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Each element is designated by a one- or two-letter chemical symbol, such as S for sulfur and Ca for calcium.
In humans, oxygen makes up 65%, carbon 18%, hydrogen 10%, and nitrogen 3%; in the atmosphere, oxygen makes up 21% and nitrogen 78%, while carbon and hydrogen are trace; in Earth’s crust, oxygen makes up 46%, hydrogen 0.1%, and carbon and nitrogen are trace.
1. Which description defines matter?
2. Which set lists the four most common elements in living organisms?
3. Which arrangement describes the main regions of an atom?
What is matter?
Anything that occupies space and has mass.
What is an element?
A unique form of matter with specific chemical and physical properties that cannot be broken down into smaller substances.
What is the smallest unit that retains an element’s chemical properties?
An atom.
Where are protons and neutrons located in an atom?
In the central nucleus.
In a neutral atom, how does the electron count relate to protons?
It equals the number of protons and the atomic number.
What do chemical reactions change between atoms, and what do they convert?
They change electron distribution and convert reactants into products.
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