Unit 1 (Chapter 2, Part 2)

Question 1

What is a form of an element that contains a different number of neutrons from the element’s most common form?

Answer 1

An isotope.

Elements exist in different forms… That is why the molecular weight on the periodic table of elements is an “average” because of all the different forms.

Question 2

What does the number to the left of an element abbreviation in superscript entail?

Answer 2

It is the atomic mass (sum or protons and neutrons)

Question 3

T/F Isotopes of an atom have similar chemical properties but may have very different physical properties.

Answer 3

True

Isotopes in nature are inherently unstable and they are measured in half-lives.

Question 4

What is half-life?

Answer 4

Half-life is the time it takes for 50% of an isotope to decay.

Question 5

What is a radioisotope?

Answer 5

A radioisotope is an isotope found in nature that is inherently unstable and usually does not exist for long periods of time. These isotopes decay and emit energy in the form of radiation which converts them to a stable form.

Question 6

BONUS: How can the metabolically important sugar molecule, glucose, be used to help people?

Answer 6

It can be chemically replaced with a radioactive isotope of fluorine (18F) to create a molecule called fluorodeoxyglucose or FDG.

18F has a half-life of 110 minutes and, when into a solution, can be injected into the bloodstream where organs use it like ordinary glucose.

Using a positron-emission tomography (PET) scan, it can detect the radioactive substances throughout the body and it can visualize organs functioning normally, or at an increased and decreased rate. This helps detect cancer because cancer cells tend to use much more glucose than regular cells.

Therefore, PET scans can reveal the presence of cancer-a disease characterized by uncontrolled cell growth.

Question 7

What elements in the vast majority of living organisms make up 95% of an organism?

Answer 7

Oxygen, carbon, hydrogen, and nitrogen.

Question 8

Which element is a major building block for all living matter?

Answer 8

Carbon

Question 9

What element is vital in all proteins?

Answer 9

Nitrogen

Question 10

Fun Fact: How can hydrogen account for about 63% of all atoms within the body, but only make up a small percentage of mass in the human body?

Answer 10

Because it is so small compared to oxygen, carbon, and nitrogen.

Question 11

What does much of the oxygen and hydrogen within the body occur in the form of (60% of mass total in humans and 95% of most plants)?

Answer 11

Water

Question 12

What is an element that is essential for normal growth and function of living organisms but is required in extremely small quantities?

Answer 12

Trace elements

Question 13

What is a molecular formula?

Answer 13

A representation of a molecule that consists of the chemical symbols for all of the atoms present and subscripts that indicate how many of those atoms are present.

Question 14

What is a molecule composed of two or more different elements?

Answer 14

A compound.

Example - H2O (Two hydrogen atoms and 1 oxygen atom bonded)

Question 15

What is one of the most important features of compound molecules?

Answer 15

Their emergent properties (like the eye example)

This means that the properties of a compound differ greatly from those of its elements.

Ex. Pure sodium (Na) is a soft, silvery metal that can be cut with a knife. When forming a compound with chlorine (CI), table salt (NaCl) results. NaCl is a white, relatively hard crystal that dissolves in water.

Question 16

What is a covalent bond?

Answer 16

A chemical bond in which two atoms share a pair of electrons.

These bonds occur between atoms whose outer shells are not full.

Question 17

What is the fundamental principle of chemistry you just read?

Answer 17

Atoms tend to be most stable when their outer shells are filled with electrons.

Question 18

What is a type of chemical formula for molecules in which each covalent bond is represented by a line indicating a pair of shared electrons?

Answer 18

A structural formula

For example: Hydrogen Flouride (HF) can be depicted as H-F

Question 19

BONUS: Depict water (H2O) as a structural formula.

Answer 19

H-O-H

Question 20

What can you associate by identifying the number of electrons needed to fill the outer shell of an atom?

Answer 20

The number of covalent (simultaneous) bonds.

