Chemical Formulas & Equations (Extra)

Question 1

The _____ isn’t actually what an atom looks like, but it’s a very simple view that helps you get started.

Answer 1

Bohr Model

Question 2

Chemical reactions are all around us, happening all the time. They’re responsible for phenomena ranging from the emergence of life on Earth to the subtle tarnishing of silver. While there are a dizzying number of possible chemical reactions, they proceed in predictable ways.

We can begin to understand these reactions by paying attention to the _____ that are exchanged when they occur.

Answer 2

electrons

Question 3

But it turns out that chemical reactions aren’t just esoteric experiments in labs — they are all around us, happening all the time.

In engines, they provide the _____ to get around. In plants, they produce the _____ we consume to survive. In industry, they produce the materials and products that power our economies and furnish our homes and offices.

Answer 3

power, sugars

Question 4

_____ are the building blocks of all matter, and all _____ of a specific element have the same behavior.

Answer 4

atoms, atoms

Question 5

Here’s a chemical. It’s a sugar, called glucose.

The black, white, and red spheres that make up this sugar are individual _____.

Answer 5

atoms

Question 6

Atoms can come together in countless _____ and _____, but when they come together in exactly the way shown above, this is the arrangement we can call a _____ of sugar.

Answer 6

arrangements, ratios, molecule

Question 7

In a single teaspoon of glucose, there are _____ of molecules, but in each one all the atoms are arranged the exact same way in _____ and in the exact same _____. Remove any of the atoms or change the way they are connected to each other, and it wouldn’t be _____ anymore!

Answer 7

billions, space, ratio, glucose

Question 8

Just as when we learn a foreign language, talking about chemistry requires that we first acquire some vocabulary to talk about _____. All _____ have a start and a finish. Anything present at the very start is called a _____. What we end up with are called _____. Lastly, to indicate that a reaction has occurred to change the reactants into the products, we draw an arrow from _____.

Answer 8

reactions, reactions, reactant, product, left to right

Question 9

Let’s look at a model of a real molecule undergoing a reaction — in this case, the break up of calcium carbonate. The spheres represent atoms, and their color denotes what kind of atom or element, they are.

In the course of this reaction from reactants to products, what is not changing?

A) The identities of the atoms involved in the reaction

B) The spatial arrangement of the atoms involved in the reaction

Answer 9

A) Here’s why: we see that while the spatial arrangement of the atoms — what they are attached to relative to one another — has changed during the reaction, their color (identity) has not, nor has the number of atoms changed. So ultimately we can conclude that, in a chemical reaction, atoms are neither created nor destroyed, and they retain their identity throughout.

Question 10

_____ cannot change the fundamental identity of the atoms involved — for example, no _____ can turn lead into gold.

But what exactly determines the _____ of an atom? We may know intuitively that an oxygen atom is different from, say, a carbon atom or an aluminum atom, but what makes them different?

Answer 10

chemical reactions, reaction, identity

Question 11

Each atom consists of two major parts: the _____ and the _____. The _____ exist in a cloud around the central _____.

Answer 11

electrons, the nucleus, electrons, nucleus

Question 12

Atoms are overall neutral, but a single atom can contain many negatively charged electrons. What does this imply about the nucleus?

A) It must be electrically neutral (no net charge).

B) It must bear a positive charge equal in magnitude to the total charge of the atom’s electrons.

C) It must bear a positive charge equal in magnitude to the total charge of the atom’s electrons.

Answer 12

B) If the atom contains many negatively charged electrons but is overall charge-neutral, it implies that there must be other positively charged particles that balance out the electrons.

In fact, the nucleus contains two different kinds of particles, only one of which is charged, but we’ll save a more detailed discussion for later in the course.

Question 13

The nucleus at the center of the atom is so stable that it can’t be changed by chemical reactions. This is because chemical reactions involve the _____ which is weak compared to the _____ that holds the nucleus together (as you can tell by its name).

This means oxygen atoms will always remain _____ atoms and hydrogen atoms will always remain _____ atoms, even when they are involved in chemical reactions.

Answer 13

electromagnetic force, strong nuclear force, oxygen, hydrogen

Question 14

As we work through ever more complicated examples of chemical reactions, a trend will emerge: _____ are the name of the game. When we boil down even the most sophisticated reactions going on in industry, nature, and our bodies, it all comes down to the _____!

Answer 14

electrons, electrons

Question 15

Understanding where the _____ are in molecules and where _____ is one of the most important tools allowing chemists to make useful and accurate predictions about _____.

