2B1 Chemistry Flashcards
Describe how chemical composition, bonding types, and intermolecular forces determine a substance’s structure and influence its physical properties.
Define:
mole concept
A counting unit for particles.
1 mole = 6.022 x 10²³ particles, converting atomic-scale quantities to macroscopic ones. This number is often referred to as Avogadro’s number, and is used as a constant in many chemical equations.
How many particles are in 1 mole?
6.022 x 10²³
1 mole is often represented with the term mol.
Define:
Molar mass
The mass of one mole of a substance (g/mol).
It is numerically equivalent to the atomic or molecular mass in atomic mass units (amu).
True or False:
The mole concept relates moles to mass.
True
The mole concept is used to convert between the number of particles and the mass of a substance.
What is the unit for molar mass?
g/mol
Molar mass is measured in grams per mole (g/mol), which indicates the mass of one mole of a substance.
What is the formula for calculating molar mass?
∑ (Atomic Mass of Element × Number of Atoms of Element)
Add the atomic mass of each element, multiplied by the number of atoms of that element in the formula, to find the molar mass.
How do you convert moles to grams?
Multiply moles by molar mass.
Molar mass (g/mol) represents the mass of one mole of a substance.
For example, to convert 2 moles of water (H₂O) to grams, multiply 2 moles by 18.016 g/mol (the molar mass of H₂O), giving you 36.032 grams.
How many moles are in 144 grams of carbon, given that the molecular mass of carbon is 12g/mol.?
12 moles
144 grams divided by 12g/mol results in 12 moles.
What is percent composition?
The mass percentage of each element in a compound.
Percent composition is used to determine the relative amounts of each element in a compound, which is helpful in stoichiometric calculations and analyzing chemical formulas.
For example, in NaCl, the percent composition of Na is 39.34%, and Cl is 60.66%.
How is percent composition calculated?
(Mass of element / Total molar mass) x 100.
For H₂O, the mass of hydrogen is 2 g and the total mass of water is 18 g, so hydrogen’s percent composition is (2 / 18) × 100 = 11.1%.
True or False:
Percent composition is used in the food industry for nutrient labeling on food packaging.
True
Percent composition helps calculate the nutrient content in food, such as proteins, fats, and carbohydrates, assisting consumers in maintaining their daily nutrient intake.
What does percent composition help determine in the construction industry?
Material purity and mixture ratios.
Ensuring proper proportions of materials like cement and sand is vital for the strength and durability of concrete.
What should the sum of the percent compositions of all elements in a compound equal?
100%.
The total percent composition confirms the accuracy of the compound’s molecular formula.
What is Avogadro’s number?
6.022×10 ^23 particles per mole.
This number is a fundamental constant that defines the number of atoms, molecules, or particles in one mole of any substance, enabling conversions between the molecular and macroscopic scale.
Fill in the blank:
Avogadro’s number converts moles to _______.
particles
Avogadro’s number provides a direct relationship between moles and individual particles (atoms, molecules, ions).
What is a chemical formula?
A representation of a compound’s elements.
It shows the types and quantities of atoms present in a compound. For instance, H₂O represents water, with two hydrogen atoms and one oxygen atom.
What does a structural formula show?
The arrangement of atoms and bonds.
Structural formulas represent how atoms are bonded in a molecule and can include electron-dot diagrams or line structures to show shared electron pairs, like the bond between H and O in H₂O.
What is the empirical formula?
The simplest whole-number ratio of elements in a compound.
It simplifies the ratio of elements. For glucose (C₆H₁₂O₆), the empirical formula is CH₂O, representing the simplest form of the compound’s elemental composition.
What is a molecular formula?
The formula that shows the actual number of atoms of each element in a molecule.
The molecular formula may be the same as or a multiple of the empirical formula.
For example, the molecular formula of glucose is C₆H₁₂O₆, while its empirical formula is CH₂O, which represents the simplest ratio of elements.
True or False:
The empirical and molecular formulas are always the same.
False
The empirical formula shows the simplest ratio of atoms, while the molecular formula provides the actual number of atoms.
For glucose, the molecular formula is C₆H₁₂O₆, but the empirical formula is CH₂O.
What is the chemical formula for water?
H₂O
Water consists of two hydrogen atoms bonded to one oxygen atom, with the formula H₂O.
Fill in the blank:
The chemical formula for calcium sulfate is _________.
CaSO₄
Calcium sulfate consists of one calcium ion (Ca²⁺) and one sulfate ion (SO₄²⁻), giving it the formula CaSO₄.