Ex. Hydrogen is 1 and Carbon is 4.

Question 21

What is the octet rule?

Answer 21

The observation that many atoms are most stable when their outermost shell is full, with eight electrons.

A common rule since many elements prefer 8 (max) electrons in its valence shell.

Question 22

Give one example of when the octet rule would not apply?

Answer 22

A bond dealing with hydrogen since its outer most shell is 1s and can only have a max of 2 electrons.

Question 23

What is a double bond?

Answer 23

A bond that occurs when the atoms of a molecule share two pairs of electrons.

Question 24

What is an example of a double bond molecule and how would it be depicted in a structural formula?

Answer 24

Oxygen (O2)

O=O

Question 25

What is the measure of an atom’s ability to attract electrons in a bond with another atom?

Answer 25

Electronegativity

Question 26

When two atoms with different electronegativities form a covalent bond, which nucleus will the shared electrons be closer to?

Answer 26

Closer to the nucleus of the atom with a higher amount of electronegativity.

This is called a polar covalent bond.

Question 27

What is the significance of a polar covalent bond?

Answer 27

The distribution of the shared electrons around the atoms creates a polarity, or difference in electric charge, across the molecule.

Question 28

In basic terms, how is the electronegativity of an atom determined?

Answer 28

The higher the nuclear charge of an atom (the more protons it has), the more “pull” it has on valence electrons. Mainly, the atomic number and size of the atom. Remember: opposites attract each other.

The more electrons an atom has in its shells, the more “push” it will have in respect to the additional electrons versus same number of protons.

Also, consider that electronegativity is also determined by how close the electrons are to the nucleus. Hence why Francium is the least electronegative.

Question 29

So, using electronegativity, how are the partial charges distributed in H2O?

Answer 29

Since oxygen has 8 protons and hydrogen has 1 proton, the oxygen atom will pull the valence electrons closer to its nucleus giving it a partial negative charge (g-) while the hydrogen atoms will have a partial positive charge (g+).

Question 30

How is electronegativity demonstrated on the periodic table of elements?

Answer 30

The height of the elements on the table corelates to the electron affinity of an element. This is also relevant to each group within the table.

Better answer: From bottom left (Francium) to upper right (Flourine). Flourine has the highest electronegativity.

Question 31

What do you call a strong bond formed between two atoms of similar electronegativities in which electrons are shared between atoms?

Answer 31

Nonpolar covalent bond

Example: Two carbon atoms , C-C, or between carbon and hydrogen atoms, C-H.

Question 32

What is a weak chemical attraction between a hydrogen atom in a polar molecule and an electronegative atom in another polar molecule?

Answer 32

Hydrogen bond (typically illustrated by dashed lines)

Question 33

How is a DNA molecule consisting of 2 twisted strands held together through its entire length?

Answer 33

Millions of hydrogen bonds

Question 34

What is a protein that acts as a catalyst to speed up a chemical reaction in a cell?

Answer 34

An enzyme

Typically, small molecules will bind to enzymes via hydrogen bonds. Because of their weak nature, the bonds are released once the molecule’s structure has been changed.

Question 35

What is another type of weak molecular attraction?

Answer 35

Van der Waals dispersion forces

Attractive forces between molecules in close proximity to each other, caused by the variations in the distribution of electron density around individual atoms.

In other words, the electrons located within the orbitals are very random. At any moment the outer shells of the atoms in a nonpolar molecule may be evenly or unevenly distributed.

Question 36

What is an ion?

Answer 36

An atom or molecule that gains or loses one or more electrons and acquires a net electric charge.

Question 37

What is a cation?

Answer 37

An ion with a net positive charge.

Ex. Na+, a sodium atom (Na) that has been stripped of 1 electron now becomes a sodium ion.

Question 38

What do you call ions with a net negative charge?

Answer 38

Anions

Question 39

What is an ionic bond?

Answer 39

It is an attraction between a positively charged ion and negatively charged ion.

