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For now, let us take the chemical symbol of an element to stand for ___ ____ of that element.
one atom
H represents ___ ____ of hydrogen.
one atom
C represents ___ ____ of carbon.
one atom
Mg represents ___ ____ of magnesium.
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A compound will be either _____ or _________.
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Atoms held together by sharing electrons are said to be __________ bonded.
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A group of covalently bonded atoms is called a ________.
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For molecular compounds, we can write a molecular formula which indicates the ______ of _____ of each element in the molecule.
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This formula tells us that __ atoms of hydrogen and __ atom of oxygen are present in the molecule.
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We can write a _______ in ____ of the element symbol or chemical formula to indicate the number of atoms or molecules involved.
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2Al represents __ _____ of aluminum.
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4 Mg represents __ _____ of magnesium.
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5H2O represents __ _________ of water.
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The numbers that appear in front of the symbols and formulas above are called ____________.
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The small numbers that appear somewhat below the chemical symbols within chemical formulas are called __________.
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For both ____________ and __________, we generally don't write their value when it is equal to 1.
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Many elements are _________, that is, they consist of individual atoms.
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There are 7 elements that exist as ________ molecules.
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The form of oxygen called _____ exists as ___.
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Sodium forms the ion ___ and chlorine forms the ion ___(which we call the ________ ion).
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The simplest way to express the ratio of ions in sodium chloride is a ___ -to-___ ratio.
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The formula of sodium chloride is written ____.
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It is true that for every ___ ion in the crystal, there is a ___ ion.
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We take the formula unit of an _____ compound to represent the smallest possible amount of that compound.
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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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Description
This quiz focuses on counting atoms in chemical formulas and understanding the chemical symbols of elements. It aims to help learners interpret symbols as representations of atoms effectively. Ideal for students looking to strengthen their knowledge of basic chemistry concepts.
