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Questions and Answers
For now, let us take the chemical symbol of an element to stand for ___ ____ of that element.
For now, let us take the chemical symbol of an element to stand for ___ ____ of that element.
one atom
H represents ___ ____ of hydrogen.
H represents ___ ____ of hydrogen.
one atom
C represents ___ ____ of carbon.
C represents ___ ____ of carbon.
one atom
Mg represents ___ ____ of magnesium.
Mg represents ___ ____ of magnesium.
A compound will be either _____ or _________.
A compound will be either _____ or _________.
Atoms held together by sharing electrons are said to be __________ bonded.
Atoms held together by sharing electrons are said to be __________ bonded.
A group of covalently bonded atoms is called a ________.
A group of covalently bonded atoms is called a ________.
For molecular compounds, we can write a molecular formula which indicates the ______ of _____ of each element in the molecule.
For molecular compounds, we can write a molecular formula which indicates the ______ of _____ of each element in the molecule.
This formula tells us that __ atoms of hydrogen and __ atom of oxygen are present in the molecule.
This formula tells us that __ atoms of hydrogen and __ atom of oxygen are present in the molecule.
We can write a _______ in ____ of the element symbol or chemical formula to indicate the number of atoms or molecules involved.
We can write a _______ in ____ of the element symbol or chemical formula to indicate the number of atoms or molecules involved.
2Al represents __ _____ of aluminum.
2Al represents __ _____ of aluminum.
4 Mg represents __ _____ of magnesium.
4 Mg represents __ _____ of magnesium.
5H2O represents __ _________ of water.
5H2O represents __ _________ of water.
The numbers that appear in front of the symbols and formulas above are called ____________.
The numbers that appear in front of the symbols and formulas above are called ____________.
The small numbers that appear somewhat below the chemical symbols within chemical formulas are called __________.
The small numbers that appear somewhat below the chemical symbols within chemical formulas are called __________.
For both ____________ and __________, we generally don't write their value when it is equal to 1.
For both ____________ and __________, we generally don't write their value when it is equal to 1.
Many elements are _________, that is, they consist of individual atoms.
Many elements are _________, that is, they consist of individual atoms.
There are 7 elements that exist as ________ molecules.
There are 7 elements that exist as ________ molecules.
The form of oxygen called _____ exists as ___.
The form of oxygen called _____ exists as ___.
Sodium forms the ion ___ and chlorine forms the ion ___(which we call the ________ ion).
Sodium forms the ion ___ and chlorine forms the ion ___(which we call the ________ ion).
The simplest way to express the ratio of ions in sodium chloride is a ___ -to-___ ratio.
The simplest way to express the ratio of ions in sodium chloride is a ___ -to-___ ratio.
The formula of sodium chloride is written ____.
The formula of sodium chloride is written ____.
It is true that for every ___ ion in the crystal, there is a ___ ion.
It is true that for every ___ ion in the crystal, there is a ___ ion.
We take the formula unit of an _____ compound to represent the smallest possible amount of that compound.
We take the formula unit of an _____ compound to represent the smallest possible amount of that compound.
It becomes slightly more difficult to count the atoms in ionic formulas when they contain ___________ ions.
It becomes slightly more difficult to count the atoms in ionic formulas when they contain ___________ ions.
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Study Notes
Counting Atoms in Chemical Formulas
- Chemical symbols represent one atom of an element, e.g., H = hydrogen, C = carbon, Mg = magnesium.
- Compounds can be ionic or molecular. Molecular compounds involve sharing electrons between atoms.
- Atoms sharing electrons are covalently bonded, forming structures known as molecules.
- Molecular formulas indicate the number of atoms of each element in a molecule.
- Water (H2O) consists of two hydrogen atoms and one oxygen atom.
- Coefficients before symbols indicate the quantity of atoms or molecules. For instance, 2Al means 2 aluminum atoms.
- Coefficients identify the number of formula units in a compound.
- Subscripts represent the number of atoms of an element within a molecule, e.g., H2O has subscripts of 2 and 1 for hydrogen and oxygen, respectively.
- A coefficient or subscript of 1 is often omitted for simplicity.
- Monatomic elements consist of individual atoms, while some elements exist as diatomic molecules (O2, N2, H2, etc.).
- Certain elements, like ozone (O3) and white phosphorus (P4), exist as polyatomic molecules.
- 2N represents two separate nitrogen atoms, whereas N2 represents a bonded nitrogen molecule.
- To count atoms in a formula: multiply the coefficient by the subscript, treating omitted values as 1.
- Ionic compounds do not form discrete molecules; they consist of ions. Positive ions lose electrons, and negative ions gain them.
- Ionic crystals form due to the attraction between positive and negative ions, ensuring an overall neutral charge.
- The formula of ionic compounds indicates the ratio of positive to negative ions, exemplified by sodium chloride (NaCl).
Sodium Chloride Example
- Sodium chloride is chemically represented as NaCl; it consists of Na+ and Cl- ions.
- NaCl represents a formula unit, not a discrete molecule, emphasizing the nature of ionic compounds.
- In ionic structures, every Na+ ion pairs with a Cl- ion without a specific association.
- Counting atoms in ionic compounds can be performed similarly to molecular compounds, considering the specific ions present.
Complex Formulas
- An ionic formula may contain polyatomic ions that require multiplying subscripts for accurate atom counting.
- For example, in (NH4)2CO3, calculate based on subscripts both inside the group and any applicable coefficients.
- When counting atoms in formulas with elements appearing multiple times, careful attention is required to avoid double counting.
- Use explicit parentheses to clarify the structure when dealing with complex formulas, as in 5(NH4)2HPO4.
Summary of Atom Counting in Complex Formulas
- Utilize coefficients, subscripts, and careful multiplication to determine the total count of atoms for elements.
- The structure of formulas can aid in counting but may not always express coefficients of 1, providing a streamlined approach for problem-solving in chemistry.
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