Model Simple Molecules - Middle School Physical Science

1. What is the total number of atoms in one molecule of $NH_3$?

   $4$ atoms total. $1$ nitrogen plus $3$ hydrogen equals $4$ atoms.

2. Identify the number of atoms in one molecule of CO$2$.

   3 atoms total. Count all atoms: 1 carbon + 2 oxygen = 3 total.

3. What is the total number of atoms in one molecule of CO$_2$?

   $3$ atoms. Count: $1$ carbon + $2$ oxygen = $3$ total.

4. What does the lack of a subscript after an element symbol (for example, C) mean?

   There is 1 atom of that element. No subscript means only one atom of that element.

5. Which model feature shows different types of atoms in the same molecule?

   Different colors or labels for different elements. Color-coding or labels distinguish between element types.

6. How many oxygen atoms are in one molecule of H$_2$O?

   $1$ oxygen atom. No subscript after O means exactly one oxygen atom.

7. How many oxygen atoms are in one molecule of Al$_2$(SO$_4$)$_3$?

   $12$ oxygen atoms. Parentheses multiply: $3 \times 4$ oxygen atoms = $12$.

8. Identify what the subscript in a chemical formula (for example, H$_2$O) tells you.

   The number of atoms of that element in one molecule. Subscripts count atoms per molecule, not total molecules.

9. Which term names a molecule made of two or more different elements chemically bonded?

   A compound. Compounds contain atoms of different elements bonded together.

10. What does a line or "stick" between spheres represent in a ball-and-stick model?

    A chemical bond holding atoms together. Lines show where atoms share electrons to form bonds.

11. Find the number of each atom type in $C_6H_{12}O_6$.

    $6$ C, $12$ H, $6$ O. Multiply each element by its subscript to count atoms.

12. Identify the correct particle model for H$_2$O: $2$ H atoms bonded to $1$ O atom.

    One O sphere bonded to two H spheres. Water has a bent shape with O in the center.

13. Which formula matches a particle model with $1$ carbon atom bonded to $2$ oxygen atoms?

    $CO_2$. Formula shows $1$ C and $2$ O atoms bonded together.

14. What does a different color or label in a particle model usually represent?

    A different element (a different type of atom). Different colors/labels distinguish between different atomic elements in models.

15. Identify the correct particle model for CO$_2$: $1$ C atom bonded to $2$ O atoms.

    One C sphere bonded to two O spheres. CO$_2$ is linear with C between two O atoms.

16. Which formula matches a particle model with $2$ hydrogen atoms bonded to $1$ oxygen atom?

    $H_2O$. Water has $2$ H atoms bonded to $1$ O atom.

17. How many hydrogen atoms are in one molecule of H$_2$O?

    $2$ hydrogen atoms. The subscript $2$ after H indicates two hydrogen atoms.

18. Which particle-level model matches HCl: two different atoms bonded or two identical atoms bonded?

    Two different atoms bonded. HCl has H and Cl atoms, which are different elements.

19. Identify the correct formula for a molecule with $2$ nitrogen atoms and $4$ oxygen atoms.

    $N_2O_4$. Subscripts indicate atom counts in the molecule.

20. Which feature in a model shows that atoms are different elements: size, color, or both?

    Both color and size can indicate different elements. Models use visual differences to distinguish elements.

21. What does the formula H$2$O indicate about the types of atoms present?

    Hydrogen and oxygen atoms are present. The formula lists all element types in the molecule.

22. How many atoms total are in one molecule of C$_2$H$_6$?

    $8$ atoms. Count: $2$ carbon + $6$ hydrogen = $8$ total.

23. What is the term for a molecule made of only one type of atom (one element)?

    An elemental molecule. Contains only one element, like O$_2$ or N$_2$.

24. Identify how many oxygen atoms are in one molecule of $H_2O$.

    $1$ oxygen atom. No subscript on $O$ means exactly $1$ oxygen atom.

25. What does the coefficient mean in $2H_2O$ compared with $H_2O$?

    It means $2$ molecules of $H_2O$. Coefficients multiply entire molecules, not individual atoms.

26. Which formula matches a particle model with $1$ carbon atom bonded to $4$ hydrogen atoms?

    $CH_4$. Methane has $1$ C atom bonded to $4$ H atoms.

27. What does each sphere represent in a particle-level model of a molecule?

    One atom. Each sphere is a single atom in the molecular structure.

28. What is the meaning of the subscript in a chemical formula such as $H_2$?

    It shows the number of atoms of that element in one molecule. Subscripts count how many atoms of that element exist in the molecule.

