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9th grade · Science · Unit 6 of 28

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.

New York State Learning Standards learning standard: HS-PS1-1 · atomic structure, electron shells and patterns in 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 New York

In the New York State Learning Standards, this is unit 6 of 28 in 9th grade Science, after Evolution & Selection 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: New York State Education Department (NYSED)

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

    The atomic number of an element is its number of…

    • shells
    • neutrons
    • protons
    • isotopes

  2. Question 2

    How many electron shells (energy levels) are used by a neutral fluorine atom?

    • 2
    • 1
    • 4
    • 3

  3. Question 3

    Metals are generally…

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

  4. Question 4

    Nitrogen (N) has atomic number 7. How many electrons does a neutral atom of it have?

    answer box

  5. Question 5

    Hydrogen (H) has atomic number 1. How many electrons does a neutral atom of it have?

    answer box

  6. Question 6

    The elements in Group 18 (the noble gases) rarely react because…

    • they are very heavy
    • their outer shells are already full
    • they have no electrons
    • they are liquids

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