Chemistry Chapter on Density and Electrons

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Questions and Answers

What is the unit of measurement for density?

kilograms per liter (kg/L)

grams per cubic centimeter (g/cm3) (correct)

grams per gallon (g/gal)

liters per cubic meter (L/m3)

If an object is less dense than the liquid it is placed in, what will happen?

It will break apart.

It will dissolve in the liquid.

It will sink to the bottom.

It will float on the surface. (correct)

What method can be used to determine the volume of a solid?

Measuring its mass

Volume displacement (correct)

Using a balance scale

Calculating its density

Which of the following is an example of a heterogeneous mixture?

Chocolate-chip ice cream Signup and view all the answers

How can density be used in calculations?

As a conversion factor to find mass Signup and view all the answers

What year was the electron discovered?

1897 Signup and view all the answers

What type of device did the scientist use to discover the electron?

Cathode ray tube Signup and view all the answers

What does the bending of particles towards a positive charge indicate?

They are negatively charged Signup and view all the answers

What model of the atom did the scientist propose?

Plum pudding model Signup and view all the answers

In the plum pudding model, negatively charged electrons are embedded like what in a pudding?

Plums Signup and view all the answers

Which statement best describes the hypothesized composition of the atom in the plum pudding model?

Atoms are composed of negatively charged electrons in a positively charged medium. Signup and view all the answers

How did the discovery of the electron impact the understanding of atomic structure?

Indicated that the atom is a complex structure with subatomic particles. Signup and view all the answers

What was the main charge of the electron discovered by the scientist?

Negative Signup and view all the answers

When performing multiplication or division with significant figures, how should the final answer be formatted?

It should have the same number of significant figures as the measurement with the lowest significant figures. Signup and view all the answers

What is the correct approach for addition and subtraction regarding significant figures?

The final answer should be written to have the same number of decimal places as the measurement with the fewest decimal places. Signup and view all the answers

In unit conversion, what is the essential element to ensure the correct transformation from one unit to another?

Ensuring all units cancel appropriately using conversion factors. Signup and view all the answers

For the problem of converting 64 lb to kg using the conversion factor 1 kg = 2.205 lb, which step must be followed?

Use 64 lb in the denominator of the conversion factor. Signup and view all the answers

If a dosage of 0.150 mg needs to be converted to mcg (where 1 mg = 1000 mcg), how should the calculation be set up?

0.150 mg x 1000 mcg/mg. Signup and view all the answers

If requesting 75 mcg of Synthroid, how many tablets can be obtained from a prescription of 0.150 mg?

6 tablets. Signup and view all the answers

To add significant zeros, which of the following may be a necessary step?

Add a decimal point and then add zeros for clarity. Signup and view all the answers

Why is it necessary to use two or more conversion factors in some unit conversions?

To ensure cancellation of the initial unit until the desired unit is achieved. Signup and view all the answers

What happens to the wavelength as frequency increases?

It decreases Signup and view all the answers

Which of the following best describes the relationship between frequency and energy?

Higher frequency correlates with higher energy Signup and view all the answers

Where is the atomic radius expected to be the largest on the periodic table?

Bottom left corner Signup and view all the answers

Which of the following statements correctly describes electron configurations?

They show the placement of electrons in orbitals Signup and view all the answers

In a covalent bond, what occurs between the atoms?

Atoms share electrons Signup and view all the answers

What is the maximum number of electrons that a p orbital can hold?

6 Signup and view all the answers

Which trend describes how electronegativity changes across the periodic table?

Increases as you go up and to the right Signup and view all the answers

According to the octet rule, how many electrons do most atoms strive to have in their outer shell?

8 Signup and view all the answers

What term is used for an ion that carries a positive charge?

Cation Signup and view all the answers

If the non-metal in an ionic compound is chlorine (Cl), what is the correct name for its ion?

Chloride Signup and view all the answers

When naming an ionic compound with a transition metal that can form multiple ions, what must be specified?

