Atoms & Elements
What does one circle in a particle model usually represent?
One atom
What holds atoms together in a molecule?
A chemical bond
What does a small number, or subscript, in a chemical formula tell you?
How many atoms of that element are present.
In a particle model, what does a line connecting two atoms represent?
A chemical bond
A mixture contains at least how many different substances?
Two
An element contains only one kind of ________.
Atom
What is a molecule?
Two or more atoms chemically bonded together.
How many hydrogen atoms are in H₂O?
2
🔵—🔵 represents two atoms of the same element bonded together. Is this an element or compound?
Element
In a mixture, are the different substances chemically bonded to one another?
No
Is O₂ an element, compound, or mixture?
Element
What is a compound?
Two or more different elements chemically bonded together.
How many TOTAL atoms are in one CO₂ molecule?
3 atoms
🔵—⚪—🔵 shows two types of atoms chemically bonded. Is it an element or compound?
Compound
Which is a mixture: pure water, oxygen gas, salt water, or carbon dioxide?
Salt water
Which is an element: CO₂, H₂O, O₂, or NaCl?
O₂
Is H₂ a molecule, a compound, or both? Explain.
A molecule only. It has bonded atoms, but they are the same element.
How many different elements are in C₆H₁₂O₆?
3 elements: carbon, hydrogen, and oxygen
A box contains several identical H₂O molecules and nothing else. Is it a pure element, pure compound, or mixture?
Pure compound
Iron filings are mixed with sand. What property could you use to separate the iron?
Magnetism — use a magnet.
O₂ is a molecule, but it is NOT a compound. Explain why.
Its atoms are bonded, making it a molecule, but both atoms are the same element.
What is the main difference between a compound and a mixture?
In a compound, different elements are chemically bonded. In a mixture, substances are together but are not chemically bonded to each other.
CO and CO₂ contain the same two elements. Why are they different substances?
They contain different numbers/ratios of oxygen atoms. CO has 1 oxygen; CO₂ has 2.
A box contains H₂O molecules and O₂ molecules. They are not bonded to each other. How should the entire sample be classified?
A mixture of substances / mixture of a compound and an element
A student says, “If two substances are together in the same container, they must form a compound.” Explain why the student is wrong.
Substances can be together without being chemically bonded. If they are not chemically bonded, they form a mixture.