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Questions and Answers
Which of the following best describes a chemical formula?
Which of the following best describes a chemical formula?
- A detailed diagram showing the arrangement of atoms in a molecule.
- A shorthand representation of molecules and compounds, indicating the type and number of atoms present. (correct)
- A list of all the elements present in a compound.
- A complete description of the physical properties of a substance.
What information does a structural formula provide that a molecular formula does not?
What information does a structural formula provide that a molecular formula does not?
- The number of each type of atom in the molecule.
- The arrangement of atoms and their connections within the molecule. (correct)
- The types of elements present in the molecule.
- The exact mass of the molecule.
What does the subscript after an element's symbol in a chemical formula indicate?
What does the subscript after an element's symbol in a chemical formula indicate?
- The number of atoms of that element that are chemically bonded in the molecule. (correct)
- The charge of the ion.
- The number of isotopes of that element.
- The number of separate atoms of that element.
What does the number before an element's symbol (e.g., 2H) represent?
What does the number before an element's symbol (e.g., 2H) represent?
Which of the following is true regarding the formulas of common gases and halogens?
Which of the following is true regarding the formulas of common gases and halogens?
In an ionic compound, which ion is written first in the chemical formula?
In an ionic compound, which ion is written first in the chemical formula?
What is the purpose of the crisscross method when writing formulas for ionic compounds?
What is the purpose of the crisscross method when writing formulas for ionic compounds?
Why is it important to simplify the subscripts in an ionic compound's formula?
Why is it important to simplify the subscripts in an ionic compound's formula?
What do prefixes in the names of covalent compounds indicate?
What do prefixes in the names of covalent compounds indicate?
What distinguishes an empirical formula from a molecular formula?
What distinguishes an empirical formula from a molecular formula?
The molecular formula of a compound is $C_6H_{12}O_6$. What is its empirical formula?
The molecular formula of a compound is $C_6H_{12}O_6$. What is its empirical formula?
A compound has the empirical formula $CH_2$. Which of the following could be its molecular formula?
A compound has the empirical formula $CH_2$. Which of the following could be its molecular formula?
If a compound's molecular formula cannot be simplified further, what is the relationship between its empirical and molecular formulas?
If a compound's molecular formula cannot be simplified further, what is the relationship between its empirical and molecular formulas?
Two different compounds can have the same ______ , but will always have different ______.
Two different compounds can have the same ______ , but will always have different ______.
Which of the following statements regarding molecular and empirical formulas is correct?
Which of the following statements regarding molecular and empirical formulas is correct?
Flashcards
What is a chemical formula?
What is a chemical formula?
A shorthand representation of molecules and compounds showing the type and number of atoms present.
What does a structural formula show?
What does a structural formula show?
Shows how atoms are connected in a molecule.
What does a subscript indicate?
What does a subscript indicate?
Indicates number of atoms bonded together.
What does coefficient indicate?
What does coefficient indicate?
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What are common gases and halogens?
What are common gases and halogens?
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How to write an ionic compound?
How to write an ionic compound?
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How to name covalent compounds?
How to name covalent compounds?
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What is an empirical formula?
What is an empirical formula?
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What is a molecular formula?
What is a molecular formula?
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How to derive empirical formula?
How to derive empirical formula?
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Study Notes
Chemical Formulas
- A chemical formula (molecular formula) is a shorthand representation of molecules and compounds
- It shows the type and number of atoms present in a molecule or compound
- It uses chemical symbols to indicate the types of atoms
- Subscripts indicate the number of each type of atom in the molecule
- The molecular formula of methane is CH4
- A structural formula shows how the atoms are connected in the molecule
- In the structural formula for methane, C refers to the carbon atom and H for the hydrogen atoms
Writing Formulas: Rules
- The formula for metals, nonmetals, and inert gases corresponds to their chemical symbol
- Calcium (Ca) and copper (Cu) are examples of metals
- Bromine (Br) and iodine (I) are examples of nonmetals
- Helium (He) and neon (Ne) are examples of inert gases
- Common gases and halogens consist of diatomic molecules, formulas written with a subscript of 2
- Hydrogen (H2), oxygen (O2), nitrogen (N2), chlorine (Cl2), fluorine (Fl2), bromine (Br2), and iodine (I2) are all diatomic molecules
- For an ionic compound, the symbol for the positive ion (cation) is written first, followed by the negative ion (anion)
- Balance the positive and negative charges (valency) to make the compound neutral by using the crisscross method
- NaCl (sodium chloride) is an example of an ionic compound formed by balancing 𝑁𝑎1+ and 𝐶𝑙1−
- Simplify the subscripts to indicate the simplest ratio of the atoms in the compound
- CuSO4 is the simplified formula for copper (II) sulfate
Formulas for Covalent Compounds
- Formulas show the actual number of atoms in the molecule
- Prefixes are used to indicate the number of atoms of a specific element in the molecule
- mono - one
- di - two
- tri - three
- tetra - four
- penta - five
- hexa - six
- hepta - seven
- octa - eight
- CO2 (carbon dioxide) contains 2 oxygen atoms
- CCl4 (carbon tetrachloride) contains 4 chlorine atoms
- N2O5 (dinitrogen pentoxide) contains 2 nitrogen atoms and 5 oxygen atoms
Empirical vs Molecular Formula
- Empirical formulas indicate the types of atoms or ions present in the compound in the simplest whole-number ratio
- Molecular formulas show the actual number of atoms present in the compound
- The empirical formula can be obtained by reducing the actual ratio in the molecular formula to the simplest form
- Glucose (C6H12O6) has a molecular ratio of 6:12:6, which simplifies to an empirical ratio of 1:2:1
- This makes the empirical formula of glucose to be CH2O
- If the actual ratio of atoms can't be simplified, the molecular formula is the same as the empirical formula
- More than one compound can have the same empirical formula because it represents the simplest ratio
- C2H4, C3H6, C4H8, C5H10, and C6H12 all share the empirical formula CH2
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