7th grade · Science · Unit 1 of 14
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.
New York State Learning 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 New York
In the New York State Learning Standards, this is unit 1 of 14 in 7th grade Science, before Circuits & Static.
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.
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
About 21% of the air is made of which element, the one we need to breathe?
🌬️- oxygen
- nitrogen
- carbon
- helium
oxygen
Hint: Air is about 78% nitrogen and 21% oxygen. Our bodies use the oxygen.
Question 2
What makes atoms of one element different from atoms of another element?
- the number of protons in the nucleus
- how fast they move
- their color
- the temperature of the room
the number of protons in the nucleus
Hint: Every hydrogen atom has 1 proton; every carbon atom has 6. That number is the atomic number.
Question 3
Element, compound or mixture? Sort each substance.
Sort into: ⚛️ element · 🧪 compound · 🥣 mixture
- 🥤carbon dioxide (CO₂)
- 🌊salt water
- 💨oxygen gas (O₂)
- 🍬table sugar (C₁₂H₂₂O₁₁)
- 🎈helium (He)
- 🌬️air
⚛️ element: oxygen gas (O₂), helium (He) · 🧪 compound: carbon dioxide (CO₂), table sugar (C₁₂H₂₂O₁₁) · 🥣 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 4
Which statement about compounds is true?
- Every compound contains a metal
- A compound always has the same elements in the same proportions
- A compound can have a different recipe each time it forms
- A compound has only one kind of atom
A compound always has the same elements in the same proportions
Hint: Water is always 2 hydrogen atoms to 1 oxygen atom, whether it's in a lake or a glass.
Question 5
Which element has the chemical symbol Ca?
Cachemical symbol- chlorine
- carbon
- calcium
- copper
calcium
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 6
Which property is typical of a solid non-metal, such as sulphur?
- easy to hammer into thin sheets
- dull and brittle
- shiny and bendable
- a good conductor of electricity
dull and brittle
Hint: Non-metals are usually poor conductors, and as solids they tend to be dull and break easily.