HS-ESS1-3: How Stars Make the Elements
Also called NGSS HS-ESS1-3 · Topic: Space Systems · Earth and Space Science
The Official Wording
Communicate scientific ideas about the way stars, over their life cycle, produce elements.
Clarification statement: Emphasis is on the way nucleosynthesis, and therefore the different elements created, varies as a function of the mass of a star and the stage of its lifetime.
Assessment boundary: Details of the many different nucleosynthesis pathways for stars of differing masses are not assessed.
NGSS Lead States, 2013 · Read it on nextgenscience.org · checked October 15, 2026
What HS-ESS1-3 Means in Plain English
Students explain how stars build new elements over their lives. A star like the sun fuses hydrogen into helium, then helium into carbon and oxygen. Much heavier stars keep going up to iron, and their explosive deaths scatter those elements and forge heavier ones.
Students compare stars by mass and life stage but do not need to memorize each fusion pathway. The idea builds on fusion in the sun (HS-ESS1-1) and links to nuclear changes in HS-PS1-8 and the periodic table in HS-PS1-1.
HS-ESS1-3 I Can Statements
- I can explain how fusion in stars builds heavier elements.
- I can compare what low-mass and high-mass stars produce.
- I can tell where elements like carbon, iron and gold come from.
HS-ESS1-3 Worked Example
A periodic table activity that traces where the atoms around us were made.
Where were the atoms in the periodic table made, and does a star's mass decide which ones it can make?
Set It Up: A blank periodic table, five colored pencils, and a reference card that says where each group of elements forms.
- Color hydrogen and helium for the Big Bang.Two cells, made before any stars
- Color carbon, nitrogen and oxygen for sun-like stars that shed their outer layers as they die.Sun-like stars: helium joins into carbon and oxygen
- Color the elements from neon to iron for massive stars, which build them in onion-like shells near the end of their lives.Massive stars only: up to iron
- Color the heaviest elements, like gold and uranium, for supernovae and collisions between the ultra-dense remains of exploded stars.Gold, platinum, uranium
- Compare which colors only massive stars or their explosions can produce.Mass sets how far element building can go
The Big Bang made hydrogen and helium, sun-like stars add carbon, nitrogen and oxygen, and massive stars and their explosions or collisions supply iron and the heaviest elements.
Why it works: Building bigger atoms takes hotter, denser cores, and going past iron absorbs energy instead of releasing it, so the heaviest elements form only in violent events.
Common Mistakes with HS-ESS1-3
Thinking the Big Bang made every element
“All atoms have existed since the beginning of the universe.”
Try this: The Big Bang made hydrogen, helium and a trace of lithium. Every heavier atom was built later inside stars or in stellar explosions.
Every star makes iron
“When the sun dies it will make iron and gold.”
Try this: The sun lacks the mass to fuse beyond carbon and oxygen. Only stars of roughly eight solar masses or more build cores of iron.
Thinking fusion can go on forever
“A big enough star just keeps fusing heavier and heavier elements.”
Try this: Fusing iron takes in energy rather than giving it out, so the core loses its energy source, collapses, and the star explodes as a supernova.
Where HS-ESS1-3 Fits
Practice HS-ESS1-3
Quick Check
- Which two elements made up nearly all the matter from the Big Bang?
- Why can't the sun make iron?
- Where did much of the gold on Earth form?