The charge of the cation Signup and view all the answers

In order to balance the charges in an ionic compound, what should you adjust?

The subscripts for cations and anions Signup and view all the answers

Which of the following is an example of a molecular compound?

H₂O Signup and view all the answers

What is the first step in naming a molecular compound?

Name the first element as it appears on the periodic table Signup and view all the answers

Which of the following is a characteristic of naming ionic compounds?

Changing the anion's name to end in '-ide' Signup and view all the answers

What should the ratio of cations to anions be in an ionic compound?

Such that the compound has a neutral charge overall Signup and view all the answers

What is the shape of a molecule with 5 bonding pairs and no lone pairs?

Trigonal bipyramidal Signup and view all the answers

What is the bond angle in a molecule with a bent shape, such as water (H₂O)?

104.5° Signup and view all the answers

Which molecule exemplifies an octahedral shape?

SF₆ Signup and view all the answers

Which statement is true regarding lone pairs and bond angles?

Lone pairs decrease bond angles. Signup and view all the answers

What defines a polar covalent bond?

Electrons are shared unequally due to different electronegativities. Signup and view all the answers

What is the bond angle in ammonia (NH₃)?

107° Signup and view all the answers

Which molecule has 5 bonds and no lone pairs on the central atom?

PCl₅ Signup and view all the answers

What is the result of having two atoms with the same electronegativity?

A nonpolar covalent bond is formed. Signup and view all the answers

Study Notes

Significant Figures

Multiplication/division: The final answer has the same number of significant figures as the measurement with the fewest significant figures.
Addition/subtraction: The final answer has the same number of decimal places as the measurement with the fewest decimal places.

Unit Conversions

Format: given unit x conversion factors = needed unit
Example: Converting pounds to kilograms:
- Given: 64 lbs
- Needed: kg
- Plan: lbs (US) --> kg (metric)
- Conversion factors: 1 kg = 2.205 lb, or 2.205 lb/1 kg, and 1 kg/2.205 lb
- Calculation: 64 lbs * (1 kg / 2.205 lb) = 29 kg

Density

Density: the relationship of an object's mass to its volume (g/cm³, g/mL, or g/L)
Every substance has a unique density.
If an object is less dense than a liquid, it will float.
Density of solids using volume displacement:
- The volume of a solid can be determined by volume displacement; when a solid is submerged in water, it displaces a volume equal to its volume.

Problem-Solving Using Density

Density can be used as a conversion factor.
If the volume and density of a sample are known, the mass in grams can be calculated.

Classifying Substances

Classify A-C as pure substances (element or compound) or mixtures (homogeneous or heterogeneous):
- Copper wire: pure substance (element)
- Chocolate chip ice cream: mixture (heterogeneous)
- Nitrox: mixture (homogeneous)
A salad dressing created with oil, vinegar, and chunks of cheese is a heterogeneous mixture.
A mouthwash containing menthol, alcohol, hydrogen peroxide, and flavoring is a homogeneous mixture.

Physical and Chemical Changes

Physical change: the physical properties of a substance change, but its identity stays the same.
- Examples: boiling water, melting ice, freezing water, dissolving salt in water
Chemical change: characteristics that indicate the ability of a substance to change into a new substance.
- Examples: burning wood, cooking food, rusting of iron, digesting food, baking a cake.

States of Matter

Solid: particles are tightly packed, resulting in a definite shape and volume.
Liquid: flows freely, taking the shape of its container but retaining nearly constant volume.
Gas: particles are widely spread, move randomly, and have neither definite shape nor volume.

Atomic Theory

Dalton (1803): Proposed the atomic theory, which laid the foundation for modern chemistry
- All matter is composed of tiny, indivisible particles called atoms
- Atoms of the same element are identical in mass and properties, but atoms of different elements have different masses and properties
- Atoms cannot be created or destroyed in a chemical reaction

Thomson (1897)

Discovered the electron—the first subatomic particle.
Used a cathode ray tube and the bending of particles towards a positive charge to prove the electron's negative charge.
Proposed the plum pudding model of the atom.

