Atoms, Elements & Compounds · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Atoms, Elements & Compounds

Science · Matter & Materials · ages 11-12
Name ______________________   Date ____________

  1. In the Bohr model of an atom, what do you find inside the nucleus?

    • Electrons only
    • Protons and neutrons
    • Protons and electrons

  2. What is an atom?

    • The smallest unit of an element that still acts like that element
    • A group of two or more elements joined together
    • Any tiny speck of dust you can see under a microscope

  3. A compound is made of only one type of atom.

    Circle one:   True   False

  4. In the formula CO₂, how many oxygen atoms are there?

    COO

    Answer: ______________

  5. The formula for water is H₂O. Which elements does it contain?

    HHO
    • Helium and oxygen
    • Hydrogen and sodium
    • Hydrogen and oxygen

  6. Maria mixes salt and pepper on a plate. She can still see and separate the grains. Is this a mixture or a compound?

    • Mixture
    • Compound
    • Element

  7. A student draws a Bohr model with all 3 electrons crammed into the nucleus alongside the protons and neutrons. What mistake did the student make?

    • The student used too many protons
    • The student forgot to draw the neutrons
    • Electrons belong in shells around the nucleus, not inside it

  8. Jayden says table salt (NaCl) is a mixture because it has two different elements in it. What is wrong with his thinking?

    • Table salt only has one type of atom, so it is an element
    • Sodium and chlorine are chemically bonded together, so NaCl is a compound, not a mixture
    • Jayden is right; any substance with two elements is a mixture
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Atoms, Elements & Compounds W1-mt_Z_Wu_77ybI-s1

  1. Protons and neutrons · Protons and neutrons pack together in the nucleus. Electrons stay outside, moving in shells around it.
  2. The smallest unit of an element that still acts like that element · An atom is the smallest unit of an element. A compound links different atoms, and dust is a chunk of matter, not one atom.
  3. False · That describes an element. A compound is made of two or more different elements joined together.
  4. 2 · The subscript 2 after O means two oxygen atoms bond with one carbon atom.
  5. Hydrogen and oxygen · H stands for hydrogen and O stands for oxygen. It's easy to mix up H with He (helium), but they are different elements.
  6. Mixture · The salt and pepper are not chemically joined, so they stay separate and can be picked apart. That makes it a mixture.
  7. Electrons belong in shells around the nucleus, not inside it · Protons and neutrons stay inside the nucleus. Electrons move around it in shells, not packed inside.
  8. Sodium and chlorine are chemically bonded together, so NaCl is a compound, not a mixture · Having more than one element doesn't make something a mixture. In NaCl the atoms are chemically bonded, which makes it a compound.
Worksheet · LightMySky