True or False:
NaCl has two sodium atoms.
False
NaCl is an ionic compound composed of one sodium atom (Na) and one chlorine atom (Cl), forming a 1:1 ratio, not two sodium atoms.
What happens to nitrogen dioxide when heated?
It forms nitrogen monoxide and oxygen.
When heated, nitrogen dioxide (NO₂) decomposes into nitrogen monoxide (NO) and oxygen gas:
2NO₂ → 2NO + O₂. This reaction is reversible, and NO₂ reforms when the gas cools.
Define:
Chemical compound
A substance containing atoms of at least two elements.
Chemical compounds are formed when atoms of different elements bond together, either covalently or ionically. These compounds have fixed compositions, like NaCl or H₂O.
What are the four common types of chemical formulas?
- Molecular Formula
- Condensed Formula
- Structural Formula
- Empirical Formula
Molecular formulas give exact atom counts, while empirical formulas show the simplest ratios. Condensed formulas group atoms together, and structural formulas show bonding.
How is a condensed formula different from a structural formula?
Condensed formulas omit bond lines.
Condensed formulas simplify molecular representations by grouping atoms, while structural formulas show every bond and atom explicitly, providing a more detailed representation of the molecule’s structure.
What is the empirical formula for butane (C₄H₁₀)?
C₂H₅
The empirical formula for butane is derived by simplifying the ratio of carbon to hydrogen atoms. Dividing both 4 and 10 by their greatest common divisor (2), we get C₂H₅.
What is the symbol for carbon?
C
C is derived from carbon, which comes from the Latin “carbo” (meaning coal).
What is the origin of the symbol Fe for iron?
From the Latin word ferrum.
Latin names are sometimes used for element symbols.
What do subscripts in chemical formulas indicate?
The number of atoms of an element in a molecule.
Subscripts are written to the lower right of the element symbol, showing the number of atoms of that element in the formula.
For H₂O, the subscript “2” means two hydrogen atoms.
What does O₂ represent?
A molecule with two oxygen atoms.
The subscript 2 indicates that the molecule consists of two oxygen atoms, forming dioxygen, the oxygen we breathe.
What’s the difference between coefficients and subscripts?
- Coefficients indicate molecule count.
- Subscripts indicate atom count.
In the chemical formula 3CO₂,
The coefficient 3 indicates there are 3 molecules of carbon dioxide.
The subscript 2 in CO₂ indicates there are 2 oxygen atoms in each molecule of carbon dioxide.
What is a superscript in chemistry?
A number indicating charge or mass.
Superscripts are often used to show the charge of ions (e.g., Na⁺), or mass numbers of isotopes (e.g., ¹⁴C)
What does Na⁺₁ represent?
A sodium ion with a +1 charge.
The “+” sign indicates that the sodium atom has lost one electron, resulting in a positively charged ion.
What is the chemical formula for methane?
CH₄
Methane consists of one carbon atom bonded to four hydrogen atoms, forming a tetrahedral structure.
True or False:
The number 1 is written as a subscript in chemical formulas.
False
In chemical formulas, the number 1 is implied but not written. For example, in H₂O, there is one oxygen atom, but no subscript is written next to the “O” (it’s implied to be 1).
What does 2H₂O represent?
Two molecules of water.
The coefficient 2 indicates two molecules of H₂O, or two water molecules, each consisting of two hydrogen atoms and one oxygen atom.
Why is periodic table nomenclature important?
It standardizes element identification and naming.
The nomenclature helps avoid confusion among elements.
Fill in the blank:
The octet rule states that atoms ideally want to have ________ electrons in their outermost electron shell.
Eight
The term octet comes from the Greek root “oct” meaning eight, referring to the stable configuration of eight electrons in the outermost shell of an atom.
How do covalent bonds differ from ionic bonds?
Covalent bonds share electrons; ionic bonds transfer electrons.
In covalent bonds, atoms share electrons to achieve a full outer shell, while ionic bonds form when one atom gives up electrons and another accepts them, creating oppositely charged ions.
What is electronegativity?
The tendency of atoms to attract electrons.
It is a measure of an atom’s ability to attract shared electrons in a bond. Nonmetals generally have higher electronegativity than metals.
True or False:
Metals have high electronegativity.
False
Metals tend to lose electrons easily and have low electronegativity, while nonmetals, which gain electrons, have higher electronegativity.
What are the four main blocks of elements?
- s-block
- p-block
- d-block
- f-block
These blocks categorize elements based on their electron configuration, with s-block and p-block elements being more chemically reactive than d-block and f-block elements.