Rutherford (1911)

Discovered the nucleus—the atom's positively charged, dense center.
Used the gold foil experiment to find the nucleus that deflected positively charges particles at large angles concluding that the atom has a small dense positively charged nucleus.

Bohr (1913)

Contributed to the atomic theory by proposing the Bohr model.
Electrons orbit the nucleus in distinct, stable energy levels.
Electrons can jump between these energy levels when absorbing or emitting energy.

Isotopes

Atoms of the same element have the same number of protons but different numbers of neutrons.

Atomic Emission Spectra

A spectrum of the electromagnetic radiation emitted by a source.
Electrons absorb energy, move to a higher energy level, and emit the energy in the form of a photon (producing color).
Different colors correspond to different amounts of energy.

Electromagnetic Radiation

Forms of energy, such as visible light, microwaves, X-rays, etc.
Travel as waves (crest and trough) at the speed of light.
Wavelength: distance between adjacent crests or troughs.
Frequency: the number of times the crest passes a point in one second
Frequency = energy
Electromagnetic spectrum (arrangement of types of radiation)
Period trends: ionization, electronegativity, atomic radius, metallic character, electronegativity

Periodic Trends

Ionization energy: increases as you go up and to the right on the periodic table
Electronegativity: increases as you go up and to the right on the periodic table
Atomic radius: increases as you go down and to the left
Metallic character: increases as you go down and to the left, decreases as you go up and to the right

Orbital Diagrams

Represent the placement of electrons in orbitals
Orbital configurations: notation that helps to show the placement

Pauli Exclusion Principle

Each orbital can hold a maximum of two electrons with opposite spins.

Valence Electrons

Determine how an atom will bond with other atoms
Atoms try to achieve a full outer electron shell (usually 8 electrons, octet rule).
Hydrogen and Helium need 2 electrons to fill their shell.

Electron Dot Diagrams (Lewis Dot Diagrams)

Show valence electrons of an atom.
In covalent bonds, pairs of electrons are shared
In ionic bonds, one atom loses electrons (forming a cation), the other gains electrons (forming an anion).

Writing Formulas for Ionic Compounds

Write the symbol for the cation (metal).
Use appropriate oxidation state to show the charge.
Write the symbol for the anion (non-metal).
Look for charge and combine with metal.
Balance charges.
Balance ratio.

Naming Ionic Compounds

Name the metal (cation) first.
Name the nonmetal (anion) with the "-ide" suffix.
- Use Roman numerals to denote charges for transition metals with multiple possible ion charges
Combine the names
Example: FeCl2 → Iron(II) chloride

Molecular Compounds

Comprised of non-metals
Use prefixes to indicate the number of each atom in the compound.
Do not use mon- for first element
Names end with -ide suffix.

VSEPR Theory (Valence Shell Electron Pair Repulsion)

Predicts molecular shapes based on the repulsion of electron pairs around a central atom.
Electron pairs repel each other, trying to get as far apart as possible.
Electron pairs arranged to minimize repulsion.
- Examples include linear (CO2), trigonal planar (BF3), tetrahedral (CH4), Trigonal Bipyramidal (PCl5), Octahedral (SF6).
Lone pairs affect the arrangement and thus the shape.
Water and Ammonia's molecular shapes are influenced by lone pairs.

Electronegativity and Polarity

Electronegativity: the ability of an atom to attract electrons in a chemical bond.
Polar covalent bond: electrons are shared unequally (one atom is more electronegative than the other). Uneven shared electrons create poles (partial positive and partial negative).
Nonpolar covalent bond: electrons are shared equally.
Polar molecules (e.g., water) have a positive and negative end, allowing them to dissolve other polar substances.

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Description

Test your knowledge on key concepts of density and the discovery of the electron. This quiz covers measurement units, atomic models, and significant figures. Answer questions related to the historical context and practical applications of these concepts in chemistry.