Each of the following statements is true, but Dalton might...

Each of the following statements is true, but Dalton might have had trouble explaining some of them with his atomic theory. Give explanations for the following statements. a. The space-filling models for ethyl alcohol and dimethyl ether are shown below. These two compounds have the same composition by mass (52\% carbon, 13\% hydrogen, and 35\% oxygen), yet the two have different melting points, boiling points, and solubilities in water. b. Burning wood leaves an ash that is only a small fraction of the mass of the original wood. c. Atoms can be broken down into smaller particles. d. One sample of lithium hydride is $87.4 \%$ lithium by mass, while another sample of lithium hydride is $74.9 \%$ lithium by mass. However, the two samples have the same chemical properties.

Each of the following statements is true, but Dalton might have had trouble explaining some of them with his atomic theory. Give explanations for the following statements.
a. The space-filling models for ethyl alcohol and dimethyl ether are shown below.
These two compounds have the same composition by mass (52\% carbon, 13\% hydrogen, and 35\% oxygen), yet the two have different melting points, boiling points, and solubilities in water.
b. Burning wood leaves an ash that is only a small fraction of the mass of the original wood.
c. Atoms can be broken down into smaller particles.
d. One sample of lithium hydride is $87.4 \%$ lithium by mass, while another sample of lithium hydride is $74.9 \%$ lithium by mass. However, the two samples have the same chemical properties.

Key Concepts

Structural Isomerism

Structural isomerism refers to compounds that share the same molecular formula but have different structural arrangements of their atoms. This difference in the spatial arrangement influences their physical properties, such as melting and boiling points, and solubility, even though they are composed of the same types and ratios of atoms. This concept highlights that chemical properties are deeply influenced by molecular structure rather than just elemental composition.

Atomic Structure and Subatomic Particles

The discovery that atoms are made up of smaller subatomic particles—protons, neutrons, and electrons—was a pivotal advancement beyond Dalton's original idea of indivisible atoms. This modern understanding explains how atoms can be altered and provides insight into nuclear reactions, bonding, and the inner mechanics of chemical behavior.

Isotopes

Isotopes are variants of a particular chemical element that have the same number of protons but different numbers of neutrons. This difference causes variations in atomic mass while leaving the chemical properties nearly unchanged. The existence of isotopes explains why samples of the same compound, like lithium hydride, can have different percent compositions by mass while exhibiting identical chemical behavior.

Conservation of Mass in Chemical Reactions

The principle of mass conservation states that mass is neither created nor destroyed in a chemical reaction. In practical situations like burning wood, while the observable residue (ash) may represent only a small fraction of the original mass, a significant portion of the mass is converted into gaseous products. This concept is critical to understanding the transformation of matter and energy during chemical reactions.

Transcript

00:01 Chapter 1, problem 65, presents us with four situations that dalton would have had trouble explaining using his atomic theory, but that are true nonetheless.

00:11 We must explain each of them, though.

00:14 So let's start with a.

00:17 It's two space -filling models for ethyl alcohol and dimethyl ether.

00:25 Both of these have the same composition of 52 % carbon, 13 % hydrogen, and 35 % oxygen.

00:46 However, each of these molecules have different boiling points, melting points, and solubilities.

00:53 So why is this the case? well, if we look at the space -filling diagrams provided in the textbook, we see that while they may have the same atoms, the structures are slightly different.

01:05 These are what are called isomers.

01:12 Isomers are two molecules that have the exact same chemical formula, but have different structures.

01:18 This gives them different properties, such as different melanchors.

01:21 Boiling points, boiling points, or solubilities.

01:24 And this explains the difference between these two molecules.

01:28 Next, let's look at part b states that when you burn wood, the ash that's left, it's only a small fraction of the mass.

01:36 If we remember the law of conservation of mass, this tells us that the delta mass should be zero.

01:48 That is, matter is neither created nor destroyed in any process.

01:54 So why is there less than matter now after we've burned wood...