In other words, when a cation binds to an anion by taking or giving an electron.

Question 40

Since covalent bonds are not rigid, what kind of example can you imagine them as?

Answer 40

Imagine the covalent bond as an axel around which joined atoms can rotate. The SHAPE of the molecule can change without breaking its covalent bond.

Question 41

What is important to understand about the three-dimensional, flexible shape of molecules?

Answer 41

It contributes to their biological properties.

The three-dimensional structure of two molecules is critical in ensuring that they are capable of specifically interacting with each other and not with other molecules.

The function of the molecules is defined by their ability to bind to each other, which in turn depends on their unique structures.

Question 42

When is an atom and ion the most stable?

Answer 42

When each of its orbitals is occupied by a full complement of electrons hence covalent and ionic bonding.

Question 43

What is a free radical?

Answer 43

A molecule containing an atom with a single unpaired electron in its outer shell.

A free radical is unstable and interacts with other molecules by removing electrons from their atoms.

Question 44

How can a chain reaction happen?

Answer 44

When free radicals “steal” an electron from their atoms, thereby filling the orbital in the free radical. In this process, a new free radical may be created from the donor molecule, setting off a chain reaction.

Question 45

How are free radicals denoted in superscript?

Answer 45

A little dot.

They can be neutral or charged.

Free radicals have an unpaired electron where the electron-proton balance can be preserved.

Question 46

How do free radicals do considerable harm to living cells?

Answer 46

By causing a cell to rupture or by damaging genetic material.

Question 47

What is a few cases of free radicals sometimes put to good use?

Answer 47

• Cells in animals create free radicals and use them to kill invading cells such as bacteria.
• People used weak solutions of hydrogen peroxide to kill bacteria, which broke down to create free radicals. (no longer practiced because of the possibility of damaging skin cells)
• Protection from free radicals is afforded by molecules that can donate electrons to the free radicals without becoming highly reactive themselves.
• Examples of protection from free radicals is vitamins C and E and plant compounds called flavonoids. That is one reason why a diet rich in fruits in vegetables is beneficial to our health.

Question 48

What is a process in which one or more substances are changed into other substances?

Answer 48

A chemical reaction.

This is by the making and breaking of chemical bonds.

Question 49

What are the three ways a chemical reaction happens?

Answer 49

1 - When two or more elements or compounds combine to form a new compound.

2 - When one compound breaks down into two or more molecules

3 - When electrons are added or removed from an atom

Question 50

What are the two similar properties that two chemical reactions share?

Answer 50

1 - They all require a source of energy so that atoms and molecules can encounter each other.

2 - Chemical reactions that occur in living organisms often require more than just Brownian motion to proceed at a reasonable rate.

Question 51

What type of energy is needed for atoms and molecules to interact with each other?

Answer 51

Heat or thermal energy. In the complete absence of heat, temperature like absolute zero, atoms and molecules would be totally stationary and unable to interact.

Question 52

What causes the phenomenon known as Brownian motion and what is needed to speed up the rate of chemical reaction?

Answer 52

Heat causes the atoms and molecules to vibrate and move and a catalyst is needed to speed up the reaction.

Question 53

What is a reactant?

Answer 53

A substance that participates in a chemical reaction and becomes changed by that reaction.

Question 54

What is a product?

Answer 54

The end result of a chemical reaction.

Ex. When methane and oxygen (CH4 + 2 O2) converts to CO2 + 2 H2O.

Question 55

What is indicated with bidirectional arrows?

Answer 55

This indicates that the reaction can proceed in both directions.

Question 56

What determines the direction a reaction will take?

Answer 56

It depends on the changes in free energy.

Question 57

What do you call a state of a chemical reaction in which the rate of formation of products equals the rate of formation of reactants?

Answer 57

Chemical equilibrium

Question 58

Where do most chemical reactions occur?

Answer 58

In watery environments.