8th grade · Science · Unit 4 of 16
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.
Alabama Course of Study content standard: 8.4 · atoms, elements and the information in the periodic table
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 Alabama
In the Alabama Course of Study, this is unit 4 of 16 in 8th grade Science, after Particles & Matter and before The Periodic Table.
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
Which particles are found in the nucleus (center) of an atom?
- only electrons
- neutrons and electrons
- protons and neutrons
- electrons and protons
protons and neutrons
Hint: Electrons move around the outside of the nucleus. Protons and neutrons are packed in the center.
Question 2
What is the chemical symbol for calcium?
⚛️calcium- C
- Ca
- Cm
- Cl
Ca
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
Element, compound or mixture? Sort each substance.
Sort into: ⚛️ element · 🧪 compound · 🥣 mixture
- 🧂table salt (NaCl)
- 🌬️air
- 🥗fruit salad
- 🟡gold (Au)
- 💨oxygen gas (O₂)
- 💧water (H₂O)
⚛️ element: gold (Au), oxygen gas (O₂) · 🧪 compound: table salt (NaCl), water (H₂O) · 🥣 mixture: air, fruit salad
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 of these elements is a metal?
- carbon
- copper
- sulphur
- oxygen
copper
Hint: Metals are usually shiny, bendable and good conductors. Copper is used in electrical wires.
Question 5
What is a compound?
💧- A substance made of only one type of atom
- Two substances stirred together but not joined
- A substance made of atoms of two or more different elements chemically combined
- A metal that has been melted down
A substance made of atoms of two or more different elements chemically combined
Hint: Water (H₂O) is a compound: hydrogen and oxygen atoms are chemically joined.
Question 6
Which element is a noble gas that almost never reacts with other elements?
- iron (Fe)
- neon (Ne)
- sodium (Na)
- chlorine (Cl)
neon (Ne)
Hint: Noble gases sit in the far right column of the periodic table. They glow in signs but rarely form compounds.