7th grade · Science · Unit 1 of 10
Atoms & Elements
Elements, compounds and chemical symbols
What your child practices
Elements versus compounds and mixtures, chemical symbols (H, O, Na, Cl, Fe, Au…), counting atoms in formulas like H₂O and C₆H₁₂O₆, metals and non-metals, and the basics of the periodic table.
Alaska content standards learning standard: MS-PS1-1 · atoms, elements, compounds and simple molecules
How we explain it
Children can open this short lesson before they practice.
- An element has only one kind of atom. A compound has two or more elements joined chemically. A mixture is substances mixed but not joined.
- Rows of the periodic table are periods; columns are groups. Metals are on the left, non-metals on the right.
- In a formula, the small number after a symbol counts the atoms just before it.
Example: How many atoms are in one molecule of H₂O? H₂ means 2 hydrogen atoms. O with no number means 1 oxygen atom. 2 + 1 = 3. Answer: 3
Atoms & Elements in Alaska
In the Alaska content standards, this is unit 1 of 10 in 7th grade Science, before Ecosystems.
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.
Question 1
Which of these elements is a metal?
- sulphur
- oxygen
- carbon
- copper
copper
Hint: Metals are usually shiny, bendable and good conductors. Copper is used in electrical wires.
Question 2
What is the chemical symbol for sodium?
⚛️sodium- Na
- Sd
- S
- So
Na
Hint: Most symbols are the first one or two letters of the name (O for oxygen, Ca for calcium). Some come from Latin names: Na (natrium) for sodium, Fe (ferrum) for iron, Au (aurum) for gold, Ag (argentum) for silver, K (kalium) for potassium, Pb (plumbum) for lead, Hg (hydrargyrum) for mercury, Sn (stannum) for tin.
Question 3
How many atoms in total does the formula H₂O₂ (hydrogen peroxide) show?
H₂O₂hydrogen peroxideanswer box
4
Hint: A small number after a symbol tells how many of that atom there are. A symbol with no small number means 1. Add them all up.
Question 4
Element, compound or mixture? Sort each substance.
Sort into: ⚛️ element · 🧪 compound · 🥣 mixture
- 🍬table sugar (C₁₂H₂₂O₁₁)
- 🌊salt water
- 💎diamond (pure carbon, C)
- 🧁baking soda (NaHCO₃)
- 🌬️air
- 🟠copper (Cu)
⚛️ element: diamond (pure carbon, C), copper (Cu) · 🧪 compound: table sugar (C₁₂H₂₂O₁₁), baking soda (NaHCO₃) · 🥣 mixture: salt water, air
Hint: An element has only one kind of atom. A compound has different elements chemically joined in a fixed ratio. A mixture is substances mixed together but not chemically joined.
Question 5
Which scientist published an early periodic table in 1869 and left gaps for elements not yet discovered?
- Albert Einstein
- Isaac Newton
- Dmitri Mendeleev
- Charles Darwin
Dmitri Mendeleev
Hint: This Russian chemist arranged elements by mass and properties, and predicted missing ones correctly.
Question 6
Which element has the chemical symbol S?
Schemical symbol- silicon
- sodium
- sulphur
- silver
sulphur
Hint: Most symbols are the first one or two letters of the name (O for oxygen, Ca for calcium). Some come from Latin names: Na (natrium) for sodium, Fe (ferrum) for iron, Au (aurum) for gold, Ag (argentum) for silver, K (kalium) for potassium, Pb (plumbum) for lead, Hg (hydrargyrum) for mercury, Sn (stannum) for tin.