Chapter 3 - Atoms: The Building Blocks of Matter

Chapter 3 - Atoms: The Building Blocks of Matter

​Three basic laws describe how matter behaves during a chemical reaction.

​Law of Conservation of Mass/Matter

​Atoms in matter get rearranged during a chemical reaction; they don't just appear or disappear.

​

If you could collect all the gas, ash, smoke, etc... from a burning log, you'd still have the same mass of materials that you started with before the log was burned.

Law of Definite Proportions

• ​No matter how large of a sample you have of a particular compound, it will always contain the same ratio of elements.

• ​For example, water is always 2 parts hydrogen to 1 part hydrogen. Or you could say "for every two hydrogen atoms you'll have 1 oxygen atom"

​Law of Multiple Proportions

• ​All this law is stating is that different compounds can be made of the same elements, but in different proportions.

• ​For example, water and hydrogen peroxide are both made of hydrogen and oxygen, but water is always made of 2 hydrogens and 1 oxygen, but hydrogen peroxide is made of 2 hydrogens and 2 oxygens.

​"Whole Number Ratios" is just referring to the fact that you can't have a PART of an atom in a compound.

• The reason that this is stated in this way is to make it clear that atoms are indivisible.

Multiple Choice

The fact that every sample of a particular chemical compound contains the same elements in exactly the same proportions by mass is known as the law of

• consevation of energy

• conservation of mass

• atomic theory

• definite proportions

Multiple Choice

Using improved chemistry equipment in the late 1700s, chemists observed that mass is neither created nor destroyed in a chemical reaction. This scientific law is called the law of

• conservation of mass

• definite proportions

• multiple proportions

• gravity

Multiple Choice

If two or more compounds are composed of the same two elements, then the ratio of the masses of the second element that is combined with a certain mass of the first element is always a ratio of small whole numbers. This statement is called the law of

• definite proportions

• multiple proportions

• atomic theory

• conservation of mass

​John Dalton proposed a theory to help explain what happens at the atomic level during a chemical reaction.

• ​Prior to his theory, scientists agreed that there were atoms, but they couldn't figure out how substances could combine to make new substances.

​Dalton's atomic theory has 5 parts...

• ​All matter is made of atoms.

• ​All atoms of a particular element are identical.

• ​Atoms can't be subdivided, created, or destroyed. (There's nothing smaller than an atom)

• ​Atoms combine in whole-number ratios to form compounds.

• ​During chemical reactions atoms are combined, separated, or rearranged. A chemical reaction simply changes how atoms are grouped together.

​Though it helped turn an idea about atoms into a theory, not all parts of Dalton's theory have proven to be correct...

• ​Atoms can actually be divided into smaller particles (protons, neutrons, and electrons, to name a few)

• ​Dalton thought atoms were solid spheres of matter.

​Not all atoms of an element are exactly the same.

• ​We now know that isotopes exist (atoms with varying numbers of neutrons, and therefore mass)

• ​There are also ions, or charged atoms due to differences in numbers of electrons.

Multiple Choice

In 1808, John Dalton established his atomic theory. Which of the following is not part of Dalton’s atomic theory?

• All matter is composed of atoms.

• An atom consists of a nucleus and a cloud of electrons.

• Atoms cannot be subdivided, created, or destroyed.

• In chemical reactions, atoms are combined, separated, or rearranged.

Multiple Choice

Which of the following statements of Dalton’s atomic theory describes conservation of mass?

• All matter is composed of atoms.

• Atoms of a given element are identical in size, mass, and other properties.

• Atoms cannot be subdivided, created, or destroyed.

• Atoms of different chemical elements combine in simple whole-number ratios to form chemical compounds.

Multiple Choice

Which of the following statements of Dalton’s atomic theory describes the law of multiple proportions?

• All matter is composed of atoms. 

• Atoms of a given element are identical in size, mass, and other properties.

• Atoms cannot be subdivided, created, or destroyed.

• Atoms of different chemical elements combine in simple whole-number ratios to form chemical compounds.

Multiple Choice

Which is one way that Dalton’s atomic theory has been shown to be incorrect?

• Atoms can change identity in chemical reactions.

• Atoms can be split into subatomic particles.

• Atoms can be destroyed by chemical reactions.

• Some atoms of a particular element are identical to atoms of other elements.

Multiple Choice

In an experiment, Alex and Rachel discover that their sample of table salt, also known as sodium chloride, NaCl, consists of 39.34% by mass sodium, Na, and 60.66% by mass chlorine, Cl. Later, Alex wonders what the percentage of Na might be in the table salt in his saltshaker at home. Rachel tells him, correctly, that it is

• 39.34%.

• 60.66%.

• 90%.

• impossible to tell, without analyzing the salt.