4. Question 4

    A compound is…

    • a single kind of atom
    • a mix of two liquids
    • two or more different elements chemically joined
    • any metal

  5. Question 5

    Magnesium has 2 valence electrons and chlorine needs 1 more. What is the formula of magnesium chloride?

    • Mg₂Cl₂
    • Mg₂Cl
    • MgCl
    • MgCl₂

  6. Question 6

    Which type of bond forms when electrons are transferred from a metal to a non-metal?

    • nuclear
    • ionic
    • physical
    • covalent

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