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9th grade · Science · Unit 3 of 10

Atoms & Electrons

Shells, valence and the periodic table

What your child practices

Protons, neutrons and electrons, drawing electron shells for the first 20 elements, valence electrons, periodic table groups and periods, and ions and isotopes.

Alaska content standards learning standard: HS-PS1-1 · atomic structure, electron shells and the periodic table

How we explain it

Children can open this short lesson before they practice.

  1. Atomic number = number of protons. A neutral atom has the same number of electrons.
  2. Shells hold 2, then 8, then 8 electrons for the first 20 elements. Outer-shell electrons are valence electrons.
  3. Ions form when atoms gain or lose electrons. Isotopes have different numbers of neutrons.

Example: Magnesium has atomic number 12. How are its electrons arranged in shells? A neutral atom has 12 electrons. Fill 2, then 8, then the rest: 12 − 10 = 2. Answer: 2, 8, 2

Atoms & Electrons in Alaska

In the Alaska content standards, this is unit 3 of 10 in 9th grade Science, after Reproduction and before Electrons & Compounds.

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: Alaska Department of Education and Early Development

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

    When an atom loses an electron, it becomes…

    • an isotope
    • a different element
    • a positive ion
    • a negative ion

  2. Question 2

    In the periodic table, elements in the same column (group) have…

    • similar chemical properties, because they have the same number of valence electrons
    • the same mass
    • the same color
    • the same number of protons

  3. Question 3

    Metals are generally…

    • good conductors of electricity and malleable
    • brittle and poor conductors
    • gases at room temperature
    • always magnetic

  4. Question 4

    How many valence electrons (electrons in the outer shell) does aluminum (Al) have?

    • 2
    • 3
    • 4
    • 13

  5. Question 5

    Which of these is a metal?

    • carbon
    • sodium
    • chlorine
    • oxygen

  6. Question 6

    Argon (Ar) has atomic number 18. How many electrons does a neutral atom of it have?

    answer box

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