Answer 15

electrons, they tend to go, reactivity

Question 16

_____ change hands like money during reactions, so we can think of them as the _____ of chemistry.

Answer 16

electrons, transactional unit

Question 17

For this class, reactions are _____. But what sorts of things happen to atoms during these transactions? For now, we won’t concern ourselves with the goings-on of atomic nuclei. To keep things simple, we’ll continue to treat atoms simply as _____.

Answer 17

all about electrons, spheres

Question 18

Suppose that, during a chemical reaction, a neutral oxygen atom were to gain two additional electrons. What is true about the new state of the atom?

A) The atom has been transformed into a different element altogether.

B) The atom is still oxygen, but with a net negative charge.

C) The atom is still oxygen, but with a net positive charge.

Answer 18

B) Electron transactions cannot alter the identity/element of the atom since they don’t involve the nucleus or the positive charge it bears. But adding two more electrons to an uncharged atom will give it a net negative charge of -2.−2.

Logically enough, the opposite is also true — losing electrons results in an atom becoming positively charged.

Question 19

Reactions can add electrons to or subtract electrons from an atom, which results in a negative or positive _____, respectively. The _____ of an atom is indicated by writing it next to the atom’s symbol.

For an oxygen atom, whose symbol is O we could represent the double negative charge like O^2-

Answer 19

charge, charge

Question 20

Table salt (sodium chloride) is represented by the formula _____, with _____ representing a sodium atom and _____ representing the chlorine atom. They are bound together to form a _____.

Answer 20

NaCl, Na, Cl, compound

Question 21

The atoms in table salt are bound together to form a compound, but what happens if we could split the atoms apart? It turns out that this is pretty easy and can be accomplished by adding water:

NaCl + H₂O ⇒ Na⁺ + Cl^-

Recalling what we discussed about atomic structure and representation of charges, how might we best describe what happens when these two atoms are broken apart in this way?

A) Sodium loses an electron, and chlorine gains an electron.

B) Sodium gains an electron, and chlorine loses an electron.

C) Sodium’s nucleus gains a positive charge, and chlorine’s nucleus loses a positive charge.

D) Sodium’s nucleus loses a positive charge, and chlorine’s nucleus gains a positive charge.

Answer 21

A) We see here that the previously paired atoms (as represented by the formula) are now separate and each has a net charge. From our earlier discussion, we might conclude that the “transaction” of electrons consists of the chlorine “taking” an electron from the sodium as they come apart. But, again, the atoms retain their fundamental identity, because the nucleus is not affected in any way by chemical reactions.

In reality, the association between sodium and chloride is slightly more complex than we’ve considered here, and we’ll delve into the details of that association (or bond) soon.

Question 22

Chemical equations are _____, in that anything that appears in exactly the same form, _____, on both sides of the equation cancels out.

NaCl + H₂O ⇒ Na⁺ + Cl^-

For example, since water is not fundamentally changed in the reaction above, the correct version of this equation looks like this:

NaCl ⇒ Na⁺ + Cl^-

Answer 22

algebraic, unchanged

Question 23

We can conceptualize the reaction that splits NaCl as an electronic “transaction,” without involving the nucleus of either atom. What can we say about the total amount of charge that exists before the reaction and after the reaction?

A) The total charge on all components is larger before the reaction.

B) The total charge on all components is the same before and after the reaction.

C) The total charge on all components is larger after the reaction.

Answer 23

B) The total number of electrons doesn’t change during the reaction. They are neither created out of thin air nor destroyed. In reactions, atoms gain and lose electrons all the time, and this tendency is actually quite predictable and will become useful for us later in the course.

Question 24

The idea that the _____ of all molecules has to be _____ before and after the reaction is one of the foundational principles of chemistry.

What this means is that while _____ can and do change hands during the course of reactions, what they _____ do is to go flying off into outer space somewhere, nor do they simply “poof” into existence.

Answer 24

total charge, the same, electrons, don’t

Question 25

if an atom gains electrons during a reaction — so has a more negative charge than it had before — we know two things.

First, the electrons had to come from _____. And second, whatever atom lost them will end up with a more _____ charge than it had before. This principle gives us the power to determine at a glance whether a reaction is _____ — even reactions we’ve never seen before.

Answer 25

somewhere, positive, feasible

Question 26

In chemical reactions, _____ are exchanged, but not _____ or _____. Rules like this allow us to understand how chemical reactions work without needing to memorize countless equations.

Answer 26

electrons, created, destroyed