How many valence electrons do elements in the s-block have?
One or two valence electrons.
Column one has one valence electron, and column two has two valence electrons.
Fill in the blank:
A Lewis dot structure is a diagram that shows bonds between atoms using ______ to represent valence electrons.
dots
These diagrams help visualize how atoms share electrons to form bonds, aiding in understanding molecular structure and reactivity.
What elements are typically found in the center of a Lewis structure?
The least electronegative element.
The center atom in a Lewis structure is usually the one that can form the most bonds, and it’s often the least electronegative.
For example, in CO₂, carbon is in the center because it’s less electronegative than oxygen. Hydrogen, being highly electronegative, always goes on the outside if only two atoms are involved.
How many electrons do noble gases have in their valence shell?
eight
Noble gases are stable with a full outer shell, except helium, which has two electrons.
What happens during chemical bonding?
Atoms transfer or share electrons.
Atoms bond to achieve a more stable electron configuration, either by sharing or transferring electrons.
In ionic bonding, what happens to the electrons?
One atom transfers electrons to the other.
The atom that donates electrons becomes positively charged (cation), while the atom that gains electrons becomes negatively charged (anion).
Define:
Covalent bonding
Atoms share electrons and form electron pairs.
True or False:
The two types of covalent bonds are non-polar and polar.
True
Non-polar covalent bonds occur when electrons are shared equally, while polar covalent bonds occur when electrons are shared unequally between atoms.
Sodium chloride is an example of what type of bond?
Ionic bond
Sodium chloride (NaCl) is an example of an ionic bond, where electrons are transferred from sodium (Na) to chlorine (Cl), resulting in oppositely charged ions that are held together by electrostatic forces.
True or False:
Water is not an example of a covalent bond.
False
Water (H₂O) is an example of a covalent bond, where electrons are shared between hydrogen and oxygen atoms.
What are hydrogen bonds?
Attractive forces between hydrogen and electronegative atoms.
Hydrogen bonds occur when hydrogen, bonded to an electronegative atom, interacts with another electronegative atom, like oxygen or nitrogen.
Fill in the blank:
In an ionic bond, the more electronegative atom becomes a/an _______.
Anion
The more electronegative atom gains electrons, becoming negatively charged (anion).
Fill in the blank:
In an ionic bond, the atom that donates the electron is called a/an _______.
Cation
The atom that donates an electron becomes positively charged and is known as the cation.
What is the effect of higher charges on ionic bond strength?
The bond strength increases.
Higher charges lead to a stronger electrostatic attraction between the ions.
True or False:
Intermolecular forces affect physical properties.
True
These forces determine properties like melting/boiling points and solubility.
What force exists between hydrogen and electronegative atoms like oxygen or nitrogen?
Hydrogen bonding
Hydrogen bonds are a type of intermolecular force that occurs when a hydrogen atom covalently bonded to an electronegative atom (such as oxygen, nitrogen, or fluorine) is attracted to another electronegative atom.
Fill in the blank:
Dipole-dipole interactions occur between _______ molecules.
polar
Polar molecules have partial positive and negative charges that attract each other.
True or False:
London dispersion forces are stronger than hydrogen bonding and dipole-dipole interactions.
False
London dispersion forces are temporary and weaker than hydrogen bonding or dipole-dipole interactions, which involve more permanent dipoles or stronger attractions.
What type of force is found in nonpolar substances?
London dispersion forces.
Nonpolar substances have weak forces, leading to lower melting/boiling points.
Fill in the blank:
A substance with weak intermolecular forces has _______ vapor pressure.
higher
Weak forces allow more molecules to escape into the gas phase, increasing vapor pressure.
What happens to boiling points as molecular surface area increases?
Boiling points increase.
Larger surface areas allow molecules to interact more strongly, raising boiling points.
What is the primary force in ionic compounds?
Electrostatic attraction
The positive and negative ions in ionic compounds attract each other, creating strong forces.
Fill in the blank:
Stronger intermolecular forces ______ vapor pressure.
lower
Molecules with stronger intermolecular forces are less likely to escape into the gas phase, resulting in a lower vapor pressure.
What is solubility?
The maximum amount of solute that dissolves in a solvent at a specific temperature.
This depends on factors like temperature, pressure (for gases), and the nature of the solute and solvent.
True or False:
“Like dissolves like” is a principle of solubility.
True
Polar solvents tend to dissolve polar solutes, and nonpolar solvents dissolve nonpolar solutes due to similar intermolecular forces.