29. What is the term for a molecule made of atoms from more than one element?

    A compound. Compounds contain atoms of different elements bonded together.

30. What does it mean if an element symbol in a formula has no subscript (for example, O in CO$_2$)?

    There is $1$ atom of that element in the molecule. No subscript means exactly one atom of that element.

31. What is the chemical formula for a molecule with 2 hydrogen atoms and 1 oxygen atom?

    H$2$O. Subscripts show the number of each atom type.

32. What is the chemical formula for a molecule modeled as $1$ C atom and $4$ H atoms?

    CH$_4$. Subscript shows four H atoms bonded to one C atom.

33. What is the total number of atoms in one molecule of NH$_3$?

    $4$ atoms. Count: $1$ nitrogen + $3$ hydrogen = $4$ total.

34. Which formula matches a particle model with $1$ nitrogen atom bonded to $3$ hydrogen atoms?

    $NH_3$. Formula shows $1$ N bonded to $3$ H atoms.

35. What does each sphere represent in a particle-level model of a molecule?

    One atom (a single particle) in the molecule. Each sphere is a visual representation of a single atom.

36. Which term names a molecule made of only one element type (for example, $O_2$)?

    An elemental molecule (a molecule of an element). Contains only one type of element, like diatomic oxygen.

37. Identify the correct formula for a molecule with $2$ carbon atoms and $6$ hydrogen atoms.

    $C_2H_6$. Subscripts show the count of each element type.

38. Identify the number of hydrogen atoms in one molecule of CH$4$.

    4 hydrogen atoms. The subscript 4 after H shows four hydrogen atoms.

39. Choose the word that describes a molecule containing more than one type of atom: element or compound?

    Compound. Compounds contain two or more different elements.

40. What is the total number of atoms in one molecule of CH$4$?

    5 atoms total. Add all atoms: 1 carbon + 4 hydrogen = 5 total.

41. What is the total number of atoms in one molecule of $CO_2$?

    $3$ atoms total. $1$ carbon plus $2$ oxygen equals $3$ atoms.

42. What is the ratio of hydrogen atoms to oxygen atoms in $H_2O$?

    $2:1$. $2$ hydrogen atoms for every $1$ oxygen atom.

43. What does a line or "stick" between atoms represent in a particle model of a molecule?

    A chemical bond holding the atoms together. Lines show atoms are connected by sharing or transferring electrons.

44. Which formula represents a molecule made of two different elements: O$2$ or CO?

    CO. CO has carbon and oxygen; O$_2$ has only oxygen.

45. What does a line or "stick" between spheres represent in a molecular model?

    A chemical bond between atoms. Lines show where atoms share electrons to form bonds.

46. What does the subscript in O$2$ tell you about the molecule?

    It has 2 oxygen atoms. Subscripts indicate the count of that element's atoms.

47. What is the ratio of carbon atoms to oxygen atoms in $CO_2$?

    $1:2$. $1$ carbon atom for every $2$ oxygen atoms.

48. What is the chemical formula for a molecule modeled as $1$ Na atom bonded to $1$ Cl atom?

    NaCl. Equal numbers mean no subscripts needed.

49. What does the coefficient in front of a formula (for example, $3$H$_2$O) represent?

    The number of molecules (or formula units). Coefficients multiply entire formulas, not individual atoms.

50. What is the correct formula for a molecule with 1 nitrogen atom and 3 hydrogen atoms?

    NH$3$. N gets no subscript (1 atom), H gets subscript 3.

51. Identify the number of oxygen atoms in one molecule of CO$2$.

    2 oxygen atoms. The subscript 2 after O indicates two oxygen atoms.

52. Identify how many hydrogen atoms are in one molecule of $CH_4$.

    $4$ hydrogen atoms. The subscript $4$ after $H$ indicates $4$ hydrogen atoms.

53. What is the correct formula for a molecule with 2 carbon atoms and 6 hydrogen atoms?

    C$2$H$6$. Subscripts show atom counts for each element.

54. Find and correct the mistake: "H$_2$O has $2$ oxygen atoms and $1$ hydrogen atom."

    Correct: H$_2$O has $2$ H atoms and $1$ O atom. Subscripts tell atom counts: $2$ is for H, not O.

55. What does it mean if an element symbol has no subscript in a formula (for example, the $O$ in $H_2O$)?

    It means there is $1$ atom of that element in the molecule. No subscript is understood as subscript $1$ by convention.

56. Which formula matches a model with $2$ different atom types and a total of $3$ atoms: H$_2$O or O$_2$?

    H$_2$O. H$_2$O has $2$ elements ($2$ H + $1$ O = $3$ atoms total).

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